CN111446429B - Poly-polyanion cathode material and preparation method and application thereof - Google Patents

Poly-polyanion cathode material and preparation method and application thereof Download PDF

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CN111446429B
CN111446429B CN202010232297.XA CN202010232297A CN111446429B CN 111446429 B CN111446429 B CN 111446429B CN 202010232297 A CN202010232297 A CN 202010232297A CN 111446429 B CN111446429 B CN 111446429B
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coating layer
tio
core
positive electrode
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CN111446429A (en
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张亚琳
张双虎
曾家江
李素丽
李俊仪
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
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    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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Abstract

The invention belongs to the technical field of anode materials, and provides a poly-polyanion anode material, a preparation method and application thereof4MnxCo3‑x(PO4)2P2O7(3>x>0) The positive electrode material is characterized in that the surface of the core is coated with a first coating layer and a second coating layer, the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; wherein the first coating layer is coated on the surface of the core, and the second coating layer is coated on the surface of the first coating layer; or the second coating layer is coated on the surface of the core, and the first coating layer is coated on the surface of the second coating layer. The positive electrode material can increase Na4MnxCo3‑x(PO4)2P2O7Discharge plateau of (3), increase of Na4MnxCo3‑x(PO4)2P2O7The electronic conductivity and the ionic conductivity of the composite lead to have excellent rate performance and cycle stability. The preparation method has the characteristics of good repeatability and high reliability.

Description

Poly-polyanion cathode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of anode materials, and particularly relates to a poly-polyanion anode material and a preparation method and application thereof.
Background
Lithium ion batteries have the characteristics of high energy density, good cycle performance, high safety and the like, and have been used as main power sources of portable equipment in the last thirty years. In recent years, its application has been expanded as an important energy source for hybrid electric vehicles, plug-in electric vehicles, pure electric and energy storage-based power stations. However, lithium element is low in storage amount in the earth crust, and sodium element is abundant and environment-friendly, so that many researchers focus on the research of the sodium ion battery.
The research on sodium ion batteries began in the eighties of the last century but developed less well than lithium ion batteries. The radius (0.102nm) of sodium ions is far larger than that (0.076nm) of lithium ions, so that the change of the material structure is large in the charging and discharging process, and the cycle life of the sodium ion battery is seriously influenced. The structure of the polyanion compound is stable and controllable, and the cycling stability and the thermal stability are also higher, so that the polyanion compound becomes a research hotspot of the anode material of the sodium-ion battery.
In the existing research on polyanion sodium ion batteries, Na4Fe3(PO4)2P2O7As a typical material, the material has a theoretical specific capacity of 129mAh/g and a discharge plateau voltage of 3.2V, and has attracted much attention due to excellent comprehensive electrical properties. But the electronic conductivity and the ionic conductivity of the material are low, so that the actual discharge capacity is small, the 0.05C rate discharge specific capacity is only 106mAh/g, the large rate discharge performance is worse, and the energy density is extremely low. Another typical material Na4Mn3(PO4)2P2O7The theoretical specific capacity of the manganese-based lithium ion battery is 129mAh/g, the voltage of a discharge platform can be increased to 3.84V, the energy density is improved, but the problem of easy dissolution of the ginger-Taylor effect of manganese causes the cycle of the manganese-based lithium ion battery and the energy density of the manganese-based lithium ion batteryThe rate capability is even worse.
Disclosure of Invention
In order to solve the defect problem of the conventional polyanion sodium-ion battery cathode material, the invention provides a polyanion cathode material, a preparation method and application thereof, wherein the polyanion cathode material is coated Na with excellent electrochemical performance4MnxCo3-x(PO4)2P2O7(3>x>0) Positive electrode material, the coated Na4MnxCo3-x(PO4)2P2O7The positive electrode material can increase Na4MnxCo3-x(PO4)2P2O7Discharge plateau of (3), increase of Na4MnxCo3-x(PO4)2P2O7The electronic conductivity and the ionic conductivity of the composite lead to have excellent rate performance and cycle stability. The preparation method has the characteristics of good repeatability and high reliability.
Specifically, the invention provides a positive electrode material, wherein the positive electrode material has a core-shell structure; the core comprises Na4MnxCo3-x(PO4)2P2O7(3>x>0) A material; coating a first coating layer and a second coating layer on the surface of the core, wherein the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; wherein the first coating layer is coated on the surface of the core, and the second coating layer is coated on the surface of the first coating layer; or the second coating layer is coated on the surface of the core, and the first coating layer is coated on the surface of the second coating layer.
