Nickel-manganese-based sodium-ion battery positive electrode material and preparation method therefor, and positive electrode sheet and sodium-ion battery

Abstract

The present application belongs to the technical field of secondary batteries. Provided are a nickel-manganese-based sodium-ion battery positive electrode material and a preparation method therefor, and a positive electrode sheet and a sodium-ion battery. The positive electrode material for a nickel-manganese-based sodium-ion battery is represented by the general formula NacNiaMnbO2, wherein a+b=1.0, 0.4≤a≤0.6, 0.4≤b≤0.6, and 0.67≤c≤1.0. The positive electrode material for a nickel-manganese-based sodium-ion battery is made of secondary particles formed by stacking primary particles. The primary particles are sheet-shaped particles, and the secondary particles are spherical particles, which having a discharge specific capacity of ≥115 mAh·g-1. The sodium-ion battery prepared from the positive electrode material for a nickel-manganese-based sodium-ion battery provided in the present application has a good cycling life and energy density, which facilitates the broadening of the application field of sodium-ion batteries.

Description

A nickel-manganese-based sodium ion battery positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery

[0001] This application claims priority to Chinese Patent Application No. 202410732373.1, filed on June 6, 2024. This application incorporates the entirety of the aforementioned Chinese Patent Application. TECHNICAL FIELD

[0002] The present application relates to the technical field of secondary batteries, in particular to a nickel-manganese-based sodium ion battery positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. BACKGROUND

[0003] Lithium ion batteries have good electrical properties and have been widely used in energy storage fields. However, with the development of economy, the consumption of lithium resources increases, and the reserves of lithium resources are low, unevenly distributed and have large price fluctuations. Therefore, it is urgent to find a substitute for lithium ion batteries.

[0004] Compared with lithium resources, sodium resources are widely distributed and have high reserves in the earth's crust. The content of sodium elements in the earth's crust is about 422 times that of lithium elements. Therefore, sodium ion batteries have cost advantages and are expected to be widely used in energy storage fields. Sodium ion batteries and lithium ion batteries have similar working principles. The storage and release of energy are realized by the extraction and intercalation process of sodium ions between the positive and negative electrodes. Currently, there are three major types of sodium ion battery positive electrode materials, including layered transition metal oxides, polyanion compounds and prussian blue analogues. Among them, layered transition metal oxide positive electrode materials have the highest capacity and similar preparation processes to ternary positive electrode materials of lithium ion batteries, attracting more and more research and attention.

[0005] However, the cycle life of the current layered transition metal oxides is generally short, and due to the large ionic radius and slow kinetics of sodium ions, it is difficult to charge and discharge. In addition, the compaction density of the layered transition metal oxide positive electrode material is usually low, which seriously affects the volume energy density of the material and becomes a major factor restricting its development.

[0006] SUMMARY

[0007] In view of the technical problems in the background art, the present application provides a nickel-manganese-based sodium ion battery positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery, aiming to solve the problems of short cycle life and low energy density of sodium ion batteries in the prior art.

[0008] In a first aspect, the embodiments of the present application provide a nickel-manganese-based sodium ion battery positive electrode material, which is represented by a general formula Na c Ni a Mn bO2 represents the following: a+b=1.0, 0.4≤a≤0.6, 0.4≤b≤0.6, 0.67≤c≤1.0; the above-mentioned nickel-manganese-based sodium-ion battery cathode material is a secondary particle formed by stacking primary particles; the primary particles are plate-shaped particles, and the secondary particles are spherical particles; the discharge specific capacity of the nickel-manganese-based sodium-ion battery cathode material is ≥115mAh·g. -1 .

[0009] In the technical solution of this application embodiment, the nickel-manganese-based sodium-ion battery cathode material can provide more sodium-ion active sites, which can alleviate the structural changes caused by repeated insertion and extraction of sodium ions. By selecting its structure and stoichiometry, the nickel-manganese-based sodium-ion battery cathode material can have both good cycle performance and energy density.

[0010] In some embodiments, the aspect ratio of the primary particles is (2.5-15): 1, the thickness is 0.1μm-1μm; and / or, the D50 particle size of the secondary particles is 3μm-5.5μm.

[0011] In this embodiment, by limiting the D50 particle size of the secondary particles, the specific surface area of ​​the nickel-manganese-based sodium-ion battery cathode material is relatively high, which is beneficial to increasing the contact area between it and the electrolyte and improving the ion transport rate. In addition, it is beneficial to reduce the electron transport path between particles. Furthermore, by limiting the aspect ratio and sheet thickness of the primary particles, there are relatively more active sites, which helps to further improve the ion insertion / extraction rate and can alleviate the structural changes caused by repeated sodium ion insertion / extraction, thus improving its cycle life.

[0012] In some embodiments, the specific surface area of ​​the nickel-manganese-based sodium-ion battery cathode material is 35 m². 2 / g-80m 2 / g.

[0013] In this embodiment, the specific surface area of ​​the nickel-manganese-based sodium-ion battery cathode material can reach 35m². 2 / g-80m 2 / g, thus allowing for more thorough contact between the nickel-manganese-based sodium-ion battery cathode material and the electrolyte, which helps to improve its energy density.

[0014] Secondly, embodiments of this application provide a method for preparing a nickel-manganese-based sodium-ion battery cathode material, comprising the following steps:

[0015] A mixed solution is prepared by mixing the first complexing agent, the first alkaline substance, and water, wherein the alkalinity of the mixed solution is 40 mmol / L-60 mmol / L and the pH value is 10-11.

