Positive electrode active material, sodium ion secondary battery containing the same, and power consumption device

Abstract

The present application relates to a particulate and Na x A y M1[M2(CN)6] δ A compound represented by the formula (1) is selected from at least one of an alkali metal element and an alkaline earth metal element, and the ionic radius of A is greater than the ionic radius of sodium; M1 and M2 are each independently selected from at least one of a transition metal element; and 0

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and particularly to a cathode active material, a sodium-ion secondary battery containing the same, and a power consumption device.

Background Art

[0002] In recent years, the demand for lithium-ion batteries has been increasing. However, due to the limited lithium resources, the sustainable development of lithium-ion batteries is restricted. As an important complement to lithium-ion batteries, sodium-ion secondary batteries have been attracting increasing attention.

[0003] Prussian blue-based materials have attracted wide attention because they have a series of advantages in commercialization, such as high capacity, a high potential plateau, a rapid sodium-ion transport channel, low cost, and easy manufacturing. However, existing Prussian blue materials are prone to deterioration of electrical and chemical properties during long-term storage. Therefore, it is necessary to improve the Prussian blue materials to further enhance their storage properties, cycle properties, etc.

Summary of the Invention

[0004] The present application has been made in view of the above problems, and an object thereof is to provide a Prussian blue material as a cathode active material with improved storage properties and cycle properties.

[0005] To achieve the above object, a first aspect of the present application provides a cathode active material that is particulate and contains a compound represented by the following formula (1): Na x A y M1[M2(CN)6] δ ·zH2O (1) In the formula, A is selected from at least one of an alkali metal element and an alkaline earth metal element, and the ionic radius of A is larger than the ionic radius of sodium. M1 and M2 are each independently selected from at least one of transition metal elements. 0 < y ≤ 0.2, 0 < x + y ≤ 2, 0 < δ ≤ 1, and 0 ≤ z ≤ 10. The particles of the positive electrode active material have a gradually changing layer in which the content of the A element shows a decreasing tendency from the particle surface toward the particle interior.

[0006] Thereby, due to the specific composition and the specific distribution of the A element, both the storage characteristics and the cycle characteristics of the positive electrode active material are improved, and compared with the Prussian blue material not doped with the A element, the specific capacity of the material does not decrease significantly.

[0007] In any embodiment, 0.04 ≤ y ≤ 0.2. By controlling the content of the A element, it becomes more difficult for the positive electrode active material to absorb water.

[0008] In any embodiment, in the particles of the positive electrode active material, the thickness of the gradually changing layer of the A element content is in the range of 10 to 100 nm, preferably in the range of 10 to 75 nm. The thickness of the gradually changing layer of the A element content is the distance from the layer where the ratio of the measured contents of Na and the A element reaches Na:A = 50 At%:50 At% to the particle surface when the element content of the positive electrode active material particles is quantitatively measured by transmission electron microscope-X-ray line scan analysis. By controlling the thickness of the gradually changing layer of the A element content, the storage characteristics, cycle characteristics, and specific capacity of the material can be further improved.

[0009] In any embodiment, the A is selected from at least one of Li, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba, preferably selected from at least one of K, Rb, Cs, Mg, and Ca, and more preferably selected from at least one of K and Cs. By selecting the A element, the storage characteristics, cycle characteristics, and specific capacity of the material can be further improved.

[0010] In any embodiment, M1 and M2 are each independently selected from at least one of Fe, Mn, Ni, Co, Cu, and Zn. By selecting the types of M1 and M2, while ensuring structural integrity, the material can have the desired electrical and chemical properties and electrical and chemical capacities.

[0011] In any embodiment, the volume average particle diameter Dv50 of the cathode active material is in the range of 1 to 5 μm, preferably in the range of 2 to 3.5 μm. By controlling the volume average particle diameter Dv50 of the material, the specific capacity of the material can be further improved.

[0012] In any embodiment, the specific surface area of the cathode active material is in the range of 1 to 10 m 2 / g, preferably in the range of 2 to 6 m 2 / g. By controlling the specific surface area of the material, the necessary doping effect can be achieved in a situation where the amount of element A used is small, and a good balance can be realized between suppressing water absorption and avoiding a decrease in the specific capacity of the material.

[0013] In any embodiment, the water content of the cathode active material is ≤ 2% by weight, preferably, the water content of the cathode active material is ≤ 0.5% by weight. The lower the water content rate, the better the cycle characteristics.

[0014] The second aspect of the present application further provides a method for manufacturing a cathode active material, and the manufacturing method includes 1) adding a cathode active material precursor, which is a compound represented by the following formula (2), to a solvent and dispersing it to obtain a suspension, Na n M1[M2(CN)6] δ (2) wherein M1 and M2 are each independently selected from at least one of transition metal elements, 0 < n ≤ 2, and 0 < δ ≤ 1, step 1, 2) After cooling the suspension obtained in Step 1, add a salt of A to the suspension in the cooled state, and perform stirring and aging. A is selected from at least one of an alkali metal element and an alkaline earth metal element, and the ionic radius of A is larger than the ionic radius of sodium. This is Step 2, 3) Filter the suspension obtained in Step 2, wash the obtained precipitate, and dry it to obtain a positive electrode active material. The positive electrode active material is in particulate form and contains a compound represented by the following formula (1). Na x A y M1[M2(CN)6] δ ·zH2O (Formula 1) In the formula, A, M1, M2, and δ are as defined above, 0 < y ≤ 0.2, 0 < x + y ≤ 2, and 0 ≤ z ≤ 10. The particles of the positive electrode active material have a gradually changing layer in which the content of the A element shows a decreasing tendency from the particle surface toward the particle interior. This is Step 3, and it includes.

[0015] Thereby, the positive electrode active material of the present application can be manufactured.

[0016] In any embodiment, the solvent in Step 1 is a polar solvent, the solubility of the positive electrode active material precursor in the solvent is 0.02 mol / L or less, and the solubility of the salt of A in the solvent is 0.05 mol / L or more. By selecting the solvent, the distribution tendency of the A element decreasing from the particle surface to the particle interior of the positive electrode active material can be controlled better.

[0017] In any embodiment, the solvent is selected from one or more of acetonitrile, adiponitrile, methanol, ethanol, water, formamide, and dimethyl sulfoxide. Preferably, the solvent is acetonitrile. By selecting the solvent, the distribution tendency of the A element decreasing from the particle surface to the particle interior of the positive electrode active material can be controlled better.