Preferably, the first coating layer is coated on the surface of the core, and the second coating layer is coated on the surface of the first coating layer.
According to the invention, the positive electrode material is used in a sodium ion battery, for example in a positive electrode of a sodium ion battery.
According to the invention, the core comprises Na4MnxCo3-x(PO4)2P2O7The material comprises manganese ions and cobalt ions at the same time, and the discharge plateau voltage of the material is higher (about 3.86V) due to the higher oxidation-reduction potentials of the manganese ions and the cobalt ions. According to the formula: the mass (volume) energy density is equal to the capacity x the discharge plateau voltage/mass (volume), and it is known that the energy density (mass energy density or volume energy density) of the material is also improved by the improvement of the discharge plateau voltage, thereby widening the application thereof.
According to the invention, said Na4MnxCo3-x(PO4)2P2O7The material is crystalline, the median particle size of the crystals being 5 to 12 μm, preferably 5 to 9 μm.
According to the invention, said Na4MnxCo3-x(PO4)2P2O7In the material, x is, for example, 1 or 2, preferably Na4MnCo2(PO4)2P2O7。
According to the invention, said Na4MnxCo3-x(PO4)2P2O7The material is a secondary particle having a median particle diameter of 5 to 12 μm, preferably 5 to 9 μm, assembled from primary particles.
According to the invention, the first coating layer is a carbon coating layer, the thickness of which is 0.01-8nm, preferably 0.1-6nm, and more preferably 1-5 nm.
According to the present invention, the carbon coating layer may be coated directly on Na4MnxCo3-x(PO4)2P2O7The surface of the material, or the carbon coating layer is coated on the surface of the second coating layer.
In the cathode material, the introduction of the carbon coating layer can inhibit Na on one hand4MnxCo3-x(PO4)2P2O7The abnormal growth of primary particles in the preparation process of the material, the primary particle granularity of the roasted product is refined, and Na is favorably used+Diffusing; on the other hand, the carbon coating is on Na4MnxCo3-x(PO4)2P2O7The conductive network formed on the surface of the material can increase the conductivity between particles, and is Na4MnxCo3-x(PO4)2P2O7The material provides electron tunneling to compensate for Na+Dynamic charge balance during de-intercalation and further increase Na4MnxCo3-x(PO4)2P2O7Electrochemical properties of the material. The TiO is2The introduction of the modified graphene coating layer also has the same effect.
According to the invention, the carbon of the first coating layer is amorphous carbon.
According to the invention, the second coating layer is TiO2Modified graphene coating, denoted TiO2A graphene coating with a thickness of 0.01-10nm, preferably 0.1-8 nm.
According to the invention, the TiO2The modified graphene coating layer is coated on the carbon-coated Na4MnxCo3-x(PO4)2P2O7The surface of the material, or, the TiO2The modified graphene coating layer is directly coated on Na4MnxCo3-x(PO4)2P2O7The surface of the material.
According to the invention, in the second coating layer, TiO2Bound to graphene in the form of a chemical bond, denoted TiO2-graphene. Specifically, the surface of graphene oxide contains many oxygen-containing functional groups such as carboxyl, hydroxyl, carbonyl and the like; by solvothermal method, TiO2The oxygen-containing groups can be combined with graphene in a chemical bond mode, and simultaneously, the oxygen-containing groups can be reduced to obtain TiO2A modified graphene coating layer. In the second coating layer, TiO2The content of (A) is 50-70 wt%, and the content of graphene is 30-50 wt%.
According to the invention, in the second coating layer, the carbon atom in the graphene is sp2Hybridization, faster electron transfer rate, TiO2The modified graphene serving as a coating layer can obviously improve Na4MnxCo3-x(PO4)2P2O7The electronic conductivity of the material; however, when only graphene is used as a coating layer, the graphene and the core material or the core material coating the first coating layer are likely to form an absolute coating shape, and particularly when the coating layer is thick, although electron conductivity is significantly improved, lithium ion transport is significantly inhibited, and performance such as capacity is significantly reduced. Thus, by selecting the TiO of the present application2And the modified graphene is used as a second coating layer, and the thickness of the second coating layer is controlled to realize the regulation and control of the performance of the second coating layer.
