Positive electrode active material and preparation method therefor, positive electrode sheet, secondary battery, and electric device

Abstract

Provided in the present application are a positive electrode active material and a preparation method therefor, 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, wherein 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 Naa2[Nib2Fec2Mnd2Me2]O2, where 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 element M 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

Positive electrode active material, preparation method thereof, positive electrode sheet, secondary battery and electric device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application 202311186588.X filed on September 14, 2023, entitled “A positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery and an electrical device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0004] After nearly a decade of extensive research from all walks of life, sodium-ion batteries have developed a cathode active material system mainly based on transition metal oxides, Prussian blue, and polyanion phosphates. Among them, transition metal oxides have relatively high specific capacity, but at the same time, their poor cycle performance and low energy density have always been important factors affecting the application of sodium-ion battery cathode active materials.

[0005] Currently, common transition metal oxides are mainly divided into two types, one is nickel-iron-manganese-based oxide, and the other is nickel-manganese-iron-copper-based oxide containing copper elements. Regardless of which of these two types, changing the different ratios of nickel, iron, manganese and copper elements can obtain sodium ion battery positive electrode active materials with different performance.

[0006] To improve the cycling performance of transition metal oxides, single-crystal transition metal oxides have emerged. For single-crystal nickel-manganese-iron-copper (NiMnFeCu)-based oxide-based quaternary cathode active materials, the addition of Cu can improve the material's structural stability and cycling performance. Furthermore, Cu has a fluxing effect, promoting single-crystal particle growth, thereby reducing the material's specific surface area and interfacial side reactions, improving cycling performance. However, the gram capacity of NiFeMnCu quaternary cathode active materials is low, limiting the material's energy density.

[0007] Summary of the Invention

[0008] The present application provides a positive electrode active material, a preparation method thereof, a positive electrode plate, a secondary battery and an electrical device to improve the energy density of a nickel-iron-manganese-copper quaternary positive electrode active material.

[0009] The first aspect of the present application provides a positive electrode active material, including a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material is a nickel-iron-manganese-copper quaternary sodium positive electrode active material; the chemical formula of the second positive electrode active material is Na a2 [Nib2 Fe c2 Mn d2 M e2 O₂, where 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 < a₂ < 0.95, 0.01 ≤ b₂ < 0.33, 0.01 ≤ c₂ < 0.33, 0.01 ≤ d₂ < 0.33, 0.01 ≤ e₂ < 0.08; further optionally, 0.02 ≤ e₂ < 0.08.

[0010] 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 a higher specific capacity relative to the first positive electrode active material, so the two are mixed to compensate for the defect of the low specific capacity of the first positive electrode active material, and thus the positive electrode active material can obtain a higher energy density, that is, specific capacity.

[0011] In any implementation manner of the first aspect, the chemical formula of the above nickel-iron-manganese-copper quaternary sodium-ion positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 Cu e1 O₂, where 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; optionally, 0.9 < a₁ < 0.95, 0.06 ≤ e₁ < 0.15. This further improves the cycle performance of the positive electrode active material.

[0012] In any implementation manner of the first aspect, optionally, in each gram of the positive electrode active material, the total molar amount of Cu atoms is e₁', and the total molar amount of the M element 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.

[0013] In any embodiment of the first aspect, the mass content of the Cu element in the positive electrode active material is 0.5% to 12%, preferably 3.5% to 4.7%. This allows for a more balanced ratio between the first positive electrode active material and the second positive electrode active material, thereby significantly improving the cycling performance and energy density of the positive electrode active material compared to a single material.

[0014] In any embodiment of the first aspect, the average mass content of Cu element in the positive electrode active material having a particle size less than or equal to DV10 is m1, and the average mass content of Cu element in the positive electrode active material having a particle size greater than or equal to DV10 is m1. V The average mass content of Cu element in the positive electrode active material is m2, m1<m2. This effectively improves the cycle performance and energy density of the positive electrode active material.

[0015] In any embodiment of the first aspect, 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 0.5μm-2μm; 2) D V 50 is 7μm-11μm; 3) D V 90 is 14μm-20μm. The above volume particle size distribution makes the gradation between particles better and is more conducive to improving compaction.

[0016] 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, wherein 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, further improving the energy density of the positive electrode active material composition.

[0017] In any embodiment of the first aspect, the average mass content of Cu in the positive electrode active material having a particle size less than or equal to D1 is m3, and the average mass content of Cu in the positive electrode active material having a particle size greater than or equal to D2 is m4, where m3 < m4. This effectively improves the cycle performance and energy density of the positive electrode active material.

[0018] In any embodiment of the first aspect, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing based on a Gaussian function using origin software, with D1 and D2 as the peak positions of the fitting peaks, to obtain at least a first fitting peak shape and a second fitting peak shape, wherein the peak particle size of the first fitting peak shape is D1, the peak particle size of the second fitting peak shape is D2, the particle size of the first positive electrode active material is within the particle size range corresponding to the second fitting peak shape, and the particle size of the second positive electrode active material is within the particle size range corresponding to the first fitting peak shape. This effectively improves the cycle performance and energy density of the positive electrode active material.

[0019] In any embodiment of the first aspect, the average particle size D1' of the first positive electrode active material is 6 μm-15 μm, optionally 8 μm-12 μm; and / or the average particle size D2' of the second positive electrode active material is 2 μm-5.5 μm, optionally 3 μm-4 μm. This effectively improves the cycle performance and energy density of the positive electrode active material.

[0020] In any embodiment of the first aspect, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing using origin software based on a Gaussian function, with D1' and D2' being used as the peak positions of the fitting peaks, respectively. During the fitting process, the fitting peak positions are maintained unchanged 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. This effectively improves the cycle performance and energy density of the positive electrode active material.

[0021] 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.

[0022] In any embodiment of the first aspect, the first positive electrode active material and the second positive electrode active material each independently have an O3 crystal phase, thereby further improving the energy density of the positive electrode active material.

[0023] In any embodiment of the first aspect, the morphology of the first cathode active material and the second cathode active material independently includes any one or more of flake, spherical, or quasi-spherical.

[0024] In any embodiment of the first aspect, in the XRD spectra of the first positive electrode active material and the second positive electrode active material, the grain size corresponding to the (003) diffraction peak, the (101) diffraction peak, and the (104) diffraction peak is D 003 、D 101 and D 104 , and meets 1.5 <D 104 / D 003 <1.7, further optional 1.55 <D 104 / D 003 <1.65, or meet 0.9 <D 101 / D 003 <1.2, further optional to 1.05 <D 101 / D 003 <1.15. The grain size ratio that satisfies the above conditions enables the positive electrode active material to have a higher particle roundness, which is more conducive to improving the compaction density of the positive electrode active material.

[0025] In any embodiment of the first aspect, the mass ratio of the first positive electrode active material to the second positive electrode active material is 5:5-9:1, and can be optionally 6:4-8:2.

[0026] In any embodiment of the first aspect, at least a portion of the surface of the first and second positive electrode active materials is independently coated; the coating comprises a sodium phosphate salt, optionally comprising NaH2PO4, Na2HPO4, Na3PO4, or (NaPO3)n; optionally, the weight content of the sodium phosphate salt in the positive electrode active material is 1000ppm-30000ppm, optionally 5000ppm-20000ppm. This consumes residual sodium on the surface of the material, thereby improving the cycling and sodium storage stability of the positive electrode active material.

[0027] In any embodiment of the first aspect, the powder compaction density of the positive electrode active material under the above 3 tons pressure is ≥3.1 g / cm 3 , optionally with a powder compaction density ≥ 3.3 g / cm 3 The increase in compaction density leads to an increase in the energy density of the material.