[0018] In any embodiment, in step 2, the suspension obtained in step 1 is cooled to 10°C or lower, preferably to a temperature range of -20 to 10°C. By controlling the reaction temperature, the distribution tendency of element A that decreases from the particle surface to the particle interior of the positive electrode active material can be better controlled.

[0019] In any embodiment, the molar ratio of A in the salt of A to sodium in the positive electrode active material precursor is 1:5 or less, preferably 1:20 to 1:5. By controlling the addition amount of the salt of A, while realizing the improvement of the storage characteristics and cycle characteristics of the positive electrode active material, it is possible to avoid the excessive decrease in the specific capacity of the material.

[0020] In any embodiment, the method for manufacturing the positive electrode active material precursor in step 1 is i) Step i of dissolving a soluble salt of transition metal element M1 and an optional Na-containing slow-release agent in water to prepare solution a; ii) Step ii of dissolving a soluble transition metal cyanide complex of transition metal element M2 in water to prepare solution b; iii) Step iii of dropping solution a into solution b under stirring, and performing stirring and aging after the dropping is completed; iv) Step iv of filtering the suspension obtained in step iii and washing and drying the obtained precipitate.

[0021] By this method, a structurally more stable material can be obtained.

[0022] In any embodiment, the molar ratio of M1 in the soluble salt of transition metal element M1 to M2 in the soluble transition metal cyanide complex of transition metal element M2 is within the range of 1:0.8 to 0.8:1, preferably within the range of 1:0.9 to 0.9:1. By controlling the molar ratio of M1 and M2, the lattice defects of the material are reduced, which is advantageous for exhibiting a higher specific capacity.

[0023] In any embodiment, in step iii, the solution is maintained within a temperature range of 20°C to 120°C, preferably within a temperature range of 60°C to 95°C. This can ensure that the particles grow into a complete shape, the degree of bending decreases, the particle size is more likely to be appropriate, and at the same time, the ratio of elements better conforms to the design requirements.

[0024] In any embodiment, the stirring and aging in step 2 are carried out at a stirring speed of 50 to 1800 rpm for 1 to 30 minutes. By controlling the conditions of stirring and aging, it is advantageous to quickly achieve a uniform doping effect.

[0025] The third aspect of the present application provides a secondary battery including the positive electrode active material of the first aspect of the present application or the positive electrode active material manufactured by the method of the second aspect of the present application.

[0026] The fourth aspect of the present application provides a power consumption device including the secondary battery according to the third aspect of the present application.

Brief Description of the Drawings

[0027]

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Modes for Carrying Out the Invention

[0028] Hereinafter, embodiments specifically disclosing the positive electrode active material of the present application, a method for manufacturing the same, a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electric power consumption device will be described in detail with reference to the drawings as appropriate. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and overlapping descriptions of substantially the same structures may be omitted. This is to prevent the following descriptions from becoming unnecessarily redundant and to facilitate the understanding of those skilled in the art. Also, the drawings and the following descriptions 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.

[0029] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. A range defined in this way may or may not include the values at both ends, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, when ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Also, when the minimum range values 1 and 2 are listed, and the maximum range values 3, 4, and 5 are listed, ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. In the present application, unless otherwise explained, the numerical range "a to b" means an abbreviated expression of any combination of real numbers between a and b, and both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is merely an abbreviated expression of combinations of these numerical values. Also, when a certain parameter is expressed as an integer ≧2, it corresponds to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] All embodiments and selectable embodiments of the present application can, unless otherwise specified, be combined with each other to form new technical solutions.

[0031] All technical features and selectable technical features of the present application can, unless otherwise explained, be combined with each other to form new technical solutions.

[0032] All steps of the present application can, unless otherwise specified, be carried out in order or randomly, preferably in order. For example, if the method includes steps (a) and (b), the method may include steps (a) and (b) carried out in order, or steps (b) and (a) carried out in order. For example, if it is said that the method may further include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0033] As used in the present application, unless otherwise specified, the terms "comprising" and "including" indicate both open and closed forms. For example, the "comprising" and "including" can indicate that other components not listed may also be included or incorporated, or can indicate that only the listed components may be included or incorporated.

[0034] In the present application, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by either A being true (or existing), B being false (or not existing), A being false (or not existing), B being true (or existing), or both A and B being true (or existing).

[0035] Existing Prussian blue materials are insufficient in terms of storage characteristics, and the electrical and chemical properties are likely to deteriorate during long-term storage. For example, when stored for a long time, the cycle characteristics of the material deteriorate.

[0036] The performance degradation of Prussian blue materials after long-term storage is closely related to the water absorption of Prussian blue materials during this period. The inventors have found that by modifying Prussian blue materials using alkali metal or alkaline earth metal ions with large ionic radii, the large-radius ions occupy the positions where crystal water could originally exist, reducing the crystal water in the lattice structure and improving the storage characteristics of Prussian blue materials. From further research, the inventors have discovered that by distributing the alkali metal or alkaline earth metal ions with large ionic radii in a specific manner within Prussian blue material particles, the storage characteristics of Prussian blue materials can be further improved, and the cycle characteristics are improved. At the same time, the decrease in the specific capacity of the material caused by doping with alkali metal or alkaline earth metal ions with large ionic radii is reduced.

[0037] The modified Prussian blue material of the present application is suitable for use as a positive electrode active material in a sodium-ion battery.

[0038] Therefore, the first aspect of the present application provides a positive electrode active material in the form of particles and containing a compound represented by the following formula (1), Na x A y M1[M2(CN)6] δ ·zH2O (1) wherein A is selected from at least one of alkali metal elements and alkaline earth metal elements, and the ionic radius of A is larger than the ionic radius of sodium. M1 and M2 are each independently selected from at least one of transition metal elements. 0 < y ≦ 0.2, 0 < x + y ≦ 2, 0 < δ ≦ 1, and 0 ≦ z ≦ 10. The particles of the positive electrode active material have a gradually changing layer in which the content of the A element shows a decreasing trend from the particle surface towards the particle interior.

[0039] When A is two or more elements, the limitation of the numerical range of y is to limit the sum of the stoichiometric numbers of each element as A.

[0040] The chemical composition of the positive electrode active material can be measured by inductively coupled plasma optical emission spectrometry (ICP). After determining x, y, and δ, the value of z can be further determined based on the water content of the material.

