CN111224093B - Electrode material with manganese concentration gradient, preparation method thereof and sodium-ion battery - Google Patents

Electrode material with manganese concentration gradient, preparation method thereof and sodium-ion battery Download PDF

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CN111224093B
CN111224093B CN201910967004.XA CN201910967004A CN111224093B CN 111224093 B CN111224093 B CN 111224093B CN 201910967004 A CN201910967004 A CN 201910967004A CN 111224093 B CN111224093 B CN 111224093B
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manganese
sodium
concentration gradient
electrode material
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CN111224093A (en
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王军
邓永红
吴唯
池上森
王曼
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Nayuan New Material Technology Wuxi Co ltd
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Southern University of Science and Technology
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    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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Abstract

The invention relates to the technical field of sodium ion batteries, and particularly provides an electrode material with a manganese concentration gradient, a preparation method of the electrode material and a sodium ion battery. The electrode material with the manganese concentration gradient has the following general formula: na (Na)xMnaMbM’cO2+d(ii) a Wherein x is more than or equal to 0.44 and less than or equal to 1.1, a is more than 0, b is more than 0, c is more than or equal to 0, d is more than or equal to 0, a + b is 1, M is selected from at least one of Ni and Co, and M' is selected from at least one of Fe, Cu, Mg, Zn, Al and Ti; the concentration of manganese ions in the electrode material gradually decreases from the surface to the inside of the electrode material. The electrode material of the invention can effectively improve the stability and rate discharge capability of the material due to the concentration gradient of manganese, so that when the material is used as the anode material of a sodium-ion battery, the energy density, the battery capacity, the rate capability and the cycle performance of the battery can be effectively improved.

Description

Electrode material with manganese concentration gradient, preparation method thereof and sodium-ion battery
Technical Field
The invention belongs to the technical field of sodium-ion batteries, and particularly relates to an electrode material with manganese concentration gradient, a preparation method of the electrode material and a sodium-ion battery.
Background
Because some lithium ion battery raw materials depend on import, the price of the lithium ion battery is too high, and therefore products capable of replacing the lithium ion battery in the fields of electric batteries and large-scale energy storage need to be searched. Among the numerous battery systems, sodium ion batteries are considered to be one of the most desirable systems. For electric vehicles and large-scale energy storage batteries, the low cost makes possible the wide range of applications for sodium ion batteries. Another advantage of low cost of the sodium ion battery is the utilization of the current collector, and since sodium ions do not form an alloy with aluminum, the traditional copper negative current collector in the lithium ion battery can be replaced by an aluminum foil with low price in the sodium ion battery. The main components of the sodium ion battery comprise a positive electrode, a negative electrode, electrolyte and a diaphragm. During charging, sodium ions are driven from the positive electrodeThe material is separated from the cathode material and finally embedded into the cathode material through the transmission of electrolyte, and the discharging process is opposite. The commonly used anode materials are hard carbon, titanium-containing oxide, etc. Commonly used cathode materials include Prussian blue, phosphate systems and layered sodium transition metal oxides (chemical formula: Na)xTMO2Wherein TM represents transition metal such as Mn, Ni, Fe, Ti and V). Compared with the anode material of the lithium ion battery, the anode material of the sodium ion battery has lower specific capacity and lower voltage platform, so that the energy density of the corresponding sodium ion battery is lower than that of the lithium ion battery. One of the main factors that restrict the energy density of sodium ion batteries is the development and utilization of the positive electrode material. Based on the present layered lithium transition metal oxide LiTMO2Successful application of the layered sodium transition metal oxide NaxTMO2Also becomes one of the most promising anode materials in the research field of sodium-ion batteries. The problems still existing in the sodium ion battery at present are mainly that the positive electrode material shows lower energy density and poorer cycle performance.
CN110112375A discloses a NaxMn1-yMyO2The positive electrode material of the sodium ion battery, wherein M is Ru, Ir, Nb, Bi, Sn, Ta or Sb, x is more than or equal to 0.3 and less than or equal to 1, and 0<y is less than or equal to 0.5, and the electron conductivity and the sodium ion mobility of the material are improved by introducing the second transition metal M, and the phase change in the sodium ion de-intercalation process under high voltage is inhibited, so that the rate capability and the cycle performance of the positive electrode material assembled into the sodium ion battery are effectively improved; CN109962215A discloses a doping modified P2 type sodium ion battery anode material Na0.67Mn0.6Fe0.4-x-yAxByO2X is more than 0 and less than or equal to 0.1, y is more than 0 and less than or equal to 0.1, and the doped cation comprises two parts: a is a metal cation participating in an oxidation reduction reaction in the charge-discharge process, B is an inert metal cation in the charge-discharge process, and the cycle and rate performance of the anode material can be effectively improved in a double-ion doping mode; CN108987708A discloses a ZrO2Coated Na0.67Ni0.167Co0.167Mn0.67O2The positive electrode material of sodium ion battery is effectiveThe cycle performance is improved; however, doping or coating by inert anions, cations can lead to a decrease in the active element content and ultimately to a decrease in the energy density of the sodium ion battery. CN109742365A discloses a positive electrode material Na of a sodium-ion battery2/3Ni1/3-xMxMn2/3O2Wherein x is more than 0 and less than 1/3, M is Cu and/or Mg, the anode material is a layered particle with hexagonal and/or strip-shaped morphology, the material can effectively inhibit unfavorable two-phase transformation of P2-O2 under high voltage, and can relieve the phenomenon of sodium/vacancy ordered pairs under a deep charging state, so that the anode material is prevented from generating serious voltage and capacity attenuation; CN109638278A discloses a positive electrode material of a sodium ion battery, which is prepared from granular NaxMnO2Wherein x is more than 0 and less than or equal to 1, NaxMnO2Each particle of the material contains MnO randomly deposited2Nanosheet, plurality of MnO2A staggered-layer stacked structure is formed among the nano sheets, and the structural characteristic of the staggered-layer stacked structure can effectively reduce Na of the materialxMnO2Phase change in the circulation process to increase Na of the materialxMnO2Thereby increasing the sodium ion transport rate, and MnO2The nano-structure characteristic also reduces the transmission path of sodium ions, and improves the conductivity and rate characteristic of the sodium ion battery; CN109607624A discloses Na with a layered-tunnel composite structure0.6Mn0.8Co0.2O2The positive electrode material of the sodium-ion battery can combine the respective advantages of a layered structure and a tunnel structure, and can solve the problems of the existing single layered structure material in the aspects of capacity and the like. However, the preparation process of the hexagonal particles, the nano-sheets or the layered-tunnel composite structure is complex, which may increase the production cost of the sodium-ion battery.
