A positive electrode active material, a method for preparing the same, a positive electrode sheet, a secondary battery, and an electric device

Abstract

The application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device. The positive electrode active material comprises a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is a nickel-iron-manganese-copper quaternary sodium battery positive electrode active material; and the chemical formula of the second positive electrode active material is Na a2 [Ni b2 Fe c2 Mn d2 M e2 ]O2, wherein 0.8<=a2<1, 0.01<=b2<0.35, 0.01<=c2<0.35, 0.01<=d2<0.35, 0<=e2<0.1, b2+c2+d2+e2=1, and the M element comprises any one or more of Zn, Ti, Zr, Mg, La, Y, Co, Cr, Al, K, V, Mo, W, Sr, Ta, Nb or Ca.

Description

TECHNICAL FIELD

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

[0002] After nearly ten years of research by various parties, sodium-ion batteries have formed positive electrode active materials mainly in the form of transition metal oxides, Prussian blue and polyanion phosphates. Among them, transition metal oxides have relatively high specific capacity, but their poor cycle performance and low energy density have been important factors affecting the application of sodium-ion battery positive electrode active materials.

[0003] The commonly used transition metal oxides are mainly divided into two types: one is nickel-iron-manganese-based oxides, and the other is nickel-manganese-iron-copper-based oxides containing copper elements. Regardless of any of the two types, changing the different proportions of nickel, iron, manganese and copper elements can obtain sodium-ion battery positive electrode active materials with different performance.

[0004] In order to improve the cycle performance of transition metal oxides, single crystal transition metal oxides have appeared. For single crystal quaternary positive electrode active materials of nickel-manganese-iron-copper-based oxides, the Cu element in them can improve the structural stability of the material and improve the cycle performance of the material. Moreover, the Cu element has a fluxing effect, which can promote the growth of single crystal particles, thereby reducing the specific surface area and interface side reactions of the material and improving the cycle performance. However, the specific capacity of nickel-iron-manganese-copper quaternary positive electrode active materials is low, which limits the energy density of the material. SUMMARY

[0005] The present application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electric device to improve the energy density of nickel-iron-manganese-copper quaternary positive electrode active materials.

[0006] The first aspect of the present application provides a positive electrode active material, which comprises a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is a nickel-iron-manganese-copper quaternary sodium battery positive electrode active material; the chemical formula of the second positive electrode active material is Na a2 [Ni b2 Fe c2 Mn d2 M e2]O2, wherein 0.8≤a2<1, 0.01≤b2<0.35, 0.01≤c2<0.35, 0.01≤d2<0.35, 0≤e2<0.1, b2+c2+d2+e2=1, the M element includes any one or more of Zn, Ti, Zr, Mg, La, Y, Co, Cr, Al, K, V, Mo, W, Sr, Ta, Nb or Ca, optionally the M element includes any one or more of Zn, Ti, Zr, Mg, Al, Co or Ca; optionally, 0.9

[0007] In the positive electrode active material of the present application, the first positive electrode active material contains copper element, so its structure is relatively stable and the cycle performance is good; the second positive electrode active material has higher gram capacity relative to the first positive electrode active material, so the mixture of the two can make up for the defect of low gram capacity of the first positive electrode active material, and thus the positive electrode active material can obtain higher energy density, i.e. gram capacity.

[0008] In any embodiment of the first aspect, the above-mentioned nickel-iron-manganese-copper quaternary sodium battery positive electrode active material has a chemical formula of Na a1 [Ni b1 Fe c1 Mn d1 Cu e1 ]O2, wherein 0.8≤a2<1, 0.01≤b2<0.35, 0.01≤c2<0.35, 0.01≤d2<0.35, 0≤e2<0.1, b2+c2+d2+e2=1, the M element includes any one or more of Zn, Ti, Zr, Mg, La, Y, Co, Cr, Al, K, V, Mo, W, Sr, Ta, Nb or Ca, optionally the M element includes any one or more of Zn, Ti, Zr, Mg, Al, Co or Ca; optionally, 0.9

[0009] In any embodiment of the first aspect, optionally, the total molar amount of Cu atoms in each gram of the positive electrode active material is e1', and the total molar amount of M elements is e2', 0.5≤e1' / e2'≤200, preferably 1≤e1' / e2'≤100, and further preferably 4≤e1' / e2'≤40. This is more conducive to improving the cycle performance and capacity of the positive electrode active material.

[0010] In any embodiment of the first aspect, the mass content of Cu element in the above-mentioned positive electrode active material is 0.5%-12%, and preferably 3.5%-4.7%. This makes the ratio of the first positive electrode active material and the second positive electrode active material more coordinated, so that the cycle performance and energy density of the positive electrode active material are more obviously improved relative to a single material.

[0011] In any embodiment of the first aspect, the positive electrode active material has a particle size of less than or equal to D V In the positive electrode active material of 10, the average mass content of Cu element is m1, and the particle size is greater than or equal to D V In the positive electrode active material of 90, the average mass content of Cu element is m2, and m1

[0012] In any embodiment of the first aspect, the positive electrode active material has a volume distribution particle size satisfying any one or more of the following conditions: 1) D V 10 is 0.5 pm to 2 pm; 2) D V 50 is 7 pm to 11 pm; 3) D V 90 is 14 pm to 20 pm. The volume particle size distribution makes the gradation between particles more optimal, which is more conducive to improving compaction.

[0013] In any embodiment of the first aspect, the volume particle size distribution curve of the positive electrode active material includes a first peak type and a second peak type, the peak value particle size of the first peak type is D1, the peak value particle size of the second peak type is D2, and D1

[0014] In any embodiment of the first aspect, the positive electrode active material having a particle size of less than or equal to D1 has an average mass content of Cu element of m3, and the positive electrode active material having a particle size of greater than or equal to D2 has an average mass content of Cu element of m4, and m3

[0015] In any embodiment of the first aspect, the peak positions of D1 and D2 are fitted peaks, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting treatment based on a Gaussian function by using origin software, at least a first fitting peak type and a second fitting peak type are obtained, the peak value particle size of the first fitting peak type is D1, the peak value particle size of the second fitting peak type is D2, the particle size of the first positive electrode active material is within the particle size range corresponding to the second fitting peak type, and the particle size of the second positive electrode active material is within the particle size range corresponding to the first fitting peak type. The cycle performance and energy density of the positive electrode active material are more effectively improved.

[0016] In any embodiment of the first aspect, the average particle size D1' of the first positive electrode active material is 6 pm to 15 pm, which can be optionally 8 pm to 12 pm; and / or the average particle size D2' of the second positive electrode active material is 2 pm to 5.5 pm, which can be optionally 3 pm to 4 pm. The cycle performance and energy density of the positive electrode active material are more effectively improved.

[0017] In any embodiment of the first aspect, the volumetric particle size distribution curve of the positive electrode active material is fitted using Origin software based on a Gaussian function, with D1' and D2' as the peak positions respectively. During the fitting process, the fitted peak positions remain unchanged, resulting in fitted peak shapes for small particles and large particles. The particle size of the first positive electrode active material falls within the range corresponding to the large particle fitted peak shape, while the particle size of the second positive electrode active material falls within the range corresponding to the small particle fitted peak shape. This allows for more effective improvement in the cycle performance and energy density of the positive electrode active material.

[0018] In any embodiment of the first aspect, the first positive electrode active material and the second positive electrode active material each independently comprise a single crystal material or have a single crystal core.

[0019] In any embodiment of the first aspect, each of the first and second positive electrode active materials independently possesses an O3 crystal phase. This further enhances the energy density of the positive electrode active material.

[0020] In any embodiment of the first aspect, the morphology of the first positive electrode active material and the second positive electrode active material each independently includes any one or more of the following: sheet-like, spherical, or near-spherical.

[0021] In any embodiment of the first aspect, in the XRD spectra of the first and second positive electrode active materials, the grain size corresponding to the (003) diffraction peak, (101) diffraction peak, and (104) diffraction peak is D. 003 D 101 and D 104 And it satisfies 1.5 <D 104 / D 003 <1.7, further option is 1.55 <D 104 / D 003 <1.65, or meets the requirement of 0.9 <D 101 / D 003 <1.2, can be further selected as 1.05 <D 101 / D 003 <1.15. The ratio of grain size that meets the above conditions gives the positive electrode active material a higher particle roundness, which is more conducive to improving the compaction density of the positive electrode active material.

[0022] In any embodiment of the first aspect, the mass ratio of the first positive electrode active material and the second positive electrode active material is 5:5-9:1, and can be selected as 6:4-8:2.

[0023] In any embodiment of the first aspect, at least part of the surface of the first positive electrode active material and the second positive electrode active material independently has a coating layer; the coating layer comprises a sodium phosphate salt, which optionally comprises NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; optionally, the weight content of the sodium phosphate salt in the positive electrode active material is 1000 ppm-30000 ppm, optionally 5000 ppm-20000 ppm. The residual Na on the surface of the material is consumed, and the cycle and sodium storage stability of the positive electrode active material are improved.

[0024] In any embodiment of the first aspect, the powder compaction density of the positive electrode active material under a pressure of 3 tons is ≥3.1 g / cm3 3 , and optionally ≥3.3 g / cm3 3 . The improvement of the compaction density leads to the improvement of the energy density of the material.