[0028] The second aspect of the present application provides a preparation method of any positive electrode active material of the first aspect, the preparation method comprising: preparing a first positive electrode active material, mixing a Ni salt solution, an Fe salt solution, a Cu salt solution and a Mn salt solution according to a set ratio to form a first mixed salt solution, adding the first mixed salt solution, a first precipitant and a first complexing agent into a reaction container, controlling the pH value and reaction temperature of the materials in the reaction container to perform a coprecipitation reaction to obtain a first positive electrode active material precursor, the pH value of which is recorded as pH1 and the pH1 is 9-12; mixing the first positive electrode active material precursor and the first sodium salt in proportion to form a first mixture, performing a first calcination treatment on the first mixture to obtain the first positive electrode active material. Materials; prepare a second positive electrode active material, mix a Ni salt solution, an Fe salt solution, a Mn salt solution and an optional salt solution containing an M element in a set proportion to form a second mixed salt solution, pump the second mixed salt solution, a second precipitant and a second complexing agent into a reaction vessel, control the pH value and reaction temperature of the materials in the reaction vessel to perform a co-precipitation reaction to obtain a second positive electrode active material precursor, the pH value is recorded as pH2 and pH2 is 11-14; mix the second positive electrode active material precursor with the second sodium salt in proportion to form a second mixture, perform a second calcination treatment on the first mixture to obtain a second positive electrode active material; mix the first positive electrode active material and the second positive electrode active material to obtain a positive electrode active material. The preparation method of the present application prepares the first positive electrode active material and the second positive electrode active material separately, which makes it easier to control the composition, morphology, crystal phase and other characteristics of each, and has higher flexibility.

[0029] In any embodiment of the second aspect, the Ni salt, Fe salt, Mn salt, Cu salt and M salt include a mixture of one or more of their respective sulfates, nitrates, oxalates or chlorides, the first precipitant and the second precipitant each independently include an aqueous solution of a mixture 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 include an aqueous solution of a mixture of one or more of ammonia water, 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.

[0030] In any embodiment of the second aspect, the first calcination treatment includes a first preliminary calcination at a first temperature and a second preliminary calcination at a second temperature, wherein 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 3-10 hours; optionally, the second temperature of the first preliminary calcination is 850-1200°C, further optionally 900-1000°C, and the holding time is 8-20 hours, further optionally 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, and optionally 0.9-0.93. The sintering temperature of the first short-frying treatment is initially low and then high, which removes moisture and promotes particle size growth.

[0031] 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°C, and the holding time is 3-8 hours; optionally, the fourth temperature of the second calcination is 700-950°C, further optionally 800-920°C, and the holding time is 8-20 hours, further optionally 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, optionally 0.9-0.93. In the second calcination treatment, the calcination temperature is first high and then low, which promotes the reaction while reducing the particle size and inhibiting particle growth.

[0032] In any embodiment of the second aspect, the preparation method further includes: mixing a phosphate compound, a first positive electrode active material and a 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 includes a mixture of one or more of NH4H2PO4, (NH4)2HPO4, (NH4)2H2P2O7, NH4H3P2O7, NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; performing a third calcination on the mixed base material 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.

[0033] The third aspect of the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material, wherein the positive electrode active material comprises any one of the positive electrode active materials provided in the first aspect; optionally, the compaction density of the positive electrode sheet is ≥3.1 g / cm 3 .

[0034] The fourth aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises any one of the positive electrode active materials provided in the first aspect.

[0035] A fifth aspect of the present application provides an electric device, including an electric device, wherein the electric device includes any one of the secondary batteries provided in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0037] FIG1 is a scanning electron microscope image of the first positive electrode active material substrate of Example 1.

[0038] FIG2 is an XRD spectrum of the first positive electrode active material substrate of Example 1.

[0039] FIG3 is a scanning electron microscope image of the second positive electrode active material substrate of Example 1.

[0040] FIG4 is an XRD spectrum of the second positive electrode active material substrate of Example 1.

[0041] FIG5 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0042] FIG. 6 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 5 .

[0043] FIG7 is a schematic diagram of a battery module according to an embodiment of the present application.

[0044] FIG8 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0045] FIG. 9 is an exploded view of the battery pack shown in FIG. 8 according to an embodiment of the present application.

[0046] FIG. 10 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0047] In the drawings, the drawings are not drawn to scale.

[0048] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0049] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, i.e., the present application is not limited to the described embodiments.

[0050] Below, the embodiments of the positive electrode active material, preparation method thereof, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0051] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0052] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0053] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0054] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0055] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or comprised.

[0056] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies 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).

[0057] [Secondary battery]

[0058] A secondary battery, also known as a rechargeable battery or a storage battery, refers to a battery that can be activated by charging after discharging so as to be used continuously.

[0059] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte. During the charging and discharging of the battery, active ions (such as lithium ions) are inserted into and extracted from between the positive electrode plate and the negative electrode plate. The electrolyte is located between the positive electrode plate and the negative electrode plate and mainly functions to conduct active ions.

[0060] [Positive electrode active material]

[0061] Since the specific capacity of the nickel-iron-manganese-copper quaternary positive electrode active material is relatively low, which limits the energy density of the material. In order to improve the energy density of the positive electrode active material, in the first embodiment of this 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-ion 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, where 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 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 < a2 < 0.95, 0.01 ≤ b2 < 0.33, 0.01 ≤ c2 < 0.33, 0.01 ≤ d2 < 0.33, 0.01 ≤ e2 < 0.08; further optionally, 0.02 ≤ e2 < 0.08.

[0062] 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 a higher specific capacity relative to the first positive electrode active material. Therefore, the two are mixed to compensate for the defect of the low specific capacity of the first positive electrode active material, so that the positive electrode active material can obtain a higher energy density, that is, specific capacity.

[0063] 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.

[0064] The nickel-iron-manganese-copper quaternary sodium-based positive electrode active material for 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 effect 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-based positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 Cu e1 O2, where 0.8 ≤ a1 < 1, 0.01 ≤ b1 < 0.33, 0.01 ≤ c1 < 0.33, 0.01 ≤ d1 < 0.33, 0.02 ≤ e1 < 0.2, and 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 to further improve the cycle performance of the positive electrode active material.

[0065] 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.

[0066] In some embodiments of the present application, optionally, per gram of positive electrode active material, the total molar amount of Cu atoms is e1', 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. By controlling the above e1' and e2', the Cu element content in the first positive electrode active material and the M element content in the second positive electrode active material are within a more suitable range, so that the first positive electrode active material obtains higher cycle stability, and at the same time, the content of the M element is limited, and the cycle stability of the second positive electrode active material is improved as much as possible while improving the capacity, so that the first positive electrode active material and the second positive electrode active material form a better coordination effect, which is more conducive to improving the cycle performance and capacity of the positive electrode active material.

[0067] In some embodiments of the present application, the mass content of the Cu element in the positive electrode active material is 0.5%-12%, preferably 3.5%-4.7%. By limiting the Cu element content in the positive electrode active material, the content of the first positive electrode active material is limited. Within this Cu element content range, the ratio of the first positive electrode active material to the second positive electrode active material is more coordinated, thereby significantly improving the cycle performance and energy density of the positive electrode active material compared to a single material.

[0068] This application uses an inductively coupled plasma spectrometer (ICP) to test and detect the elemental components in the positive electrode active material; a scanning electron microscope (SEM) combined with an X-ray energy dispersive spectrometer (EDS) is used to test the elemental distribution on the particle surface. The particles with the Cu element distribution are the first positive electrode active material, and the particles containing the doped M element are the second positive electrode active material. EDS is used to test the elemental content of the first positive electrode active material and the second positive electrode active material.

[0069] 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 Dv10 is m1, and the average mass content of Cu element in the positive electrode active material with a particle size greater than or equal to Dv10 is m1. v The average mass content of Cu in the positive electrode active material of 90% is m2, where m1 < m2. Under the above conditions, the positive electrode active material with larger particle size is mostly the first positive electrode active material containing Cu, while the positive electrode active material with smaller particle size is mostly the second positive electrode active material. The large particles of the first positive electrode active material have better structural stability and fewer interfacial side reactions, providing better cycling performance for the positive electrode active material. The small particles of the second positive electrode active material take advantage of their small particle size to provide higher energy density for the positive electrode active material. The gradation of the particle sizes of the two effectively improves the cycling performance and energy density of the positive electrode active material.

