CN117038854A - Sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide on surface and preparation method thereof - Google Patents

Sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide on surface and preparation method thereof Download PDF

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CN117038854A
CN117038854A CN202311182661.6A CN202311182661A CN117038854A CN 117038854 A CN117038854 A CN 117038854A CN 202311182661 A CN202311182661 A CN 202311182661A CN 117038854 A CN117038854 A CN 117038854A
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transition metal
sodium
metal oxide
cerium
positive electrode
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夏晖
王童
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Anna Nanjing Energy Technology 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide, wherein the bulk phase of the positive electrode material is layered transition metal oxide Na x MO 2 The composition comprises a coating layer uniformly coated on the surface of a bulk phase, wherein the coating layer is formed by CeO 2 The composition, bulk phase and coating layer have no transition metal offset or vacancy; the layered transition metal oxide Na x MO 2 Is OP miscible phase, wherein M is transition metal ion Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3+ 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following; x is the molar ratio and takes the value of 0.75 to 0.85. The invention also discloses a preparation method and application of the sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide. The positive electrode material can effectively inhibit transition metal migration, dissolution, surface amorphization and other problems on the surface of the layered transition metal oxide material, and has the advantages of low cost, high initial efficiency and long cycle life.

Description

Sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide on surface and preparation method thereof
Technical Field
The invention relates to the technical field of sodium ion battery anode materials, in particular to a sodium-electricity layered transition metal oxide anode material with cerium oxide coated on the surface and a preparation method thereof.
Background
Layered transition metal oxide Na x MO 2 (M is a transition metal element) sodium resources are considered to be one of the most promising positive electrode materials of sodium-ion batteries because of the advantages of low price, wide sources, high theoretical specific capacity and the like.
Layered transition metal oxide Na x MO 2 Mainly comprises O3 and P2 type layered transition metal oxides, but the reported O3 and P2 type layered oxides Na x MO 2 There are disadvantages in electrochemical properties. Such as O3-NaMnO 2 The positive electrode material is capable of providing a discharge capacity of up to 197mAh/g (j. Electrochem. Soc.,2011,158, a 1307), but is susceptible to distortion of the lattice structure during charge and discharge due to slippage of the oxygen layer, resulting in rapid capacity decay thereof. Compared with O3-NaMnO 2 ，P2-Na 0.67 MnO 2 The positive electrode material has good rate performance, but when charged to a high potential, the P2 phase also generates a slip of the oxygen layer, a phase transition from P2 to O2 occurs, and a drastic unit cell volume change occurs therewith, which is very unfavorable as a commercial sodium ion battery electrode material (angel. Chem. Int. Ed.,2016,128,12952).
Compared with pure O phase and pure P phase, the OP mixed phase layered transition metal oxide has higher first effect of pure O phase and also has a more stable structure of pure P phase. However, the OP miscible phase as a manganese-based material still has intrinsic defects inherent to the manganese-based material, and there is a great room for improvement in electrochemical performance. Therefore, the modification of the layered transition metal oxide positive electrode material for the sodium ion battery is important for improving the electrochemical stability of the layered transition metal oxide positive electrode material.
Surface coating is a common material modification method, but the currently reported surface coating modified materials still have certain defects in electrochemical performance. Such as P3 phase material Na after phosphate surface coating 0.65 Mn 0.75 Ni 0.25 O 2 (Yu Wang,2019,372,1066) the circulation of material can be increased from 76.4% to 92.4% at 0.2C, but only from 130.2mAh/g to 133.6mAh/g in capacity. By Al 2 O 3 P2 phase material N after surface coating a0.5 Mn 0.5 Co 0.5 O 2 (Hari Vignesh Ramasamy,2019,564,467) can be increased from 154mAh/g to 174mAh/g at 0.5C, but can only be increased from 75% to 78% in terms of cycling.