[0025] The second aspect of the present application provides a preparation method of any one of the positive electrode active materials of the first aspect, which comprises: preparing a first positive electrode active material, mixing a Ni salt solution, a Fe salt solution, a Cu salt solution and a Mn salt solution in a set proportion to form a first mixed salt solution, adding the first mixed salt solution, a first precipitating agent and a first complexing agent into a reaction container, controlling the pH value and the reaction temperature of the materials in the reaction container to perform a co-precipitation reaction to obtain a first positive electrode active material precursor, the pH value being recorded as pH1 and pH1 being 9-12; mixing the first positive electrode active material precursor and a first sodium salt in a proportion to form a first mixture, and performing a first calcination treatment on the first mixture to obtain the first positive electrode active material; preparing a second positive electrode active material, mixing a Ni salt solution, a Fe salt solution, a Mn salt solution and an optional salt solution containing an element M in a set proportion to form a second mixed salt solution, pumping the second mixed salt solution, a second precipitating agent and a second complexing agent into a reaction container, controlling the pH value and the reaction temperature of the materials in the reaction container to perform a co-precipitation reaction to obtain a second positive electrode active material precursor, the pH value being recorded as pH2 and pH2 being 11-14; mixing the second positive electrode active material precursor and a second sodium salt in a proportion to form a second mixture, and performing a second calcination treatment on the first mixture to obtain the second positive electrode active material; and mixing the first positive electrode active material and the second positive electrode active material to obtain the positive electrode active material. The preparation method of the present application separately prepares the first positive electrode active material and the second positive electrode active material, and is more flexible in adjusting and controlling the respective composition, morphology, crystal phase and other characteristics.

[0026] In any embodiment of the second aspect, the Ni salt, Fe salt, Mn salt, Cu salt, and M salt comprise one or more of their respective sulfates, nitrates, oxalates, or chlorides; the first precipitant and the second precipitant each independently comprise an aqueous solution of one or more of sodium hydroxide, sodium carbonate, potassium carbonate, or potassium hydroxide; the first complexing agent and the second complexing agent each independently comprise an aqueous solution of one or more of ammonia, ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate, or citric acid; optionally, the concentration of the first complexing agent is 1 to 2 mol / L, and the concentration of the second complexing agent is 0.5 to 1 mol / L.

[0027] In any embodiment of the second aspect, the first calcination treatment includes a first initial calcination at a first temperature and a first calcination at a second temperature, wherein the first temperature is lower than the second temperature; optionally, the first initial calcination temperature is 700-900°C, and the holding time is 3-10 hours; optionally, the second calcination temperature is 850°C-1200°C, more preferably 900°C-1000°C; the holding time is 8-20 hours, more preferably 12-18 hours; and / or the molar ratio of sodium in the first sodium salt to the metal element in the first positive electrode active material precursor is 0.8-0.95, preferably 0.9-0.93. The sintering temperature of the first short-frying treatment is initially low and then increases, removing moisture while simultaneously promoting particle size growth.

[0028] In any embodiment of the second aspect, the second calcination treatment includes a second initial calcination at a third temperature and a second calcination at a fourth temperature, wherein the third temperature is higher than the fourth temperature. Optionally, the third temperature of the second initial calcination is 850-1000℃, and the holding time is 3-8 hours. Optionally, the fourth temperature of the second calcination is 700℃-950℃, more preferably 800℃-920℃; the holding time is 8-20 hours, more preferably 9-15 hours; and / or the molar ratio of sodium in the second sodium salt to the metal element in the second positive electrode active material precursor is 0.8-0.95, preferably 0.9-0.93. The calcination temperature in the second calcination treatment is initially high and then decreases, promoting the reaction while simultaneously reducing the particle size and inhibiting particle growth.

[0029] In any embodiment of the second aspect, the preparation method further comprises: mixing the phosphate compound, the first positive electrode active material and the second positive electrode active material to form a mixed base material, and optionally, a ratio of a weight of the phosphate compound to a total weight of the first positive electrode active material and the second positive electrode active material is 1000 ppm-30000 ppm, and optionally 5000 ppm-20000 ppm, and the phosphate compound comprises a mixture of one or more of NH4H2PO4, (NH4)2HPO4, (NH4)2H2P2O7, NH4H3P2O7, NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; and performing third calcination on the mixed base material to obtain the positive electrode active material, and optionally, a temperature of the third calcination is 200-500°C, and preferably 300-400°C, and a time is 5-15h, and preferably 7-10h.

[0030] The third aspect of the present application provides a positive electrode tab, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, and the positive electrode film layer comprises the positive electrode active material provided in the first aspect. 3 .

[0031] The fourth aspect of the present application provides a secondary battery, comprising a positive electrode tab, a negative electrode tab and an electrolyte, and the positive electrode tab comprises the positive electrode active material provided in the first aspect.

[0032] The fifth aspect of the present application provides an electric device, comprising the electric device comprising the secondary battery provided in the fourth aspect. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0034] Figure 1 The scanning electron microscope image of the first positive electrode active material substrate of Example 1.

[0035] Figure 2 The XRD spectrum of the first positive electrode active material substrate of Example 1.

[0036] Figure 3 The scanning electron microscope image of the second positive electrode active material substrate of Example 1.

[0037] Figure 4 XRD pattern of the second positive electrode active material substrate of Example 1.

[0038] Figure 5 is a schematic view of a secondary battery according to an embodiment of the present application.

[0039] Figure 6 is Figure 5 is an exploded view of the secondary battery according to an embodiment of the present application.

[0040] Figure 7 is a schematic view of a battery module according to an embodiment of the present application.

[0041] Figure 8 is a schematic view of a battery pack according to an embodiment of the present application.

[0042] Figure 9 is Figure 8 is an exploded view of the battery pack according to an embodiment of the present application.

[0043] Figure 10 is a schematic view of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0044] In the drawings, the drawings are not drawn to scale.

[0045] Explanation of Reference Numerals:

[0046] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 top cap assembly. DETAILED DESCRIPTION

[0047] Embodiments of the present application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following examples and the drawings are intended to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, i.e., the present application is not limited to the described examples.

[0048] Hereinafter, embodiments of the positive electrode active material, the method for producing the same, the secondary battery, and the electric device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0049] The ranges disclosed herein are meant to be inclusive of the endpoints and include the end values in the range. Ranges can be combined to form new ranges, e.g., a range of "60-120 and 80-110" is understood to include 60-110 and 80-120. Further, if a minimum range value is listed as 1 and a maximum range value is listed as 3, 4, and 5, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, in which a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer > 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0051] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0052] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0053] If not otherwise specified, "including" and "containing" mentioned in the present application are open-ended. For example, "including" and "containing" can mean that other components not listed can also be included or contained.

[0054] If not specifically stated, the term "or" in this application is inclusive. For example, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0055] [Secondary battery]

[0056] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can continue to be used by activating active materials through charging after the battery is discharged.

[0057] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charging and discharging process of the battery, active ions (such as lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte is between the positive electrode sheet and the negative electrode sheet, and mainly serves to conduct active ions.

[0058] [Positive electrode active material]

[0059] Since the specific capacity of the nickel-iron-manganese-copper quaternary positive electrode active material is low, the energy density of the material is limited. In order to improve the energy density of the positive electrode active material, in the first embodiment of the present application, a positive electrode active material is provided, which includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is a nickel-iron-manganese-copper quaternary sodium battery positive electrode active material; the chemical formula of the second positive electrode active material is Na a2 [Ni b2 Fe c2 Mn d2 M e2 ]O2, wherein 0.8≤a2<1, 0.01≤b2<0.35, 0.01≤c2<0.35, 0.01≤d2<0.35, 0≤e2<0.1, b2+c2+d2+e2=1, the M element includes any one or more of Zn, Ti, Zr, Mg, La, Y, Co, Cr, Al, K, V, Mo, W, Sr, Ta, Nb or Ca, optionally the M element includes any one or more of Zn, Ti, Zr, Mg, Al, Co or Ca; optionally, 0.9

[0060] In the positive electrode active material of the present application, the first positive electrode active material contains copper element, so its structure is relatively stable and the cycle performance is good; the second positive electrode active material has higher gram capacity than the first positive electrode active material, so the mixture of the two can make up for the defect of low gram capacity of the first positive electrode active material, and thus the positive electrode active material can obtain higher energy density, i.e. gram capacity.

[0061] In some embodiments, a2 can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or 0.999. In some embodiments, b2 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.33 or 0.34. In some embodiments, c2 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.33 or 0.34. In some embodiments, d2 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.33 or 0.34. In some embodiments, e2 can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.75 or 0.79.

[0062] The nickel-iron-manganese-copper quaternary sodium battery positive electrode active material used in some embodiments of the present application can be selected from conventional positive electrode active materials of this type. In order to further exert the improvement of copper on the structural stability of the positive electrode active material, in some embodiments, the chemical formula of the nickel-iron-manganese-copper quaternary sodium battery positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 Cu e1 ]O2, wherein 0.8≤a1<1, 0.01≤b1<0.33, 0.01≤c1<0.33, 0.01≤d1<0.33, 0.02≤e1<0.2, b1+c1+d1+e1=1. In some embodiments, optionally, 0.9<a1<0.95, 0.06≤e1<0.15, on the basis of selecting high sodium, the content of copper element is further controlled, so that the cycle performance of the positive electrode active material is further improved.

[0063] In some embodiments, a1 can be 0.8, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, or 0.999. In some embodiments, b1 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or 0.32. In some embodiments, c1 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or 0.32. In some embodiments, d1 can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or 0.32. In some embodiments, e1 can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.15, 0.17, 0.18, or 0.19.

[0064] In some embodiments of the present application, the total molar amount of Cu atoms is e1’ and the total molar amount of M elements is e2’ per gram of positive electrode active material, 0.5≤e1’ / e2’≤200, preferably 1≤e1’ / e2’≤100, and more preferably 4≤e1’ / e2’≤40. By controlling e1’ and e2’ as described above, the content of Cu elements in the first positive electrode active material and the content of M elements in the second positive electrode active material are within a more suitable range, which allows the first positive electrode active material to have higher cycle stability, while limiting the content of M elements to improve the cycle stability of the second positive electrode active material as much as possible, so that the first positive electrode active material and the second positive electrode active material form a better matching effect, which is more conducive to improving the cycle performance and capacity of the positive electrode active material.