[0041] The mechanism is not clear, but the applicant has also discovered that due to the specific composition of the positive electrode active material and the specific distribution of element A, both the storage characteristics and cycle characteristics of the positive electrode active material are improved, and the specific capacity of the material does not decrease significantly compared to the Prussian blue material without element A being doped.

[0042] In some embodiments, 0.04 ≦ y ≦ 0.2. By controlling the content of element A, the water absorption of the positive electrode active material can be further reduced.

[0043] In some embodiments, in the particles of the positive electrode active material, the thickness of the layer with a gradually changing content of element A is in the range of 10 to 100 nm, for example, 10 to 90 nm, 10 to 80 nm, 10 to 75 nm, 10 to 60 nm, 10 to 60 nm, 10 to 30 nm, 10 to 25 nm, 20 to 100 nm, 20 to 90 nm, 20 to 80 nm, 20 to 50 nm, 20 to 40 nm, 30 to 100 nm, 30 to 90 nm, 30 to 80 nm, 30 to 75 nm, 30 to 60 nm. The thickness of the layer with a gradually changing content of element A refers to the distance from the layer where the ratio of the measured contents of Na and element A reaches Na:A = 50 At%:50 At% to the particle surface when the element content of the positive electrode active material particles is quantitatively measured by transmission electron microscopy - X-ray line scan analysis.

[0044] In the present application, the layer satisfying the content of a specific element measured by the transmission electron microscope-X-ray line scan analysis method means an abstract layer composed of all points satisfying the content of the specific element inside the particles, and does not mean a layer having an actual thickness. At% means the percentage of the number of atoms of Na or element A in the sum of the number of atoms of Na and element A, and is measured by the transmission electron microscope-X-ray line scan analysis method. The transmission electron microscope-X-ray line scan analysis method is implemented by using a transmission electron microscope (STEM, ThermoFisher, Talos F200i) in combination with a side-insertable scalable energy dispersive X-ray spectroscopy (EDS, ThermoFisher) to perform line scan analysis of the materials in the display.

[0045] By controlling the thickness of the layer with a gradually changing content of element A, the storage characteristics, cycle characteristics, and specific capacity of the material can be further improved.

[0046] In some embodiments, the content of Na in the outermost layer of the positive electrode active material is in the range of 0.1 At% to 15 At% with respect to the total number of atoms of Na and A in the outermost layer. The outermost layer refers to the region between the layer where the ratio of the contents of Na and A is Na:A = 10 At%:90 At% and the particle surface when the element content of the positive electrode active material particles is quantitatively measured by the transmission electron microscope-X-ray line scan analysis method.

[0047] In some embodiments, A is selected from at least one of Li, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba, preferably selected from at least one of K, Rb, Cs, Mg, and Ca, and more preferably selected from at least one of K and Cs. By selecting element A, the storage characteristics, cycle characteristics, and specific capacity of the material can be further improved.

[0048] In some embodiments, M1 and M2 are each independently selected from at least one of Fe, Mn, Ni, Co, Cu, and Zn. By selecting the types of M1 and M2, while ensuring structural integrity, the material can have the desired electrical and chemical properties and electrical and chemical capacities.

[0049] In some embodiments, the volume-average particle diameter Dv50 of the positive electrode active material is in the range of 1 to 5 μm, preferably in the range of 2 to 3.5 μm. By controlling the volume-average particle diameter Dv50 of the material, the specific capacity of the material can be further improved. The volume-average particle diameter Dv50 can be measured by common methods known to those skilled in the art. For example, referring to the recommended standard GB / T 19077.1-2016, it can be measured using a laser particle size analyzer (such as Malvern Master Size 3000). The physical definition of Dv50 is the corresponding particle size when the cumulative volume distribution percentage of the material particles reaches 50%.

[0050] In some embodiments, the specific surface area of the positive electrode active material is in the range of 1 to 10 m 2 / g, preferably in the range of 2 to 6 m 2 / g. By controlling the specific surface area of the material, the necessary doping effect can be achieved in a situation where the amount of element A used is small, and the doping is uniform, achieving a doping effect as wide as possible with as little element A as possible. Also, uniform doping is advantageous for achieving a good balance between suppressing water absorption and avoiding a decrease in the specific capacity of the material. The specific surface area can be measured by common methods known to those skilled in the art. For example, based on the recommended standard GB / T 19587-2004, after measuring the gas adsorption amount on the solid surface at different relative pressures at a certain low temperature, the monolayer adsorption amount of the sample is obtained based on the Brunauer-Emmett-Teller (BET) multilayer adsorption theory and its formula, and the specific surface area of the solid is calculated.

[0051] In some embodiments, the water content of the positive electrode active material is ≤ 2% by weight, preferably, the water content of the positive electrode active material is ≤ 0.5% by weight. The water content refers to the saturated water absorption amount after the material is completely dehydrated and then placed in a drying chamber with a dew point of -30°C for at least one day. During the operation of the battery, the water in the positive electrode active material moves simultaneously with the insertion and extraction of Na ions, dissolves in the electrolyte and decomposes to generate an irreversible reaction, which affects the cycle characteristics. Therefore, the lower the water content, the better the cycle characteristics. The water content is determined by heating the positive electrode active material placed for the above-mentioned at least one day to remove water and measuring the resulting mass reduction amount.

[0052] The second aspect of the present application provides a method for manufacturing a positive electrode active material including the following steps.

[0053] 1) Step 1: Add a positive electrode active material precursor, which is a compound represented by the following formula (2), to a solvent and disperse it to obtain a suspension. Na n M1[M2(CN)6] δ (2) In the formula, M1 and M2 are each independently selected from at least one of transition metal elements, 0 < n ≤ 2, and 0 < δ ≤ 1.

[0054] 2) Step 2: After cooling the suspension obtained in Step 1, add a salt of A to the suspension in the cooled state, and perform stirring and aging, wherein A is selected from at least one of alkali metal elements and alkaline earth metal elements, and the ionic radius of A is larger than the ionic radius of sodium.

[0055] 3) Step 3: Filter the suspension obtained in Step 2, wash and dry the obtained precipitate to obtain a positive electrode active material. The positive electrode active material is in a particulate form and contains a compound represented by the following formula (1). Na x A y M1[M2(CN)6] δ ·zH2O (1) In the formula, A, M1, M2, and δ are as defined above, 0 < y ≤ 0.2, 0 < x + y ≤ 2, and 0 ≤ z ≤ 10. The particles of the positive electrode active material have a gradually changing layer in which the content of the A element shows a decreasing trend from the particle surface toward the particle interior.