Disclosure of Invention
The invention aims at solving the problem of poor electrochemical performance of the existing sodium-electricity layered transition metal oxide positive electrode material, and provides a sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide on the surface and a preparation method thereof, wherein under the condition of specific phase composition, a surface coating technology of a one-step sintering method is adopted to obtain an OP mixed phase, and CeO is uniformly coated on the surface 2 The problems of transition metal migration, dissolution, surface amorphization and the like on the surface of the layered transition metal oxide material are effectively inhibited, and the preparation of the positive electrode material is low in cost, high in initial efficiency and long in cycle life.
The first aspect of the invention relates to a sodium-electric layered transition metal oxide positive electrode material coated with cerium oxide, the positive electrode material has a layered transition metal oxide Na as a bulk phase x MO 2 The composition comprises a coating layer uniformly coated on the surface of a bulk phase, wherein the coating layer is formed by CeO 2 The composition, bulk phase and coating layer have no transition metal offset or vacancy;
the layered transition metal oxide Na x MO 2 Is OP miscible phase, wherein M is transition metal ion Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3+ 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following; x is the molar ratio and takes the value of 0.75 to 0.85.
In an alternative embodiment, the thickness of the coating is 1 to 20nm.
The second aspect of the invention relates to a preparation method of the sodium-electricity layered transition metal oxide positive electrode material with the surface coated with cerium oxide, which comprises the following steps:
the preparation method comprises the steps of taking a transition metal source, a sodium source and a cerium source as raw materials, ball-milling and uniformly mixing according to stoichiometric ratio, performing heat treatment under air atmosphere, and cooling to obtain the sodium-electricity layered transition metal oxide anode material with the surface coated with cerium oxide.
In an alternative embodiment, the transition metal source, the corresponding transition metal ion, is Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3+ 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following.
In an alternative embodiment, the transition metal source is a transition metal salt or a transition metal oxide or a transition metal hydroxide; the transition metal salt is carbonate, acetate, nitrate, chloride, sulfate, borate or phosphate of transition metal.
In alternative embodiments, the sodium source is one or more of sodium carbonate, sodium nitrate, sodium sulfate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate, and sodium hydroxide.
In alternative embodiments, the source of cerium is one or more of cerium carbonate, cerium nitrate, cerium sulfate, cerium phosphate, cerium hydroxide, cerium chloride, cerium oxide, and cerium oxide.
In an alternative embodiment, the quality of the transition metal source and the sodium source are in accordance with the layered transition metal oxide Na x MO 2 The stoichiometric ratio of (2) is formulated, and the mass of the cerium source is 0.1-10% of the total mass of the transition metal source and the sodium source.
In an alternative embodiment, the conditions of the heat treatment are: heat treatment is carried out for 15-18 h at 900+/-10 ℃.
The third aspect of the invention relates to an application of the sodium-electric layered transition metal oxide positive electrode material with the surface coated with cerium oxide in sodium ion batteries.
Compared with the prior art, the invention has the remarkable beneficial effects that:
the invention discloses a sodium-electricity layered transition metal oxide anode material coated with cerium oxide on the surface, which synthesizes OP mixed phase layered transition metal oxide by regulating and controlling the Na/Mn ratio and sintering temperature, and simultaneously coats CeO on the surface of the OP mixed phase layered transition metal oxide by a one-step sintering method 2 Layer, surface CeO 2 Is coated with a coating that inhibits surface Na 2 CO 3 More Na is allowed to enter the bulk phase of the material, so that the material has higher Na content, and the combined bulk phase has an OP phase, so that the final positive electrode material presents higher initial effect, and meanwhile, the stability of the structure is ensured;
in addition, the coating layer CeO 2 The intrinsic characteristics of the material improve the electronic conductivity of the material, ceO 2 The coating layer can also inhibit the dissolution of transition metal, so that the structural stability of the material is improved to a great extent, and the material has better cycle performance.
The invention utilizes CeO 2 Layered metal oxide (Na) mixed with OP x MO 2 ) Phase separation characteristics in the synthesis process, and surface-coated CeO is synthesized by a one-step sintering method 2 The OP mixed phase layered transition metal oxide positive electrode material has even and firm coating layer, so that the material has excellent electrical property.
Drawings
Fig. 1 is an XRD spectrum of the samples prepared in examples 1, 2, 3, 4, 5 of the present invention, and comparative example 1.