[0016] adding a nickel salt, a manganese salt, a second complexing agent, and a second basic substance to the mixed solution, performing a first co-precipitation reaction, controlling the alkalinity of the reaction system of the first co-precipitation reaction to be 40-60 mmol / L and the pH value to be 10-11, to obtain a first reaction slurry;

[0017] adding a second complexing agent and a second basic substance to the first reaction slurry, adjusting the alkalinity of the first reaction slurry to be 60-100 mmol / L and the pH value to be 11-12, performing a second co-precipitation reaction, controlling the alkalinity of the reaction system of the second co-precipitation reaction to be 60-100 mmol / L and the pH value to be 11-12, to obtain a nickel-manganese layered hydroxide precursor;

[0018] mixing the nickel-manganese layered hydroxide precursor with a sodium source and calcining to obtain a nickel-manganese-based sodium-ion battery positive electrode material;

[0019] In the embodiment, the alkalinity of the reaction system of the first co-precipitation reaction is less than the alkalinity of the reaction system of the second co-precipitation reaction, the pH value of the reaction system of the first co-precipitation reaction is less than the pH value of the reaction system of the second co-precipitation reaction, and the reaction time of the first co-precipitation reaction is 10-40 min and the reaction time of the second co-precipitation reaction is 24-48 h.

[0020] In the embodiment, the nucleation and growth process of the precursor is regulated by changing the solution environment in the co-precipitation reaction process, thereby affecting the growth orientation of the primary particles and the stacking mode of the secondary particles, forming spherical secondary particles stacked by flaky primary particles, and improving the cycle performance and energy density of the nickel-manganese-based sodium-ion battery positive electrode material.

[0021] In some embodiments, the reaction temperature of the first co-precipitation reaction and the second co-precipitation reaction is 30-60°C.

[0022] In the embodiment, the reaction can be carried out quickly and smoothly by controlling the reaction temperature.

[0023] In some embodiments, the first co-precipitation reaction and the second co-precipitation reaction are carried out under stirring at 400-1000 rpm.

[0024] In the embodiment, the reaction can be carried out more fully and the product generated is more uniform by stirring.

[0025] In some embodiments, the calcination conditions are: heating to 400-600°C, holding for 4-6 h, then heating to 700-900°C, and holding for 10-25 h.

[0026] In this embodiment, the step of temperature programmed calcination can make the heat treatment process more sufficient, and the structure of the nickel-manganese-based sodium-ion battery cathode material is more complete and uniform, which helps to improve the electrochemical performance of the cathode material.

[0027] In some embodiments, the nickel salt is at least one of nickel sulfate, nickel nitrate, and nickel chloride; and / or, the manganese salt is at least one of manganese sulfate, manganese nitrate, and manganese chloride; and / or, the first complexing agent and the second complexing agent are each independently at least one of ammonia, nitrilotriacetic acid, and ethylenediaminetetraacetic acid; and / or, the first alkaline substance and the second alkaline substance are each independently at least one of sodium hydroxide and potassium hydroxide; and / or, the sodium source is at least one of sodium hydroxide, sodium carbonate, and sodium nitrate.

[0028] In this embodiment, the nickel salt, the manganese salt, the complexing agent, the alkaline substance, and the sodium source are all commonly used raw materials in the field, which are widely available and low in price, and are conducive to industrial production.

[0029] In some embodiments, the ratio of the amount of substance of nickel element to the amount of substance of manganese element in the nickel salt and the manganese salt is (4-6):(4-6); and / or, the ratio of the total amount of substance of nickel element and manganese element to the amount of substance of sodium element in the nickel-manganese layered hydroxide precursor and the sodium source is 1:(0.67-1.05).

[0030] In this embodiment, the nickel element plays a role in providing a skeleton in the nickel-manganese-based sodium-ion battery cathode material, and a too small proportion of the nickel element will result in poor cycle stability, and a too high proportion of the nickel element will increase the cost; by limiting the ratio of the amount of substance of nickel element to the amount of substance of manganese element as described above, on the one hand, the cycle stability of the battery can be improved, and on the other hand, the cost can be controlled, thereby expanding the application range. The ratio of the total amount of substance of nickel element and manganese element to the amount of substance of sodium element is limited as described above because a too small proportion of sodium element will reduce the content of sodium ions that can be provided, and the specific capacity of the battery will be reduced; and a too high proportion of sodium element will produce more impurities, which will affect the capacity and the processing performance of the positive electrode sheet; by limiting the ratio of the amount of substance as described above, the battery can have a high energy density and processing performance.

[0031] In some embodiments, the first complexing agent and the second complexing agent are ammonia, and the first alkaline substance and the second alkaline substance are sodium hydroxide; in addition, the step of adding the nickel salt, the manganese salt, the second complexing agent, and the second alkaline substance to the mixed solution to perform the first coprecipitation reaction to obtain the first reaction slurry comprises:

[0032] The nickel salt and the manganese salt are mixed with water to obtain a nickel-manganese binary salt solution, the second complexing agent is mixed with water to obtain a complexing agent solution, and the second alkaline substance is mixed with water to obtain an alkaline solution;

[0033] The nickel-manganese binary salt solution, the complexing agent solution and the alkaline solution are added into the mixed solution to perform a first co-precipitation reaction to obtain a first reaction slurry;

[0034] The solubility of the metal ions in the nickel-manganese binary salt solution is 1.5-2.5 mol / L; the concentration of NH3·H2O in the complexing agent solution is 2-6 mol / L; and the concentration of the alkaline substance in the alkaline solution is 3-5 mol / L.

[0035] In addition, the volume ratio of the ammonia water to water in the mixed solution is 1: (3-13), and the ammonia water is concentrated ammonia water with a mass fraction of NH3·H2O of 25-28%.