Disclosure of Invention
Aiming at the problems of low active element content, low battery energy density and the like caused by doping or coating of the conventional sodium-ion battery positive electrode material, the invention provides an electrode material with manganese concentration gradient and a preparation method thereof.
Further, the invention also provides a sodium ion battery containing the electrode material with the manganese concentration gradient.
In order to achieve the purpose, the technical scheme of the invention is as follows:
an electrode material having a manganese concentration gradient, the battery material having a manganese concentration gradient having the general formula:
NaxMnaMbM’cO2+d；
wherein x is more than or equal to 0.44 and less than or equal to 1.1, a is more than 0, b is more than 0, c is more than or equal to 0, d is more than or equal to 0, a + b is 1, M is selected from at least one of Ni and Co, and M' is selected from at least one of Fe, Cu, Mg, Zn, Al and Ti;
the concentration of manganese ions in the electrode material gradually decreases from the surface to the inside of the electrode material.
Correspondingly, the preparation method of the electrode material with the manganese concentration gradient comprises the following steps:
step S01, providing a solution containing M ions, a solution containing manganese ions and a precipitant, mixing the solution containing M ions, the solution containing manganese ions and the precipitant simultaneously by adopting a coprecipitation method, wherein the adding speed of the solution containing M ions is higher than that of the solution containing manganese ions at the initial stage of reaction, and the adding speed of the solution containing M ions at the later stage of reaction is lower than that of the solution containing manganese ions, so that the concentration of manganese ions in the obtained product is gradually reduced from the surface to the inside of the product; controlling the pH value in the reaction system to be 7.5-13.5 in the whole reaction process to obtain a transition metal salt precipitation precursor with manganese concentration gradient;
or providing a plurality of parts of mixed solution containing manganese ions and M ions, wherein the M ions and the manganese ions in the mixed solution have concentration difference, and the plurality of parts of mixed solution at least comprise one part of first mixed solution with high M ion concentration and low manganese ion concentration and one part of second mixed solution with low M ion concentration and high manganese ion concentration;
adopting a coprecipitation method, adding a mixed solution containing low manganese ion concentration for reaction, then adding a mixed solution containing high manganese ion concentration for reaction, simultaneously adding a precipitator solution, and controlling the pH value in a reaction system to be 7.5-13.5 to obtain a transition metal salt precipitation precursor with manganese concentration gradient;
high and low are relative concepts in the invention, and the high M ion concentration and the low manganese ion concentration mean that the concentration of M ions is higher than that of manganese ions in the same mixed solution system; the concentration of the low M ions and the concentration of the high manganese ions mean that the concentration of the M ions is lower than that of the manganese ions in the same mixed solution system;
s02, mixing and heating sodium-containing compounds, M' salt and the transition metal salt precipitation precursor with the manganese concentration gradient according to the stoichiometric ratio to obtain the electrode material with the manganese concentration gradient, which is shown in the following general formula:
NaxMnaMbM’cO2+d；
wherein x is more than or equal to 0.44 and less than or equal to 1.1, a is more than 0, b is more than 0, c is more than or equal to 0, d is more than or equal to 0, a + b is 1, M is selected from at least one of Ni and Co, and M' is selected from at least one of Fe, Cu, Mg, Zn, Al and Ti.
Further, the sodium ion battery comprises a positive electrode active material, wherein the positive electrode active material comprises the electrode material with the manganese concentration gradient, or the electrode material with the manganese concentration gradient prepared by the preparation method of the electrode material with the manganese concentration gradient.
The invention has the technical effects that:
compared with the prior art, the electrode material with the manganese concentration gradient provided by the invention has the advantages that the manganese has the concentration gradient, so that the content of active elements can be effectively maintained, and the stability and the rate discharge capacity of the material are improved, so that when the electrode material is used as a positive electrode material of a sodium-ion battery, the energy density, the capacity, the rate performance and the cycle performance of the battery can be effectively improved.
The preparation method of the electrode material with the manganese concentration gradient, disclosed by the invention, has the characteristics of cheap and easily-obtained raw materials, simple preparation process, high yield and the like, and the obtained electrode material with the manganese concentration gradient has the characteristics of high purity and the like.