Fig. 2 is an XRD spectrum of the samples prepared in example 3 and comparative example 2 of the present invention.
FIG. 3 is an SEM image of samples obtained in examples and comparative examples of the present invention; where a is the sample of example 1, b is the sample of example 2, c is the sample of example 3, d is the sample of example 4, e is the sample of example 5, f is the sample of comparative example 1, and g is the sample of comparative example 2.
FIG. 4 is a TEM image of samples obtained in examples of the present invention and comparative examples; where a is the sample of example 3 and b is the sample of comparative example 1.
FIG. 5 is a graph showing the first cycle of charge and discharge at a current density of 0.1A/g for the samples prepared in comparative example 1, examples 1, 2, 3, 4, 5.
FIG. 6 is a graph showing the first charge and discharge cycles at a current density of 0.1A/g for the samples prepared in comparative example 2 and example 3.
FIG. 7 is a graph of 2000 cycles of long cycles at a current density of 1A/g for samples prepared in comparative example 1, examples 1, 2, 3, 4, 5.
FIG. 8 is a graph of 2000 cycles of long cycles at a current density of 1A/g for the samples prepared in comparative example 2 and example 3.
Detailed Description
For a better understanding of the technical content of the present invention, specific examples are set forth below, along with the accompanying drawings.
Aspects of the invention are described in this disclosure with reference to the drawings, in which are shown a number of illustrative embodiments. The embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in more detail below, may be implemented in any of a wide variety of ways.
The invention designs a novel positive electrode material for sodium ion batteries, which is prepared by coating CeO on the surface of a sodium-electricity layered transition metal oxide with an OP mixed phase 2 The layer can effectively inhibit transition metal migration, dissolution, surface amorphization and other problems on the surface of the layered transition metal oxide material, and the layered transition metal oxide anode material for the sodium ion battery with low cost, high first efficiency and long cycle life is prepared.
In an exemplary embodiment of the present invention, there is provided a sodium-electric layered transition metal oxide positive electrode material surface-coated with cerium oxide, the positive electrode material having a bulk phase of layered transition metal oxide Na x MO 2 The composition comprises a coating layer uniformly coated on the surface of a bulk phase, wherein the coating layer is formed by CeO 2 The composition, bulk phase and coating layer have no transition metal offset or vacancy;
the layered transition metal oxide Na x MO 2 Is OP miscible phase, wherein M is transition metal ion Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3+ 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following; x is the molar ratio and takes the value of 0.75 to 0.85.
It should be understood that when M is two or more, the molar ratio between the different transition metal ions is not limited, and the total transition metal ion molar ratio is only required to be 1.
In an alternative embodiment, the thickness of the coating is 1 to 20nm.
By coating the surface of the material to a certain extent, the surface of the material can obtain new physical, chemical and other new functions, thereby greatly improving the dispersibility of the material and the compatibility with other substances. The common coating methods mainly comprise the following types: mechanical mixing, solid phase reaction, hydrothermal, sol-gel, precipitation and deposition. Among them, the solid phase method is the simplest and most convenient for synthesis and is most suitable for commercialization.
However, when the surface coating is performed by the current solid phase method, the surface coating is often combined with a sol-gel method or a precipitation method, or the whole process flow is relatively complicated by secondary sintering, and the problems of uneven and unstable coating are easy to occur.
Accordingly, in another exemplary embodiment of the present invention, there is provided a method for preparing the above-described surface-coated cerium oxide sodium-electric layered transition metal oxide positive electrode material, comprising the steps of:
the preparation method comprises the steps of taking a transition metal source, a sodium source and a cerium source as raw materials, ball-milling and uniformly mixing according to stoichiometric ratio, performing heat treatment under air atmosphere, and cooling to obtain the sodium-electricity layered transition metal oxide anode material with the surface coated with cerium oxide.
In an alternative embodiment, the transition metal source, in the transition metal source,the corresponding transition metal ion is Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3+ 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following.
In an alternative embodiment, the transition metal source is a transition metal salt or a transition metal oxide or a transition metal hydroxide; the transition metal salt is carbonate, acetate, nitrate, chloride, sulfate, borate or phosphate of transition metal.