[0036] In this embodiment, the amount of the ammonia water is limited as above to facilitate preparation of an aqueous solution with a basicity of 40-60 and a pH value of 10-11, and the concentrations of nickel and manganese in the nickel-manganese binary salt solution, the concentration of NH3·H2O and the concentration of the alkali are limited as above to facilitate subsequent control of the reaction rate and preparation of a nickel-manganese-based sodium ion battery cathode material with complete structure and uniform size.

[0037] In some embodiments, the addition speed of the alkaline solution in the first co-precipitation reaction process is 0.1-0.4 mL / min, and the addition speed of the complexing agent solution is 0.2-0.4 mL / min.

[0038] In the second co-precipitation reaction process, the addition speed of the alkaline solution is 0.4-0.6 mL / min, and the addition speed of the complexing agent solution is 0.4-0.8 mL / min.

[0039] In the first co-precipitation reaction and the second co-precipitation reaction processes, the addition speed of the nickel-manganese binary salt solution is 0.3-1 mL / min.

[0040] In this embodiment, by limiting the addition speeds of the various solutions, the basicity in the first co-precipitation reaction process can be maintained at 40-60 mmol / L, and the pH value can be maintained at 10-11; the basicity in the second co-precipitation reaction process can be maintained at 60-80 mmol / L, and the pH value can be maintained at 11-12; in the first co-precipitation reaction process, the precursor is still in a nucleation stage and grows along the (010) crystal plane, which is conducive to the formation of flaky nuclei; in the second co-precipitation reaction process, the precursor is in a growth stage, which can make the nuclei accumulate along the (101) crystal plane direction to form spherical secondary particles stacked by flaky primary particles, and is conducive to the transmission of sodium ions.

[0041] In a third aspect, the embodiments of the present application provide a positive electrode sheet, comprising a current collector and a positive electrode material, a conductive agent and a binder on one side or both sides of the current collector, wherein the positive electrode material is the nickel-manganese-based sodium ion battery positive electrode material of the first aspect of the present application, and has good electrochemical performance.

[0042] In a fourth aspect, the embodiments of the present application provide a sodium ion battery, comprising the positive electrode sheet of the third aspect of the present application, and thus has good cycle performance and energy density.

[0043] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the following detailed description can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0045] FIG. 1 is a scanning electron microscope image of the nickel-manganese layered hydroxide in the embodiment 1 of the present application;

[0046] FIG. 2 is a scanning electron microscope image of the nickel-manganese-based sodium ion battery positive electrode material in the embodiment 1 of the present application;

[0047] FIG. 3 is an XRD spectrum of the nickel-manganese-based sodium ion battery positive electrode material in the embodiment 1 of the present application;

[0048] FIG. 4 is a first cycle charge-discharge specific capacity test diagram of the nickel-manganese-based sodium ion battery positive electrode material in the embodiment 1 of the present application;

[0049] FIG. 5 is a cycle performance test diagram of the nickel-manganese-based sodium ion battery positive electrode material in the embodiment 1 of the present application. DETAILED DESCRIPTION

[0050] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof. Unless otherwise required by context, singular terms shall include pluralities and vice versa. Unless otherwise required by context, the use herein of the singular is also to be construed as a use of the plural and vice versa.

[0052] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise explicitly and specifically limited.

[0053] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification is not necessarily all referring to the same embodiment, or to a particular embodiment, or to a particular set of embodiments, and is not intended to exclude other embodiments or aspects of the application. It will be explicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0054] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0055] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two), and similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0056] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as limiting the embodiments of the present application, which do not indicate or imply that the indicated devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0057] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixedly connected, or can be detachably connected, or can be integrated; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium, or can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0058] As described in the background art of the present application, due to the low reserves and large consumption of lithium resources, current research shows that sodium ion batteries are expected to replace lithium ion batteries and be applied in the field of energy storage. However, the ionic radius of sodium ions is large, and it is difficult to charge and discharge and deintercalate. In addition, the cycle life of existing sodium ion batteries is generally short, and therefore, it is urgent to provide a sodium ion battery with good energy density and cycle life to broaden the application field of sodium ion batteries.

[0059] In order to solve the technical problems of short cycle life and low energy density of sodium ion batteries, the present application provides a nickel-manganese-based sodium ion battery positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. By adjusting the stoichiometric ratio of each element in the nickel-manganese-based sodium ion battery positive electrode material and its structure, the energy density and cycle life of the nickel-manganese-based sodium ion battery positive electrode material can be effectively improved, and the electrochemical performance of the positive electrode sheet and the secondary battery is also improved.

[0060] In a first aspect, the embodiments of the present application provide a nickel-manganese-based sodium ion battery positive electrode material, which is represented by a general formula Na c Ni a Mn b O2, wherein a+b=1.0, 0.4≤a≤0.6, 0.4≤b≤0.6, 0.67≤c≤1.0; the nickel-manganese-based sodium ion battery positive electrode material is a secondary particle formed by stacking primary particles; the primary particles are flaky particles, and the secondary particles are spherical particles; the discharge specific capacity of the nickel-manganese-based sodium ion battery positive electrode material is ≥115 mAh·g -1 .

[0061] In the description of the embodiments of the present application, the term "stoichiometric ratio" refers to the ratio of the coefficients of different chemical elements in the general formula.

[0062] The nickel-manganese-based sodium ion battery positive electrode material is a research and development hotspot at present. The presence of nickel element helps to improve the theoretical capacity and conductivity of the material, and the presence of manganese element can provide good ion transmission performance and high cycle stability. By limiting the stoichiometric ratio of the nickel-manganese-based sodium ion battery positive electrode material as described above, the comprehensive electrochemical performance of the nickel-manganese-based sodium ion battery positive electrode material can be improved, so that the nickel-manganese-based sodium ion battery positive electrode material has good energy density and cycle life. In addition, the morphology of the nickel-manganese-based sodium ion battery positive electrode material also affects its electrochemical performance. The secondary particles formed by the stacking of flaky primary particles have a large specific surface area, a large contact area with the electrolyte, high specific capacity, and help to improve the energy density of the nickel-manganese-based sodium ion battery positive electrode material.