[0056] The descriptions and limitations of M1, M2, A, x, y, δ, and z in the part describing the positive electrode active material are also similarly applicable to the manufacturing method of the positive electrode active material.

[0057] By controlling the reaction temperature, the above method can achieve a specific distribution of the A element in the positive electrode active material particles.

[0058] In some embodiments, the solvent in Step 1 is a polar solvent, the solubility of the positive electrode active material precursor in the solvent is 0.02 mol / L or less, and the solubility of the salt of A in the solvent is 0.05 mol / L or more. By selecting the solvent, the distribution tendency of the A element decreasing from the particle surface to the particle interior of the positive electrode active material can be better controlled.

[0059] In some embodiments, the solvent is selected from one or more of acetonitrile, adiponitrile, methanol, ethanol, water, formamide, and dimethyl sulfoxide. Preferably, the solvent is acetonitrile. By selecting the solvent, the distribution tendency of the A element decreasing from the particle surface to the particle interior of the positive electrode active material can be better controlled.

[0060] In some embodiments, in Step 2, the suspension obtained in Step 1 is cooled to 10°C or lower, preferably to a temperature range of -20 to 10°C. By controlling the reaction temperature, the distribution tendency of the A element decreasing from the particle surface to the particle interior of the positive electrode active material can be better controlled.

[0061] In some embodiments, the molar ratio of A in the salt of A to sodium in the cathode active material precursor is 1:5 or less, preferably 1:20 to 1:5. By controlling the addition amount of A, a cathode active material with a desired composition can be obtained, while realizing the improvement of the storage characteristics and cycle characteristics of the cathode active material and avoiding excessive reduction of the specific capacity of the material.

[0062] In some embodiments, the cathode active material precursor in step 1 is produced by a method including the following steps.

[0063] i) Step i: Dissolve a soluble salt of transition metal element M1 and an optional Na-containing sustained release agent in water to prepare solution a.

[0064] ii) Step ii: Dissolve a soluble transition metal cyanide complex of transition metal element M2 in water to prepare solution b.

[0065] iii) Step iii: Drop solution a into solution b under stirring, and perform stirring and aging after the dropping is completed.

[0066] iv) Step iv: Filter the suspension obtained in step iii, wash the obtained precipitate, and dry it.

[0067] The cathode active material precursor produced by this method is helpful for obtaining a material with few defects, high sodium content, and stable structure.

[0068] In some embodiments, the molar ratio of M1 in the soluble salt of transition metal element M1 to M2 in the soluble transition metal cyanide complex of transition metal element M2 is in the range of 1:0.8 to 0.8:1, preferably in the range of 1:0.9 to 0.9:1. By controlling the molar ratio of M1 and M2, it is beneficial to reduce the lattice defects of the material, store more Na, and exhibit a higher specific capacity.

[0069] In some embodiments, in step iii, the solution is maintained within a temperature range of 20°C to 120°C, preferably within a temperature range of 60°C to 95°C, and preferably within a temperature range of 70°C to 80°C. An appropriate synthesis temperature can ensure that the particles grow into a complete shape, the degree of bending decreases, the particle size is more likely to be appropriate, and at the same time, the ratio of elements better conforms to the design requirements.

[0070] In some embodiments, in step 2, the stirring and aging are performed at a stirring speed of 50 to 1800 rpm for 1 to 30 minutes. Controlling the conditions of stirring and aging is advantageous for quickly achieving a uniform doping effect.

[0071] In some embodiments, the dispersion in step 1 can be carried out by selecting an appropriate method by those skilled in the art. In some embodiments, in step 1, ultrasonic treatment and stirring are used to assist the dispersion.

[0072] In some embodiments, the Na-containing sustained-release agent in step i is at least one selected from sodium citrate, sodium ascorbate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium chloride, sodium sulfate, and sodium acetate.

[0073] In some embodiments, in step i, the molar ratio of the transition metal element M1 to the sustained-release agent is 1:0.1 to 10. Preferably, the molar ratio of the transition metal element M1 to the sustained-release agent is 1:1 to 5.

[0074] The anion of the soluble salt of the transition metal element M1 in step i is not particularly limited as long as the salt is a soluble salt. In some embodiments, the soluble salt of the transition metal element M1 is a salt of a weak acid such as divalent sulfate, nitrate, chloride, or oxalate. Its concentration in the solution is, for example, within the range of 0.01 mol / L to 1 mol / L.

[0075] In some embodiments, the sodium-containing sustained-release agent in step i is at least one selected from sodium citrate, sodium ascorbate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium chloride, sodium sulfate, and sodium acetate.

[0076] In some embodiments, the soluble transition metal cyanide complex in step ii is sodium divalent transition metal cyanide. Its concentration in the solution is, for example, in the range of 0.01 mol / L to 1 mol / L.

[0077] In some embodiments, in step iii, the stirring speed is in the range of 200 rpm to 1200 rpm.

[0078] In some embodiments, in step iii, solution a is dropped at a rate of 0.1 ml / min to 10 ml / min, for example, at a rate of 1 ml / min to 5 ml / min.

[0079] In some embodiments, in step iii, the aging is carried out for 0.01 h to 48 h, for example, 12 h to 24 h, and the aging can be carried out, for example, under stirring.

[0080] The washing in step iv can be carried out by those skilled in the art by selecting an appropriate solvent. In some embodiments, in step iv, the washing can be carried out using a mixture of deionized water and ethanol, ethanol, acetone, etc., and can be carried out once or multiple times.

[0081] The drying in step iv can be carried out by those skilled in the art by selecting an appropriate drying method. In some embodiments, in step iv, the drying is carried out by vacuum drying, for example, at a temperature in the range of 0 to 300 °C, for example, 120 °C to 150 °C, and the vacuum degree is, for example, 10 to 15 mTorr.

[0082] In step 2, the anion of the salt of A is not particularly limited. In some embodiments, the anion of the salt of A is Cl - , SO4 2- , NO3 - , C2O4 2- , PO4 3- and is selected from one of them, preferably SO4 2- , NO3 - , C2O4 2- and is one of them.

[0083] The drying in step 3 can be carried out by a person skilled in the art selecting an appropriate drying method. In some embodiments, in step 3, the drying is carried out by vacuum drying, for example, at a temperature in the range of 0 to 300 °C, for example, 120 °C to 150 °C, and the degree of vacuum is, for example, 100 to 150 mTorr.