According to the sodium ion battery, the active substance of the anode is the electrode material with the manganese concentration gradient, so that the problems that the content of active elements is reduced due to traditional doping or coating, the energy density of the battery is low when the battery is used for the sodium ion battery and the like are solved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 shows Na having the structure of P2 prepared in example 10.67Ni0.33Mn0.67O2XRD pattern of (a);
FIG. 2 shows Na having the structure of P2 prepared in example 20.67Ni0.33Mn0.67O2XRD pattern of (a);
FIG. 3 shows Na having the structure of P2 prepared in example 30.67Ni0.33Mn0.67O2XRD pattern of (a);
FIG. 4 shows Na having the structure of P3 prepared in example 40.67Ni0.33Mn0.67O2XRD pattern of (a);
FIG. 5 shows Na having the structure of P3 prepared in example 50.67Ni0.33Mn0.67O2XRD pattern of (a);
FIG. 6 shows Na having the structure of P3 prepared in example 60.67Ni0.33Mn0.67O2XRD pattern of (a);
FIG. 7 shows NaNi having O3 structure prepared in example 70.45Cu0.05Mg0.05Mn0.45O2XRD pattern of (a);
FIG. 8 shows Na having the structure of P3 prepared in example 60.67Ni0.33Mn0.67O2SEM interface picture and Mn edge EDS energy spectrum analysis;
FIG. 9 shows Na having a general P3 structure prepared by a conventional method0.67Ni0.33Mn0.67O2SEM interface picture and Mn edge EDS energy spectrum analysis;
fig. 10 is a graph showing the first charge and discharge when the sodium ion battery of example 1 is applied to the present invention;
fig. 11 is a graph of rate and cycle performance of a sodium ion battery according to application example 1 of the present invention;
FIG. 12 is a graph showing the rate curves of sodium ion batteries according to application examples 2 to 4 and comparative examples of the present invention;
fig. 13 is a graph showing cycle performance of sodium ion batteries according to application example 4 of the present invention and comparative example.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
In one aspect of the invention, an electrode material having a manganese concentration gradient is provided. The electrode material with the manganese concentration gradient has the following general formula:
NaxMnaMbM’cO2+d；
wherein x is more than or equal to 0.44 and less than or equal to 1.1, a is more than 0, b is more than 0, c is more than or equal to 0, d is more than or equal to 0, a + b + c is 1, M is selected from at least one of Ni and Co, and M' is selected from at least one of Fe, Cu, Mg, Zn, Al and Ti;
in the above-mentioned electrode material having a manganese concentration gradient, the manganese ion concentration decreases from the surface to the inside.
The technical solution of the present invention is explained in further detail below.
The electrode material with the manganese concentration gradient can be a sodium transition metal oxide with a P2 structure, a sodium transition metal oxide with a P3 structure, a sodium transition metal oxide with an O3 structure, or any mixture formed by the sodium transition metal oxides with the three structures, such as a mixture of two oxides of the sodium transition metal oxide with the P2 structure and the sodium transition metal oxide with the P3 structure; a mixture of two oxides of sodium transition metal oxide of the structure P2 and sodium transition metal oxide of the structure O3; a mixture of two oxides of sodium transition metal oxide of the structure P3 and sodium transition metal oxide of the structure O3; or a mixture of three oxides of sodium transition metal oxide with a P2 structure, sodium transition metal oxide with a P3 structure and sodium transition metal oxide with an O3 structure.
Specifically, the electrode material having a manganese concentration gradient may be Na of the P2 structure0.67Ni0.33Mn0.67O2Na of the structure P30.67Ni0.33Mn0.67O2NaNi of O3 structure0.45Cu0.05Mg0.05Mn0.45O2At least one of (1). The manganese concentration gradient difference of the electrode materials with the manganese concentration gradient maintains the content of active elements, improves the stability and rate discharge capacity of the materials, and can effectively improve the energy density and the battery capacity of the battery when the electrode materials are used as the positive electrode active material of the sodium ion battery to be assembled into the sodium ion battery, so that the battery has good rate performance and cycle performance.
Accordingly, in a second aspect of the present invention, there is provided a method for preparing the electrode material having a manganese concentration gradient, comprising the steps of:
(a1) providing a plurality of parts of mixed solution containing manganese ions and M ions, wherein the M ions and the manganese ions of the mixed solution have concentration difference, and at least one part of the mixed solution with high M ion concentration and low manganese ion concentration and one part of the mixed solution with low M ion concentration and high manganese ion concentration are included in the plurality of parts of mixed solution;
(b1) adding a mixed solution containing low manganese ions for reaction, adding a mixed solution containing high manganese ions for reaction, simultaneously adding a precipitant solution, and controlling the pH value in the reaction system to be 7.5-13.5 to obtain a transition metal salt precipitation precursor with manganese concentration gradient by adopting a coprecipitation method;
(c1) and mixing and heating the sodium-containing compound, the M' salt and the transition metal salt precipitation precursor with the manganese concentration gradient according to the stoichiometric ratio to obtain the electrode material with the manganese concentration gradient.
High and low are relative concepts in the invention, and the high M ion concentration and the low manganese ion concentration mean that the M ion concentration is higher than the manganese ion concentration in the same mixed solution system; the low M ion concentration and the high manganese ion concentration mean that the M ion concentration is lower than the manganese ion concentration in the same mixed solution system, and the manganese ion concentration in the mixed solution with the adjacent high manganese ion concentration is higher than the manganese ion concentration in the mixed solution with the low manganese ion concentration.
The M ion involved in the step (a1) is derived from M salt, and specifically can be derived from at least one of sulfuric acid M, acetic acid M and nitric acid M; the manganese ions can be derived from manganese salt, and specifically can be at least one of manganese sulfate, manganese acetate and manganese nitrate;
in the step (b1), a precipitant is required for the coprecipitation reaction. The precipitator used in the method is a mixed solution of at least one of sodium carbonate and sodium hydroxide and ammonia water, the pH value of a reaction system is adjusted to be 7.5-13.5 by dropwise adding the precipitator solution, and salts can be subjected to coprecipitation in the pH range to generate a transition metal salt precipitation precursor with a manganese concentration gradient.
In the step (c1), when the sodium-containing compound and the precursor for precipitation of the transition metal salt are mixed, the molar ratio of sodium in the sodium-containing compound is: transition metal salt precipitation precursor with manganese concentration gradient: m' salt (0.22-0.55): 1 (0-0.2), the effect is not greatly different according to the molar ratio of 0.22:1 to 0.55:1, and the aim is to introduce sodium ions; the M 'ion is at least one of iron-containing compound, copper-containing compound, magnesium-containing compound, zinc-containing compound, aluminum-containing compound and titanium-containing compound, and the addition of the M' salt plays a role in further doping. Preferably, the sodium-containing compound is at least one of sodium carbonate, sodium acetate, sodium bicarbonate, sodium oxalate and sodium hydroxide, and after the reaction of the sodium-containing compounds is finished, new impurities are not introduced, so that the purity of the product is further improved.