[0063] Further, in some embodiments, the diameter-thickness ratio of the primary particles is (2.5-15):1, the sheet thickness is 0.1 μm-1 μm; and / or, the D50 particle size of the secondary particles is 3 μm-5.5 μm.

[0064] In the description of the embodiments of the present application, the term "diameter-thickness ratio" refers to the ratio of the long side of the circumscribed rectangle of the flaky particle and the sheet thickness of the flaky particle.

[0065] In the technical solution of the embodiments of the present application, the size of the primary particles and the secondary particles is limited as described above, which is to improve the specific surface area of the positive electrode material and to reduce the irreversible capacity. In addition, when the size of the primary particles and the secondary particles meets the above limitation, the sintering process is not easy to break, and the structural integrity is higher, which helps to improve the cycle performance of the nickel-manganese-based sodium ion battery positive electrode material.

[0066] Further, in some embodiments, the D50 particle size of the secondary particles is 4.2 μm-5.5 μm.

[0067] In the technical solution of the embodiments of the present application, the D50 particle size of the secondary particles is further optimized, which has better dispersibility and is easier to prepare uniform slurry, which has a certain effect on improving the cycle stability of the secondary battery prepared from the nickel-manganese-based sodium ion battery positive electrode material.

[0068] Further, in some embodiments, the specific surface area of the nickel-manganese-based sodium ion battery positive electrode material is 35 m 2 / g-80 m 2 / g.

[0069] In the technical solution of the embodiments of the present application, by limiting the specific surface area of the nickel-manganese-based sodium ion battery positive electrode material, the nickel-manganese-based sodium ion battery positive electrode material has good energy density and cycle stability.

[0070] In a second aspect, the present application provides a preparation method of a nickel-manganese-based sodium ion battery positive electrode material, comprising the following steps:

[0071] The first complexing agent, the first basic substance and water are mixed to prepare a mixed solution, wherein the alkalinity of the mixed solution is 40-60 mmol / L and the pH value is 10-11 of an aqueous solution;

[0072] The nickel salt, the manganese salt, the second complexing agent and the second basic substance are added to the mixed solution to perform a first co-precipitation reaction, the alkalinity of the reaction system of the first co-precipitation reaction is controlled to be 40-60 mmol / L and the pH value is controlled to be 10-11, and a first reaction slurry is obtained;

[0073] The second complexing agent and the second basic substance are added to the first reaction slurry to adjust the alkalinity of the first reaction slurry to be 60-100 mmol / L and the pH value to be 11-12, a second co-precipitation reaction is performed, the alkalinity of the reaction system of the second co-precipitation reaction is controlled to be 60-100 mmol / L and the pH value is controlled to be 11-12, and a nickel-manganese layered hydroxide precursor is obtained;

[0074] The nickel-manganese layered hydroxide precursor is mixed with a sodium source and calcined to obtain a nickel-manganese-based sodium ion battery positive electrode material.

[0075] The alkalinity of the reaction system of the first co-precipitation reaction is less than the alkalinity of the reaction system of the second co-precipitation reaction, the pH value of the reaction system of the first co-precipitation reaction is less than the pH value of the reaction system of the second co-precipitation reaction, and the reaction time of the first co-precipitation reaction is 10-40 min and the reaction time of the second co-precipitation reaction is 24-48 h.

[0076] In the description of the embodiments of the present application, the term "alkalinity" refers to the ability of water to absorb protons, which is tested by acid titration.

[0077] In the technical solution of the embodiments of the present application, the growth orientation of the particles is controlled by adjusting the alkalinity and the pH value. In the first co-precipitation reaction, i.e. the nucleation stage, the above-mentioned limitations on the alkalinity and the pH value can promote the growth of the (010) crystal plane, which is conducive to the formation of flaky crystal nuclei with large crystal planes. In the second co-precipitation reaction, i.e. the growth stage, the above-mentioned limitations on the alkalinity and the pH value are conducive to the stacking of primary particles in the (101) crystal plane direction, and thus secondary particles stacked by primary particles with high aspect ratio and conducive to sodium ion transport are synthesized.

[0078] Further, in some embodiments, oxygen in the aqueous solution is discharged before the first co-precipitation reaction; in addition, the first co-precipitation reaction and the second co-precipitation reaction are performed under the protection of inert gas to improve the purity of the product.

[0079] Further, in some embodiments, the reaction temperature of the first co-precipitation reaction and the second co-precipitation reaction is 30-60℃; and / or, the first co-precipitation reaction and the second co-precipitation reaction are carried out under stirring at a speed of 400-1000 rpm.

[0080] In the technical solution of the embodiments of the present application, the above-mentioned limitation of the reaction temperature can on the one hand improve the reactivity of the raw materials and improve the reaction rate, and on the other hand the reaction rate will not be too fast, and it is easier to control the nucleation and growth process, so that the reaction can be carried out quickly and smoothly; the stirring speed can affect the collision frequency of the reactants, and by limiting the stirring speed as mentioned above, on the one hand, the collision frequency of the reactants is moderate, with a relatively fast reaction rate, and on the other hand, the controllability of the nucleation and growth process is high, and the secondary particles with a one-time particle sheet thickness and a suitable diameter-thickness ratio can be formed, which can ensure that the nickel-manganese-based sodium-ion battery cathode material has good mechanical properties while also having good electrochemical performance.