In alternative embodiments, the sodium source is one or more of sodium carbonate, sodium nitrate, sodium sulfate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate, and sodium hydroxide.
In alternative embodiments, the source of cerium is one or more of cerium carbonate, cerium nitrate, cerium sulfate, cerium phosphate, cerium hydroxide, cerium chloride, cerium oxide, and cerium oxide.
In an alternative embodiment, the quality of the transition metal source and the sodium source are in accordance with the layered transition metal oxide Na x MO 2 The stoichiometric ratio of (2) is formulated, and the mass of the cerium source is 0.1-10% of the total mass of the transition metal source and the sodium source.
In an alternative embodiment, the conditions of the heat treatment are: heat treatment is carried out for 15-18 h at 900+/-10 ℃.
In other exemplary embodiments of the present invention, there is also provided the use of the foregoing surface-coated cerium oxide sodium-electric layered transition metal oxide cathode material in sodium-ion batteries, wherein the surface-coated cerium oxide sodium-electric layered transition metal oxide cathode material is used in sodium-ion batteries, and the batteries exhibit excellent rate performance and cycle stability.
For a better understanding, the present invention will be further described with reference to several specific examples, but the processing technique is not limited thereto, and the present invention is not limited thereto.
In the following examples and comparative examples, the addition amount of the cerium source was Mn in terms of the mass of the cerium source 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 The percentage of the total mass is calculated.
Example 1
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 The mixture is uniformly mixed with 0.1 weight percent cerium nitrate ball milling (400 r/min,6 h) according to the molar ratio of Na to Ni to Fe, mn=0.75:0.2:0.3:0.5 (wherein the Na source is excessive by 2 percent), and then the mixture is heated for 15h at 900 ℃ and cooled to obtain the surface-coated layered transition metal oxide powder.
Example 2
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 Uniformly mixing Na, ni, fe and Mn=0.75:0.2:0.3:0.5 (wherein the Na source is excessive by 2%), and 1wt% cerium nitrate for ball milling (400 r/min,6 h), heating at 900 ℃ for 15h, and cooling to obtain the surface-coated layered transition metal oxide powder.
Example 3
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 Uniformly mixing Na, ni and Fe according to the molar ratio of Mn=0.75:0.2:0.3:0.5 (wherein the Na source is excessive by 2%), and 2wt% cerium nitrate ball milling (400 r/min,6 h), heating at 900 ℃ for 15h, and cooling to obtain the surface-coated layered transition metal oxide powder.
Example 4
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 In a molar ratio of Na: ni: fe: mn=0.75:0.2:0.3:0.5 (where Na source is 2% excess), and 5wt% of nitroAnd (3) uniformly mixing cerium acid ball milling (400 r/min,6 h), heating at 900 ℃ for 15h, and cooling to obtain the surface-coated layered transition metal oxide powder.
Example 5
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 Uniformly mixing Na, ni and Fe according to the molar ratio of Mn=0.75:0.2:0.3:0.5 (wherein the Na source is excessive by 2%), and 10wt% cerium nitrate ball milling (400 r/min,6 h), heating at 900 ℃ for 15h, and cooling to obtain the surface-coated layered transition metal oxide powder.
Example 6
Setting 0.8mol Na 0.85 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 Uniformly mixing Na, ni and Fe according to the molar ratio of Mn=0.85:0.2:0.3:0.5 (wherein the Na source is excessive by 2%), and 2wt% cerium nitrate ball milling (400 r/min,6 h), heating at 900 ℃ for 15h, and cooling to obtain the surface-coated layered transition metal oxide powder.
Comparative example 1
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 Ball milling (400 r/min,6 h) is carried out according to the molar ratio of Na to Ni to Fe to Mn=0.75:0.2:0.3:0.5 (wherein the Na source is excessive by 2%), heating treatment is carried out for 15h at 900 ℃, and cooling is carried out, thus obtaining Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 As a positive electrode material.