TiO2Is a rich, low-cost and environment-friendly material, and has high conductivity and stable structure. Thus, TiO is added2Preparing TiO by compounding with graphene2A graphene material, which will have a stronger electronic conductivity. In addition, as a coating material, TiO2Graphene is a three-dimensional structure whose thickness can be controlled below 10nm, thus not hindering ion transport and avoiding Na4MnxCo3-x(PO4)2P2O7The direct contact of the material and the electrolyte reduces the violent degree of the contact reaction of the anode and the electrolyte, reduces the dissolution of transition metal, and improves Na4MnxCo3-x(PO4)2P2O7Structural stability and cycle performance of the material.
According to the present invention, the carbon coating layer accounts for 0.1 to 2.5 wt%, more preferably 0.8 to 1.5 wt%, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, or 2.5 wt% of the positive electrode material.
According to the invention, in the positive electrode material, the TiO2The percentage by mass of the graphene coating layer is 0.1 to 3% by weight, more preferably 0.5 to 1.5% by weight, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6% by weight0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, or 3 wt%.
According to the invention, the median particle diameter of the cathode material is 5-12 μm, preferably 5-9 μm, and the specific surface area is 7-11g/m2And the powder resistivity of the anode material is less than or equal to 5.0 omega cm.
According to the invention, the morphology structure of the cathode material is secondary spherical particles with the median particle size of 5-12 μm, preferably 5-9 μm, which are assembled by primary particles with the median particle size of 100-300nm, and the morphology is favorable for the rapid transfer of charges, and improves Na+And (3) the de-intercalation dynamics optimizes the rate performance of the material.
The invention also provides a preparation method of the cathode material, which comprises the following steps:
(1) mixing a carbon source, a phosphorus source, a cobalt source, a manganese source and a sodium source, spray drying and carrying out heat treatment;
(2) mixing the product of step (1) with TiO2Mixing, drying and sintering the modified graphene to prepare the cathode material, wherein the cathode material has a core-shell structure; the core comprises Na4MnxCo3-x(PO4)2P2O7(3>x>0) A material; coating a first coating layer and a second coating layer on the surface of the core, wherein the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; wherein the first coating layer is coated on the surface of the core, and the second coating layer is coated on the surface of the first coating layer.
The invention also provides a preparation method of the cathode material, which comprises the following steps:
(i) adding TiO into the mixture2Mixing the modified graphene, a phosphorus source, a cobalt source, a manganese source and a sodium source, spray drying and carrying out heat treatment;
(ii) mixing the product obtained in the step (i) with a carbon source, spray-drying, and sintering to obtain the cathode material, wherein the cathode material has a core-shell structure; the coreIncluding Na4MnxCo3-x(PO4)2P2O7(3>x>0) A material; coating a first coating layer and a second coating layer on the surface of the core, wherein the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; the second coating layer is coated on the surface of the core, and the first coating layer is coated on the surface of the second coating layer.
According to the present invention, in the step (1) and the step (ii), the carbon source is at least one selected from the group consisting of glucose, citric acid, chitosan, urea, sucrose, polyacrylamide, polyvinyl alcohol, phenol resin, and epoxy resin.
According to the invention, in step (1), the carbon source is added in an amount of Na4MnxCo3-x(PO4)2P2O71-10 wt%, such as 2-8 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt% of the mass of the material.
According to the invention, in step (ii), the TiO2The addition amount of the modified graphene is Na4MnxCo3-x(PO4)2P2O70.1-3 wt%, such as 0.5-1.5 wt%, such as 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, or 3.0 wt% of the mass of the material.
According to the invention, in the step (1) and the step (i), the phosphorus source is at least one selected from ammonium dihydrogen phosphate, sodium pyrophosphate, ammonium pyrophosphate, phosphoric acid, sodium dihydrogen phosphate and disodium hydrogen phosphate; the cobalt source is selected from at least one of cobalt acetate, cobalt sulfate, cobalt nitrate, cobalt oxide, cobalt oxalate and cobalt chloride; the manganese source is selected from at least one of manganese nitrate, manganous acetate, manganese dioxide and manganese hydroxide, and the sodium source is selected from at least one or more of sodium pyrophosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium acetate, sodium nitrate and sodium citrate; the molar ratio of the phosphorus source, the cobalt source, the manganese source and the sodium source to Na4MnxCo3-x(PO4)2P2O7The molar ratio of each substance in the material is the same.