[0081] Further, in some embodiments, the alkalinity and pH value of the reaction system of the first co-precipitation reaction and the reaction system of the second co-precipitation reaction are controlled by adjusting the amount of the second complexing agent and the basic substance.

[0082] In the technical solution of the embodiments of the present application, only the amount of the second complexing agent and the second basic substance needs to be controlled to control the growth direction of the crystal grains in the nucleation and growth stage.

[0083] Further, in some embodiments, after the second co-precipitation reaction is completed, the nickel-manganese layered hydroxide precursor is obtained by concentration, washing and drying.

[0084] Further, in some embodiments, the calcination conditions are as follows: heating to 400-600℃, holding for 4-6h, and then heating to 700-900℃, holding for 10-25h.

[0085] In the technical solution of the embodiments of the present application, the two-stage heating can make the precursor uniformly heated, reduce the thermal stress, and generate a nickel-manganese-based sodium-ion battery cathode material with certain mechanical properties, which is helpful to improve the cycle stability of the cathode material.

[0086] Further, in some embodiments, the nickel salt is at least one of nickel sulfate, nickel nitrate and nickel chloride; the manganese salt is at least one of manganese sulfate, manganese nitrate and manganese chloride; the first complexing agent and the second complexing agent are each independently at least one of ammonia, nitrilotriacetic acid and ethylenediaminetetraacetic acid; the first basic substance and the second basic substance are each independently at least one of sodium hydroxide and potassium hydroxide; and the sodium source is at least one of sodium hydroxide, sodium carbonate and sodium nitrate.

[0087] In the technical scheme of the embodiment of the present application, the nickel salt, the manganese salt, the complexing agent, the alkaline substance and the sodium source can be obtained by purchase, and the sources are wide.

[0088] Further, in some embodiments, the substance amount ratio of the nickel element and the manganese element in the nickel salt and the manganese salt is (4-6) : (4-6), and the total substance amount ratio of the nickel element and the manganese element to the substance amount of the sodium element in the sodium source is 1 : (0.67-1.05).

[0089] In the technical scheme of the embodiment of the present application, the nickel element has a skeleton-providing effect in the crystal formation process, and by limiting the substance amount ratio of the nickel element and the manganese element and the total substance amount ratio of the nickel element and the manganese element to the substance amount of the sodium element, the cycle stability of the battery can be improved; if the content of the nickel element is too high, the production cost will be affected; the sodium element has a sodium ion-providing effect, and if the amount of the sodium element is too small, the energy density of the battery will be reduced, and if the content of the sodium element is too high, a heterogeneous phase will be generated, the specific capacity of charge and discharge will be reduced, in addition, the residual alkali will be increased, the roughness of the sodium ion battery cathode material will be increased, and the processing performance will be affected.

[0090] Further, in some embodiments, the first complexing agent and the second complexing agent are ammonia water, and the first alkaline substance and the second alkaline substance are sodium hydroxide.

[0091] Further, in some embodiments, the step of adding the nickel salt, the manganese salt, the second complexing agent and the second alkaline substance into the mixed solution to perform the first coprecipitation reaction to obtain the first reaction slurry comprises the following steps.

[0092] The nickel salt and the manganese salt are mixed with water to obtain a nickel-manganese binary salt solution, the second complexing agent is mixed with water to obtain a complexing agent solution, and the second alkaline substance is mixed with water to obtain an alkaline solution;

[0093] The nickel-manganese binary salt solution, the complexing agent solution and the alkaline solution are added into the mixed solution to perform the first coprecipitation reaction to obtain the first reaction slurry;

[0094] The concentration of NH3·H2O in the complexing agent solution is 2 mol / L-6 mol / L; and the concentration of the alkaline substance in the alkaline solution is 3 mol / L-5 mol / L.

[0095] In addition, the volume ratio of the ammonia water to water in the mixed solution is 1 : (3-13), and the ammonia water is concentrated ammonia water.

[0096] In the technical scheme of the embodiment of the present application, the components of the mixed solution and the components of the complexing agent solution and the alkaline solution are limited, which helps to control the alkalinity and pH value of the reaction system. The concentration of metal ions in the nickel-manganese binary salt solution has a great influence on the reaction rate. Controlling within the above range can make the reaction proceed stably and generate uniform nickel-manganese-based sodium-ion battery positive electrode materials.

[0097] Further, in some embodiments, the addition speed of the alkaline solution in the first co-precipitation reaction process is 0.1 mL / min-0.4 mL / min, and the addition speed of the complexing agent solution is 0.2 mL / min-0.4 mL / min; the addition speed of the alkaline solution in the second co-precipitation reaction process is 0.4 mL / min-0.6 mL / min, and the addition speed of the complexing agent solution is 0.4 mL / min-0.8 mL / min; the addition speed of the nickel-manganese binary salt solution in the first co-precipitation reaction and the second co-precipitation reaction is 0.3 mL / min-1 mL / min.

[0098] In the technical scheme of the embodiment of the present application, the above-mentioned limitation of the addition speed of different solutions can make the product of the first co-precipitation reaction be flaky particles, and the product of the second co-precipitation reaction be spherical secondary particles stacked by flaky primary particles.

[0099] In a third aspect, the embodiment of the present application provides a positive electrode sheet, which comprises a current collector and a positive electrode material, a conductive agent and a binder on one side or both sides of the current collector. The positive electrode material is the nickel-manganese-based sodium-ion battery positive electrode material provided in the first aspect of the present application, and therefore has good cycle performance and energy density.

[0100] In a fourth aspect, the embodiment of the present application provides a sodium-ion battery, which comprises the positive electrode sheet of the third aspect of the present application, and therefore has good electrochemical performance and good application prospect.