[0070] The above average mass content of Cu element is calculated by scanning single particles in EDS mode under a scanning electron microscope to detect the Cu element content in each single particle, and taking the average value after scanning multiple single particles.

[0071] In some embodiments of the present application, 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 0.5μm-2μm; 2) D V 50 is 7μm-11μm; 3) D V 90 is 14μm-20μm. The above volume particle size distribution makes the gradation between particles better and is more conducive to improving compaction.

[0072] The volume particle size distribution of the positive electrode active material is measured using a particle size testing device such as a laser particle size analyzer.

[0073] On the basis of achieving energy density improvement by combining the components of the first positive electrode active material and the second positive electrode active material, in some embodiments, the volume particle size distribution curve of the above-mentioned 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 a combination of large particle size and small particle size to achieve particle grading, which is beneficial to further improve the compaction density of the positive electrode active material, thereby further improving the energy density of the positive electrode active material composition.

[0074] In some embodiments, the average mass content of Cu in the positive electrode active material with a particle size less than or equal to D1 is m3, and the average mass content of Cu in the positive electrode active material with a particle size greater than or equal to D2 is m4, where m3<m4. Under the above conditions, the positive electrode active material with a larger 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 smaller 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 fewer interfacial side reactions, providing better cycle performance for the positive electrode active material; the second positive electrode active material with small particles takes advantage of its small particle size to provide a higher energy density for the positive electrode active material. The grading of the particle sizes of the two more effectively improves the cycle performance and energy density of the positive electrode active material.

[0075] In some embodiments, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing based on a Gaussian function using origin software, 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 conditions, when the second positive electrode active material is mixed with the first positive electrode active material, the gaps between the particles of the second positive electrode active material are more fully filled, thereby more effectively improving the cycle performance and energy density of the positive electrode active material.

[0076] In some embodiments of the present application, the average particle size D1' of the first positive electrode active material is 6 μm-15 μm, optionally 8 μm-12 μm; the average particle size D2' of the second positive electrode active material is 2 μm-5.5 μm, optionally 3 μm-4 μm. As a small-particle positive electrode active material, the second positive electrode active material better fills the intergranular spaces of the first positive electrode active material, resulting in significantly improved cycling performance and energy density of the positive electrode active material.

[0077] When the positive electrode active material is used 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 performed simultaneously. The first positive electrode active material and the second positive electrode active material are marked according to the presence or absence of Cu element content in the EDS results. 30 first positive electrode active materials and 30 second positive electrode active materials are selected in the same field of view, and the particle size of each is measured. Five areas are randomly selected and the above operation is performed to calculate the average particle sizes D1' and D2' of the first positive electrode active material and the second positive electrode active material.

[0078] In some embodiments of the present application, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing based on a Gaussian function using origin software, with D1' and D2' respectively being the peak positions of the fitting peaks. During the fitting process, the fitting peak positions are kept unchanged 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. When the volume particle size distribution curve of the positive electrode active material does not show a clearly distinguished peak particle size, after peak fitting is performed based on the above-mentioned average particle sizes D1' and D2', if the obtained fitting peak type meets the above-mentioned conditions, the second positive electrode active material, when mixed with the first positive electrode active material, has a more sufficient filling effect on the particle gaps of the second positive electrode active material, thereby more effectively improving the cycle performance and energy density of the positive electrode active material.

[0079] The first and second cathode active materials of the present application may be single crystal materials, single crystal-like materials, or secondary spherical particles. In some embodiments of the present application, the first and second cathode active materials each independently comprise single crystal materials or have a single crystal core. Single crystal structures have greater structural stability, thereby further improving the cycling stability of the material.

[0080] 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 each second positive electrode active material independently have an O3 crystal phase.

[0081] In some embodiments of the present application, the morphology of the first and second positive electrode active materials each independently includes any one or more of a flake, a sphere, or a quasi-spherical shape. During compression, the particles of the flake material support each other, resulting in a lower compaction than that of a sphere or a quasi-spherical shape. In some embodiments, the morphology of the first and second positive electrode active materials each independently includes any one or more of a sphere or a quasi-spherical shape.

[0082] 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, optionally, in the XRD spectra of the first positive electrode active material and the second positive electrode active material, the grain size corresponding to the (003) diffraction peak, the (101) diffraction peak, and the (104) diffraction peak is D 003 、D 101 and D 104 , and meets 1.5 <D 104 / D 003 <1.7, further optional 1.55 <D 104 / D 003 <1.65, or meet 0.9 <D 101 / D 003 <1.2, further optional to 1.05 <D 101 / D 003 <1.15. For sodium-ion cathode active materials with an O3 structure, the grain sizes corresponding to the (104), (101), and (003) diffraction peaks are related to the particle thickness along these crystal planes. The ratio of the corresponding grain sizes determines the thickness ratio of the material in different directions. A grain size ratio that satisfies the above conditions results in a higher particle roundness in the cathode active material, which is more conducive to increasing the compaction density of the cathode active material.

[0083] The above XRD spectrum was obtained by the following test method: XRD spectrum test was performed using an X-ray diffractometer (Bruker D8 Advance). First, the powder sample was placed on the sample stage, flattened with a glass sheet, and then placed in the sample chamber and irradiated with X-rays to obtain the XRD spectrum.

[0084] The corresponding grain size is calculated using the Scherrer formula. The Scherrer formula is D = (K·γ) / (B·cosθ). K is the Scherrer constant, γ is the wavelength of the X-ray, B is the half-width at half-maximum of the diffraction peak, θ is the Bragg diffraction angle, and D is the thickness perpendicular to the crystal plane.

[0085] 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 to the second positive electrode active material is 5:5-9:1, and can be optionally 6:4-8:2.

[0086] In order to consume the residual Na on the surface of the material and improve the circulation and sodium storage stability, in some embodiments of the present application, the above-mentioned first positive electrode active material and the second positive electrode active material each independently have a coating layer, and the coating layer includes sodium phosphate salt, optionally the sodium phosphate salt includes NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)6 (sodium hexametaphosphate); optionally, the weight content of sodium phosphate salt in the positive electrode active material is 1000ppm-30000ppm, optionally 5000ppm-20000ppm.

[0087] In some embodiments of the present application, the powder compaction density of the positive electrode active material under 3 tons of pressure is ≥3.1 g / cm 3 , optionally with a powder compaction density ≥ 3.3 g / cm 3 The increase in compaction density leads to an increase in the energy density of the material.

[0088] In a second embodiment of the present application, a method for preparing any one of the above-mentioned positive electrode active materials is provided, the preparation method comprising:

[0089] preparing a first positive electrode active material, mixing a Ni salt solution, an Fe salt solution, a Cu salt solution, and a Mn salt solution in a set proportion to form a first mixed salt solution, pumping the first mixed salt solution, a first precipitant, and a first complexing agent into a reactor, controlling the pH value and reaction temperature of the materials in the reactor to perform a coprecipitation reaction to obtain a first positive electrode active material precursor, wherein the pH value is recorded as pH1 and the pH1 is 9-12; mixing the first positive electrode active material precursor and a first sodium salt in proportion to form a first mixture, and performing a first calcination treatment on the first mixture to obtain the first positive electrode active material;

[0090] preparing a second positive electrode active material, mixing a Ni salt solution, an Fe salt solution, a Mn salt solution, and an optional salt solution containing an M element in a set proportion to form a second mixed salt solution, pumping the second mixed salt solution, a second precipitant, and a second complexing agent into a reactor, controlling the pH value and reaction temperature of the materials in the reactor to perform a coprecipitation reaction to obtain a second positive electrode active material precursor, wherein the pH value is recorded as pH2 and the pH2 is 11-14; mixing the second positive electrode active material precursor and a second sodium salt in proportion to form a second mixture, and performing a second calcination treatment on the first mixture to obtain a second positive electrode active material;

[0091] The first positive electrode active material and the second positive electrode active material are mixed to obtain a positive electrode active material.