According to the invention, in the step (1) and the step (i), the mixing is carried out in a ball mill, for example, deionized water is added in the mixing process, and various materials can be fully mixed in the material mixing process; wherein the deionized water is added in an amount of 20 to 40 wt% of the solid component, for example, 30 wt%.
According to the invention, in the step (1) and the step (i), the temperature of the spray drying is 180-220 ℃, for example 200 ℃, and spherical particles with the median diameter of 5-12 μm are prepared by spray drying; the purpose of the spray drying is to dry and granulate the mixed material to obtain spherical particles.
According to the invention, in steps (1) and (i), the heat treatment is carried out under an inert atmosphere, such as argon.
According to the invention, in the step (1) and the step (i), the temperature of the heat treatment is 250-350 ℃, and the time of the heat treatment is 4-8 h. During the heat treatment, a carbon source or TiO2And mixing the modified graphene with a phosphorus source, a cobalt source, a manganese source and a sodium source, and carrying out preliminary pre-reaction to obtain an intermediate.
According to the invention, in step (2), the mixing is carried out under stirring, for example, by mixing TiO2Ultrasonically dispersing the modified graphene in an aqueous solution to obtain a dispersion system, adding the product obtained in the step (1), and stirring and mixing.
According to the invention, in the step (ii), the carbon source is added into the product obtained in the step (i), and then a proper amount of water is added, and the mixture is subjected to ball milling and uniform mixing.
According to the invention, in the step (ii), the temperature of the spray drying is 180-220 ℃, for example 200 ℃, and spherical particles with the median diameter of 5-12 μm are prepared through the spray drying; the purpose of the spray drying is to dry and granulate the mixed material to obtain spherical particles.
According to the invention, in step (2), the step (1)Product with TiO2The mass ratio of the modified graphene is 100 (0.1-3), and more preferably 100 (0.5-1.5).
According to the present invention, in the step (ii), the mass ratio of the product of the step (i) to the carbon source is 1 to 10 wt%, and more preferably 2 to 8 wt%.
According to the invention, in steps (2) and (ii), the sintering is carried out, for example, under an inert atmosphere, such as argon.
According to the invention, in step (2) and step (ii), the sintering temperature is 500-700 ℃, such as 550 ℃, 600 ℃, 650 ℃, 700 ℃; the sintering time is 8-14h, such as 8h, 10h, 12h or 14 h.
According to the invention, in step (2) and step (i), the TiO2The modified graphene is prepared by a solvothermal method, for example, comprising the following steps:
a) mixing graphene oxide with TiO2Mixing powder materials, adding a solvent, and carrying out a solvothermal reaction;
b) optionally, the method also comprises the steps of cooling, centrifuging, washing and drying after the reaction is finished.
According to the invention, in step a), the graphene oxide is, for example, graphene oxide prepared by Hummers method. The TiO is2The powder being, for example, commercially available TiO type P252。
According to the invention, in step a), the graphene oxide is mixed with TiO2The mass ratio of the powder is 5:5 to 3:7, for example 5:5, 4:6 or 3: 7.
According to the invention, in the step a), the solvent is a mixed solvent of deionized water and absolute ethyl alcohol, and the volume ratio of the deionized water to the absolute ethyl alcohol is (1-4):1, such as 2: 1.
According to the invention, in step a), the temperature of the solvothermal reaction is 110-130 ℃, for example 120 ℃; the solvothermal reaction time is 12 to 36h, for example 24 h.
In the invention, the oxygen-containing functional group in the graphene oxide can be reduced to form graphene by adopting a solvothermal method, and meanwhile, TiO is reduced2Chemically bonded to oxygen-containing functional groups to form TiO2-graphene。
The invention also provides application of the cathode material as a cathode active material of a sodium-ion battery.
The invention also provides a positive electrode for the sodium-ion battery, which comprises the positive electrode material.
The invention also provides a sodium ion battery which comprises the positive electrode.
The invention has the beneficial effects that:
the invention provides a polyanion anode material, a preparation method and application thereof, and the anode material and a sodium ion battery comprising the anode material have the following advantages:
1) lithium ions in the lithium ion battery only have one-dimensional channels, while sodium ions in the sodium ion battery are 3-dimensional channels, and have higher ionic conductivity compared with the lithium battery.