Comparative example 2
Setting 0.8mol Na 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 In Mn 2 O 3 、NiO、Fe 2 O 3 、Na 2 CO 3 According to mole ofThe molar ratio of Na to Ni to Fe is equal to Mn=0.75:0.2:0.3:0.5, wherein the excessive Na source is 2 percent, ball milling (400 r/min,6 h) is carried out, after the uniform mixing, the heating treatment is carried out for 15h at 900 ℃, and the Na is obtained after cooling 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 As a positive electrode material.
Na obtained above 0.75 Ni 0.2 Fe 0.3 Mn 0.5 O 2 Adding 2wt% cerium source, heating at 900 deg.c for 15 hr, and cooling to obtain surface coated layered transition metal oxide powder.
XRD
XRD measurements were performed on the materials obtained in examples 1-5, and comparative examples 1-2, and the results are shown in FIGS. 1 and 2.
As can be seen from the figure, the samples of examples 1 to 5 were found to have O phase, P phase and CeO phase 2 The characteristic peaks of the positive electrode material obtained by the method of the invention are proved to be mainly composed of O phase, P phase and CeO 2 Composition, and as the mass of the Ce source increases, ceO 2 The peaks of the phases are stronger and stronger, which indicates CeO 2 The duty cycle in the material is increasing.
The sample of comparative example 1 consisted of O phase and P phase, and the sample of comparative example 2 obtained by two-step sintering was also composed of O phase, P phase and CeO 2 The composition, but with a large number of peaks, indicates non-uniform coating, and, based on a comparison of comparative example 1 and examples 1-5, it can be demonstrated that CeO 2 The layer is wrapped on the surface of the bulk phase.
SEM、TEM
SEM and TEM tests were conducted on the materials obtained in examples 1-5 and comparative examples 1-2, and the results are shown in FIGS. 3 and 4.
As can be seen from SEM images, the samples of the comparative example and the example are in irregular plate-shaped morphology, and the surface of the bulk phase of the sample modified by adopting the cerium source is provided with a coating layer in combination with TEM, and the coating layer on the surface of the material is more and more obvious along with the increase of the mass of the cerium source, and the surface CeO of the example 3 is more and more obvious 2 The thickness of the coating layer is about 3nm, and the thickness of the coating layer needs to be controlled within 1-20 nm to ensure the final electrochemical performance.
Can be from aboveProved by the invention, the surface-coated CeO is successfully synthesized 2 The sodium-electric layered transition metal oxide of the layer, and the sodium-electric layered transition metal oxide is an OP mixed phase.
Preparation of electrode and electrochemical performance test thereof
Mixing the prepared positive electrode material with superconducting carbon black (Super P) and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1 are evenly mixed and then dissolved in N-methyl pyrrolidone (NMP) and coated on the surface of an aluminum foil, and then dried in a vacuum oven at 80 ℃ for 10 hours, thus obtaining the surface-coated layered transition metal oxide electrode.
The surface-coated layered transition metal oxide electrode is used as a positive electrode, a sodium metal sheet is used as a negative electrode, and 1.0mol/L NaPF 6 And (3) taking propylene carbonate as electrolyte, assembling the propylene carbonate into a half cell in a glove box in an argon atmosphere, and detecting electrochemical properties of the surface-coated layered transition metal oxide electrode material, wherein the electrochemical properties comprise specific capacity, rate capability, cycling stability and first coulombic efficiency, and the test voltage range is 2-4V.
The test results are shown in Table 1 and FIGS. 5-8.
TABLE 1
As can be seen in combination with FIGS. 5-8 and Table 1, ceO 2 The addition of the coating layer significantly improved the first effect of the material, which was as high as 98% when 2% wt cerium nitrate was added (as shown in fig. 5). In addition, the sample sintered in one step by the present invention has higher initial efficiency (98%) and higher specific capacity (103.5 mAh/g) (as shown in FIG. 6).
CeO 2 The addition of the coating significantly improved the recycling of the material, and 19% when 2% wt cerium nitrate was added (as shown in fig. 7). Further, the cycle retention by the one-step sintering of the present invention was higher (84.2%), and the specific capacity was higher (77.7 mAh/g) (as shown in FIG. 8).