[0065] In some embodiments of the present application, the mass content of Cu elements in the positive electrode active material described above is 0.5%-12%, preferably 3.5%-4.7%. By limiting the content of Cu elements in the positive electrode active material, the content of the first positive electrode active material is limited, and within this range of Cu element content, the ratio of the first positive electrode active material and the second positive electrode active material is more coordinated, thereby making the cycle performance and energy density of the positive electrode active material have a more obvious improvement compared to a single material.

[0066] The present application uses an inductively coupled plasma spectrometer (ICP) to test and detect the elemental composition in the positive electrode active material; uses a scanning electron microscope (SEM) combined with an X-ray energy spectrometer (EDS) to test the elemental distribution on the particle surface, the Cu element distribution particle is the first positive electrode active material, and the particle containing the doped M element is the second positive electrode active material, and the EDS is used to test the elemental content of the first positive electrode active material and the second positive electrode active material.

[0067] In some embodiments, the particle size of the positive electrode active material described above is less than or equal to D v The average mass content of Cu element in the positive electrode active material of 10 is m1, and the particle size is greater than or equal to D v The average mass content of Cu element in the positive electrode active material of 90 is m2, and m1 Under the above condition restrictions, the positive electrode active material with larger particle size of the positive electrode active material is mostly the first positive electrode active material containing Cu, and the positive electrode active material with smaller particle size is mostly the second positive electrode active material. The first positive electrode active material with large particles has better structural stability and less interface side reaction, which provides better cycle performance for the positive electrode active material; the second positive electrode active material with small particles provides higher energy density for the positive electrode active material by taking advantage of its small particle size, and the gradation of the particle size of the two makes the cycle performance and energy density of the positive electrode active material more effectively improved.

[0068] The average mass content of Cu element described above is calculated by scanning single particles under the EDS mode of the scanning electron microscope, detecting the Cu element content in each single particle, and taking the average value after scanning multiple single particles.

[0069] In some embodiments of the present application, the volume distribution particle size of the positive electrode active material described above satisfies any one or more of the following conditions: 1), D V 10 is 0.5 μm-2 μm; 2), D V 50 is 7 μm-11 μm; 3), D V 90 is 14 μm-20 μm. The volume particle size distribution described above makes the gradation between particles more optimal, which is more conducive to improving the compaction.

[0070] The volume particle size distribution of the positive electrode active material described above is determined by using a laser particle size analyzer and other particle size testing equipment.

[0071] On the basis of the component matching of the first positive electrode active material and the second positive electrode active material to realize the improvement of the energy density, in some embodiments, the volume particle size distribution curve of the positive electrode active material includes a first peak type and a second peak type, the peak particle size of the first peak type is D1, the peak particle size of the second peak type is D2, and D1 < D2. The positive electrode active material adopts the matching mode of large particle size and small particle size, realizes the particle grading, and is thus beneficial to further improving the compaction density of the positive electrode active material, thereby further improving the energy density of the positive electrode active material composition.

[0072] In some embodiments, the average mass content of Cu element in the positive electrode active material with a particle size less than or equal to D1 is m3, the average mass content of Cu element in the positive electrode active material with a particle size greater than or equal to D2 is m4, and m3 < m4. Under the above condition limitation, the positive electrode active material with a large particle size (greater than or equal to D2) is mostly the first positive electrode active material containing Cu, and the positive electrode active material with a small particle size (less than or equal to D1) is mostly the second positive electrode active material. The first positive electrode active material with large particles has better structural stability and less interface side reaction, and provides better cycle performance for the positive electrode active material; the second positive electrode active material with small particles provides higher energy density for the positive electrode active material by taking advantage of its small particle size, and the grading of the particle sizes of the two makes the cycle performance and energy density of the positive electrode active material more effectively improved.

[0073] In some embodiments, the origin software is used to perform peak fitting processing on the volume particle size distribution curve of the positive electrode active material based on Gaussian function, with D1 and D2 as the peak positions of the fitting peaks, to obtain at least a first fitting peak type and a second fitting peak type, the peak particle size of the first fitting peak type is D1, and the peak particle size of the second fitting peak type is D2. The particle size of the first positive electrode active material is within the particle size range corresponding to the second fitting peak type, and the particle size of the second positive electrode active material is within the particle size range corresponding to the first fitting peak type. Under the above condition limitation, the second positive electrode active material has a more sufficient filling effect on the particle gap of the second positive electrode active material when mixed with the first positive electrode active material, thereby making the cycle performance and energy density of the positive electrode active material more effectively improved.

[0074] In some embodiments of the present application, the average particle size D1' of the first positive electrode active material is 6 μm-15 μm, and can be optionally 8 μm-12 μm; and the average particle size D2' of the second positive electrode active material is 2 μm-5.5 μm, and can be optionally 3 μm-4 μm. The second positive electrode active material as the small particle size positive electrode active material has a better filling effect on the particle gap of the first positive electrode active material, thereby making the cycle performance and energy density of the positive electrode active material more significantly improved.

[0075] When the positive electrode active material is taken as the test object, the positive electrode active material is placed under a scanning electron microscope for observation at a magnification of 3000 times, and an EDS element mapping test is simultaneously performed. According to whether the Cu element content exists in the EDS result, the first positive electrode active material and the second positive electrode active material are marked. In the same field of view, 30 first positive electrode active materials and 30 second positive electrode active materials are selected respectively, the particle sizes of the respective positive electrode active materials are measured, and 5 random regions are selected for the above operation. The average particle sizes D1' and D2' of the first positive electrode active material and the second positive electrode active material are calculated.

[0076] In some embodiments of the present application, the peak positions of D1' and D2' are taken as the peak positions of the fitting peaks, and the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing based on a Gaussian function by using origin software. In the fitting process, the fitting peak positions are kept unchanged, and a small particle fitting peak type and a large particle fitting peak type are obtained. The particle size of the first positive electrode active material is within the particle size range corresponding to the large particle fitting peak type, and the particle size of the second positive electrode active material is within the particle size range corresponding to the small particle fitting peak type. When there is no obvious peak particle size in the volume particle size distribution curve of the positive electrode active material, after peak fitting based on the average particle sizes D1' and D2', the fitting peak type obtained satisfies the above conditions. When the second positive electrode active material is mixed with the first positive electrode active material, the particle gap of the second positive electrode active material is more fully filled, so that the cycle performance and energy density of the positive electrode active material are more effectively improved.

[0077] The first positive electrode active material and the second positive electrode active material of the present application can be single crystal materials or quasi-single crystal materials or secondary spherical particles. In some embodiments of the present application, the first positive electrode active material and the second positive electrode active material each independently comprise a single crystal material or have a single crystal core. The single crystal structure has better structural stability, and thus the cycle stability of the material can be further improved.

[0078] In order to further improve the energy density of the positive electrode active material of the present application, in some embodiments of the present application, the first positive electrode active material and the second positive electrode active material each independently have an O3 crystal phase.

[0079] In some embodiments of the present application, the morphology of the first positive electrode active material and the second positive electrode active material each independently comprises any one or more of a flaky shape, a spherical shape or a quasi-spherical shape. The flaky material is supported between particles during pressing, resulting in lower compaction than spherical and quasi-spherical shapes. In some embodiments, the morphology of the first positive electrode active material and the second positive electrode active material each independently comprises any one or more of a spherical shape or a quasi-spherical shape.

[0080] In some embodiments of the present application, in order to improve the roundness of the first positive electrode active material and / or the second positive electrode active material, the grain sizes corresponding to the (003) diffraction peak, the (101) diffraction peak and the (104) diffraction peak in the XRD spectrum of the first positive electrode active material and the second positive electrode active material are respectively D 003 , D 101 and D 104 , and satisfy 1.5 < D 104 / D 003 < 1.7, further optionally 1.55 < D 104 / D 003 < 1.65, or 0.9 < D 101 / D 003 < 1.2, further optionally 1.05 < D 101 / D 003 < 1.15. The grain sizes of the sodium battery positive electrode active material with O3 structure corresponding to the (104), (101) and (003) diffraction peaks are related to the particle thickness along the crystal plane, and the ratio of the corresponding grain sizes determines the thickness ratio of the material in different directions. The ratio of the grain sizes satisfying the above conditions makes the positive electrode active material have higher particle roundness, thereby being more conducive to improving the compaction density of the positive electrode active material.

[0081] The XRD spectrum is obtained by the following method: XRD pattern test is performed by using an X-ray diffractometer (Bruker D8 Advance). First, the powder sample is placed on a sample table, and the powder sample is flattened by a glass sheet, and then placed in a sample chamber, and irradiated by X-rays to obtain an XRD pattern.

[0082] The corresponding grain size is calculated by the following method: the Scherrer formula is used to calculate the particle size of the corresponding crystal plane of the material. The Scherrer formula is D = (K·γ) / (B·cosθ). K is the Scherrer constant, γ is the wavelength of X-rays, B is the half-height width of the diffraction peak, θ is the Bragg diffraction angle, and D is the thickness perpendicular to the crystal plane direction.

[0083] In some embodiments of the present application, in order to improve the synergistic effect of the two, the mass ratio of the first positive electrode active material and the second positive electrode active material is 5:5-9:1, and optionally 6:4-8:2.

[0084] To consume the residual Na on the surface of the material and improve the cycle and sodium storage stability, in some embodiments of the present application, the first positive electrode active material and the second positive electrode active material each independently have a coating layer, and the coating layer comprises a sodium phosphate salt, which optionally comprises NaH2PO4, Na2HPO4, Na3PO4, or (NaPO3)6 (sodium hexametaphosphate); optionally, the weight content of the sodium phosphate salt in the positive electrode active material is 1000 ppm to 30000 ppm, or 5000 ppm to 20000 ppm.