[0101] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not specified in the examples, it is carried out according to the technology or condition described in the literature in the art or according to the product instruction. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be obtained from the market.

[0102] I. Preparation method

[0103] The ammonia used in the examples and comparative examples is concentrated ammonia with a mass fraction of NH3·H2O of 25%-28%.

[0104] Alkalinity test method: phenolphthalein alkalinity titration method is selected, 20 mL of sample is taken every hour during the reaction, the supernatant is separated after standing, 2-3 drops of phenolphthalein are added, at this time the solution is red; titration is carried out at room temperature 25℃ with standard 0.010 mol / L hydrochloric acid solution until the solution just turns colorless.

[0105] pH value test method: real-time monitoring is carried out during the reaction by using a Leici pH meter; before use, calibration is carried out in standard solutions with pH values of 6.86 and 9.18 at room temperature 25℃.

[0106] Example 1

[0107] An embodiment of the nickel-manganese-based sodium ion battery positive electrode material provided in the application has the following preparation method:

[0108] S1, a nickel-manganese binary salt solution is prepared by mixing nickel and manganese elements in a molar ratio of 1:1.01, and the total concentration of metal ions in the nickel-manganese binary salt solution is 2 mol / L; a sodium hydroxide solution with a concentration of 5 mol / L is prepared; an ammonia water solution with a concentration of 6 mol / L is prepared; the solvents of the above solutions are all water;

[0109] S2, 36% of the total volume of the reaction kettle is deionized water, the reaction kettle is heated to 50℃ and then stirred at a speed of 600 rpm, then high-purity nitrogen is introduced into the reaction kettle for 30 min to remove oxygen in the reaction kettle; 5.12% of the volume of the reaction kettle is concentrated ammonia water, and then sodium hydroxide solution is added to obtain an aqueous solution with an alkalinity of 45-55 mmol / L and a pH value of 10.4-10.8;

[0110] S3, the nickel-manganese binary salt solution, the sodium hydroxide solution and the ammonia water solution are simultaneously introduced into the reaction kettle for first co-precipitation reaction, the feeding speed of the nickel-manganese binary salt solution is kept at 0.5 mL / min, the feeding speed of the sodium hydroxide solution is 0.25 mL / min, and the feeding speed of the ammonia water solution is 0.3 mL / min; during the first co-precipitation reaction, the alkalinity is maintained at 45-55 mmol / L, and the pH value is maintained at 10.4-10.8, and the reaction is carried out for 30 min;

[0111] S4, the nickel-manganese binary salt solution, the sodium hydroxide solution and the ammonia solution are simultaneously fed into the reactor to perform a second co-precipitation reaction, the feeding speed of the nickel-manganese binary salt solution is maintained at 0.4 mL / min, the feeding speed of the sodium hydroxide solution is 0.45 mL / min, and the feeding speed of the ammonia solution is 0.4 mL / min; during the second co-precipitation reaction, the alkalinity is maintained at 70-90 mmol / L, the pH value is maintained at 11.3-11.7, and the reaction is performed for 36 h; the reaction product is concentrated, then washed with deionized water, and finally dried at 110°C for 24 h to obtain a nickel-manganese layered hydroxide precursor;

[0112] S5, the nickel-manganese layered hydroxide precursor is mixed with sodium hydroxide, wherein the ratio of the total amount of substance of nickel and manganese elements to the amount of substance of sodium element is 1:1, then ground, placed in a tube furnace for calcination, heated to 500°C at a heating rate of 5°C / min and maintained for 6 h, then heated to 750°C at a heating rate of 5°C / min and maintained for 20 h, oxygen is continuously fed during the entire calcination process, and then cooled to room temperature to obtain a nickel-manganese-based sodium ion battery positive electrode material.

[0113] Example 2-3

[0114] The examples of the nickel-manganese-based sodium ion battery positive electrode material of the present application differ from the preparation method of Example 1 only in that the feeding speeds of the sodium hydroxide solution and the ammonia solution during the first co-precipitation reaction and the second co-precipitation reaction are different, as shown in Table 1.

[0115] Example 4-5

[0116] The examples of the nickel-manganese-based sodium ion battery positive electrode material of the present application differ from the preparation method of Example 1 only in that the reaction times during the first co-precipitation reaction and the second co-precipitation reaction are different, as shown in Table 1.

[0117] Comparative Example 1

[0118] Comparative Example 1 is a nickel-manganese-based sodium ion battery positive electrode material, and the difference between its preparation method and that of Example 1 is that in S2, 8.3% of concentrated ammonia water based on the volume of the reactor is added to the reactor, and then the sodium hydroxide solution is added dropwise to obtain an aqueous solution with an alkalinity of 70-90 mmol / L and a pH value of 11.3-11.7.

[0119] Comparative Example 2

[0120] Comparative Example 2 is a nickel-manganese-based sodium ion battery positive electrode material, and the difference between its preparation method and that of Example 1 is that the feeding speeds of the sodium hydroxide solution and the ammonia solution during the first co-precipitation reaction and the second co-precipitation reaction are different, and the reaction times are different, as shown in Table 1.

[0121] Table 1

[0122] Examples 6-7

[0123] An embodiment of the nickel-manganese-based sodium-ion battery cathode material of the present application differs from Example 1 only in that the molar ratio of nickel element to manganese element in the nickel-manganese binary salt solution is different; in Example 6, the molar ratio of nickel element to manganese element is 2:3, and in Example 7, the molar ratio of nickel element to manganese element is 3:2.