2)Na4Fe3(PO4)2P2O7The discharge plateau voltage of (1) is only 3.2V, while Na4MnxCo3-x(PO4)2P2O7In particular Na4MnCo2(PO4)2P2O7The voltage of the discharge platform is increased to 3.86V, so that the energy density is improved, and the application of the discharge platform is expanded.
3)TiO2The introduction of the graphene coating layer and the carbon coating layer improves the electronic conductivity of the material, so that the material has better rate performance, meets the requirement of high-rate charge and discharge, and has more stable structure and longer cycle life.
4) The anode material is secondary spherical particles assembled by primary particles with the median particle size of 100-300nm, and the structure is more beneficial to the desorption of sodium ions due to TiO2The introduction of the graphene coating layer and the carbon coating layer inhibits the growth of the nucleus, so that the particle size of the nucleus material particles is reduced, the extraction path of sodium ions is shortened, and the ion conductivity is further improved.
5) The preparation process has high operation reliability, rich raw material resources and wide industrial application prospect.
Detailed Description
The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
Example 1:
the method comprises the following steps: TiO 22Preparation of graphene
Taking 0.3g of graphene oxide prepared by a Hummers method, adding the graphene oxide into 100g of a mixed solvent of deionized water and absolute ethyl alcohol with the volume ratio of 2:1, performing ultrasonic dispersion for 1 hour, and then adding 0.7g of TiO2Powder (commercially available P25) was stirred continuously for 2h to give a homogeneous dispersion.
Then transferring the suspension into a polytetrafluoroethylene kettle for hydrothermal treatment, and heating for 24 hours at 120 ℃; cooling, centrifuging, washing with water, and vacuum drying at 60 deg.C to obtain TiO2Modified graphene, denoted TiO2-graphene。
Step two: na (Na)4MnCo2(PO4)2P2O7Preparation of the/C intermediate
Weighing Na according to the molar ratio of 1.02:1:2:2.044P2O7、Mn(NO)3、(CH3COO)2Co and NH4H2PO4Adding citric acid and deionized water for ball milling, wherein the adding amount of citric acid is theoretically capable of generating Na4MnCo2(PO4)2P2O75 wt% of the mass (calculated as the content of Co or Mn) and the amount of deionized water added was 30 wt% of the solid content. Spray drying the mixture after ball milling at 200 deg.C, and heating at 300 deg.C under argon protection for 6h to obtain Na4MnCo2(PO4)2P2O7a/C intermediate.
Step three: TiO 22-graphene@Na4MnCo2(PO4)2P2O7Preparation of/C
0.15g of TiO was weighed2Adding graphene into 15mL of deionized water, and performing ultrasonic dispersion for 2 hours; 10g of Na was added thereto4MnCo2(PO4)2P2O7The intermediate/C is continuously stirred for 5 hours, centrifuged and dried in vacuum for 12 hours to obtain solid; sintering the obtained solid for 10h at 600 ℃ under the protection of argon atmosphere to obtain TiO2-graphene@Na4MnCo2(PO4)2P2O7/C。
Step four: electrical property detection of finished product
The positive electrode material prepared by the embodiment and the sodium sheet are assembled into the button cell, and the charge and discharge performance of the button cell is tested, wherein the voltage range is 1.7-4.6V.
Example 2:
the procedure is as in example 1, except that TiO is present in step III2The amount of graphene added was 0.05 g.
Example 3:
the procedure is as in example 1, except that TiO is present in step III2-graphene is added in an amount of 0.30 g.
Example 4:
the procedure is as in example 1, except that in step three the solid is sintered for 14h at 500 ℃ under argon.
Example 5:
the procedure is as in example 1, except that in step three the solid is sintered at 700 ℃ for 8h under argon.
Example 6:
the operation process is the same as that ofExample 1, except that the amount of citric acid added in the second step is such that Na is theoretically generated4MnCo2(PO4)2P2O710 wt% of the mass (calculated as Co or Mn content).
Example 7:
the procedure is as in example 1, except that the amount of citric acid added in step two is such that Na is theoretically formed4MnCo2(PO4)2P2O71 wt% of the mass (calculated as Co or Mn content).
Example 8:
the operation process is the same as that of example 1, except that the carbon source in the second step is glucose, the heat treatment temperature is 250 ℃, and the sintering time is 4 h.