[0084] Hereinafter, with reference to the drawings as appropriate, the secondary battery, battery module, battery pack, and power consumption device of the present application will be described.

[0085] In one embodiment of the present application, a sodium ion secondary battery is provided.

[0086] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. In the charge and discharge process of the battery, active ions reciprocate between the positive electrode sheet and the negative electrode sheet for insertion and desorption. The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is installed between the positive electrode sheet and the negative electrode sheet, mainly plays a role of preventing short circuit between the positive and negative electrodes, and at the same time can allow ions to pass through.

[0087] [Positive Electrode Sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, and the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or the positive electrode active material manufactured by the method of the second aspect of the present application.

[0088] As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is provided on one or both of the two opposing surfaces of the positive electrode current collector.

[0089] In some embodiments, the positive electrode current collector can use a metal foil or a composite current collector. As the metal foil, for example, an aluminum foil can be used. The composite current collector can include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] In some embodiments, the positive electrode film layer can optionally further include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0091] In some embodiments, the positive electrode film layer can optionally further include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0092] In some embodiments, the positive electrode sheet can be manufactured by the following method. Components for manufacturing the positive electrode sheet, such as a positive electrode active material, a conductive agent, a 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 applied to a positive electrode current collector and, through steps such as drying and cold pressing, a positive electrode sheet can be obtained.

[0093] [Negative electrode sheet] 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, and the negative electrode film layer contains a negative electrode active material.

[0094] As an example, the negative electrode current collector has two surfaces facing each other in its own thickness direction, and the negative electrode film layer is provided on either one or both of the two opposing surfaces of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As the metal foil, for example, a copper foil can be used. The composite current collector can include a polymer base material layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base (such as a base of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, known anode active materials for secondary batteries can be used as the anode active material. As an example, the anode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material can be selected from at least one of silicon alone, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of tin alone, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as the anode active material of the battery may be used. These anode active materials may be used alone, or two or more of them may be used in combination.

[0097] In some embodiments, the anode film layer can optionally further include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments, the anode film layer can optionally further include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the anode film layer can optionally further include other auxiliaries such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0100] In some embodiments, the negative electrode sheet can be manufactured by the following method. Components for manufacturing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry. The negative electrode slurry is applied to a negative electrode current collector, and through steps such as drying and cold pressing, a negative electrode sheet can be obtained.

[0101] [Electrolyte] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not particularly limit the type of electrolyte, and it can be selected as needed. For example, the electrolyte may be liquid, gel, or a complete solid.

[0102] In some embodiments, the electrolyte is in a liquid state, that is, an electrolytic solution. The electrolytic solution contains an electrolyte salt and a solvent.

[0103] In some embodiments, the electrolyte salt can be selected from NaClO4, NaPF6, NaBF4, NaTFSI (sodium bis(trifluoromethanesulfonyl)imide), NaFSI (sodium bis(fluorosulfonyl)imide), NaDFOB (sodium difluorooxalate borate), etc.

[0104] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4 - butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0105] In some embodiments, the electrolytic solution further selectively contains additives. For example, the additives may include a negative electrode film forming additive and a positive electrode film forming additive, and further may include additives that can improve specific characteristics of the battery, such as additives that improve overcharge characteristics of the battery, additives that improve high temperature or low temperature characteristics of the battery, and the like.

[0106] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of the separator, and any known porous structure separator having good chemical stability and mechanical stability can be selected.

[0107] 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 may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0108] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be manufactured into an electrode assembly through a winding process or a lamination process.

[0109] In some embodiments, the secondary battery can include an exterior material. The exterior material is used to enclose the above electrode assembly and electrolyte.

[0110] In some embodiments, the exterior material of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The exterior material of the secondary battery may also be a soft pack such as a pouch-type soft pack. The material of the soft pack may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0111] The present application does not particularly limit the shape of the secondary battery, and it may be cylindrical, rectangular, or any other arbitrary shape. For example, FIG. 1 shows a rectangular-structured secondary battery 5 as an example.

[0112] In some embodiments, referring to FIG. 2, the exterior material can include a housing 51 and a cover plate 53. The housing 51 includes a bottom plate and side plates connected to the bottom plate, and an accommodation cavity surrounded by the bottom plate and the side plates is formed. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to seal the accommodation cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed within the accommodation cavity. The electrolyte is impregnated within the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select according to specific actual requirements.

[0113] In some embodiments, the secondary battery can be assembled into a battery module. The number of secondary batteries included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the use and capacity of the battery module.

[0114] FIG. 3 shows a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary method. Also, the plurality of secondary batteries 5 can be fixed by fastening means.

[0115] Preferably, the battery module 4 may further include an outer case having an accommodation space for accommodating a plurality of secondary batteries 5.

[0116] In some embodiments, the battery module can be further assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0117] FIGS. 4 and 5 show a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery case and a plurality of battery modules 4 installed in the battery case. The battery case can include an upper housing 2 and a lower housing 3. The upper housing 2 can cover the lower housing 3 and form a sealed space for accommodating the battery module 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0118] Further, the present application also provides a power consumption device including at least one of the secondary battery, battery module, or battery pack according to the present application. The secondary battery, battery module, or battery pack may be used as a power source of the power consumption device or as an energy storage element of the power consumption device. The power consumption device can include, but is not limited to, mobile devices (such as mobile phones, notebook computers, 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.), trains, ships, satellites, energy storage systems, etc.

[0119] As the power consumption device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0120] FIG. 6 shows a power consumption device as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the requirements for high power and high energy density of the secondary battery of the power consumption device, a battery pack or a battery module can be used.

[0121] Another example of the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is generally required to be lightweight and thin, and a secondary battery can be used as a power source. Examples

[0122] Hereinafter, examples of the present application will be described. The examples described below are illustrative only, and are merely for explaining the present application, and should not be construed as limiting the present application. When specific techniques or conditions are not shown in the examples, they are carried out according to the techniques or conditions described in the literature in this field or according to the product manuals. When the manufacturer of the reagents or equipment used is not described, all are common commercially available products.