[0085] In some embodiments of the present application, the powder compaction density of the positive electrode active material under a pressure of 3 tons is ≥ 3.1 g / cm3. 3 Optionally, the powder compaction density is ≥ 3.3 g / cm3. 3 The increase in the compaction density leads to an increase in the energy density of the material.

[0086] In a second embodiment of the present application, a preparation method of any of the above positive electrode active materials is provided, and the preparation method comprises:

[0087] The first positive electrode active material is prepared, a Ni salt solution, a Fe salt solution, a Cu salt solution, and a Mn salt solution are mixed in a set ratio to form a first mixed salt solution, the first mixed salt solution, a first precipitating agent, and a first complexing agent are pumped into a reaction kettle, and a coprecipitation reaction is performed by controlling the pH value and the reaction temperature of the materials in the reaction kettle to obtain a first positive electrode active material precursor, the pH value is recorded as pH1 and pH1 is 9-12; the first positive electrode active material precursor is mixed with a first sodium salt in a certain ratio to form a first mixture, and the first mixture is subjected to a first calcination treatment to obtain the first positive electrode active material.

[0088] The second positive electrode active material is prepared, a Ni salt solution, a Fe salt solution, a Mn salt solution, and an optional salt solution containing an element M are mixed in a set ratio to form a second mixed salt solution, the second mixed salt solution, a second precipitating agent, and a second complexing agent are pumped into a reaction kettle, and a coprecipitation reaction is performed by controlling the pH value and the reaction temperature of the materials in the reaction kettle to obtain a second positive electrode active material precursor, the pH value is recorded as pH2 and pH2 is 11-14; the second positive electrode active material precursor is mixed with a second sodium salt in a certain ratio to form a second mixture, and the first mixture is subjected to a second calcination treatment to obtain the second positive electrode active material.

[0089] The first positive electrode active material and the second positive electrode active material are mixed to obtain the positive electrode active material.

[0090] The preparation method controls the particle size of the precursor through a co-precipitation process, and then forms the corresponding positive electrode active material through calcination. The calcination conditions refer to the calcination conditions of conventional sodium battery positive electrode active materials, such as calcination in an air or oxygen atmosphere. The preparation method of the present application separately prepares the first positive electrode active material and the second positive electrode active material, which is easier to control the composition, morphology, crystal phase and other characteristics of each, and has high flexibility.

[0091] In addition to the incorporation of copper elements to increase the particle size of the first positive electrode active material precursor, the particle size can also be controlled by controlling the pH value during the co-precipitation process, the addition amount of the complexing agent. In some embodiments, pH1 is 10-11.5; pH2 is 12-13.5.

[0092] The raw materials used in the present application can also be used as reference for the preparation of sodium battery positive electrode active materials. In some embodiments of the present application, the above-mentioned Ni salt, Fe salt, Mn salt, Cu salt and M salt include one or more mixtures of their respective sulfate, nitrate, oxalate or chloride, the first precipitant and the second precipitant each independently include an aqueous solution of one or more mixtures of sodium hydroxide, sodium carbonate, potassium carbonate or potassium hydroxide; the first complexing agent and the second complexing agent each independently include an aqueous solution of one or more mixtures of ammonia, ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate or citric acid; optionally, the concentration of the first complexing agent is 1-2 mol / L, and the concentration of the second complexing agent is 0.5-1 mol / L. The amount of the complexing agent is further used to adjust the particle size of the precursor obtained by co-precipitation.

[0093] The calcination conditions will cause differences in the morphology of the obtained positive electrode active material. In some embodiments, in order to obtain a first positive electrode active material with better roundness, the first calcination process includes a first preliminary calcination at a first temperature and a first calcination at a second temperature, and the first temperature is lower than the second temperature; optionally, the first temperature of the first preliminary calcination is 700-900°C, and the holding time is 3h-10h; optionally, the second temperature of the first calcination is 850°C-1200°C, further optionally 900°C-1000°C; the holding time is 8h-20h, further optionally 12h-18h. The sintering temperature of the first short calcination process is first low and then high, which helps to remove water and also helps to grow the particle size.

[0094] In some embodiments, the molar ratio of sodium in the first sodium salt to the metal elements in the first positive electrode active material precursor is 0.8-0.95, optionally 0.9-0.93.

[0095] In some embodiments, to obtain the second positive electrode active material with better roundness, the second calcination process comprises a process of second preliminary calcination at a third temperature and second calcination at a fourth temperature, and the third temperature is higher than the fourth temperature; optionally, the third temperature of the second preliminary calcination is 850-1000℃, and the holding time is 3h-8h; optionally, the fourth temperature of the second calcination is 700℃-950℃, further optionally 800℃-920℃; and the holding time is 8h-20h, further optionally 9h-15h. The calcination temperature in the second calcination process is first high and then low, which promotes the reaction and reduces the particle size at the same time, and inhibits the growth of particles.

[0096] In some embodiments, the molar ratio of sodium in the second sodium salt to the metal element in the second positive electrode active material precursor is 0.8-0.95, optionally 0.9-0.93.

[0097] In some embodiments of the present application, the above preparation method further comprises: mixing the phosphate compound, the first positive electrode active material and the second positive electrode active material to form a mixed base material, optionally, the ratio of the weight of the phosphate compound to the total weight of the first positive electrode active material and the second positive electrode active material is 1000ppm-30000ppm, optionally 5000ppm-20000ppm, and the phosphate compound comprises one or more of a mixture of NH4H2PO4, (NH4)2HPO4, (NH4)2H2P2O7, NH4H3P2O7, NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; and the mixed base material is subjected to third calcination to obtain the positive electrode active material, optionally, the temperature of the third calcination is 200℃-500℃, preferably 300℃-400℃, and the time is 5h-15h, preferably 7h-10h. Through the above process, the surface residual sodium of the first positive electrode active material and the second positive electrode active material as the core structure is consumed, and the prepared sodium phosphate salt coating layer can also protect the core structure, avoid direct contact with the electrolyte, reduce the occurrence of interface side reactions, and thus improve the cycle performance of the positive electrode active material.

[0098] In some embodiments of the present application, a positive electrode active material is also provided, and the chemical formula of the positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 G g1O2, the element G includes any one or more of Cu, Zn, Ti, Zr, Mg, La, Y, Co, Cr, Al, K, V, Mo, W, Sr, Ta, Nb, or Ca, and optionally the element G includes any one or more of Cu, Zn, Ti, Zr, Mg, Al, Co, or Ca; wherein 0.8

[0099] In some embodiments, the morphology of the positive electrode active material described above independently includes any one or more of a flaky shape, a spherical shape, or a quasi-spherical shape. This improves the compaction density of the positive electrode active material.

[0100] In some embodiments, in the XRD spectrum of the positive electrode active material described above, the grain sizes corresponding to the (003) diffraction peak, the (101) diffraction peak, and the (104) diffraction peak are D 003 , D 101 , and D 104 , respectively, and satisfy 1.5 < D 104 / D 003 < 1.7, further optionally 1.55 < D 104 / D 003 < 1.65, or 0.9 < D 101 / D 003 < 1.2, further optionally 1.05 < D 101 / D 003 < 1.15. This further improves the roundness of the positive electrode active material.

[0101] In some embodiments, the powder compaction density of the positive electrode active material described above is ≥ 3.0 g / cm 3 .

[0102] [Positive electrode sheet]

[0103] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0104] As an example, the positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector itself, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0105] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] In some embodiments, the positive electrode active material is any one of the positive electrode active materials provided in the above embodiments.

[0107] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0108] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. 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.

[0109] In some embodiments, the positive electrode tab can be prepared by dispersing the above-described components for preparing the positive electrode tab, e.g., the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the same to a drying, cold-pressing, or the like process to obtain the positive electrode tab.

[0110] In some embodiments, the positive electrode film layer has a compaction density ≥ 3.1 g / cm 3 , and the test method is as follows:

[0111] To obtain a battery tab that meets the processability requirements, a punch press is used to punch out a positive electrode tab having a diameter of 14 mm, and an electronic balance and a table digital thickness gauge are used to measure the mass m c and the thickness d c of the positive electrode tab, respectively. A tab puncher is used to punch out a sufficient number of aluminum foil substrates having a diameter of 14 mm, and an electronic balance and a table digital thickness gauge are used to measure the mass mAl and the thickness dAl of the aluminum foil substrates, respectively.

[0112] The compaction density p c of the positive electrode tab = (m c -mAl) / (π (φ / 2) x (dc - dAl) x 10^ 6

[0113] wherein: p c is the positive electrode sheet compaction density, in units of grams per cubic centimeter (g / cm3); 3

[0114] m c is the positive electrode sheet mass, in units of grams (g);

[0115] mAl is the aluminum foil substrate mass, in units of grams (g);

[0116] φ is the positive electrode sheet diameter, in units of millimeters (mm);

[0117] d c is the positive electrode sheet thickness, in units of micrometers (pm);

[0118] dAl is the aluminum foil substrate thickness, in units of micrometers (pm).

[0119] In testing the elemental composition, crystal form, and volume particle size distribution of the positive electrode active material in the positive electrode sheet, the positive electrode film layer on the positive electrode sheet is scraped off using a powder scraping method, crushed, and then the binder is dissolved in a solvent, filtered, and dried, and then the respective tests described above are performed.

[0120] [Negative electrode sheet]

[0121] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0122] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0123] In some embodiments, the negative electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can include a high molecular material base layer and a metal layer formed on at least one surface of the high molecular material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a high molecular material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0124] ​In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0125] In some embodiments, the negative film layer can further optionally include a binder. As an example, the binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative film layer can further optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0127] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0128] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0129] [Electrolyte]

[0130] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The present application does not have a specific limitation on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0131] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0132] In some embodiments, the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bisfluorosulfonimide, sodium bis-trifluoromethanesulfonimide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluoroboric oxalate, sodium difluoroboric bisoxalate, sodium difluoroboric bisoxalate phosphate, and sodium tetrafluoroboric oxalate phosphate.