Example 9:
the operation process is the same as that of example 1, except that the carbon source in the second step is urea, the heat treatment temperature is 350 ℃, and the sintering time is 8 hours.
Example 10:
the operation process is the same as that of example 1, except that the step one:
taking 0.4g of graphene oxide prepared by a Hummers method, adding the graphene oxide into 100g of a mixed solvent of deionized water and absolute ethyl alcohol with the volume ratio of 6:3, performing ultrasonic dispersion for 1 hour, and then adding 0.6g of TiO2The powder (commercially available P25) was continuously stirred for 2h to give a uniformly dispersed suspension.
Then transferring the suspension into a polytetrafluoroethylene kettle for hydrothermal treatment, and heating for 24 hours at 120 ℃; cooling, centrifuging, washing with water, and vacuum drying at 60 deg.C to obtain TiO2Modified graphene, denoted TiO2-graphene。
Example 11:
the operation process is the same as that of example 1, except that the step one:
taking 0.5g of graphene oxide prepared by a Hummers method, adding the graphene oxide into 100g of a mixed solvent of deionized water and absolute ethyl alcohol with the volume ratio of 6:3, performing ultrasonic dispersion for 1 hour, and then adding 0.5g of TiO2The powder (commercially available P25) was continuously stirred for 2 hours and dispersed uniformlyAnd (3) suspension.
Then transferring the suspension into a polytetrafluoroethylene kettle for hydrothermal treatment, and heating for 24 hours at 120 ℃; cooling, centrifuging, washing with water, and vacuum drying at 60 deg.C to obtain TiO2Modified graphene, denoted TiO2-graphene。
Example 12:
the operation process is the same as that of example 1, except that the steps two and three:
step two: na (Na)4MnCo2(PO4)2P2O7/TiO2Preparation of-graphene intermediates
0.15g of TiO was weighed2Graphene was added to 15mL of deionized water and dispersed with ultrasound for 2h, denoted as solution A. Separately, 4.31g of Na was weighed4P2O7、2.31g Mn(NO)3、5.63g(CH3COO)2Co and 3.73g NH4H2PO4Then, the solution A is added into the powder, 38.77g of deionized water is additionally added, and then ball milling dispersion is carried out. After uniform dispersion, spray drying is carried out at 200 ℃ to obtain solid powder. Heating the solid powder under the protection of argon at 300 ℃ for 6h to obtain Na4MnCo2(PO4)2P2O7/TiO2-a graphene intermediate.
Step three: c @ Na4MnCo2(PO4)2P2O7/TiO2Preparation of graphene
Weighing 10g of Na4MnCo2(PO4)2P2O7/TiO2-graphene intermediate, 0.5g citric acid and 35g deionized water, ball milled and mixed, and spray dried at 200 ℃. Finally sintering the obtained solid for 10h at 600 ℃ under the protection of argon atmosphere to obtain C @ Na4MnCo2(PO4)2P2O7/TiO2-graphene。
Comparative example 1:
the method comprises the following steps: na (Na)4MnCo2(PO4)2P2O7Preparation of
Weighing Na according to the molar ratio of 1.02:1:2:2.044P2O7、Mn(NO)3、(CH3COO)2Co and NH4H2PO4And adding deionized water for ball milling, wherein the deionized water is added according to the solid-liquid mass ratio of 7: 3. Spray drying the mixture after ball milling at 200 ℃, keeping the temperature of 300 ℃ under the protection of argon, heating for 6h, and sintering at 600 ℃ for 10h to obtain Na serving as a product4MnCo2(PO4)2P2O7。
Step two: electrical property detection of finished product
The button cell is assembled by adopting the anode material prepared by the comparative example and the sodium sheet, and the charge and discharge performance of the button cell is tested, wherein the voltage range is 1.7-4.6V.