[0124] Examples 8-9

[0125] An embodiment of the nickel-manganese-based sodium-ion battery cathode material of the present application differs from Example 1 only in that in S5, the molar ratio of the total amount of nickel element and manganese element to the amount of sodium element is different; in Example 8, the molar ratio of the total amount of nickel element and manganese element to the amount of sodium element is 1:0.70, and in Example 9, the molar ratio of the total amount of nickel element and manganese element to the amount of sodium element is 1:0.84.

[0126] Comparative Example 3

[0127] A nickel-manganese-based sodium-ion battery cathode material, the preparation method of which differs from Example 1 only in that the molar ratio of nickel element to manganese element in the nickel-manganese binary salt solution is different, and the molar ratio of nickel element to manganese element is 0.3:0.7.

[0128] Comparative Example 4

[0129] A nickel-manganese-based sodium-ion battery cathode material, the preparation method of which differs from Example 1 only in that in S5, the molar ratio of the total amount of nickel element and manganese element to the amount of sodium element is different, and the molar ratio of the total amount of nickel element and manganese element to the amount of sodium element is 1:1.16.

[0130] II. Test Methods

[0131] 1. Morphology test: field emission scanning electron microscope, model MERLIN Compact, magnification 50k times.

[0132] 2. Compaction density test: refer to GB / T 24533 for determination of powder compaction density;

[0133] 3. Specific surface area test: refer to GB / T 19587 gas adsorption BET method for determination of specific surface area of solid substances;

[0134] 4. Electrochemical performance test: the nickel-manganese-based sodium ion battery positive electrode materials in the examples and comparative examples were assembled into button cells, and electrochemical performance test was carried out, and the assembly and test method was as follows:

[0135] (1) Preparation of positive electrode sheet: the positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 87:5:8, N-methyl pyrrolidone (NMP) with a solid-liquid ratio of 65:35 was added to form a uniform electrode slurry, then the electrode slurry was uniformly coated on an aluminum foil, vacuum dried and cut into a circular electrode sheet, and then transferred to a glove box for standby.

[0136] (2) Battery assembly: metal sodium was used as the counter electrode, glass fiber was used as the separator, sodium perchlorate was used as the solute of the electrolyte, propylene carbonate, ethylene carbonate and fluoroethylene carbonate (volume ratio 1:1:0.05) were used as the solvent of the electrolyte, the concentration of sodium perchlorate in the electrolyte was 1 mol / L, and CR2032 button cells were assembled, and the whole assembly process was carried out in an argon-filled glove box. The button cells were placed for 6 h and then used for subsequent electrochemical performance test.

[0137] (3) Using constant current charge and discharge mode, charge and discharge test was carried out at a current density of 0.1C, the charge cut-off voltage was 4.0V, and the discharge cut-off voltage was 2.0V, and the discharge specific capacity test results were recorded in Table 2. After three charge and discharge tests at a current density of 0.1C, 100 charge and discharge cycles were carried out at a current density of 1C, and the discharge specific capacity of the 103rd test was divided by the discharge specific capacity of the 4th test to obtain the capacity retention rate η of 100 times 1C cycle, and the results were recorded in Table 2.

[0138] III. Analysis of test results of examples and comparative examples

[0139] The compaction density of the positive electrode material of the examples and comparative examples and the electrochemical performance test results of the button cells prepared from the positive electrode material are recorded in Table 2.

[0140] Table 2

[0141] From Table 2, it can be seen that the battery prepared from the nickel-manganese-based sodium ion battery positive electrode material in the examples of the present application has relatively high discharge specific capacity and capacity retention rate, and the discharge specific capacity can reach 115mAh·g -1 The above is helpful to improve the energy density; in addition, the capacity retention rate is high, which can reach more than 60%, and has good cycle performance.

[0142] The alkalinity and pH value in the first coprecipitation reaction process in Comparative Example 1 are too high, and the specific discharge capacity is low; the duration of the second coprecipitation reaction in Comparative Example 2 is too short, and the specific discharge capacity is also low; the amount of substance of nickel element and manganese element in Comparative Example 3 is too small, and the specific discharge capacity obviously decays; the amount of substance of nickel element and manganese element and the amount of substance of sodium element in Comparative Example 4 are too small, the specific discharge capacity is low, and the cycle stability obviously decays.

[0143] FIG. 1 is a scanning electron microscope image of the nickel-manganese layered hydroxide precursor in Example 1, from which it can be seen that it is a spherical secondary particle stacked by flaky primary particles; FIG. 2 is a scanning electron microscope image of the nickel-manganese-based sodium ion battery positive electrode material in Example 1, from which it can be seen that it is also a spherical secondary particle stacked by flaky primary particles; from the above test results, it can be seen that the nickel-manganese-based sodium ion battery positive electrode material with flaky primary particles and spherical secondary particles stacked by flaky primary particles can be prepared by the method disclosed in the present application. FIG. 3 is an XRD image of the nickel-manganese-based sodium ion battery positive electrode material in Example 1, from which it can be seen that the prepared nickel-manganese-based sodium ion battery positive electrode material is Na c Ni a Mn b O2, wherein a = 0.5, b = 0.5, and c = 1. FIG. 4 is a first cycle charge-discharge specific capacity test image of the nickel-manganese-based sodium ion battery positive electrode material in Example 1, from which it can be seen that the first cycle charge-discharge specific capacity can reach more than 130 mAh·g-1, and the energy density is high. FIG. 5 is a cycle performance test image of the nickel-manganese-based sodium ion battery positive electrode material in Example 1, from which it can be seen that the cycle stability is relatively good, and the capacity retention rate after 100 cycles can reach more than 70%.