[0133] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0134] In some embodiments, the electrolyte solution can further optionally include an additive. As an example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0135] [Separator]

[0136] In some embodiments, the secondary battery further includes a separator. The separator is disposed between the positive electrode tab and the negative electrode tab, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing active ions to pass therethrough. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0137] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0138] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0139] In some embodiments, the secondary battery includes a secondary battery cell, or includes a battery module and a battery pack.

[0140] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-described electrode assembly and the electrolyte.

[0141] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0142] The shape of the secondary battery cell is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, Figure 5 is a square structure of a secondary battery cell 5 as an example.

[0143] In some embodiments, referring to Figure 6 , the outer package can include a shell 51 and a cover plate 53. The shell 51 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 shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, which can be selected by those skilled in the art according to the specific actual needs.

[0144] In some embodiments, the secondary battery cell can be assembled into a battery module, and the number of secondary battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0145] Figure 7 is a battery module 4 as an example. Referring to Figure 7 , in the battery module 4, a plurality of secondary battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of secondary battery cells 5 can be fixed by fasteners.

[0146] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary battery cells 5 are received in the receiving space.

[0147] 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 one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0148] Figure 8 and Figure 9 is a battery pack 1 as an example. Referring to Figure 8 and Figure 9In the battery pack 1, a battery case and a plurality of battery modules 4 disposed in the battery case can be included. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 is capable of being disposed on the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0149] In addition, the application also provides a power utilization device, which comprises the secondary battery provided by the application. The secondary battery can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0150] As the power utilization device, the secondary battery monomer, the battery module or the battery pack can be selected according to the use requirement thereof.

[0151] Figure 10 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of the power utilization device for high power and high energy density of the secondary battery, the battery pack or the battery module can be used.

[0152] [Embodiment]

[0153] Hereinafter, the embodiments of the application will be described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0154] Embodiment 1

[0155] The first positive electrode active material precursor was prepared by a coprecipitation reaction:

[0156] A mixed aqueous solution of sulphate with a concentration of 2 mol / L is prepared according to the molar ratio of Ni, Fe, Cu and Mn elements in the first positive electrode active material set in Table 1, and a 4 mol / L aqueous solution of sodium hydroxide and an aqueous ammonia solution with a concentration of 2 mol / L (the aqueous ammonia solution as a first complexing agent) are also prepared. Pure water with a volume ratio of 30% is added to a reaction kettle, and the mixed aqueous solution of sulphate and the first complexing agent are pumped into the reaction kettle at the same flow rate. The flow rates of the mixed aqueous solution of sulphate and the first complexing agent are kept constant, and the stirring speed is set to 1000 r / min. The reaction is carried out at a constant temperature in the range of 60°C. A precipitating agent is added to adjust the pH in the reaction kettle during the reaction, and the pH is kept constant at about 11. A precursor slurry is obtained by continuous reaction synthesis. Then, the precursor slurry is centrifuged, washed, filtered, and dried to obtain a first positive electrode active material precursor product.

[0157] The first positive electrode active material precursor and sodium carbonate are mixed, and the molar ratio of Na element to the total moles of metal elements in the first positive electrode active material precursor is 0.93. After mixing by a high-speed mixer, calcination is performed, wherein the initial calcination temperature is 800°C, the time is 5h, the secondary calcination temperature is 950°C, the time is 15h, and the atmosphere is air. A first positive electrode active material substrate is obtained.

[0158] A second positive electrode active material precursor is prepared by a co-precipitation reaction:

[0159] A mixed aqueous solution of sulphate with a concentration of 2 mol / L is prepared according to the molar ratio of Ni, Fe, Mn and Ti elements in the second positive electrode active material set in Table 1, and a 4 mol / L aqueous solution of sodium hydroxide and an aqueous ammonia solution with a concentration of 1 mol / L (the aqueous ammonia solution as a second complexing agent) are also prepared. Pure water with a volume ratio of 30% is added to a reaction kettle, and the mixed aqueous solution of sulphate and the second complexing agent are pumped into the reaction kettle at the same flow rate. The flow rates of the mixed aqueous solution of sulphate and the second complexing agent are kept constant, and the stirring speed is set to 1000 r / min. The reaction is carried out at a constant temperature in the range of 60°C. A precipitating agent is added to adjust the pH in the reaction kettle during the reaction, and the pH is kept constant at about 13. A precursor slurry is obtained by continuous reaction synthesis. Then, the precursor slurry is centrifuged, washed, filtered, and dried to obtain a second positive electrode active material precursor product.

[0160] The second positive electrode active material precursor and sodium carbonate are mixed, and the molar ratio of Na element to the total moles of metal elements in the first positive electrode active material precursor is 0.93. After mixing by a high-speed mixer, calcination is performed, wherein the initial calcination temperature is 950°C, the time is 6h, the secondary calcination temperature is 750°C, the time is 12h, and the atmosphere is air. A second positive electrode active material substrate is obtained.

[0161] The first positive electrode active material substrate and the second positive electrode active material substrate are mixed in a certain mass ratio, and then mixed and sintered with NH4H2PO4, the proportion of NH4H2PO4 relative to the total mass of the first positive electrode active material substrate and the second positive electrode active material substrate is 10000ppm; after mixing, calcination is carried out, the calcination temperature is 300℃, the time is 8h, the atmosphere is air, and finally the positive electrode active material coated with Na4H2PO4 compound on the surface is obtained, which is called positive electrode active material composition.

[0162] Examples 2 to 7

[0163] The preparation of the first positive electrode active material substrate and the second positive electrode active material substrate is the same as in Example 1.

[0164] The mass ratio of the first positive electrode active material substrate and the second positive electrode active material substrate is adjusted, and the coating layer is set according to the method of Example 1 to obtain the positive electrode active material of each example.

[0165] Example 8

[0166] On the basis of Example 1, the coprecipitation pH value when preparing the first positive electrode active material substrate is adjusted to 11.5, and the concentration of the first complexing agent in the material in the reaction kettle is 1mol / L, to obtain a first positive electrode active material substrate with a DV50 of 6μm.

[0167] Example 9

[0168] On the basis of Example 1, the coprecipitation pH value when preparing the first positive electrode active material substrate is adjusted to 10, and the concentration of the first complexing agent used is 1mol / L, to obtain a first positive electrode active material substrate with a DV50 of 15μm.

[0169] Example 10

[0170] On the basis of Example 1, the coprecipitation pH value when preparing the first positive electrode active material substrate is adjusted to 10.8, and the concentration of the first complexing agent used is 1.5mol / L, to obtain a first positive electrode active material substrate with a DV50 of 8μm.

[0171] Example 11

[0172] On the basis of Example 1, the coprecipitation pH value when preparing the first positive electrode active material substrate is adjusted to 10.5, and the concentration of the first complexing agent used is 1.5mol / L, to obtain a first positive electrode active material substrate with a DV50 of 12μm.

[0173] Example 12

[0174] On the basis of Example 1, the coprecipitation pH value when preparing the first positive electrode active material substrate is adjusted to 12, and the concentration of the first complexing agent used is 2 mol / L, to obtain a first positive electrode active material substrate with a DV50 of 4 μm.

[0175] Example 13

[0176] On the basis of Example 1, the coprecipitation pH value when preparing the first positive electrode active material substrate is adjusted to 9, and the concentration of the first complexing agent used is 1 mol / L, to obtain a first positive electrode active material substrate with a DV50 of 18 μm.

[0177] Example 14

[0178] On the basis of Example 1, the coprecipitation pH value when preparing the second positive electrode active material substrate is adjusted to 13, and the concentration of the second complexing agent used is 0.5 mol / L, to obtain a second positive electrode active material substrate with a DV50 of 2 μm.

[0179] Example 15

[0180] On the basis of Example 1, the coprecipitation pH value when preparing the second positive electrode active material substrate is adjusted to 12, and the concentration of the second complexing agent used is 0.5 mol / L, to obtain a second positive electrode active material substrate with a DV50 of 5.5 μm.

[0181] Example 16

[0182] On the basis of Example 1, the coprecipitation pH value when preparing the second positive electrode active material substrate is adjusted to 14, and the concentration of the second complexing agent used is 1 mol / L, to obtain a second positive electrode active material substrate with a DV50 of 1 μm.

[0183] Example 17

[0184] On the basis of Example 1, the coprecipitation pH value when preparing the second positive electrode active material substrate is adjusted to 11, and the concentration of the second complexing agent used is 1 mol / L, to obtain a second positive electrode active material substrate with a DV50 of 7 μm.

[0185] Examples 18 and 19

[0186] On the basis of Example 1, the amounts of copper sulfate and nickel sulfate used when preparing the first positive electrode active material substrate are adjusted, to obtain first positive electrode active material substrates Na 0.93 Ni 0.31 Fe 0.33 Mn 0.34 Cu 0.02 O2, Na 0.93 Ni 0.1 Fe 0.34 Mn 0.33 Cu0.2 O2.

[0187] Examples 20-24

[0188] On the basis of Example 1, during the preparation of the second positive electrode active material substrate, replace titanium sulfate with magnesium sulfate, zirconium sulfate, aluminum sulfate, calcium sulfate and zinc sulfate respectively to obtain each second positive electrode active material substrate. See Table 2 for details.

[0189] Example 25

[0190] On the basis of Example 24, remove the coating layer.