[0123] Example 1 1. Production of the positive electrode active material (1) Weigh 19.3624 g of sodium ferrocyanide decahydrate, 35.292 g of sodium citrate monohydrate, and 7.9164 g of manganese chloride tetrahydrate. Add the above sodium ferrocyanide decahydrate to 100 ml of deionized water, stir for 30 min to form solution b. Add manganese chloride tetrahydrate and sodium citrate monohydrate to 100 ml of deionized water, stir for 30 min to form solution a, and after uniformly stirring, drop it into the above solution b. The dropping rate is 1 ml / min. After the dropping is completed, stir for 24 h, the stirring rate is 400 rpm, the temperature is 80 °C, and a suspension is formed. Filter the solid material in the above suspension with a Buchner funnel, and wash it 3 times with deionized water until no sodium salt and transition metal ions remain in the product. Dry the obtained material in a vacuum at 120 °C for 24 h, with a relative vacuum degree < -0.1 Mpa, to obtain 10 g of Prussian blue Na2MnFe(CN)6 precursor.

[0124] (2) Add the above 10 g of Prussian blue precursor to 100 ml of acetonitrile, disperse it ultrasonically for 10 min to form a suspension, and cool the solution to -20 °C. Weigh 0.745 g of potassium chloride and add it to the above suspension, and continue stirring for 30 min for aging. The stirring rate is 400 rpm and the temperature is -20 °C.

[0125] (3) Filter the solid material in the suspension with a Buchner funnel and wash it three times with ether at -20 °C until no sodium salt, potassium salt, and transition metal ions remain in the product. Vacuum dry the obtained material at 120 °C for 24 h with a relative vacuum degree of -0.085 MPa to obtain the cathode active material. Its chemical formula is determined by ICP test to be Na 1.9 K 0.1 MnFe(CN)6 and is confirmed by EDS line scan detection. The obtained cathode active material particles have a gradual change layer in which the content of K element shows a decreasing trend from the particle surface to the particle interior of the cathode active material particles. Example 2

[0126] In step (2), control the temperature of the suspension at -5 °C, and manufacture the cathode active material in the same steps as in Example 1 except that the ether used for washing in step (3) is at -5 °C. Example 3

[0127] In step (2), control the temperature of the suspension at 5 °C, and manufacture the cathode active material in the same steps as in Example 1 except that the ether used for washing in step (3) is at 5 °C. Example 4

[0128] In step (2), control the temperature of the suspension at 10 °C, and manufacture the cathode active material in the same steps as in Example 1 except that the ether used for washing in step (3) is at 10 °C. Example 5

[0129] Manufacture the cathode active material in the same steps as in Example 4 except that the solvent used in step (2) is water. Example 6

[0130] Manufacture the cathode active material in the same steps as in Example 3 except that the solvent used in step (2) is methanol. Example 7

[0131] The positive electrode active material was produced in the same steps as in Example 3, except that the solvent used in step (2) was formamide. Example 8

[0132] The positive electrode active material was produced in the same steps as in Example 3, except that the solvent used in step (2) was dimethyl sulfoxide. Example 9

[0133] In step (2), the positive electrode active material was produced in the same steps as in Example 1, except that the addition amount of potassium chloride was 0.894 g. Example 10

[0134] In step (2), the positive electrode active material was produced in the same steps as in Example 1, except that the addition amount of potassium chloride was 0.298 g. Example 11

[0135] In step (2), the positive electrode active material was produced in the same steps as in Example 1, except that 1.065 g of potassium chloride was added to the suspension. Example 12

[0136] In step (1), the positive electrode active material was produced in the same steps as in Example 3, except that the temperature at which solution a and solution b were reacted was 60°C. Example 13

[0137] (1), the positive electrode active material was produced in the same steps as in Example 3, except that the temperature at which solution a and solution b were reacted was 95°C. Example 14

[0138] In step (1), the positive electrode active material was produced in the same steps as in Example 3, except that the temperature at which solution a and solution b were reacted was 50°C. Example 15

[0139] In step (1), the positive electrode active material was produced in the same steps as in Example 3, except that the temperature at which solution a and solution b were reacted was 106°C. Comparative Example 1

[0140] 10 g of Prussian blue Na2MnFe(CN)6 was prepared according to step (1) of Example 1. Comparative Example 2

[0141] In step (2), the temperature of the suspension was controlled at 20°C, and the positive electrode active material was produced in the same steps as in Example 1 except that the diethyl ether used for washing in step (3) was at 20°C.

[0142] Manufacture of Battery (1) Manufacture of Positive Electrode Sheet The positive electrode active material, conductive agent carbon black (Super-P), and binder polyvinylidene fluoride (PVDF) produced in each of the above Examples and Comparative Examples were added to N-methylpyrrolidone (NMP) at a mass ratio of 7:2:1, and stirred with a rotor for 1 - 3 h to produce a slurry. The slurry was applied onto a current collector aluminum foil with a thickness of 150 μm. After drying in a vacuum drying box at 90 - 110°C for 10 - 15 h, it was naturally cooled to room temperature to obtain a positive electrode sheet. The produced positive electrode sheet was cut into small circular sheets with a diameter of 14 mm using a cutting machine.

[0143] (2) Manufacture of Negative Electrode Sheet Type II commercial hard carbon negative electrode active material purchased from Kuraray Japan, conductive agent carbon black (Super-P), binder styrene butadiene rubber (SBR), and dispersant sodium carboxymethyl cellulose (CMC-Na) were added to deionized water at a mass ratio of 90:2:4:4, and stirred with a rotor for 1 - 3 h to produce a slurry. The slurry was applied onto a current collector copper foil, and the coating amount was determined based on the absolute capacity of the positive electrode, with the negative electrode absolute capacity:positive electrode absolute capacity = 1.16, and the absolute capacity (mAh) = initial discharge reversible specific capacity (mAh / g) * total weight of the active material (g). The measurement method of the reversible specific capacity is as follows. After drying in a vacuum drying box at 90 - 110°C for 10 - 15 h, it was naturally cooled to room temperature to obtain a negative electrode sheet. The produced negative electrode sheet was cut into small circular sheets with a diameter of 16 mm using a cutting machine.

[0144] (3) Preparation of Electrolyte In an argon atmosphere glove box with a water content of < 10 ppm, equal volumes of ethylene carbonate (EC) and diethyl carbonate (DEC) were uniformly mixed to obtain an organic solvent. Fluoroethylene carbonate (FEC) as an additive was added to the organic solvent, and then sodium salt NaPF6 was uniformly dissolved in the above organic solvent to obtain an electrolyte. The mass percentage of FEC in the electrolyte is 2%, and the concentration of the sodium salt is 1 mol / L.