[0092] The above preparation method controls the particle size of the precursor through a coprecipitation process, and then forms the corresponding positive electrode active material through calcination. After mixing, the positive electrode active material of the present application can be prepared. The calcination conditions refer to the calcination conditions of conventional sodium battery positive electrode active materials, such as calcination in air or oxygen atmosphere. The preparation method of the present application prepares the first positive electrode active material and the second positive electrode active material separately, which makes it easier to control the respective composition, morphology, crystal phase and other characteristics, and has higher flexibility.

[0093] In addition to increasing the particle size of the first positive electrode active material precursor by incorporating copper, the particle size can also be controlled by controlling the pH value during the coprecipitation process, the amount of complexing agent added, etc. In some embodiments, pH 1 is optionally 10-11.5; pH 2 is 12-13.5.

[0094] The raw materials used in this application can also be referenced to the commonly used raw materials for preparing sodium positive electrode active materials. In some embodiments of this application, the above-mentioned Ni salt, Fe salt, Mn salt, Cu salt, and M salt include a mixture of one or more of their respective sulfates, nitrates, oxalates, or chlorides; the first precipitant and the second precipitant each independently include an aqueous solution of a mixture 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 include an aqueous solution of a mixture 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. The particle size of the precursor obtained by co-precipitation is further adjusted by the amount of the complexing agent.

[0095] Calcination conditions can lead to differences in the morphology of the resulting positive electrode active material. In some embodiments, to obtain a first positive electrode active material with better roundness, a first calcination treatment is selected that includes a first initial calcination at a first temperature and a second initial calcination at a second temperature, where 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 initial calcination temperature is 850-1200°C, further optionally 900-1000°C, and the holding time is 8-20 hours, further optionally 12-18 hours. The sintering temperature of the first short calcination treatment is initially low and then high, which removes moisture and promotes particle size growth.

[0096] In some embodiments, 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 to 0.95, and can be optionally 0.9 to 0.93.

[0097] In some embodiments, to obtain a second positive electrode active material with better roundness, the second calcination process 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°C, and the holding time is 3-8 hours; optionally, the fourth temperature of the second calcination is 700-950°C, further optionally 800-920°C, and the holding time is 8-20 hours, further optionally 9-15 hours. In the second calcination process, the calcination temperature is first high and then low, which promotes the reaction while reducing the particle size and inhibiting particle growth.

[0098] 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 to 0.95, and can be optionally 0.9 to 0.93.

[0099] In some embodiments of the present application, the above-mentioned preparation method further includes: mixing a phosphate compound, a first positive electrode active material and a 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 includes a mixture of one or more of NH4H2PO4, (NH4)2HPO4, (NH4)2H2P2O7, NH4H3P2O7, NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; performing a third calcination on the mixed base material to obtain a 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. The above process consumes the residual sodium on the surface of the first positive electrode active material and the second positive electrode active material serving as the core structure. The prepared sodium phosphate coating layer can also protect the core structure, prevent it from direct contact with the electrolyte, reduce the occurrence of interfacial side reactions, and thus improve the cycle performance of the positive electrode active material.

[0100] In some embodiments of the present application, a positive electrode active material is further provided, the chemical formula of the positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 G g1O2, the G element 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. Optionally, the G element includes any one or more of Cu, Zn, Ti, Zr, Mg, Al, Co or Ca; where 0.8 ≤ a1 < 1, 0.01 ≤ b1 < 0.33, 0.01 ≤ c1 < 0.33, 0.01 ≤ d1 < 0.33, 0.001 ≤ g1 < 0.2, and b1 + c1 + d1 + g1 = 1; optionally, 0.9 < a1 < 0.95, 0.06 ≤ e1 < 0.15. The positive electrode active material satisfying this range has a higher specific capacity or stable cycling performance compared to other sodium battery positive electrode active materials.

[0101] In some embodiments, the morphologies of the above positive electrode active materials independently include any one or more of sheet-like, spherical or quasi-spherical shapes. To improve the tap density of the positive electrode active material.

[0102] In some embodiments, in the XRD pattern of the above positive electrode active material, the grain sizes corresponding to the (003) diffraction peak, (101) diffraction peak, and (104) diffraction peak are 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 satisfy 0.9 < D 101 / D 003 < 1.2, further optionally 1.05 < D 101 / D 003 < 1.15. To further improve the roundness of the positive electrode active material.

[0103] In some embodiments, the tap density of the powder of the above positive electrode active material ≥ 3.0 g / cm 3 .

[0104] [Positive electrode sheet]

[0105] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

[0106] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0107] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the positive electrode active material is any one of the positive electrode active materials provided in the above embodiments of the present application.

[0109] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may 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 acrylate resin.

[0110] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0112] In some embodiments, the compaction density of the positive electrode film is ≥3.1 g / cm 3 , the test method is:

[0113] Obtain battery electrodes that meet the machinability requirements, use a punch to punch out positive electrodes with a diameter of 14 mm, and use an electronic balance and a desktop digital thickness gauge to measure the mass m of the positive electrodes. c , thickness d c ; Use a punching machine to punch out a sufficient number of aluminum foil substrates with a diameter of 14 mm, and use an electronic balance and a desktop digital thickness gauge to measure the mass mA1 and thickness dAl of the aluminum foil substrates respectively.

[0114] Positive electrode compaction density

[0115] Where: cis the compacted density of the positive electrode, in grams per cubic centimeter (g / cm 3 );

[0116] m c is the mass of the positive electrode, in grams (g);

[0117] mA1 is the mass of the aluminum foil substrate, in grams (g);

[0118] is the diameter of the positive electrode sheet, in millimeters (mm);

[0119] d c is the thickness of the positive electrode sheet, in micrometers (μm);

[0120] dAl is the thickness of the aluminum foil substrate in micrometers (μm).

[0121] When 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 by the powder scraping method, crushed, and the binder therein is dissolved by a solvent. After filtering and drying, the corresponding tests can be performed using the aforementioned methods.

[0122] [Negative electrode]

[0123] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0124] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0125] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0126] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0127] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may 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).

[0128] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0130] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0131] [Electrolytes]

[0132] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0133] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0134] In some embodiments, the electrolyte salt can be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalatoborate, sodium dioxalatoborate, sodium difluorodioxalatophosphate, and sodium tetrafluorooxalatophosphate.

[0135] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl 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, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0136] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0137] [Isolation film]

[0138] In some embodiments, the secondary battery further includes a separator. This separator is positioned between the positive and negative electrode sheets, primarily preventing short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not specifically limit the type of separator; any known porous separator with good chemical and mechanical stability may be used.

[0139] 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, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0140] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0141] In some embodiments, the secondary battery includes a secondary battery cell, or includes a battery module and a battery pack.

[0142] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0143] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] The present application has no particular limitation on the shape of the secondary battery cell, which can be cylindrical, square, or any other shape. For example, FIG5 shows a secondary battery cell 5 with a square structure as an example.

[0145] In some embodiments, referring to Figure 6, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may 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 connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0146] In some embodiments, secondary battery cells may be assembled into a battery module. The battery module may contain one or more secondary battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0147] Figure 7 shows an example battery module 4. Referring to Figure 7 , within the battery module 4, multiple secondary battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary battery cells 5 may be secured together using fasteners.

[0148] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of secondary battery cells 5 are accommodated in the accommodation space.

[0149] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0150] Figures 8 and 9 illustrate an example battery pack 1. Referring to Figures 8 and 9 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] In addition, the present application also provides an electrical device, which includes the secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0152] As the electrical device, a secondary battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0153] Figure 10 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0154] [Example]

[0155] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0156] Example 1

[0157] The first positive electrode active material precursor is prepared by coprecipitation reaction:

[0158] According to the molar ratio of Ni, Fe, Cu and Mn elements in the first positive electrode active material set in Table 1, a sulfate mixed aqueous solution with a concentration of 2 mol / L is prepared, and at the same time, a 4 mol / L sodium hydroxide aqueous solution and a 2 mol / L ammonia aqueous solution (ammonia aqueous solution is used as the first complexing agent) are prepared. Pure water with a volume ratio of 30% is added to the reactor, and the above-mentioned sulfate mixed aqueous solution and the first complexing agent are pumped into the reactor at the same flow rate. The flow rate of the sulfate mixed aqueous solution and the first complexing agent is kept constant, and the stirring speed is set to 1000r / min. The reaction is carried out at a constant temperature within a temperature range of 60°C. A precipitant is added during the reaction to adjust the pH in the reactor and keep the pH constant at about 11. The precursor slurry is synthesized by continuous reaction. The precursor slurry is then centrifuged, washed, filtered, and dried to obtain a first positive electrode active material precursor product.