[0191] Example 26

[0192] Referring to the process of Example 24, the first positive electrode active material substrate has a first firing temperature of 700°C and a sintering time of 3h, and a second firing temperature of 900°C and a sintering time of 12h; the second positive electrode active material substrate has a first firing temperature of 850°C and a sintering time of 3h, and a second firing temperature of 700°C and a sintering time of 10h; the rest is the same as Example 24 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0193] Example 27

[0194] Referring to the process of Example 24, the first positive electrode active material substrate has a first firing temperature of 900°C and a sintering time of 10h, and a second firing temperature of 1000°C and a sintering time of 18h; the second positive electrode active material substrate has a first firing temperature of 950°C and a sintering time of 8h, and a second firing temperature of 900°C and a sintering time of 18h; the rest is the same as Example 24 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0195] Example 28

[0196] On the basis of Example 1, during the preparation of the second positive electrode active material substrate, no titanium sulfate is added, and the rest is the same as Example 1 to obtain the second positive electrode active material substrate Na 0.93 Ni 0.33 Fe 0.33 Mn 0.34 O2.

[0197] Examples 29-33

[0198] Referring to the process of Example 1, adjust the amount of each metal element according to the element composition of Table 1 and Table 2, and the rest is the same as Example 1 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0199] Example 34

[0200] The first positive electrode active material substrate has a first burn-in temperature of 700°C, a sintering time of 3h, and a second burn-in temperature of 900°C, a sintering time of 12h, and the second positive electrode active material substrate has a first burn-in temperature of 850°C, a sintering time of 3h, and a second burn-in temperature of 700°C, a sintering time of 10h, and the rest is the same as in Example 1 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0201] Example 35

[0202] The first positive electrode active material substrate has a first burn-in temperature of 900°C, a sintering time of 10h, and a second burn-in temperature of 1000°C, a sintering time of 18h, and the second positive electrode active material substrate has a first burn-in temperature of 950°C, a sintering time of 8h, and a second burn-in temperature of 900°C, a sintering time of 18h, and the rest is the same as in Example 1 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0203] Example 36

[0204] The first positive electrode active material substrate has a first burn-in temperature of 780°C, a sintering time of 4h, and a second burn-in temperature of 920°C, a sintering time of 15h, and the second positive electrode active material substrate has a first burn-in temperature of 900°C, a sintering time of 5h, and a second burn-in temperature of 720°C, a sintering time of 12h, and the rest is the same as in Example 1 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0205] Example 37

[0206] The first positive electrode active material substrate has a first burn-in temperature of 820°C, a sintering time of 6h, and a second burn-in temperature of 970°C, a sintering time of 18h, and the second positive electrode active material substrate has a first burn-in temperature of 950°C, a sintering time of 7h, and a second burn-in temperature of 800°C, a sintering time of 15h, and the rest is the same as in Example 1 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0207] Example 38

[0208] The first positive electrode active material substrate has a first burn-in temperature of 900°C, a sintering time of 10h, and a second burn-in temperature of 1100°C, a sintering time of 20h, and the rest is the same as in Example 1 to obtain the corresponding first positive electrode active material substrate.

[0209] Example 39

[0210] Reference to the process of Example 1, the first positive electrode active material substrate has a first firing temperature of 900°C, a sintering time of 10h, and a second firing temperature of 1100°C, a sintering time of 20h; the second positive electrode active material substrate has a first firing temperature of 980°C, a sintering time of 10h, and a second firing temperature of 930°C, a sintering time of 18h; the rest is the same as Example 1, to obtain the corresponding first positive electrode active material substrate and the second positive electrode active material substrate.

[0211] Example 40

[0212] Reference to the process of Example 1, the first positive electrode active material substrate has a first firing temperature of 900°C, a sintering time of 10h, and a second firing temperature of 1100°C, a sintering time of 25h; the rest is the same as Example 1, to obtain the corresponding first positive electrode active material substrate.

[0213] Example 41

[0214] Reference to the process of Example 1, the first positive electrode active material substrate has a first firing temperature of 900°C, a sintering time of 10h, and a second firing temperature of 1100°C, a sintering time of 25h; the rest is the same as Example 1, to obtain the corresponding first positive electrode active material substrate.

[0215] Example 42

[0216] Reference to the process of Example 1, the second positive electrode active material substrate has a first firing temperature of 1050°C, a sintering time of 8h, and a second firing temperature of 930°C, a sintering time of 18h; the rest is the same as Example 1, to obtain the corresponding second positive electrode active material substrate.

[0217] Examples 43 to 46

[0218] Adjust the amount of NH4H2PO4 used to obtain positive electrode active materials with different amounts of Na4H2PO4 compound coating, and the obtained products are shown in Tables 1 and 2, respectively.

[0219] Example 47

[0220] Without coating treatment, directly use the first positive electrode active material substrate and the second positive electrode active material substrate of Example 1 as the corresponding first positive electrode active material and the second positive electrode active material, and the rest is the same as the treatment of Example 1.

[0221] Example 48

[0222] Without coating treatment, directly use the first positive electrode active material substrate and the second positive electrode active material substrate of Example 29 as the corresponding first positive electrode active material and the second positive electrode active material, and the rest is the same as the treatment of Example 29.

[0223] Example 49

[0224] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 30 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 30.

[0225] Example 50

[0226] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 22 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 22.

[0227] Example 51

[0228] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 23 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 23.

[0229] Example 52

[0230] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 34 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 34.

[0231] Example 53

[0232] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 35 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 35.

[0233] Example 54

[0234] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 36 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 36.

[0235] Example 55

[0236] The first positive electrode active material substrate and the second positive electrode active material substrate of Example 37 were directly used as the corresponding first positive electrode active material and second positive electrode active material without coating treatment, and the rest was the same as that of Example 37.

[0237] Example 56

[0238] The process of Reference Example 1 was referred to, the first positive electrode active material substrate was primary fired at 700℃ for 5h, and secondary fired at 750℃ for 15h; the rest was the same as that of Example 1, to obtain the corresponding polycrystalline first positive electrode active material substrate.

[0239] Example 57

[0240] Referring to the process of Example 1, the first positive electrode active material substrate has a first firing temperature of 700°C and a sintering time of 5h, and the second positive electrode active material substrate has a first firing temperature of 800°C and a sintering time of 3h; the rest is the same as Example 1, to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0241] Example 58

[0242] Referring to the process of Example 1, the first positive electrode active material substrate has a first firing temperature of 700°C and a sintering time of 5h, and the second positive electrode active material substrate has a first firing temperature of 800°C and a sintering time of 3h; the rest is the same as Example 1, to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0243] Test:

[0244] Positive electrode active material element composition test: determined by inductively coupled plasma spectrometer (ICP). The powder samples of the first positive electrode active material substrate and the second positive electrode active material substrate are respectively dissolved in the sample chamber, the sample solution is evaporated by plasma to form gaseous atoms, and light radiation is excited to produce. The collector collects the spectral line intensity to obtain the quantitative content of elements.

[0245] The element composition of each positive electrode active material substrate is basically the same as the set ratio of elements in the raw material.

[0246] Sample morphology characterization: the surface morphology of the positive electrode active material is characterized by a field emission scanning electron microscope (Sigma300) of Germany ZEISS company. Figure 1 The scanning electron microscope image of the first positive electrode active material substrate in Example 1 is recorded. Figure 3 The scanning electron microscope image of the second positive electrode active material substrate in Example 1 is recorded.

[0247] Sample volume particle size distribution characterization: a laser particle size analyzer (Malvern Company, model: Mastersizer3000) is used to test the particle size distribution of the first positive electrode active material substrate, the second positive electrode active material substrate and the formed positive electrode active material composition in each example, respectively, to obtain the particle size volume distribution graph of the first positive electrode active material substrate, the particle size volume distribution graph of the second positive electrode active material substrate and the particle size volume distribution graph of the positive electrode active material composition.

[0248] Particle size distribution characterization of the positive electrode active material composition: the positive electrode active material composition is placed under a scanning electron microscope for observation at a magnification of 3000 times, while EDS element mapping test is carried out, and the first positive electrode active material and the second positive electrode active material are marked according to whether Cu element content exists in the EDS result. In the same field of view, 30 first positive electrode active materials and 30 second positive electrode active materials are selected respectively, the particle size is measured, and 5 random areas are selected for the above operation. Finally, the average particle sizes D1' and D2' of the first positive electrode active material and the second positive electrode active material are calculated. Subsequently, D1' and D2' are taken as the peak positions of the fitting peaks, and the origin software is used to perform peak fitting processing on the volume particle size distribution graph of the positive electrode active material composition based on the Gaussian function. The fitting peak position is kept unchanged during the process, and the volume particle size distribution graph of the positive electrode active material composition is decomposed into a small particle fitting peak type and a large particle fitting peak type. The large particle fitting peak type is basically coincided with the particle size volume distribution graph of the first positive electrode active material, and the small particle fitting peak type is basically coincided with the particle size volume distribution graph of the second positive electrode active material, which indicates that the peak fitting processing result is reliable.

[0249] Characteristic element distribution characterization of the positive electrode active material composition: the positive electrode active material composition is placed under a scanning electron microscope for observation at a magnification of 3000 times, while EDS element mapping test is carried out, and the first positive electrode active material and the second positive electrode active material are marked according to whether Cu element content exists in the EDS result. In the same field of view, 30 first positive electrode active materials and 30 second positive electrode active materials are selected respectively, the average mass content of Cu element is calculated, and 5 random areas are selected for the above operation. The average mass content of Cu element of the small particle fitting peak with a particle size less than or equal to DV10 is marked as m1, which is basically 0. The average mass content of Cu element of the large particle fitting peak with a particle size greater than or equal to DV90 is marked as m2, and m2 is basically the same as the Cu content in the respective first positive electrode material. Therefore, m1 < m2.