[0145] (4) Separator A PE separator is used as the separator.

[0146] (5) Fabrication of Button-Type All-Solid-State Battery In an argon-filled glove box, the above components were assembled to fabricate a CR 2032 button-type all-solid-state battery as the following secondary battery. Performance Test Method

[0147] 1. Test of Cathode Active Material (1) ICP Test The substance to be measured was heated to 500 °C and calcined for 2 h, and then cooled to room temperature. After adding aqua regia to dissolve the calcined product, elemental analysis was performed by inductively coupled plasma optical emission spectrometry (ICP, Ametek, model number: SPECTRO ARCOS ICP-OES). The ratio of each element was obtained by this test, and from the ratio of each element, the chemical formula Na x A y M1[M2(CN)6] δ in which x, y, and δ are determined.

[0148] (2) Detection by Transmission Electron Microscopy - X-ray Line Scan Analysis (EDS Line Scan) An electron microscope (STEM, ThermoFisher, Talos F200i) was used in combination with a side-insertable scalable energy-dispersive X-ray spectroscopy (EDS, ThermoFisher) to perform line scan analysis of the materials in the display. The acceleration voltage was 50 kV, the magnification was 100 kx, and the beam current was between 500 and 1000 pA. Line scan spectra of the number of counts of Na and A elements were obtained. From the ratio of the number of Na and A elements, the layer with Na:A = 50 At%:50 At% and the surface of the cathode active material were determined, and the thickness of the gradually changing layer could be obtained. Five positions on the cathode active material particles were randomly selected to measure the thickness of the gradually changing layer respectively, and the arithmetic mean was taken for the measurement results and recorded as the thickness of the gradually changing layer in Table 1.

[0149] Similarly, based on the ratio of the number of Na and A elements, the layer with Na:A = 10 At%:90 At% was determined. This layer is the inner boundary of the outermost layer, and the surface of the cathode active material is the outer boundary of the outermost layer. For the EDS line scan curves of the two elements Na and A, by performing curve integration between the inner and outer boundaries of the outermost layer, the ratio of the total content of the two elements was obtained, and thereby the Na content in the outermost layer was measured.

[0150] (3) Water content test After the cathode active materials produced in the examples and comparative examples were completely dehydrated, they were placed in a drying chamber with a dew point of -30 °C for 1 day. Then, it was taken out and heated to 200 °C and held for 30 minutes. The mass of the substance to be measured before and after heating was measured with an electronic balance, and the difference between the two was calculated. This was divided by the mass of the substance to be measured before heating to obtain the water content of the substance to be measured.

[0151] (4) Dv50 test Refer to the recommended standard GB / T 19077.1-2016 and measure using a laser particle size analyzer (such as Malvern Master Size 3000).

[0152] The physical definition of Dv50 is the corresponding particle size when the cumulative volume distribution percentage of the material particles reaches 50%.

[0153] (5) Specific surface area test The specific surface area test refers to GB / T 19587-2017, uses the test method for analyzing the specific surface area by the nitrogen adsorption method for measurement, and is calculated by the BET (Brunauer Emmett Teller) method. The test for analyzing the specific surface area by the nitrogen adsorption method was carried out on a Tri-Star 3020 type specific surface area and pore size analysis test device produced by Micromeritics, USA.

[0154] 2. Battery performance test [Reversible specific capacity] Manufacture of button-type half-cell The positive electrode sheet, electrolyte and separator are all the same as those of the above button-type full cell. A metal sodium sheet (a small circular sheet with a diameter of 13 mm) was used for the negative electrode, and a nickel mesh was used as the negative electrode current collector. The above-mentioned parts were assembled in an argon-protected glove box to form a CR 2032 button-type half-cell.

[0155] In the voltage range of 2.5~4.0V, at 25°C, the charge and discharge of the above button-type half-cell were carried out at a current density of 20 mA / g, the capacity in the first charge and discharge process of the battery was recorded, and the capacity was divided by the mass of the positive electrode active material to obtain the reversible specific capacity. The results of the first discharge reversible specific capacity test of the batteries manufactured using the positive electrode active materials of each example and comparative example are shown in Table 1 below.

[0156] [Storage characteristics] At 25°C, the secondary batteries manufactured in each example and comparative example were charged at a 1C rate until the charge cut-off voltage reached 4V, then charged at a constant voltage until the current reached 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current at a 0.33C rate until the discharge cut-off voltage reached 2V to obtain the initial capacity of the battery. Thereafter, at 25°C, the battery was charged at a 1C rate until the charge cut-off voltage reached 4V, then charged at a constant voltage until the current reached 0.05C. At this time, the battery was in a fully charged state. The fully charged battery was placed in an incubator at 60°C for storage. After storage for 100 days, the capacity of the battery was measured. Specifically, it was charged at a 1C rate until the charge cut-off voltage reached 4V, then charged at a constant voltage until the current reached 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current at a 0.33C rate until the discharge cut-off voltage reached 2V to obtain the capacity of the battery after storage. The percentage of the capacity of the battery after storage with respect to the initial capacity of the battery was calculated and entered in Table 1 as the storage characteristics for 100 days.

[0157] [Long-term cycle characteristics] At 25°C, the secondary batteries manufactured in the examples and comparative examples were charged at a constant current at a 1C rate until the charge cut-off voltage reached 4V, then charged at a constant voltage until the current was ≤ 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current at a 1C rate until the discharge cut-off voltage reached 2V to measure the discharge capacity of the first cycle of the battery. After allowing it to stand for 5 minutes, this was one charge-discharge cycle. A cycle charge-discharge test was performed on the battery according to this method, with a total of 200 cycles, and the discharge capacity of the last cycle was obtained. 200-cycle capacity retention rate (%) = discharge capacity of the last cycle / discharge capacity of the first cycle.

[0158]

Table 1

[0159]

Table 2

[0160] By EDS line scan detection, it was confirmed that the distribution state of element A in Examples 1 to 15 all showed a decreasing trend from the particle surface to the particle interior of the positive electrode active material, while the distribution state of element A in Comparative Example 2 showed an increasing trend from the particle surface to the particle interior of the positive electrode active material.