[0144] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A nickel-manganese-based sodium-ion battery cathode material, characterized in that, Na c Ni a Mn b O2 represents, wherein, a+b=1.0, 0.4<=a<=0.6, 0.4<=b<=0.6, 0.67<=c<=1.0; the nickel-manganese-based sodium ion battery positive electrode material is secondary particles stacked by primary particles; the primary particle is a flaky particle, and the secondary particle is a spherical particle; the discharge specific capacity of the nickel-manganese-based sodium ion battery positive electrode material is >=115 mAh·g -1 .

2. The nickel-manganese-based sodium-ion battery cathode material of claim 1, wherein, The primary particles have a ratio of diameter to thickness of (2.5-15):1 and a flake thickness of 0.1 μm-1 μm; and / or The secondary particles have a D50 particle size of 3 μm-5.5 μm.

3. The nickel-manganese-based sodium-ion battery cathode material of claim 1 or 2, characterized in that, The specific surface area of the nickel-manganese-based sodium ion battery positive electrode material is 35 m 2 / g-80 m 2 / g.

4. A method of preparing the nickel-manganese-based sodium-ion battery cathode material according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: The first complexing agent and the first basic substance are mixed with water to prepare a mixed solution, wherein the alkalinity of the mixed solution is 40 mmol / L-60 mmol / L and the pH value is 10-11; The nickel salt, the manganese salt, the second complexing agent and the second basic substance are added to the mixed solution to perform a first co-precipitation reaction, the alkalinity of the reaction system of the first co-precipitation reaction is controlled to be 40 mmol / L-60 mmol / L and the pH value is controlled to be 10-11, and a first reaction slurry is obtained; The second complexing agent and the second basic substance are added to the first reaction slurry to adjust the alkalinity of the first reaction slurry to 60 mmol / L-100 mmol / L and the pH value to 11-12, a second co-precipitation reaction is performed, the alkalinity of the reaction system of the second co-precipitation reaction is controlled to be 60 mmol / L-100 mmol / L and the pH value is controlled to be 11-12, and a nickel-manganese layered hydroxide precursor is obtained; The nickel-manganese layered hydroxide precursor is mixed with a sodium source and calcined to obtain the nickel-manganese-based sodium ion battery positive electrode material; The alkalinity of the reaction system of the first co-precipitation reaction is less than the alkalinity of the reaction system of the second co-precipitation reaction, the pH value of the reaction system of the first co-precipitation reaction is less than the pH value of the reaction system of the second co-precipitation reaction, the reaction time of the first co-precipitation reaction is 10 min-40 min, and the reaction time of the second co-precipitation reaction is 24 h-48 h.

5. The preparation method according to claim 4, wherein The reaction temperature of the first co-precipitation reaction and the second co-precipitation reaction is 30°C-60°C; and / or The first co-precipitation reaction and the second co-precipitation reaction are performed under stirring at 400 rpm-1000 rpm; and / or The calcination is performed by heating to 400°C-600°C, holding for 4 h-6 h, then heating to 700°C-900°C, and holding for 10 h-25 h.

6. The preparation method according to claim 4 or 5, wherein The nickel salt is at least one of nickel sulfate, nickel nitrate and nickel chloride; and / or The manganese salt is at least one of manganese sulfate, manganese nitrate and manganese chloride; and / or The first complexing agent is at least one of ammonia, nitrilotriacetic acid and ethylenediaminetetraacetic acid; and / or The second complexing agent is at least one of ammonia, nitrilotriacetic acid and ethylenediaminetetraacetic acid; and / or The first basic substance is at least one of sodium hydroxide and potassium hydroxide; and / or The second basic substance is at least one of sodium hydroxide and potassium hydroxide; and / or The sodium source is at least one of sodium hydroxide, sodium carbonate and sodium nitrate; and / or The molar ratio of nickel element to manganese element in the nickel salt and the manganese salt is (4-6):(4-6); and / or ​ The ratio of the total amount of substance of nickel element and manganese element to the amount of substance of sodium element in the nickel-manganese layered hydroxide precursor and the sodium source is 1:(0.67-1.05).

7. The production method according to claim 6, wherein The step of adding a nickel salt, a manganese salt, a second complexing agent and a second alkaline substance into the mixed solution to perform a first coprecipitation reaction to obtain a first reaction slurry comprises: The nickel salt and the manganese salt are mixed with water to obtain a nickel-manganese binary salt solution, the second complexing agent is mixed with water to obtain a complexing agent solution, and the second alkaline substance is mixed with water to obtain an alkaline solution; The nickel-manganese binary salt solution, the complexing agent solution and the alkaline solution are added into the mixed solution to perform a first coprecipitation reaction to obtain a first reaction slurry; The solubility of metal ions in the nickel-manganese binary salt solution is 1.5 mol / L-2.5 mol / L; the concentration of NH3·H2O in the complexing agent solution is 2 mol / L-6 mol / L; and the concentration of alkaline substance in the alkaline solution is 3 mol / L-5 mol / L.

8. The preparation method of claim 7, wherein, During the first coprecipitation reaction, the addition speed of the alkaline solution is 0.1 mL / min-0.4 mL / min, and the addition speed of the complexing agent solution is 0.2 mL / min-0.4 mL / min; During the second coprecipitation reaction, the addition speed of the alkaline solution is 0.4 mL / min-0.6 mL / min, and the addition speed of the complexing agent solution is 0.4 mL / min-0.8 mL / min; During the first coprecipitation reaction and the second coprecipitation reaction, the addition speed of the nickel-manganese binary salt solution is 0.3 mL / min-1 mL / min.

9. A positive electrode sheet characterized by comprising: The positive electrode material is the positive electrode material according to any one of claims 1-3 or the positive electrode material prepared by the preparation method according to any one of claims 4-8.

10. A sodium-ion battery, characterized in that, The positive electrode plate comprises the positive electrode material according to claim 9.

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