When the sodium-containing compound, the transition metal salt precipitation precursor with the manganese concentration gradient and the M' salt are mixed, a mechanical grinding mode can be adopted, the sodium-containing compound and the transition metal salt precipitation precursor with the manganese concentration gradient can also be prepared into turbid liquid, the turbid liquid is mixed and is prepared into slurry through ultrasonic oscillation treatment, and the slurry is dried, ball-milled and the like, so that the sodium-containing compound and the transition metal salt precipitation precursor with the manganese concentration gradient are uniformly mixed.
In the step (c1), the heating sintering conditions were as follows: keeping the temperature at 600-1000 ℃ for 1-20 h. If the temperature can be increased to 800 ℃, the temperature is kept for 10 h; or heating to 900 ℃, and preserving the heat for 10 hours; heating to 1000 ℃, and preserving heat for 10 hours; or heating to 600 ℃, and preserving the heat for 20 hours; or heating to 700 ℃, preserving the heat for 15h and the like, heating and sintering, and naturally cooling to room temperature.
The invention also provides another preparation method, which comprises the following steps:
(a2) providing a solution containing M ions and a solution containing manganese ions;
(b2) dropwise adding the solution simultaneously by adopting a coprecipitation method, wherein the dropwise adding speed of the solution containing M ions is higher than the acceleration of the solution containing manganese ions at the initial stage of reaction, the dropwise adding speed of the solution containing M ions is lower than the dropwise adding speed of the solution containing manganese ions at the later stage of reaction, so as to ensure that the concentration of manganese ions in the obtained product is gradually reduced from the surface to the inside, and controlling the pH value in a reaction system to be 7.5-13.5 by using a precipitator, so as to obtain a transition metal salt precipitation precursor with manganese concentration gradient;
(c2) and mixing the sodium-containing compound, the M' salt and the transition metal salt precipitation precursor with the manganese concentration gradient according to the stoichiometric ratio, and heating and sintering to obtain the electrode material with the manganese concentration gradient.
Wherein, the M ion involved in the step (a2) is derived from M salt, specifically at least one of sulfuric acid M, acetic acid M and nitric acid M; the manganese ions can be derived from manganese salt, and specifically can be at least one of manganese sulfate, manganese acetate and manganese nitrate;
in the step (b2), a precipitant is required for the coprecipitation reaction. The precipitator used in the method is a mixed solution of at least one of sodium carbonate and sodium hydroxide and ammonia water, the pH value of a reaction system is adjusted to be 7.5-13.5 by dropwise adding the precipitator solution, and salts can be subjected to coprecipitation in the pH range to generate a transition metal salt precipitation precursor with a manganese concentration gradient.
In the step (c2), when the sodium-containing compound and the precursor for precipitation of the transition metal salt are mixed, the molar ratio of sodium in the sodium-containing compound is: transition metal salt precipitation precursor with manganese concentration gradient: m' salt (0.22-0.55): 1 (0-0.2), the effect is not greatly different according to the molar ratio of 0.22:1 to 0.55:1, and the aim is to introduce sodium ions; the M 'ion is at least one of iron-containing compound, copper-containing compound, magnesium-containing compound, zinc-containing compound, aluminum-containing compound and titanium-containing compound, and the addition of the M' salt plays a role in further doping.
Preferably, the sodium-containing compound is at least one of sodium carbonate, sodium acetate, sodium bicarbonate, sodium oxalate and sodium hydroxide, and after the reaction of the sodium-containing compounds is finished, new impurities are not introduced, so that the purity of the product is further improved.
When the sodium-containing compound and the transition metal salt precipitation precursor with the manganese concentration gradient are mixed, a mechanical grinding mode can be adopted, the sodium-containing compound and the transition metal salt precipitation precursor with the manganese concentration gradient can also be prepared into turbid liquid, the turbid liquid is mixed and is prepared into slurry through ultrasonic oscillation treatment, and the slurry is dried, ball-milled and the like, so that the sodium-containing compound and the transition metal salt precipitation precursor with the manganese concentration gradient are uniformly mixed.
Step (c2), the heating sintering conditions were as follows: keeping the temperature at 600-1000 ℃ for 1-20 h. If the temperature can be increased to 800 ℃, the temperature is kept for 10 h; or heating to 900 ℃, and preserving the heat for 10 hours; heating to 1000 ℃, and preserving heat for 10 hours; or heating to 600 ℃, and preserving the heat for 20 hours; or heating to 700 ℃, preserving the heat for 15h and the like, heating and sintering, and naturally cooling to room temperature.
The preparation method has the characteristics of cheap and easily obtained raw materials, simple preparation process, high yield and the like, and the obtained electrode material with the manganese concentration gradient has the characteristics of high purity and the like.
The invention also provides a positive plate and a sodium ion battery, wherein the positive active material comprises the electrode material with the manganese concentration gradient.
The positive plate takes an electrode material with a manganese concentration gradient as a positive active material, and also contains a conductive agent and a binder. Specifically, an electrode material with a manganese concentration gradient is mixed with a conductive agent, a binder and a solvent to prepare anode slurry, the anode slurry is coated on the surfaces of an anode current collector, such as aluminum foil, and the like, and an anode sheet is prepared through drying, rolling and cutting. The mass ratio of the electrode material with the manganese concentration gradient, the conductive agent and the binder in the positive plate is 80:10:10 or 90:5: 5. In preparing the positive electrode slurry, the solvent may be N-methylpyrrolidone (NMP).
The sodium ion battery comprises the positive plate, or the positive active material contains the electrode material with the manganese concentration gradient.
The negative active material of the sodium ion battery provided by the invention is hard carbon or titanium-containing oxide.
The electrolyte is 1M NaPF6Electrolyte solution of (EC: DMC ═ 1:1), 1M NaPF6Electrolyte of/PC, 1M NaClO4(EC: PC ═ 1:1) in which EC: DMC ═ 1:1 represents a solvent formed from ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1, PC represents propylene carbonate, EC: PC represents a solvent formed by ethylene carbonate and propylene carbonate according to the volume ratio of 1: 1.