[0159] The first positive electrode active material precursor and sodium carbonate are mixed, wherein the molar ratio of the Na element to the total molar ratio of the metal elements in the first positive electrode active material precursor is 0.93; after mixing in a high-speed mixer, the mixture is calcined, wherein the initial calcination temperature is 800°C and the time is 5 hours, the secondary calcination temperature is 950°C and the time is 15 hours, and the atmosphere is air, to obtain a first positive electrode active material substrate.

[0160] The second positive electrode active material precursor is prepared by coprecipitation reaction:

[0161] According to the molar ratio of Ni, Fe, Mn and Ti elements in the second positive electrode active material set in Table 1, a sulfate mixed aqueous solution with a concentration of 2 mol / L is prepared, and at the same time, a 4 mol / L sodium hydroxide aqueous solution and a 1 mol / L ammonia aqueous solution (ammonia aqueous solution is used as a second complexing agent) are prepared. Pure water with a volume ratio of 30% is added to the reactor, and the above-mentioned sulfate mixed aqueous solution and the second complexing agent are pumped into the reactor at the same flow rate. The flow rate of the sulfate mixed aqueous solution and the second complexing agent is kept constant, and the stirring speed is set to 1000 r / min. The reaction is carried out at a constant temperature within a temperature range of 60°C. A precipitant is added during the reaction to adjust the pH in the reactor, and the pH is kept constant at about 13 during the reaction. The precursor slurry is synthesized by continuous reaction. The precursor slurry is then centrifuged, washed, filtered, and dried to obtain a second positive electrode active material precursor product.

[0162] The second positive electrode active material precursor and sodium carbonate are mixed, wherein the molar ratio of the Na element to the total molar ratio of the metal elements in the first positive electrode active material precursor is 0.93; after mixing in a high-speed mixer, the mixture is calcined, wherein the initial calcination temperature is 950°C and the time is 6 hours, the secondary calcination temperature is 750°C and the time is 12 hours, and the atmosphere is air, to obtain a second positive electrode active material substrate.

[0163] 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, where the ratio of NH4H2PO4 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 at a calcination temperature of 300°C, a time of 8h, and an air atmosphere, finally obtaining a positive electrode active material with a surface coated with a Na4H2PO4 compound, which is called a positive electrode active material composition.

[0164] Examples 2 to 7

[0165] The preparation of the first positive electrode active material substrate and the second positive electrode active material substrate is the same as that in Example 1.

[0166] The mass ratio of the first positive electrode active material substrate to the second positive electrode active material substrate was adjusted, and a coating layer was provided according to the method of Example 1 to obtain the positive electrode active materials of each example.

[0167] Example 8

[0168] Based on Example 1, the coprecipitation pH value during the preparation of the first cathode active material substrate was adjusted to 11.5, the concentration of the first complexing agent in the material in the reactor was 1 mol / L, and a first cathode active material substrate with a DV50 of 6 μm was obtained.

[0169] Example 9

[0170] On the basis of Example 1, the coprecipitation pH value in preparing the first cathode active material substrate was adjusted to 10, the concentration of the first complexing agent used was 1 mol / L, and a first cathode active material substrate with a DV50 of 15 μm was obtained.

[0171] Example 10

[0172] On the basis of Example 1, the coprecipitation pH value in preparing the first cathode active material substrate was adjusted to 10.8, the concentration of the first complexing agent used was 1.5 mol / L, and a first cathode active material substrate with a DV50 of 8 μm was obtained.

[0173] Example 11

[0174] Based on Example 1, the coprecipitation pH value during the preparation of the first cathode active material substrate was adjusted to 10.5, the concentration of the first complexing agent used was 1.5 mol / L, and a first cathode active material substrate with a DV50 of 12 μm was obtained.

[0175] Example 12

[0176] On the basis of Example 1, the coprecipitation pH value in preparing the first cathode active material substrate was adjusted to 12, the concentration of the first complexing agent used was 2 mol / L, and a first cathode active material substrate with a DV50 of 4 μm was obtained.

[0177] Example 13

[0178] Based on Example 1, the coprecipitation pH value during the preparation of the first cathode active material substrate was adjusted to 9, the concentration of the first complexing agent used was 1 mol / L, and a first cathode active material substrate with a DV50 of 18 μm was obtained.

[0179] Example 14

[0180] On the basis of Example 1, the coprecipitation pH value in preparing the second cathode active material substrate was adjusted to 13, the concentration of the second complexing agent used was 0.5 mol / L, and a second cathode active material substrate with a DV50 of 2 μm was obtained.

[0181] Example 15

[0182] On the basis of Example 1, the coprecipitation pH value in preparing the second cathode active material substrate was adjusted to 12, the concentration of the second complexing agent used was 0.5 mol / L, and a second cathode active material substrate with a DV50 of 5.5 μm was obtained.

[0183] Example 16

[0184] On the basis of Example 1, the coprecipitation pH value in preparing the second cathode active material substrate was adjusted to 14, the concentration of the second complexing agent used was 1 mol / L, and a second cathode active material substrate with a DV50 of 1 μm was obtained.

[0185] Example 17

[0186] On the basis of Example 1, the coprecipitation pH value in preparing the second cathode active material substrate was adjusted to 11, the concentration of the second complexing agent used was 1 mol / L, and a second cathode active material substrate with a DV50 of 7 μm was obtained.

[0187] Examples 18 and 19

[0188] On the basis of Example 1, the amounts of copper sulfate and nickel sulfate used in the preparation of the first positive electrode active material substrate were adjusted to obtain the first positive electrode active material substrate 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 Cu 0.2 O2.

[0189] Examples 20 to 24

[0190] On the basis of Example 1, when preparing the second positive electrode active material substrate, magnesium sulfate, zirconium sulfate, aluminum sulfate, calcium sulfate and zinc sulfate were used to replace titanium sulfate to obtain the second positive electrode active material substrates, as shown in Table 2.

[0191] Example 25

[0192] Based on Example 24, the coating layer was removed.

[0193] Example 26

[0194] Referring to the process of Example 24, the initial calcination temperature of the first positive electrode active material substrate is 700°C, the sintering time is 3 hours, the secondary calcination temperature is 900°C, and the sintering time is 12 hours; the initial calcination temperature of the second positive electrode active material substrate is 850°C, the sintering time is 3 hours, the secondary calcination temperature is 700°C, and the sintering time is 10 hours; the rest is the same as Example 24, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0195] Example 27

[0196] Referring to the process of Example 24, the initial calcination temperature of the first positive electrode active material substrate is 900°C, the sintering time is 10 hours, the secondary calcination temperature is 1000°C, and the sintering time is 18 hours; the initial calcination temperature of the second positive electrode active material substrate is 950°C, the sintering time is 8 hours, the secondary calcination temperature is 900°C, and the sintering time is 18 hours; the rest is the same as Example 24, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0197] Example 28

[0198] On the basis of Example 1, titanium sulfate was not added during the preparation of the second positive electrode active material substrate, and the rest of the preparation was the same as in Example 1.

[0199] Example 1, obtaining the second positive electrode active material substrate Na 0.93 Ni 0.33 Fe 0.33 Mn 0.34 O2.

[0200] Examples 29-33

[0201] Referring to the process of Example 1, the amount of each metal element was adjusted according to the elemental composition in Table 1 and Table 2, and the rest was the same as in Example 1 to obtain the corresponding first positive electrode active material substrate and second positive electrode active material substrate.