Comparative example 2:
the method comprises the following steps: na (Na)4MnCo2(PO4)2P2O7Preparation of/C
Weighing Na according to the molar ratio of 1.02:1:2:2.044P2O7、Mn(NO)3、(CH3COO)2Co and NH4H2PO4Adding citric acid and deionized water for ball milling, wherein the adding amount of citric acid is theoretically capable of generating Na4MnCo2(PO4)2P2O75 wt% of the mass (calculated by the content of Co or Mn), deionized water was added in a solid-liquid mass ratio of 7: 3. Spray drying the mixture after ball milling at 200 ℃, keeping the temperature of 300 ℃ under the protection of argon, heating for 6h, and sintering at 600 ℃ for 10h to obtain Na serving as a product4MnCo2(PO4)2P2O7/C。
Step two: electrical property detection of finished product
The button cell is assembled by adopting the anode material prepared by the comparative example and the sodium sheet, and the charge and discharge performance of the button cell is tested, wherein the voltage range is 1.7-4.6V.
Table 1 comparison of electrical properties of the batteries prepared in example 1 and comparative examples 1 to 2
Figure BDA0002429629510000131
As can be seen from Table 1 above, the TiO of example 12-graphene@Na4MnCo2(PO4)2P2O7The gram capacity exertion, rate capability and cycling stability of the/C cathode material are obviously improved compared with those of the cathode materials prepared in comparative examples 1 and 2.
Table 2 comparison of electrical properties of batteries prepared in examples 1-3
Figure BDA0002429629510000132
As can be seen from Table 2 above, when TiO is used2The amount of graphene added was 3.0 wt%, and both the discharge capacity and rate capability were reduced, probably because of TiO2Graphene on Na4MnCo2(PO4)2P2O7The excessive enrichment of the surface of the/C hinders the transmission of ions to a certain extent, so that the transmission of electrons and ions is unbalanced, the gram capacity is reduced, and the multiplying power performance is reduced. When the addition amount is 0.5 wt%, the conductivity improvement is limited, so that the gram capacity exertion and rate capability are not as good as 1.5 wt%.
Table 3 comparison of electrical properties of the batteries prepared in examples 1, 4 to 5
Figure BDA0002429629510000133
As can be seen from Table 3, the difference between the properties of the products obtained by sintering at low temperature for a long time and sintering at high temperature for a short time is substantially equivalent.
Table 4 comparison of electrical properties of the batteries prepared in examples 1, 6 to 7
Figure BDA0002429629510000141
As can be seen from Table 4 above, too much or too little carbon source can seriously affect the performance of the material. This is probably because Na when the amount of carbon added is too small4MnCo2(PO4)2P2O7The particle size is not easy to control, the particles are larger, and the ionic conductivity is reduced; when the amount of carbon added is too high, the surface coating layer prevents the migration of sodium ions, and thus the performance is degraded.
Table 5 comparison of electrical properties of the batteries prepared in examples 1, 8-9
Figure BDA0002429629510000142
As can be seen from Table 5 above, the electrical properties of the final product obtained from different carbon sources at different heat treatment temperatures and times are substantially equivalent. Wherein, the heat treatment temperature and the heat preservation time of the carbon source are mainly determined according to the temperature and the time required by the carbonization of the carbon source.
Table 6 comparison of electrical properties of batteries prepared in examples 1, 10-11
Figure BDA0002429629510000143
As can be seen from Table 6 above, in the preparation of TiO2In graphene, the electrical properties decrease as the amount of graphene oxide added increases. This may be due to an increased amount of graphene oxide and TiO2The amount is reduced, so that TiO is formed2The worse the 3-dimensional structure of graphene; and the increase of the graphene oxide can cause the increase of Na4MnCo2(PO4)2P2O7the/C forms a complete coating, thereby reducing ionic conductance, resulting in a reduction in gram capacity, rate capability, and the like.
Table 7 comparison of electrical properties of batteries prepared in examples 1 and 12
Figure BDA0002429629510000151
As can be seen from Table 7 above, the reaction product of TiO2The graphene coating layer is directly coated on the surface of the core material, and the carbon coating layer is coated on the TiO2Capacity and rate of the battery (example 12) made of the positive electrode material on the surface of graphene coating are improved compared with the battery without coating (comparative example 1) or only coated with carbon layer (comparative example 2), and TiO is coated on the surface of the core material directly compared with the carbon coating layer under the same coating amount2The capacity and rate of the battery composed of the positive electrode material with the carbon coating layer coated on the surface of the carbon coating layer are slightly reduced. This is probably because TiO2When the graphene coating layer is directly coated on the surface of the core material, the coating uniformity is inferior to that of the carbon coating layer, so that the effect of inhibiting the growth of the nuclear crystal particles is not good, and the improvement of the ion conductivity is not obvious.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A positive electrode material, wherein the positive electrode material has a core-shell structure;
the core comprises Na4MnxCo3-x(PO4)2P2O7A material wherein 3>x>0, the Na4MnxCo3-x(PO4)2P2O7The material is secondary particles with the median diameter of 5-12 mu m, which are assembled by primary particles;
coating a first coating layer and a second coating layer on the surface of the core, wherein the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; wherein the first coating layer is coated on the surface of the core, and the second coating layer is coated on the surface of the first coating layer; or the second coating layer is coated on the surface of the core, and the first coating layer is coated on the surface of the second coating layer;
the morphology structure of the anode material is secondary spherical particles with the median particle size of 5-12 mu m, which are assembled by primary particles with the median particle size of 100-300 nm.