The diaphragm of the sodium ion battery provided by the invention is a polyolefin microporous membrane such as polyethylene, polypropylene and the like, such as a Celgard diaphragm.
In order to more effectively explain the technical solution of the present invention, a plurality of specific examples are described below.
Example 1
Na with P2 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) preparing 200mL of 1mol/L nickel sulfate solution and 400mL of 1mol/L manganese sulfate solution, and preparing a precipitator simultaneously, wherein the precipitator contains 1mol/L ammonium carbonate and 0.1mol/L ammonia water.
(b) Dropwise adding the nickel sulfate solution, the manganese sulfate solution and a precipitant obtained in the step (a) at the same time to perform coprecipitation reaction, wherein the titration speed of the nickel sulfate solution in the first stage of the reaction is 100mL/h, and the titration speed of the manganese sulfate solution is 50 mL/h; the titration speed of the nickel sulfate solution at the second stage of the reaction is 100mL/h, and the titration speed of the manganese sulfate solution is 350 mL/h; the pH value is always controlled to be about 8.0, and a carbonate precursor with manganese concentration gradient is obtained, wherein the molecular formula is Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor with the manganese concentration gradient and sodium carbonate according to the molar ratio of 1:0.335, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 20 hours at the constant temperature of 950 ℃, and naturally cooling the mixture to the room temperature to obtain the material sample electrode with the manganese concentration gradient.
XRD testing was performed on the material sample obtained in example 1, and the detailed test results are shown in FIG. 1.
The XRD spectrum shown in fig. 1 is consistent with the standard XRD spectrum of P2, and it is confirmed that the obtained material has a P2 structure, and thus it can be confirmed that the material prepared in example 1 has a Na structure of P20.67Ni0.33Mn0.67O2。
Example 2
Na with P2 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) preparing 200mL of 1mol/L nickel sulfate solution, 400mL of 1mol/L manganese sulfate solution and simultaneously preparing a precipitator, wherein the precipitator contains 1mol/L ammonium carbonate and 0.1mol/L ammonia water.
(b) Dropwise adding the nickel sulfate solution, the manganese sulfate solution and a precipitant obtained in the step (a) at the same time to perform coprecipitation reaction, wherein the titration speed of the nickel sulfate solution in the first stage of the reaction is 50mL/h, the titration speed of the manganese sulfate solution is 25mL/h, and the time of the first stage is 1 h; the titration speed of the nickel sulfate solution in the second stage of the reaction is 50mL/h, the titration speed of the manganese sulfate is 50mL/h, the duration of the second stage1 h; the titration speed of the nickel sulfate solution in the third stage of the reaction is 50mL/h, the titration speed of the manganese sulfate solution is 125mL/h, and the time of the third stage is 1 h; the titration speed of the nickel sulfate solution at the fourth stage of the reaction is 50mL/h, the titration speed of the manganese sulfate solution is 200mL/h, and the time of the fourth stage is 1 h; controlling the pH value to be about 8.0 all the time to obtain the carbonate precursor with the manganese concentration gradient, wherein the molecular formula of the carbonate precursor with the manganese concentration gradient is Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor with the manganese concentration gradient and sodium carbonate according to the molar ratio of 1:0.335, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 20 hours at the constant temperature of 950 ℃, and naturally cooling the mixture to the room temperature to obtain a material sample with the manganese concentration gradient.
XRD testing was performed on the material sample obtained in example 2, and the detailed test results are shown in FIG. 2.
The XRD spectrum shown in fig. 2 is consistent with the standard XRD spectrum of P2, and it is confirmed that the obtained material has a P2 structure, and thus it can be confirmed that the material prepared in example 2 has a Na structure of P20.67Ni0.33Mn0.67O2。
Example 3
Na with P2 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) preparing 200mL of 1mol/L nickel sulfate solution and 400mL of 1mol/L manganese sulfate solution, and preparing a precipitator simultaneously, wherein the precipitator contains 1mol/L sodium carbonate and 0.1mol/L ammonia water.
(b) Dropwise adding the nickel sulfate solution, the manganese sulfate solution and a precipitant obtained in the step (a) at the same time for coprecipitation reaction, wherein the titration speed of the nickel sulfate solution is 100mL/h and the titration speed of the manganese sulfate solution is 50mL/h in the first hour of the reaction; the titration speed of the nickel sulfate solution in the second hour of the reaction is 75mL/h, and the titration speed of the manganese sulfate solution is 100 mL/h; the titration speed of the nickel sulfate solution in the third hour of the reaction is 25mL/h, and the titration speed of the manganese sulfate solution is 250 mL/h; the pH value is always controlled to be about 8.0, and a carbonate precursor with manganese concentration gradient is obtainedThe molecular formula of the carbonate precursor with the manganese concentration gradient is Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor with the manganese concentration gradient and sodium carbonate according to the molar ratio of 1:0.335, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 20 hours at the constant temperature of 950 ℃, and naturally cooling the mixture to the room temperature to obtain a material sample with the manganese concentration gradient.
XRD testing was performed on the sample obtained in example 3, and the detailed test results are shown in FIG. 3.
The XRD spectrum shown in fig. 3 is consistent with the standard XRD spectrum of P2, and it is confirmed that the obtained material has a P2 structure, and thus it can be confirmed that the material prepared in example 3 has a Na structure of P20.67Ni0.33Mn0.67O2。
Example 4
Na with P3 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) nickel sulfate and manganese sulfate are mixed according to a molar ratio of 2:1 in proportion, mixing and dissolving in water to prepare a first mixed solution with the total concentration of transition metal ions of 1 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 2 is mixed and dissolved in water to prepare a second mixed solution with the total concentration of transition metal ions of 1 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 5 are mixed and dissolved in water to prepare a third mixed solution with the total concentration of transition metal ions of 1 mol/L; preparing a precipitator, wherein the precipitator contains 1mol/L sodium carbonate and 0.1mol/L ammonia water.