[0202] Example 34

[0203] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 700°C, the sintering time is 3 hours, the secondary calcination temperature is 900°C, and the sintering time is 12 hours; the initial calcination temperature of the second positive electrode active material substrate is 850°C, the sintering time is 3 hours, the secondary calcination temperature is 700°C, and the sintering time is 10 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0204] Example 35

[0205] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 900°C, the sintering time is 10 hours, the secondary calcination temperature is 1000°C, and the sintering time is 18 hours; the initial calcination temperature of the second positive electrode active material substrate is 950°C, the sintering time is 8 hours, the secondary calcination temperature is 900°C, and the sintering time is 18 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0206] Example 36

[0207] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 780°C, the sintering time is 4 hours, the secondary calcination temperature is 920°C, and the sintering time is 15 hours; the initial calcination temperature of the second positive electrode active material substrate is 900°C, the sintering time is 5 hours, the secondary calcination temperature is 720°C, and the sintering time is 12 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0208] Example 37

[0209] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 820°C, the sintering time is 6 hours, the secondary calcination temperature is 970°C, and the sintering time is 18 hours; the initial calcination temperature of the second positive electrode active material substrate is 950°C, the sintering time is 7 hours, the secondary calcination temperature is 800°C, and the sintering time is 15 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0210] Example 38

[0211] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 900°C, the sintering time is 10 hours, the secondary calcination temperature is 1100°C, and the sintering time is 20 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate is obtained.

[0212] Example 39

[0213] Referring to the process of Example 1, the first firing temperature of the second positive electrode active material substrate is 980°C, the sintering time is 10 hours, the second firing temperature is 930°C, and the sintering time is 18 hours; the rest is the same as Example 1, and the corresponding second positive electrode active material substrate is obtained.

[0214] Example 40

[0215] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 900°C, the sintering time is 10 hours, the secondary calcination temperature is 1100°C, and the sintering time is 20 hours; the initial calcination temperature of the second positive electrode active material substrate is 980°C, the sintering time is 10 hours, the secondary calcination temperature is 930°C, and the sintering time is 18 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0216] Example 41

[0217] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 900°C, the sintering time is 10h, the secondary calcination temperature is 1100°C, and the sintering time is 25h; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate is obtained.

[0218] Example 42

[0219] Referring to the process of Example 1, the first calcination temperature of the second positive electrode active material substrate is 1050°C, the sintering time is 8 hours, the second calcination temperature is 930°C, and the sintering time is 18 hours; the rest is the same as Example 1, and the corresponding second positive electrode active material substrate is obtained.

[0220] Examples 43 to 46

[0221] By adjusting the amount of NH4H2PO4 used, positive electrode active materials with different Na4H2PO4 compound coating amounts were obtained. The obtained products are shown in Tables 1 and 2, respectively.

[0222] Example 47

[0223] Without coating treatment, the first positive electrode active material substrate and the second positive electrode active material substrate of Example 1 were directly used as the corresponding first positive electrode active material and the second positive electrode active material, and the rest of the treatment was the same as that of Example 1.

[0224] Example 48

[0225] No coating treatment was performed, and the first positive electrode active material substrate and the second positive electrode active material substrate of Example 29 were directly used as the corresponding first positive electrode active material and the second positive electrode active material, and the rest of the treatment was the same as that of Example 29.

[0226] Example 49

[0227] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as that of Example 30.

[0228] Example 50

[0229] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as that of Example 22.

[0230] Example 51

[0231] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as that of Example 23.

[0232] Example 52

[0233] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as that of Example 34.

[0234] Example 53

[0235] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as in Example 35.

[0236] Example 54

[0237] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as in Example 36.

[0238] Example 55

[0239] No coating treatment was performed, and 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 the second positive electrode active material, and the rest of the treatment was the same as in Example 37.

[0240] Example 56

[0241] Referring to the process of Example 1, the initial sintering temperature of the first positive electrode active material substrate is 700°C, the sintering time is 5 hours, the secondary sintering temperature is 750°C, and the sintering time is 15 hours; the rest is the same as Example 1, and the corresponding polycrystalline first positive electrode active material substrate is obtained.

[0242] Example 57

[0243] Referring to the process of Example 1, the primary sintering temperature of the second positive electrode active material substrate is 800°C, the sintering time is 3 hours, the secondary sintering temperature is 700°C, and the sintering time is 12 hours; the rest is the same as Example 1, and the corresponding polycrystalline second positive electrode active material substrate is obtained.

[0244] Example 58

[0245] Referring to the process of Example 1, the initial calcination temperature of the first positive electrode active material substrate is 700°C, the sintering time is 5 hours, the secondary calcination temperature is 750°C, and the sintering time is 15 hours; the initial calcination temperature of the second positive electrode active material substrate is 800°C, the sintering time is 3 hours, the secondary calcination temperature is 700°C, and the sintering time is 12 hours; the rest is the same as Example 1, and the corresponding first positive electrode active material substrate and second positive electrode active material substrate are obtained.

[0246] test:

[0247] Elemental composition of the positive electrode active material: Determined using an inductively coupled plasma spectrometer (ICP). Powder samples of the first and second positive electrode active material substrates are dissolved in a sample chamber. Plasma is used to evaporate the sample solution to form gaseous atoms, which are excited to generate light radiation. Spectral line intensities are collected by a collector to obtain quantitative elemental content.

[0248] The element composition of each positive electrode active material substrate is substantially the same as the set ratio of elements in the raw materials.

[0249] Sample morphology characterization: A field emission scanning electron microscope (Sigma300) from ZEISS, Germany, was used to characterize the surface morphology of the positive electrode active material. FIG1 shows a scanning electron microscope image of the first positive electrode active material substrate in Example 1.

[0250] FIG3 shows a scanning electron microscope image of the second positive electrode active material substrate in Example 1.

[0251] Characterization of sample volume particle size distribution: A laser particle size analyzer (Malvern, model: Mastersizer 3000) was used to perform particle size distribution tests on the first positive electrode active material substrate, the second positive electrode active material substrate, and the formed positive electrode active material composition of each embodiment to obtain a particle size volume distribution diagram of the first positive electrode active material substrate, a particle size volume distribution diagram of the second positive electrode active material substrate, and a particle size volume distribution diagram of the positive electrode active material composition.

[0252] Characterization of the particle size distribution of the positive electrode active material composition: The positive electrode active material composition was observed under a scanning electron microscope at a magnification of 3000 times, and an EDS element mapping test was performed simultaneously. The first positive electrode active material and the second positive electrode active material were marked according to the presence of Cu element content in the EDS results. 30 first positive electrode active materials and 30 second positive electrode active materials were selected in the same field of view, and their particle sizes were measured. Five areas were randomly selected and the above operation was performed. Finally, the average particle size D1' of the first positive electrode active material and the second positive electrode active material was calculated. and D2'; then, with D1' and D2' as the peak positions of the fitting peaks, the origin software was used to perform peak fitting processing on the volume particle size distribution diagram of the positive electrode active material composition based on the Gaussian function. During the process, the fitting peak position was kept unchanged, and the volume particle size distribution diagram of the positive electrode active material composition was decomposed into a small particle fitting peak type and a large particle fitting peak type. The large particle fitting peak type basically coincided with the particle size volume distribution diagram of the first positive electrode active material, and the small particle fitting peak type basically coincided with the particle size volume distribution diagram of the second positive electrode active material, indicating that the peak fitting processing result is reliable.

[0253] Characterization of the characteristic element distribution of the positive electrode active material composition: The positive electrode active material composition was observed under a scanning electron microscope with a magnification of 3000 times, and an EDS element mapping test was performed at the same time. The first positive electrode active material and the second positive electrode active material were marked according to whether the Cu element content existed in the EDS results. 30 first positive electrode active materials and 30 second positive electrode active materials were selected in the same field of view, and the average mass content of the Cu element was calculated. Five areas were randomly selected for the above operation; the average mass content of the Cu element of the fitting peak of small particles with a particle size less than or equal to DV10 was recorded as m1, which was basically 0, and the average mass content of the Cu element of the fitting peak of large particles with a particle size greater than or equal to DV90 was recorded as m2, and m2 was basically the same as the Cu content in each first positive electrode material, so m1<m2.