[0250] XRD test: XRD pattern test is carried out by using an X-ray diffractometer (Bruker D8 Advance). First, the powder samples of the first positive electrode active material substrate, the second positive electrode active material substrate and the formed positive electrode active material composition are placed on the sample table, and the powder samples are compacted by using a glass sheet. Then, the samples are placed in the sample chamber, and X-ray is used for irradiation to obtain the XRD pattern. The corresponding grain size is calculated by the following method: the Scherrer formula is used to calculate the particle size of the corresponding crystal face of the material. The Scherrer formula is D=(K·γ) / (B·cosθ). K is the Scherrer constant, γ is the wavelength of X-ray, B is the half-height width of the diffraction peak, θ is the Bragg diffraction angle, and D is the thickness perpendicular to the crystal face direction.

[0251] Figure 2The XRD pattern of the first positive electrode active material substrate of Example 1 is recorded. Figure 4 The XRD pattern of the second positive electrode active material substrate of Example 1 is recorded.

[0252] Sample powder compaction density:

[0253] The compaction density of the positive electrode active material 3T under pressure is determined according to GB / T 24533-2019. The top column and upper gasket are removed, 1 g of sample is weighed in the sleeve to 0.0001 g, and the weight is recorded as m. The powder compaction density = 10m / SxH, m is the sample weight, in grams (g); H is the thickness of the sample after compaction, in millimeters (mm); S is the cross-sectional area of the top column, in square centimeters (cm 2 ).

[0254] Sample electrode sheet compaction density characterization:

[0255] To obtain a battery electrode sheet that meets the processability requirements, a punch machine is used to punch out a positive electrode sheet with a diameter of 14 mm, and an electronic balance, a table digital thickness gauge are used to measure the mass m c , thickness d c of the positive electrode sheet, respectively; a sufficient number of aluminum foil sheets with a diameter of 14 mm are punched out using a sheet punching machine, and an electronic balance, a table digital thickness gauge are used to measure the mass mAl, thickness dAlof the aluminum foil sheet, respectively.

[0256] The positive electrode sheet compaction density p c =(m c -mAl) / (p(φ / 2)x(d c -dAl))x10 ^6

[0257] Where: p c is the positive electrode sheet compaction density, in grams per cubic centimeter (g / cm 3 );

[0258] m c is the mass of the positive electrode sheet, in grams (g);

[0259] mAl is the mass of the aluminum foil sheet, in grams (g);

[0260] p is the diameter of the positive electrode sheet, in millimeters (mm);

[0261] d c is the thickness of the positive electrode sheet, in microns (pm);

[0262] dAl is the thickness of the aluminum foil sheet, in microns (pm).

[0263] The test results of the above part are recorded in Table 1, and some results are recorded in Table 2.

[0264]

[0265]

[0266]

[0267]

[0268]

[0269]

[0270] The coating content described above means that the first positive electrode active material and the second positive electrode active material have the same coating content. The mass ratio is the mass ratio of the first positive electrode active material substrate and the second positive electrode active material substrate.

[0271] Performance test:

[0272] Preparation of button cell:

[0273] The positive electrode active material, PVDF, and conductive carbon are added to a certain amount of NMP in a ratio of 90:5:5, and the slurry is prepared by stirring in a dry room. The above slurry is coated on an aluminum foil, dried, and cold-pressed to prepare a positive electrode sheet. Sodium sheet is used as the negative electrode, and the electrolyte is 1 mol / L NaPF6 / (EC+DEC+DMC, volume ratio 1:1:1). The button cell is assembled in a button cell box.

[0274] Button cell initial gram capacity test method:

[0275] At 1.5-4.0V, charge at 0.1C to 4.0V, then charge at 4.0V to current≤0.05mA, stand for 2min, then discharge at 0.1C to 1.5V, the discharge capacity at this time is the initial gram capacity.

[0276] Preparation of full cell:

[0277] The positive electrode active material composition of each example and comparative example was mixed with a conductive agent acetylene black and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 95:3:2 in an N-methyl pyrrolidone solvent system, and then coated on an aluminum foil, dried and cold-pressed to obtain a positive electrode sheet. A negative electrode active material hard carbon, a conductive agent acetylene black, a binder styrene butadiene rubber (SBR) and a thickening agent sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 95:2:2:1 in a deionized water solvent system, and then coated on a copper foil, dried and cold-pressed to obtain a negative electrode sheet. A PE porous polymer film was used as a separator. The positive electrode sheet, the separator and the negative electrode sheet were stacked in order, with the separator between the positive electrode and the negative electrode to play a role of separation, and then wound to obtain a bare battery cell. The bare battery cell was placed in an outer package, injected with a prepared base electrolyte (1 mol / L NaPF6 / (EC+DEC+DMC, volume ratio 1:1:1)) and packaged to obtain a full battery.

[0278] Full battery 25 / 45℃ cycle performance test:

[0279] At 25℃ or 45℃, the constant temperature environment, 1.5-4.0V, according to 1C charge to 4.0V, then 4.0V constant voltage charge to current≤0.05mA, static 5min, then according to 1C discharge to 1.5V, capacity recorded as Dn(n=0,1,2……), repeat the previous process until the capacity fading to 80%.

[0280] The test results are recorded in Table 2.

[0281] Table 2

[0282]

[0283]

[0284]

[0285] According to the data comparison of the examples and comparative example 1, it can be found that the specific capacity of the positive electrode active material composition in the examples is obviously improved when the second positive electrode active material is mixed; according to the data comparison of the examples and comparative example 2, it can be found that the cycle performance of the positive electrode active material composition in the examples is obviously improved when the first positive electrode active material is mixed.

[0286] According to the data comparison of example 1 and examples 34-42, it can be found that when the first positive electrode active material and / or the second positive electrode active material is in a spherical shape, the compaction of the formed composition is obviously improved compared with the compaction of the composition in a sheet shape, and by controlling the D 104 / D 003 After the roundness of the crystal grains is improved, the tap density and the gravimetric capacity can also be further improved.

[0287] In addition, according to the comparison of Examples 1 to 7, it can be found that as the ratio of the first positive electrode active material and the second positive electrode active material changes, both the gravimetric capacity and the cycle performance change, and when the ratio changes such that e1’ / e2’ is between 4 to 40, and the copper mass content in the positive electrode active material composition is between 3.5%-4.7%, both the gravimetric capacity and the cycle performance of the positive electrode active material composition are better.

[0288] According to the comparison of Example 1, Examples 43 to 46, it can be seen that a proper amount of the coating layer has a significant effect on improving the cycle performance of the positive electrode active material composition.

[0289] Although the present application has been described with reference to the preferred embodiments, various modifications can be made to it without departing from the scope of the application, and equivalent components therein can be substituted. In particular, the technical features mentioned in each embodiment can be combined in any manner as long as there is no structural conflict. 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, comprising a first positive electrode active material and a second positive electrode active material, the first positive electrode active material being a nickel-iron-manganese-copper quaternary sodium battery positive electrode active material; the chemical formula of the second positive electrode active material is Na a2 [Ni b2 Fe c2 Mn d2 M e2 ]O2, wherein 0.8≤a2<1, 0.01≤b2<0.35, 0.01≤c2<0.35, 0.01≤d2<0.35, 0≤e2<0.1, b2+c2+d2+e2=1, and the M element comprises any one or more of Zn, Ti, Zr, Mg, La, Y, Co, Cr, Al, K, V, Mo, W, Sr, Ta, Nb or Ca.

2. The positive electrode active material according to claim 1, wherein The M element includes any one or more of Zn, Ti, Zr, Mg, Al, Co, or Ca.

3. The positive electrode active material according to claim 1 or 2, wherein 0.9 < a2 < 0.95, 0.01 < b2 < 0.33, 0.01 < c2 < 0.33, 0.01 < d2 < 0.33, 0.01 < e2 < 0.

08.

4. The positive electrode active material according to claim 1 or 2, wherein 0.02≤e2<0.08。 5. The positive electrode active material according to claim 1 or 2, wherein The chemical formula of the nickel-iron-manganese-copper quaternary sodium battery positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 Cu e1 ]O2, wherein 0.8≤a1<1, 0.01≤b1<0.33, 0.01≤c1<0.33, 0.01≤d1<0.33, 0.02≤e1<0.2, b1+c1+d1+e1=1.

6. The positive electrode active material according to claim 5, wherein 0.9 < a1 < 0.95, 0.06 < e1 < 0.

15.

7. The positive electrode active material according to claim 5, wherein The total molar amount of Cu atoms in the positive electrode active material is e1', and the total molar amount of the M element is e2', and 0.5 < e1' / e2' < 200 per gram of the positive electrode active material.

8. The positive electrode active material according to claim 7, wherein 1 < e1' / e2' < 100.

9. The positive electrode active material according to claim 7, wherein 4 < e1' / e2' < 40.

10. The positive electrode active material according to claim 1 or 2, wherein The mass content of Cu element in the positive electrode active material is 0.5%-12%.

11. The positive electrode active material according to claim 10, wherein The mass content of Cu element in the positive electrode active material is 3.5%-4.7%.

12. The positive electrode active material according to claim 1 or 2, wherein The positive electrode active material particle size is less than or equal to D V The average mass content of Cu element in the positive electrode active material of 10 is m1, and the particle size is greater than or equal to D V The average mass content of Cu element in the positive electrode active material of 90 is m2, and m1 < m2.

13. The positive electrode active material according to claim 1 or 2, wherein The volume distribution particle size of the positive electrode active material satisfies any one or more of the following conditions: 1), D V 10 is 0.5 μm - 2 μm; 2), D V 50 is 7 μm - 11 μm; 3), D V 90 is 14 μm - 20 μm.

14. The positive electrode active material according to claim 1 or 2, wherein The volume particle size distribution curve of the positive electrode active material includes a first peak type and a second peak type, the peak value particle size of the first peak type is D1, the peak value particle size of the second peak type is D2, and D1 < D2.