(b) Dropwise adding the mixed solution obtained in the step (a) and a precipitator simultaneously for coprecipitation reaction so as to ensure that the pH value of a reaction system is 8.0, and the first mixed solution added in the first stage of the reaction is 100 mL; 100mL of the second mixed solution added in the second stage; the third mixed solution is added in 200mL in the third stage, the pH value is always controlled to be about 8.0, and the carbonate precursor with the manganese concentration gradient is obtained, wherein the molecular formula of the carbonate precursor with the manganese concentration gradient is Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor with the manganese concentration gradient and sodium carbonate according to the molar ratio of 1:0.335, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 10 hours at the constant temperature of 800 ℃, and naturally cooling the mixture to the room temperature to obtain a material sample with the manganese concentration gradient.
XRD testing was performed on the sample obtained in example 4, and the detailed test results are shown in FIG. 4.
The XRD spectrum shown in fig. 4 is consistent with that of P3, and it is confirmed that the obtained material has a P3 structure, and thus it can be confirmed that the material prepared in example 4 has Na of a P3 structure0.67Ni0.33Mn0.67O2。
Example 5
Na with P3 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) nickel sulfate and manganese sulfate are mixed according to a molar ratio of 3: 1 in proportion, mixing and dissolving in water to prepare a first mixed solution with the total concentration of transition metal ions of 1 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 3, mixing and dissolving in water to prepare a second mixed solution with the total concentration of transition metal ions being 1 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 6, mixing and dissolving in water to prepare a third mixed solution with the total concentration of transition metal ions being 1 mol/L; meanwhile, a precipitator is prepared, and the precipitator contains 1mol/L sodium carbonate and 0.1mol/L ammonia water.
(b) Dropwise adding the mixed solution obtained in the step (a) and a precipitator simultaneously for coprecipitation reaction to ensure the pH value of a reaction system, wherein the volume of the first mixed solution added in the first reaction stage is 100 mL; reacting 100mL of second mixed solution added in the second stage; 175mL of the third mixed solution is added in the third stage of the reaction, and the pH value is controlled to be about 8.0, so that a carbonate precursor with a manganese concentration gradient is obtained, wherein the molecular formula of the carbonate precursor with the manganese concentration gradient is Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor with the manganese concentration gradient and sodium carbonate according to the molar ratio of 1:0.335, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 10 hours at the constant temperature of 800 ℃, and naturally cooling the mixture to room temperature to obtain a material sample with the manganese concentration gradient.
XRD testing was performed on the sample obtained in example 5, and the detailed test results are shown in FIG. 5.
The XRD spectrum shown in fig. 5 is consistent with that of P3, and it is confirmed that the obtained material has a P3 structure, and thus it can be confirmed that the material prepared in example 5 has Na of a P3 structure0.67Ni0.33Mn0.67O2。
Example 6
Na with P3 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) nickel sulfate and manganese sulfate are mixed according to a molar ratio of 4: 1 in proportion, mixing and dissolving in water to prepare a first mixed solution with the total concentration of transition metal ions of 1 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 4 are mixed and dissolved in water to prepare a second mixed solution with the total concentration of transition metal ions being 1 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 7 in a proportion, and dissolving the mixture in water to prepare a third mixed solution with the total concentration of transition metal ions of 1 mol/L; and simultaneously preparing a precipitator, wherein the precipitator contains 1mol/L sodium carbonate and 0.1mol/L ammonia water.
(b) Dropwise adding the mixed solution obtained in the step (a) and a precipitator simultaneously to ensure the pH value of a reaction system, wherein the first mixed solution added in the first stage of the reaction is 100 mL; reacting 100mL of second mixed solution added in the second stage; the third mixed solution added in the third reaction stage is 160mL, the pH value is controlled to be about 8.0, and the carbonate precursor with the manganese concentration gradient is obtained, wherein the molecular formula of the carbonate precursor with the manganese concentration gradient is Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor with the manganese concentration gradient and sodium carbonate according to the molar ratio of 1:0.335, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 15 hours at the constant temperature of 800 ℃, and naturally cooling the mixture to the room temperature to obtain a material sample with the manganese concentration gradient.
XRD testing was performed on the sample obtained in example 6, and the detailed test results are shown in FIG. 6.
The XRD spectrum shown in fig. 6 is consistent with that of P3, and it is confirmed that the obtained material has a P3 structure, and thus it can be confirmed that the material prepared in example 6 has Na of a P3 structure0.67Ni0.33Mn0.67O2。
The SEM scan and EDS analysis were performed simultaneously on the material obtained in example 6, and the results are shown in FIG. 8.
As can be seen from fig. 8, Mn has a significant concentration gradient, and the Mn concentration gradually decreases from the surface of the material to the inside of the material.
Example 7
NaNi with O3 structure0.45Cu0.05Mg0.05Mn0.45O2The preparation method comprises the following steps:
(a) nickel sulfate and manganese sulfate are mixed according to a molar ratio of 4: 1 in a proportion of 1, and dissolving the mixture in water to prepare a first mixed solution with the total concentration of transition metal ions of 2 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1:1 is mixed and dissolved in water to prepare a second mixed solution with the total concentration of transition metal ions being 2 mol/L; nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 4, mixing and dissolving in water to prepare a third mixed solution with the total concentration of transition metal ions being 2 mol/L; and simultaneously preparing a precipitator, wherein the precipitator contains 2mol/L of sodium hydroxide and 0.2mol/L of ammonia water.
(b) Dripping the mixed solution obtained in the step (a) and a precipitator simultaneously to ensure the pH value of a reaction system, wherein the first mixed solution added in the first reaction stage is 100 mL; the second mixed solution added in the second stage of the reaction is 100 mL; the third mixed solution added in the third reaction stage is 100mL, the pH value of the precipitator is controlled to be about 12.0, and the hydroxide precursor with the manganese concentration gradient is obtained, wherein the molecular formula of the hydroxide precursor with the manganese concentration gradient is Ni0.5Mn0.5(OH)2。
(c) Mixing the hydroxide precursor with the manganese concentration gradient with sodium carbonate, magnesium acetate and copper acetate according to the molar ratio of 18:10:1:1, placing the mixture in a resistance heating air atmosphere furnace, sintering the mixture for 5 hours at the constant temperature of 500 ℃, then sintering the mixture for 20 hours at the constant temperature of 900 ℃, and naturally cooling the mixture to the room temperature to obtain a material sample with the manganese concentration gradient.