2. The positive electrode material according to claim 1, wherein the Na is4MnxCo3-x(PO4)2P2O7The material is Na4MnCo2(PO4)2P2O7。
3. The positive electrode material according to claim 1, wherein the first coating layer is a carbon coating layer having a thickness of 0.01 to 8 nm; the carbon of the first coating layer is amorphous carbon.
4. The positive electrode material according to any one of claims 1 to 3, wherein the second coating layer is TiO2Modified graphene coating layer, the TiO2The thickness of the modified graphene coating layer is 0.01-10 nm;
in the second coating layer, TiO2The content of (A) is 50-70 wt%, and the content of graphene is 30-50 wt%.
5. The positive electrode material according to any one of claims 1 to 3, wherein the carbon coating layer accounts for 0.1 to 2.5 wt% of the positive electrode material; TiO 22The modified graphene coating layer accounts for 0.1-3 wt%.
6. The method for producing a positive electrode material according to any one of claims 1 to 5, wherein the method comprises the steps of:
(1) mixing a carbon source, a phosphorus source, a cobalt source, a manganese source and a sodium source, spray drying and carrying out heat treatment;
(2) mixing the product of step (1) with TiO2Mixing, drying and sintering the modified graphene to prepare the cathode material, wherein the cathode material has a core-shell structure, and the morphology structure of the cathode material is a primary particle group with the median particle size of 100-300nmPacked secondary spherical particles with the median diameter of 5-12 mu m; the core comprises Na4MnxCo3-x(PO4)2P2O7Materials, 3>x>0, the Na4MnxCo3-x(PO4)2P2O7The material is secondary particles with the median diameter of 5-12 mu m, which are assembled by primary particles; coating a first coating layer and a second coating layer on the surface of the core, wherein the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; wherein the first coating layer is coated on the surface of the core, and the second coating layer is coated on the surface of the first coating layer; alternatively, the first and second electrodes may be,
the method comprises the following steps:
(i) adding TiO into the mixture2Mixing the modified graphene, a phosphorus source, a cobalt source, a manganese source and a sodium source, spray drying and carrying out heat treatment;
(ii) mixing the product obtained in the step (i) with a carbon source, spray-drying, and sintering to prepare the cathode material, wherein the cathode material has a core-shell structure, and the morphology structure of the cathode material is secondary spherical particles with a median particle size of 5-12 μm, which are assembled by primary particles with a median particle size of 100-300 nm; the core comprises Na4MnxCo3-x(PO4)2P2O7Materials, 3>x>0, the Na4MnxCo3-x(PO4)2P2O7The material is secondary particles with the median diameter of 5-12 mu m, which are assembled by primary particles; coating a first coating layer and a second coating layer on the surface of the core, wherein the first coating layer and the second coating layer form a shell, the first coating layer is a carbon coating layer, and the second coating layer is TiO2A modified graphene coating layer; the second coating layer is coated on the surface of the core, and the first coating layer is coated on the surface of the second coating layer.
7. The preparation method according to claim 6, wherein in the step (1) and the step (i), the temperature of the heat treatment is 250 ℃ to 350 ℃, and the time of the heat treatment is 4h to 8 h;
in the step (2) and the step (ii), the sintering temperature is 500-700 ℃, and the sintering time is 8-14 h.
8. Use of the positive electrode material as claimed in any one of claims 1 to 5 as a positive electrode active material for a sodium ion battery.
9. A positive electrode for a sodium-ion battery, comprising the positive electrode material according to any one of claims 1 to 5.
10. A sodium ion battery comprising the positive electrode of claim 9.
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