[0161] Compared with Comparative Example 1, it can be seen that the positive electrode active material particles in the examples have a layer doped with element A on the surface, resulting in a significantly reduced water content and significantly improved both cycle characteristics and storage characteristics. Compared with Comparative Example 2, when the positive electrode active material particles have a gradually changing layer with the content of element A showing a decreasing trend from the particle surface to the particle interior, the water content is lower and the specific capacity, cycle characteristics, and storage characteristics are superior compared to the case where the content of element A shows an increasing trend from the particle surface to the particle interior.

[0162] When the thickness of the gradually changing layer is within the range of 10 to 100 nm, the positive electrode active material has good storage characteristics, cycle characteristics, and specific capacity. In particular, when the thickness of the gradually changing layer is within the range of 10 to 75 nm, the storage characteristics, cycle characteristics, and specific capacity are further improved.

[0163] It should be noted that the present application is not limited to the above embodiments. The above embodiments are merely illustrative, and any embodiments having a configuration substantially the same as the technical idea and exhibiting the same operational effects within the scope of the technical solution of the present application are included in the technical scope of the present application. Also, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art added to the embodiments, as well as other forms constructed by combining some components in the embodiments, are also included in the scope of the present application.

Explanation of Reference Numerals

[0164] 1 Battery pack 2 Upper housing 3 Lower housing 4 Battery module 5 Secondary battery 51 Housing 52 Electrode assembly 53 Cap assembly

Claims

1. A positive electrode active material, which is particulate and contains a compound represented by the following formula (1), Na ｘ A ｙ M1[M2(CN) ６ δ ·zH ２ O (1)​ wherein, A is selected from at least one of an alkali metal element and an alkaline earth metal element, and the ionic radius of A is larger than the ionic radius of sodium, M1 is selected from at least one of transition metal elements, M2 is Fe, 0 < y ≤ 0.2, 0 < x + y ≤ 2, 0 < δ ≤ 1 and 0 ≤ z ≤ 10, and the particles of the positive electrode active material have a gradual change layer in which the content of the A element shows a decreasing tendency from the particle surface toward the particle interior, a positive electrode active material.

2. The positive electrode active material according to Claim 1, wherein 0.04 ≤ y ≤ 0.

2.

3. In the particles of the positive electrode active material, the thickness of the A element content gradual change layer is in the range of 10 to 100 nm, and the thickness of the A element content gradual change layer is the distance from the layer where the ratio of the measured contents of Na and A elements reaches Na:A = 50 At%:50 At% to the particle surface when the element content of the positive electrode active material particles is quantitatively measured by transmission electron microscope-X-ray line scan analysis, the positive electrode active material according to Claim 1.

4. The positive electrode active material according to any one of Claims 1 to 3, wherein A is selected from at least one of K, Rb, Cs, Ca, Sr, and Ba.

5. The positive electrode active material according to any one of Claims 1 to 4, wherein M1 is selected from at least one of Fe, Mn, Ni, Co, Cu, and Zn.

6. The positive electrode active material according to any one of Claims 1 to 5, wherein the volume average particle diameter Dv50 of the positive electrode active material is in the range of 1 to 5 μm.

7. The specific surface area of the positive electrode active material is in the range of 1 to 10 m ２ / g, and the positive electrode active material according to any one of claims 1 to 6.

8. The positive electrode active material according to any one of Claims 1 to 7, wherein the water content of the positive electrode active material is ≤ 2% by weight.

9. Adding a positive electrode active material precursor, which is a compound represented by the following formula (2), to a solvent and dispersing it to obtain a suspension, Na ｎ M1[M2(CN) ６ δ (2)​ wherein M1 is selected from at least one of transition metal elements, M2 is Fe, 0 < n ≤ 2, and 0 < δ ≤ 1 in Step 1, and after cooling the suspension obtained in Step 1, adding a salt of A to the suspension in the cooled state and performing stirring and aging, where A is selected from at least one of an alkali metal element and an alkaline earth metal element, and the ionic radius of A is larger than the ionic radius of sodium in Step 2, Filter the suspension obtained in Step 2, wash the obtained precipitate, and dry it to obtain a positive electrode active material. The positive electrode active material is particulate and contains a compound represented by the following formula (1). Na ｘ A ｙ M1[M2(CN) ６ δ ·zH ２ O (1)​ In the formula, A, M1, M2, and δ are as defined above, 0 < y ≤ 0.2, 0 < x + y ≤ 2, and 0 ≤ z ≤ 10. The particles of the positive electrode active material have a step 3 in which the content of the A element has a gradually changing layer showing a decreasing tendency from the particle surface toward the particle interior. The solvent in Step 1 is a polar solvent. In Step 2, cool the suspension obtained in Step 1 to 10°C or lower. The stirring and aging in Step 2 are carried out at a stirring speed of 50 to 1800 rpm for 1 to 30 minutes. In Step 3, the drying is carried out at a temperature in the range of 0 to 300°C and a vacuum degree of 100 to 150 mTorr. A method for producing a positive electrode active material.

10. In Step 1, the solubility of the positive electrode active material precursor in the solvent is 0.02 mol / L or less, and the solubility of the salt of A in the solvent is 0.05 mol / L or more. The method according to claim 9.

11. The solvent is selected from one or more of acetonitrile, adiponitrile, methanol, ethanol, water, formamide, and dimethyl sulfoxide. The method according to claim 9 or 10.

12. The molar ratio of A in the salt of A to sodium in the positive electrode active material precursor is less than or equal to 1:

5. The method according to any one of claims 9 to 11.

13. The method for producing the positive electrode active material precursor in Step 1 is as follows. Step i: Dissolve a soluble salt of transition metal element M1 and an optional Na-containing sustained release agent in water to prepare solution a. Step ii: Dissolve a soluble transition metal cyanide complex of transition metal element M2 in water to prepare solution b. Step iii: Drop solution a into solution b with stirring, and perform stirring and aging after the dropping is completed. Step iv: Filter the suspension obtained in Step iii, wash the obtained precipitate, and dry it. The method according to any one of claims 9 to 12.

14. The molar ratio of M1 in the soluble salt of transition metal element M1 to M2 in the soluble transition metal cyanide complex of transition metal element M2 is in the range of 1:0.8 to 0.8:

1. The method according to claim 13.

15. The method according to claim 13 or 14, wherein in step iii, both the solution a and the solution b are maintained within a temperature range of 20°C to 120°C.

16. A secondary battery comprising a positive electrode active material according to any one of claims 1 to 8.

17. A power consumption device comprising the secondary battery according to claim 16.

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