[0254] XRD testing: XRD patterns were tested using an X-ray diffractometer (Bruker D8 Advance). First, powder samples of the first and second cathode active material substrates, as well as the resulting cathode active material composition, were placed on a sample stage, compacted with a glass sheet, and then placed in a sample chamber. X-rays were then irradiated to obtain XRD patterns. The corresponding grain size was calculated using the Scherrer formula, which is D = (K·γ) / (B·cosθ). K is the Scherrer constant, γ is the wavelength of the X-ray, B is the half-width at half-maximum of the diffraction peak, θ is the Bragg diffraction angle, and D is the thickness perpendicular to the crystal plane.

[0255] FIG2 shows an XRD spectrum of the first cathode active material substrate of Example 1. FIG4 shows an XRD spectrum of the second cathode active material substrate of Example 1.

[0256] Sample powder compaction density:

[0257] Determine the compaction density of the positive electrode active material under a pressure of 3T according to GB / T 24533-2019. Remove the top pin and upper gasket, weigh 1g of the sample in the sleeve, accurate to 0.0001g, and record the weight as m. Powder compaction density = 10m / S×H, where 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 pin in square centimeters (cm 2 ).

[0258] Characterization of sample pole piece compaction density:

[0259] Obtain battery electrodes that meet the machinability requirements, use a punch to punch out positive electrodes with a diameter of 14 mm, and use an electronic balance and a desktop digital thickness gauge to measure the mass m of the positive electrodes. c , thickness d c ; Use a punching machine to punch out a sufficient number of aluminum foil substrates with a diameter of 14 mm, and use an electronic balance and a desktop digital thickness gauge to measure the mass mA1 and thickness dAl of the aluminum foil substrates respectively.

[0260] Positive electrode compaction density

[0261] Where: c is the compacted density of the positive electrode, in grams per cubic centimeter (g / cm 3 );

[0262] m c is the mass of the positive electrode, in grams (g);

[0263] mA1 is the mass of the aluminum foil substrate, in grams (g);

[0264] is the diameter of the positive electrode sheet, in millimeters (mm);

[0265] d c is the thickness of the positive electrode sheet, in micrometers (μm);

[0266] dAl is the thickness of the aluminum foil substrate in micrometers (μm).

[0267] Some of the above test results are recorded in Table 1, and some are recorded in Table 2.

[0268] The coating layer content mentioned above means that the first positive electrode active material and the second positive electrode active material have the same coating layer content. The mass ratio refers to the mass ratio of the first positive electrode active material substrate to the second positive electrode active material substrate.

[0269] Performance testing:

[0270] Prepare button cells:

[0271] The positive electrode active material, PVDF, and conductive carbon are added to a certain amount of NMP in a ratio of 90:5:5, stirred in a drying room to form a slurry, coated on aluminum foil, dried, and cold-pressed to form a positive electrode sheet. A sodium sheet is used as the negative electrode, and the electrolyte is 1 mol / L NaPF6 / (EC+DEC+DMC, volume ratio of 1:1:1). The button battery is assembled in a button box.

[0272] Test method for initial gram capacity after power-off:

[0273] At 1.5-4.0V, charge to 4.0V at 0.1C, then charge at constant voltage at 4.0V to a current ≤ 0.05mA, let stand for 2 minutes, and then discharge to 1.5V at 0.1C. The discharge capacity at this time is the initial gram capacity.

[0274] Preparation of full battery:

[0275] The positive electrode active material composition of each embodiment and comparative example is used as the positive electrode active material, and is thoroughly stirred and mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system in a weight ratio of 95:3:2. The mixture is then coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet. The negative electrode active material hard carbon, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener carbon methyl cellulose sodium (CMC) are thoroughly stirred and mixed in a deionized water solvent system in a weight ratio of 95:2:2:1. The mixture is then coated on a copper foil, dried, and cold-pressed to obtain a negative electrode sheet. A PE porous polymer film is used as a separator. The positive electrode sheet, separator, and negative electrode sheet are stacked in order so that the separator is in the middle of the positive and negative electrodes to serve as an isolation film, and then wound to obtain a bare battery cell. The bare cell was placed in an outer package, injected with the prepared basic electrolyte (1 mol / L NaPF6 / (EC+DEC+DMC, volume ratio of 1:1:1)) and encapsulated to obtain a full battery.

[0276] Fully electric 25 / 45℃ cycle performance test:

[0277] At a constant temperature of 25°C or 45°C, charge the battery at 1.5-4.0V at 1C to 4.0V, then charge at 4.0V with a constant voltage until the current is ≤ 0.05mA. Let it sit for 5 minutes, then discharge the battery at 1C to 1.5V. The capacity is recorded as Dn (n=0, 1, 2...). Repeat the previous process until the capacity fades to 80%.

[0278] The test results are recorded in Table 2.

[0279] Table 2

[0280] According to the data comparison between the embodiment and comparative example 1, it can be found that in the embodiment, when the second positive electrode active material is mixed, the gram capacity of the positive electrode active material composition is significantly improved compared with the case where the first positive electrode active material is used alone; according to the data comparison between the embodiment and comparative example 2, it can be found that in the embodiment, when the first positive electrode active material is mixed, the cycle performance of the positive electrode active material composition is significantly improved compared with the case where the second positive electrode active material is used alone.

[0281] According to the data comparison of Example 1 and Examples 34 to 42, it can be found that when the first positive electrode active material and / or the second positive electrode active material has a spherical morphology, the compaction of the formed composition is significantly improved compared to the compaction of the composition with a flake morphology, and by controlling D 104 / D 003 After improving the roundness of the grains, the compaction and gram capacity can also be further improved.

[0282] 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 to the second positive electrode active material changes, the gram capacity and cycle performance both change. When the ratio of the two changes so that e1' / e2' is between 4 and 40, and the copper mass content in the positive electrode active material composition is between 3.5% and 4.7%, the gram capacity and cycle performance of the positive electrode active material composition are both good.

[0283] According to the comparison between Example 1 and Examples 43 to 46, it can be seen that an appropriate content of the coating layer has a significant effect on improving the cycle performance of the positive electrode active material composition.

[0284] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions 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, wherein the first positive electrode active material is a nickel-iron-manganese-copper quaternary sodium 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 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.

2. The positive electrode active material according to claim 1, wherein The second positive electrode active material has one or more of the following characteristics: 1) The M element includes any one or more of Zn, Ti, Zr, Mg, Al, Co or Ca; 2) 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。 3. The positive electrode active material according to claim 1 or 2, wherein 0.02≤e2<0.08。 4. The positive electrode active material according to claim 1, wherein The chemical formula of the nickel-iron-manganese-copper quaternary sodium positive electrode active material is Na a1 [Ni b1 Fe c1 Mn d1 Cu e1 ]O2, where 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.

5. The positive electrode active material according to claim 4, wherein The positive electrode active material has one or more of the following characteristics: 1) 0.9 <a1<0.95,0.06≤e1<0.15。 2) In each gram of the positive electrode active material, the total molar amount of Cu atoms is e1', the total molar amount of M elements is e2', and 0.5≤e1' / e2'≤200.

6. The positive electrode active material according to claim 5, wherein 1≤e1' / e2'≤100.

7. The positive electrode active material according to claim 6, wherein 4≤e1' / e2'≤40.

8. The positive electrode active material according to any one of claims 1 to 7, wherein The mass content of Cu element in the positive electrode active material is 0.5%-12%.

9. The positive electrode active material according to claim 8, wherein The mass content of Cu element in the positive electrode active material is 3.5%-4.7%.

10. The positive electrode active material according to any one of claims 1 to 9, wherein The particle size of the positive electrode active material is less than or equal to D V The average mass content of Cu 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, m1<m2.