XRD testing was performed on the sample obtained in example 7, and the detailed test results are shown in FIG. 7.
The XRD spectrum shown in fig. 7 is consistent with the standard XRD spectrum of O3, and it was confirmed that the obtained material has an O3 structure, and thus it can be confirmed that the sample of the material prepared in example 7 is NaNi having an O3 structure0.45Cu0.05Mg0.05Mn0.45O2。
Example 8
Na with P3 structure0.67Ni0.33Mn0.67O2The preparation method comprises the following steps:
(a) nickel sulfate and manganese sulfate are mixed according to a molar ratio of 1: 2 are mixed and dissolved in water to prepare a mixed solution with the total concentration of transition metal ions of 1 mol/L; a solution containing 3mol/L of sodium carbonate and 0.3mol/L of ammonia water is used as a precipitator.
(b) Dripping the mixed solution obtained in the step (a) and a precipitator simultaneously, and controlling the pH value to be about 8.0 to obtain a common carbonate precursor with the molecular formula of Ni0.33Mn0.67CO3。
(c) Mixing the carbonate precursor and sodium carbonate according to the molar ratio of 1:0.335, then placing the mixture into a resistance heating air atmosphere furnace, sintering for 5h at the constant temperature of 500 ℃, then sintering for 10h at the constant temperature of 800 ℃, and naturally cooling to the room temperature to obtain the common sodium transition metal oxide with the P3 structure.
SEM and EDS tests were performed on the sample obtained in example 8, and the detailed test results are shown in FIG. 9. As can be seen from fig. 9, Mn is uniformly distributed in the interior of the material, and no change in concentration gradient occurs.
In order to prove the performance of the material obtained by the invention, the materials prepared in examples 3, 4, 5, 6 and 8 are respectively used as positive electrode materials of sodium-ion batteries to assemble the sodium-ion batteries, and corresponding performance tests are carried out.
Application example 1
A sodium ion battery, the preparation method comprises the following steps:
(1) na having the structure of P2 obtained in example 30.67Ni0.33Mn0.67O2Mixing the positive electrode active material with conductive carbon black and polyvinylidene fluoride (PVdF) binder according to the mass ratio of 8:1:1, dissolving the mixture in N-methyl pyrrolidone (NMP) solvent to prepare positive electrode slurry, coating the positive electrode slurry on aluminum foil, drying and cutting to obtain the positive electrode sheet.
(2) Assembling the positive plate obtained in the step (1), sodium metal and a Celgard diaphragm into a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is 1M NaPF6An electrolyte solution formed by dissolving in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (in a volume ratio EC: DMC ═ 1: 1). After assembly, the voltage was stabilized by standing for 24 hours, and the charge and discharge test was performed, and the test results are shown in fig. 10.
Specifically, the test mode is as follows: at 20mA g-1The current density of (A) is in the range of 2.0-4.1V for charging and discharging. From the first charge-discharge graph 10, it can be seen that the obtained P2Na having a manganese concentration gradient0.67Ni0.33Mn0.67O2The positive electrode material exhibited about 92mAh g-1High specific discharge capacity.
And meanwhile, the multiplying power performance and the cycle performance of the material are tested, and the specific result is shown in fig. 11.
Specifically, the test mode is as follows: at 20mA g-1Is charged at a voltage in the range of 2.0-4.1V and at 20, 40, 100, 200, 400, 1000, 2000 and 4000mA g-1The current density of the current is discharged for 5 circles in sequence to carry out the multiplying power performance test. As can be seen from the rate performance FIG. 11, the obtained P2Na having a manganese concentration gradient0.67Ni0.33Mn0.67O2The capacity retention rate of the anode material is up to more than 80% under 40C discharge current density, and the anode material shows excellent rate discharge performance.
Application example 2
A sodium ion battery, the preparation method comprises the following steps:
(1) na having the structure of P3 obtained in example 40.67Ni0.33Mn0.67O2And as a positive electrode active material, mixing the conductive carbon black and the PVdF binder according to a mass ratio of 8:1:1, dissolving the mixture in an N-methylpyrrolidone (NMP) solvent to prepare positive electrode slurry, coating the positive electrode slurry on an aluminum foil, drying and cutting to obtain the positive electrode sheet.
(2) Assembling the positive plate obtained in the step (1), sodium metal and a Celgard diaphragm into a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is 1M NaPF6An electrolyte solution formed by dissolving in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (in a volume ratio of EC: DMC of 1: 1). And standing for 24h, and testing after the voltage is stabilized.
Application example 3
A sodium ion battery, the preparation method comprises the following steps:
(1) na having the structure of P3 obtained in example 50.67Ni0.33Mn0.67O2And as a positive electrode active material, mixing the conductive carbon black and the PVdF binder according to a mass ratio of 8:1:1, dissolving the mixture in an N-methylpyrrolidone (NMP) solvent to prepare positive electrode slurry, coating the positive electrode slurry on an aluminum foil, drying and cutting to obtain the positive electrode sheet.
(2) Assembling the positive plate obtained in the step (1), sodium metal and a Celgard diaphragm into a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is 1M NaPF6The electrolyte solution formed in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (in a volume ratio EC: DMC ═ 1:1) was left to stand for 24h and after voltage stabilization was tested.
Application example 4
A sodium ion battery, the preparation method comprises the following steps:
(1) na having the structure of P3 obtained in example 60.67Ni0.33Mn0.67O2As a positive electrode active material, the positive electrode active material is mixed with conductive carbon black and a PVdF binder according to the mass ratio of 8:1:1, then the mixture is dissolved in an N-methyl pyrrolidone (NMP) solvent to prepare positive electrode slurry, and the positive electrode slurry is coated on an aluminum foil and dried and cut to obtain the positive electrode slurryAnd (4) a positive plate.