15. The positive electrode active material of claim 14, wherein, The average mass content of Cu element in the positive electrode active material with a particle size less than or equal to the D1 is m3, and the average mass content of Cu element in the positive electrode active material with a particle size greater than or equal to the D2 is m4, and m3 < m4.

16. The positive electrode active material of claim 14, wherein, The volume particle size distribution curve of the positive electrode active material is subjected to peak separation fitting processing based on a Gaussian function by taking D1 and D2 as the peak positions of fitting peaks, respectively, to obtain at least a first fitting peak type and a second fitting peak type, the peak value particle size of the first fitting peak type is D1, the peak value particle size of the second fitting peak type is D2, the particle size of the first positive electrode active material is within the particle size range corresponding to the second fitting peak type, and the particle size of the second positive electrode active material is within the particle size range corresponding to the first fitting peak type.

17. The positive electrode active material according to claim 1 or 2, wherein The average particle size D1' of the first positive electrode active material is 6-15 μm; and / or the average particle size D2' of the second positive electrode active material is 2-5.5 μm.

18. The positive electrode active material according to claim 17, wherein The average particle size D1' of the first positive electrode active material is 8-12 μm.

19. The positive electrode active material according to claim 17, wherein The average particle size D2' of the second positive electrode active material is 3-4 μm.

20. The positive electrode active material of claim 17, wherein, The volume particle size distribution curve of the positive electrode active material is subjected to peak separation fitting processing based on a Gaussian function by taking D1' and D2' as the peak positions of fitting peaks, respectively, to obtain a small particle fitting peak type and a large particle fitting peak type, the particle size of the first positive electrode active material is within the particle size range corresponding to the large particle fitting peak type, and the particle size of the second positive electrode active material is within the particle size range corresponding to the small particle fitting peak type.

21. The positive electrode active material according to claim 1 or 2, wherein The first positive electrode active material and the second positive electrode active material each independently include a single crystal material or have a single crystal core.

22. The positive electrode active material according to claim 1 or 2, wherein Each of the first positive electrode active material and each of the second positive electrode active material independently has an O3 crystal phase.

23. The positive electrode active material according to claim 1 or 2, wherein The morphology of each of the first positive electrode active material and the second positive electrode active material independently includes any one or more of flaky, spherical or spheroidal.

24. The positive electrode active material of claim 1 or 2, wherein, In XRD patterns of the first positive electrode active material and the second positive electrode active material, the crystal grain sizes corresponding to the (003) diffraction peak, the (101) diffraction peak, and the (104) diffraction peak, respectively, are D 003 , D 101 , and D 104 , and satisfy 1.5 < D 104 / D 003 < 1.7, or satisfy 0.9 < D 101 / D 003 < 1.

2.

25. The positive electrode active material of claim 24, wherein, 1.55 < D 104 / D 003 <1.

65.

26. The positive electrode active material of claim 24, wherein, 1.05 < D 101 / D 003 <1.

15.

27. The positive electrode active material according to claim 1 or 2, wherein The mass ratio of the first positive electrode active material and the second positive electrode active material is 5:5-9:

1.

28. The positive electrode active material according to claim 1 or 2, wherein The mass ratio of the first positive electrode active material and the second positive electrode active material is 6:4-8:

2.

29. The positive electrode active material according to claim 1 or 2, wherein At least part of the surface of each of the first positive electrode active material and the second positive electrode active material independently has a coating layer; the coating layer includes a sodium phosphate salt.

30. The positive electrode active material according to claim 29, wherein The sodium phosphate salt includes NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n.

31. The positive electrode active material according to claim 29, wherein The weight content of the sodium phosphate salt in the positive electrode active material is 1000 ppm -30000 ppm.

32. The positive electrode active material according to claim 31, wherein The weight content of the sodium phosphate salt in the positive electrode active material is 5000 ppm -20000 ppm.

33. The positive electrode active material according to claim 1 or 2, wherein 3. The powder compaction density of the positive active material under 3 tons pressure is ≥ 3.1 g / cm 3 .

34. The positive electrode active material according to claim 33, wherein 3. The powder compaction density of the positive active material under 3 tons pressure is ≥ 3.3 g / cm 3 .

35. A method of producing the positive electrode active material according to any one of claims 1 to 34, wherein The preparation method comprises: Preparation of the first positive electrode active material, mixing the Ni salt solution, the Fe salt solution, the Cu salt solution and the Mn salt solution according to a set ratio to form a first mixed salt solution, adding the first mixed salt solution, a first precipitating agent and a first complexing agent into a reaction container, controlling the pH value and the reaction temperature of the materials in the reaction container to perform a co-precipitation reaction to obtain the first positive electrode active material precursor, the pH value is recorded as pH1 and pH1 is 9-12; mixing the first positive electrode active material precursor and a first sodium salt according to a ratio to form a first mixture, and performing a first calcination treatment on the first mixture to obtain the first positive electrode active material; Preparation of the second positive electrode active material, mixing the Ni salt solution, the Fe salt solution, the Mn salt solution and the optional salt solution containing the element M according to a set ratio to form a second mixed salt solution, pumping the second mixed salt solution, a second precipitating agent and a second complexing agent into a reaction container, controlling the pH value and the reaction temperature of the materials in the reaction container to perform a co-precipitation reaction to obtain the second positive electrode active material precursor, the pH value is recorded as pH2 and pH2 is 11-14; mixing the second positive electrode active material precursor and a second sodium salt according to a ratio to form a second mixture, and performing a second calcination treatment on the first mixture to obtain the second positive electrode active material; Mixing the first positive electrode active material and the second positive electrode active material to obtain the positive electrode active material.

36. The method of manufacturing according to claim 35, wherein, The Ni salt, Fe salt, Mn salt, Cu salt and M salt comprise one or more of a sulfate, nitrate, oxalate or chloride of each; the first precipitant and the second precipitant each independently comprise an aqueous solution of one or more of sodium hydroxide, sodium carbonate, potassium carbonate or potassium hydroxide; the first complexing agent and the second complexing agent each independently comprise an aqueous solution of one or more of ammonia, ammonium chloride, ammonium sulfate, ammonium carbonate, ammonium bicarbonate or citric acid.

37. The method of manufacturing according to claim 36, wherein, The concentration of the first complexing agent is 1-2 mol / L, and the concentration of the second complexing agent is 0.5-1 mol / L.

38. The method of manufacturing according to any one of claims 35 to 37, wherein, The first calcination process comprises a process of first preliminary firing at a first temperature and first firing at a second temperature, and the first temperature is lower than the second temperature; and / or the molar ratio of sodium in the first sodium salt to metal elements in the first positive electrode active material precursor is 0.8-0.

95.

39. The method of manufacturing according to claim 38, wherein, The first temperature of the first preliminary firing is 700-900℃, and the holding time is 3h-10h.

40. The method of manufacturing according to claim 38, wherein, The second temperature of the first firing is 850℃-1200℃, and the holding time is 8h-20h.

41. The method of manufacturing according to claim 40, wherein, The second temperature of the first firing is 900℃-1000℃.

42. The method of manufacturing according to claim 40, wherein, The holding time of the first firing is 12h-18h.

43. The method of manufacturing according to claim 38, wherein, The molar ratio of sodium in the first sodium salt to metal elements in the first positive electrode active material precursor is 0.9-0.

93.

44. The method of making according to any one of claims 35 to 37, wherein, The second calcination process comprises a process of second preliminary firing at a third temperature and second firing at a fourth temperature, and the third temperature is higher than the fourth temperature; and / or the molar ratio of sodium in the second sodium salt to metal elements in the second positive electrode active material precursor is 0.8-0.

95.

45. The method of manufacturing according to claim 44, wherein, The third temperature of the second preliminary firing is 850-1000℃, and the holding time is 3h-8h.

46. The method of manufacturing according to claim 44, wherein, The fourth temperature of the second firing is 700℃-950℃, and the holding time is 8h-20h.

47. The method of manufacturing according to claim 46, wherein, The fourth temperature of the second firing is 800℃-920℃.

48. The method of manufacturing according to claim 46, wherein, The holding time of the second firing is 9h-15h.

49. The method of manufacturing according to claim 44, wherein, The molar ratio of sodium in the second sodium salt to metal elements in the second positive electrode active material precursor is 0.9-0.

93.

50. The method of making according to any one of claims 35 to 37, wherein, The preparation method further comprises: mixing a phosphate compound, the first positive electrode active material and the second positive electrode active material to form a mixed base material, the phosphate compound comprising one or more of NH4H2PO4, (NH4)2HPO4, (NH4)2H2P2O7, NH4H3P2O7, NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; performing third calcination on the mixed base material to obtain the positive electrode active material.

51. The method of manufacturing according to claim 50, wherein, The ratio of the weight of the phosphate compound to the total weight of the first positive electrode active material and the second positive electrode active material is 1000 ppm-30000 ppm.

52. The method of manufacturing according to claim 51, wherein, The ratio of the weight of the phosphate compound to the total weight of the first positive electrode active material and the second positive electrode active material is 5000 ppm-20000 ppm.

53. The method of manufacturing according to claim 50, wherein, The third calcination has a temperature of 200°C to 500°C and a time of 5 hours to 15 hours.

54. The method of manufacturing according to claim 53, wherein, The third calcination has a temperature of 300°C to 400°C.

55. The method of manufacturing according to claim 53, wherein, The third calcination has a time of 7 hours to 10 hours.

56. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, wherein, The positive electrode active material includes the positive electrode active material of any one of claims 1 to 34.

57. The cathode sheet of Claim 56, wherein, The compacted density of the positive electrode plate is ≥ 3.1 g / cm 3 .

58. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the positive electrode sheet comprising a positive electrode active material, wherein, The positive electrode active material includes the positive electrode active material of any one of claims 1 to 34.

59. An electrical device comprising an electrical device, wherein, The electric device includes the secondary battery of claim 58.

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