11. The positive electrode active material according to any one of claims 1 to 10, 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: 0.5μm-2μm; 2) D V 50: 7μm-11μm; 3) D V 90 is 14μm-20μm.

12. The positive electrode active material according to any one of claims 1 to 11, 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 particle size of the first peak type is D1, the peak particle size of the second peak type is D2, and D1<D2.

13. The positive electrode active material according to claim 12, wherein The positive electrode active material has one or more of the following characteristics: 1) The average mass content of Cu in the positive electrode active material with a particle size less than or equal to D1 is m3, and the average mass content of Cu in the positive electrode active material with a particle size greater than or equal to D2 is m4, m3<m4; 2) Taking D1 and D2 as the peak positions of the fitting peaks respectively, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing based on the Gaussian function using origin software to obtain at least a first fitting peak type and a second fitting peak type, wherein the peak particle size of the first fitting peak type is D1, 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.

14. The positive electrode active material according to any one of claims 1 to 13, wherein The positive electrode active material has one or more of the following characteristics: 1) The average particle size D1' of the first positive electrode active material is 6 μm-15 μm; 2) The average particle size D2' of the second positive electrode active material is 2 μm-5.5 μm; 3) The average particle size D1' of the first positive electrode active material is 8 μm-12 μm; 4) The average particle size D2' of the second positive electrode active material is 3 μm-4 μm; 5) Taking D1' and D2' as the peak positions of the fitting peaks respectively, the volume particle size distribution curve of the positive electrode active material is subjected to peak fitting processing based on the Gaussian function using origin software, and the fitting peak position is kept unchanged during the fitting process 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.

15. The positive electrode active material according to any one of claims 1 to 14, wherein The positive electrode active material has one or more of the following characteristics: 1) 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; 2) The first positive electrode active material and the second positive electrode active material each independently have an O3 crystal phase; 3) The morphology of the first positive electrode active material and the second positive electrode active material independently includes any one or more of flake, spherical or quasi-spherical shapes; 4) In the XRD spectra of the first positive electrode active material and the second positive electrode active material, 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 , and meets 1.5 <D 104 / D 003 <1.7, or meet 0.9 <D 101 / D 003 <1.2; 5) The mass ratio of the first positive electrode active material to the second positive electrode active material is 5:5-9:

1.

16. The positive electrode active material according to claim 15, wherein The positive electrode active material has one or more of the following characteristics: 1)、1.55<D 104 / D 003 <1.65; 2)、1.05<D 101 / D 003 <1.15; 3) The mass ratio of the first positive electrode active material to the second positive electrode active material is 6:4-8:

2.

17. The positive electrode active material according to any one of claims 1 to 16, wherein The positive electrode active material has one or more of the following characteristics: 1) At least part of the surface of the first positive electrode active material and the second positive electrode active material are independently coated; the coating layer comprises sodium phosphate; 2) The powder compaction density of the positive electrode active material under 3 tons of pressure is ≥3.1g / cm 3 .

18. The positive electrode active material according to claim 17, wherein 1) The sodium phosphate salt includes NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; 2) The weight content of the sodium phosphate salt in the positive electrode active material is 1000ppm-30000ppm; 3) The weight content of the sodium phosphate salt in the positive electrode active material is 5000ppm-20000ppm; 4) The powder compaction density of the positive electrode active material under 3 tons of pressure is ≥3.3g / cm 3 .

19. A method for preparing a positive electrode active material according to any one of claims 1 to 18, wherein: The preparation method comprises: Prepare a first positive electrode active material, mix a Ni salt solution, an Fe salt solution, a Cu salt solution and a Mn salt solution according to a set ratio to form a first mixed salt solution, add the first mixed salt solution, a first precipitant and a first complexing agent into a reaction container, control the pH value and reaction temperature of the materials in the reaction container to perform a coprecipitation reaction, and obtain the first positive electrode active material precursor, wherein the pH value is recorded as pH1 and pH1 is 9-12; mix the first positive electrode active material precursor and the first sodium salt according to a ratio to form a first mixture, and perform a first calcination treatment on the first mixture to obtain the first positive electrode active material; Prepare a second positive electrode active material, mix a Ni salt solution, an Fe salt solution, a Mn salt solution and an optional salt solution containing an M element according to a set ratio to form a second mixed salt solution, pump the second mixed salt solution, a second precipitant and a second complexing agent into a reaction container, control the pH value and reaction temperature of the materials in the reaction container to perform a coprecipitation reaction to obtain a second positive electrode active material precursor, wherein the pH value is recorded as pH2 and pH2 is 11-14; mix the second positive electrode active material precursor and a second sodium salt according to a proportion to form a second mixture, and perform a second calcination treatment on the first mixture to obtain the second positive electrode active material; The first positive electrode active material and the second positive electrode active material are mixed to obtain a positive electrode active material.

20. The preparation method according to claim 19, wherein: The Ni salt, Fe salt, Mn salt, Cu salt and M salt include a mixture of one or more of their respective sulfates, nitrates, oxalates or chlorides, and the first precipitant and the second precipitant each independently include sodium hydroxide, An aqueous solution of one or more of 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.

21. The preparation method according to claim 19 or 20, wherein: The first calcination treatment includes a process of performing a first initial calcination at a first temperature and a first calcination at a second temperature, and the first temperature is lower than the second temperature; and / or a molar ratio of sodium in the first sodium salt to a metal element in the first positive electrode active material precursor is 0.8 to 0.

95.

22. The preparation method according to claim 20 or 21, wherein: The preparation method has one or more of the following characteristics: 1) The concentration of the first complexing agent is 1-2 mol / L; 2) The concentration of the second complexing agent is 0.5-1 mol / L 3) The first temperature of the first initial firing is 700-900°C, and the holding time is 3h-10h; 4) The second temperature of the first firing is 850°C-1200°C; the holding time is 8h-20h; 5) The second temperature of the first firing is 900°C-1000°C; 6) The first burning heat preservation time is 12h-18h; 7) The molar ratio of sodium in the first sodium salt to the metal element in the first positive electrode active material precursor is 0.9 to 0.

93.

23. The preparation method according to any one of claims 19 to 22, wherein The second calcination treatment includes a process of performing a second initial calcination at a third temperature and a second calcination 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 the metal element in the second positive electrode active material precursor is 0.8 to 0.

95.

24. The preparation method according to claim 23, wherein: The preparation method has one or more of the following characteristics: 1) The third temperature of the second primary firing is 850-1000°C, and the holding time is 3h-8h; 2) The fourth temperature of the second firing is 700°C-950°C; the holding time is 8h-20h; 3) The fourth temperature of the second firing is 800°C-920°C; 4) The second heating time is 9-15 hours; 5) The molar ratio of sodium in the second sodium salt to the metal element in the second positive electrode active material precursor is 0.9 to 0.

93.

25. The preparation method according to any one of claims 19 to 24, 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; The mixed base material is subjected to a third calcination to obtain the positive electrode active material.

26. The preparation method according to claim 25, wherein: The preparation method has one or more of the following characteristics: 1) 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; 2) 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 5000ppm-20000ppm; 3) The phosphate compound includes a mixture of one or more of NH4H2PO4, (NH4)2HPO4, (NH4)2H2P2O7, NH4H3P2O7, NaH2PO4, Na2HPO4, Na3PO4 or (NaPO3)n; 4) the temperature of the third calcination is 200°C-500°C, and the time is 5h-15h; 5) The temperature of the third calcination is 300° C.-400° C.; 6) The third calcination time is 7h-10h.

27. 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, wherein the positive electrode film layer comprises a positive electrode active material, wherein: The positive electrode active material includes the positive electrode active material according to any one of claims 1 to 18.

28. The positive electrode sheet according to claim 27, wherein: The compaction density of the positive electrode sheet is ≥3.1g / cm 3 .

29. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active material, wherein: The positive electrode active material includes the positive electrode active material according to any one of claims 1 to 18.

30. An electrical device, comprising an electrical device, wherein: The electric device comprises the secondary battery according to claim 29.

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