(2) Assembling the positive plate obtained in the step (1), sodium metal and a Celgard diaphragm into a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is 1M NaPF6The electrolyte solution formed in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (in a volume ratio EC: DMC ═ 1:1) was left to stand for 24h and after voltage stabilization was tested.
Comparative example
A sodium ion battery, the preparation method comprises the following steps:
(1) na having a general P3 structure obtained in example 80.67Ni0.33Mn0.67O2And as a positive electrode active material, mixing the conductive carbon black and the PVdF binder according to a mass ratio of 8:1:1, dissolving the mixture in an N-methylpyrrolidone (NMP) solvent to prepare positive electrode slurry, coating the positive electrode slurry on an aluminum foil, drying and cutting to obtain the positive electrode sheet.
(2) Assembling the positive plate obtained in the step (1), sodium metal and a Celgard diaphragm into a sodium-ion battery, wherein the electrolyte of the sodium-ion battery is 1M NaPF6The electrolyte solution formed in a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) (in a volume ratio EC: DMC ═ 1:1) was left to stand for 24h and after voltage stabilization was tested.
The sodium ion batteries obtained in the examples 2-4 and the comparative example are subjected to the rate performance test in the following manner: at 20mA g-1Is charged at a voltage in the range of 2.0-4.1V and at 20, 40, 100, 200, 400, 1000, 2000 and 4000mA g-1The current density of (2) was discharged for 5 cycles in sequence to perform a rate capability test, and the test results are shown in fig. 12.
From the rate capability FIG. 12, the obtained P3 Na having a manganese concentration gradient0.67Ni0.33Mn0.67O2The positive electrode material application examples 2, 3 and 4 all exhibited more excellent rate discharge performance than the comparative example.
FIG. 13 is a graph showing the cycle characteristics of application example 4 and comparative example, and it can be seen from FIG. 13 that the charging current density is 10mA g/g in the voltage range of 2.0 to 4.1V-1(0.1C), discharge Current Density 2000mA g-1(20C) Conditions of (2)Next, after 200 cycles, the capacity retention rate of the battery of application example 4 is still as high as more than 75%; the capacity retention of the comparative example was less than 40%.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (9)

1. An electrode material having a manganese concentration gradient, wherein the battery material having a manganese concentration gradient has the general formula:
NaxMnaMbM’cO2+d；
wherein x is more than or equal to 0.44 and less than or equal to 1.1, a is more than 0, b is more than 0, c is more than or equal to 0, d is more than or equal to 0, and a + b + c =1, M is selected from at least one of Ni and Co, and M' is selected from at least one of Fe, Cu, Mg, Zn, Al and Ti;
the concentration of manganese ions in the electrode material is gradually reduced from the surface to the inside of the electrode material;
the preparation process of the electrode material with the manganese concentration gradient comprises the following steps:
providing a solution containing M ions, a solution containing manganese ions and a precipitator, mixing the solution containing M ions, the solution containing manganese ions and the precipitator simultaneously by adopting a coprecipitation method, wherein the adding speed of the solution containing M ions is higher than that of the solution containing manganese ions at the initial stage of reaction, and the adding speed of the solution containing M ions is lower than that of the solution containing manganese ions at the later stage of reaction, so that the concentration of manganese ions in the obtained product is gradually reduced from the surface to the inside of the product; controlling the pH value in the reaction system to be 7.5-13.5 in the whole reaction process to obtain a transition metal salt precipitation precursor with manganese concentration gradient;
and mixing and heating sodium-containing compounds, M' salt and the transition metal salt precipitation precursor with the manganese concentration gradient according to the stoichiometric ratio to obtain the electrode material with the manganese concentration gradient.
2. The electrode material having a manganese concentration gradient according to claim 1, wherein the crystal structure of the electrode material having a manganese concentration gradient is at least one of a P2 crystal structure, a P3 crystal structure, and an O3 crystal structure.
3. The electrode material having a manganese concentration gradient according to claim 1, wherein the electrode material having a manganese concentration gradient is Na having a P2 structure0.67Ni0.33Mn0.67O2Na of the structure P30.67Ni0.33Mn0.67O2NaNi of O3 structure0.45Cu0.05Mg0.05Mn0.45O2At least one of (a).
4. The electrode material having a manganese concentration gradient according to claim 1, wherein said precipitant is a mixed solution of ammonia and at least one of sodium carbonate and sodium hydroxide, wherein the concentration of said at least one of sodium carbonate and sodium hydroxide is (1-5) mol/L; the concentration of the ammonia water is (0.1-0.2) mol/L.
5. The electrode material having a manganese concentration gradient according to claim 1, wherein the ratio of sodium in said sodium-containing compound is, in terms of mole ratios: transition metal salt precipitation precursor with manganese concentration gradient: m' salt = (0.22-0.55) 1 (0-0.2).
6. The electrode material having a manganese concentration gradient according to claim 1, wherein the heating condition is constant temperature sintering at 600 to 1000 ℃ for 1 to 20 hours.
7. The electrode material having a manganese concentration gradient according to claim 1, wherein said M ions are derived from at least one of sulfuric acid M, acetic acid M, nitric acid M;
the manganese ions are selected from at least one of manganese sulfate, manganese acetate and manganese nitrate;
the sodium-containing compound is at least one of sodium hydroxide, sodium oxalate, sodium bicarbonate, sodium carbonate and sodium acetate.
8. The electrode material having a manganese concentration gradient according to claim 1, wherein said M' ions are derived from at least one of an iron-containing compound, a copper-containing compound, a magnesium-containing compound, a zinc-containing compound, an aluminum-containing compound, a titanium-containing compound.
9. A sodium ion battery comprising a positive electrode active material, wherein the positive electrode active material comprises the electrode material having a manganese concentration gradient according to any one of claims 1 to 8.
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