As can be seen from the test junctions of comparative examples 1-2 and example 3, the materialCeO on the surface of the material 2 Is coated with a coating that inhibits surface Na 2 CO 3 More Na is led to enter the bulk phase of the material, so that the material has higher Na content, thereby improving the initial effect of the battery, and CeO is coated under the condition of OP mixed phase 2 The positive electrode material after the layer makes the battery show higher initial effect, which shows that the positive electrode material of the invention has the advantages of OP mixed phase and CeO on the surface 2 The layer improves the first effect.
Furthermore, ceO 2 The coating layer can also inhibit the dissolution of transition metal, so that the structural stability of the material is improved to a great extent, and the material has better cycle performance; when the cerium source is added to 2% wt, the electrochemical performance is the best; when the cerium source continues to increase, ceO 2 The coating layer becomes thicker, and electrons and Na are increased + The mass transfer resistance of diffusion deteriorates the electrochemical properties of the material.
While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Those skilled in the art will appreciate that various modifications and adaptations can be made without departing from the spirit and scope of the present invention. Accordingly, the scope of the invention is defined by the appended claims.

Claims (10)

1. A sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide is characterized in that the bulk phase of the positive electrode material is layered transition metal oxide Na x MO 2 The composition comprises a coating layer uniformly coated on the surface of a bulk phase, wherein the coating layer is formed by CeO 2 The composition, bulk phase and coating layer have no transition metal offset or vacancy;
the layered transition metal oxide Na x MO 2 Is OP miscible phase, wherein M is transition metal ion Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3+ 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following; x is the molar ratio and takes the value of 0.75 to 0.85.
2. The surface-coated ceria sodium-electric layered transition metal oxide positive electrode material according to claim 1, wherein the thickness of the coating layer is 1 to 20nm.
3. A method for preparing the surface-coated ceria sodium-electrical layered transition metal oxide positive electrode material according to any one of claims 1 to 2, comprising the steps of:
the preparation method comprises the steps of taking a transition metal source, a sodium source and a cerium source as raw materials, ball-milling and uniformly mixing according to stoichiometric ratio, performing heat treatment under air atmosphere, and cooling to obtain the sodium-electricity layered transition metal oxide anode material with the surface coated with cerium oxide.
4. The method for preparing a surface-coated cerium oxide sodium-electric layered transition metal oxide positive electrode material according to claim 3, wherein the transition metal source is a transition metal ion of Ni 2+ 、Ni 3+ 、Fe 3+ 、Cu 2+ 、Co 3+ 、Cr 3 + 、Zn 2+ 、Ti 4+ 、V 5+ 、Nb 5+ 、Li + 、Mn 3+ 、Mn 4+ One or more of the following.
5. The method for preparing a surface-coated ceria sodium-electrical layered transition metal oxide positive electrode material according to claim 3, wherein the transition metal source is a transition metal salt or a transition metal oxide or a transition metal hydroxide; the transition metal salt is carbonate, acetate, nitrate, chloride, sulfate, borate or phosphate of transition metal.
6. The method for preparing a surface-coated cerium oxide sodium-electric layered transition metal oxide positive electrode material according to claim 3, wherein the sodium source is one or more of sodium carbonate, sodium nitrate, sodium sulfate, sodium phosphate, sodium fluoride, sodium iodide, sodium oxalate, and sodium hydroxide.
7. The method for preparing a surface-coated ceria-based sodium-electrical layered transition metal oxide positive electrode material according to claim 3, wherein the source of cerium is one or more of cerium carbonate, cerium nitrate, cerium sulfate, cerium phosphate, cerium hydroxide, cerium chloride, cerium oxide, and cerium oxide.
8. The method for preparing a surface-coated cerium oxide sodium-electric layered transition metal oxide cathode material according to claim 3, wherein the quality of the transition metal source and the sodium source is in accordance with the layered transition metal oxide Na x MO 2 The stoichiometric ratio of (2) is formulated, and the mass of the cerium source is 0.1-10% of the total mass of the transition metal source and the sodium source.
9. The method for preparing a surface-coated ceria sodium-electrical layered transition metal oxide positive electrode material according to claim 3, wherein the heat treatment conditions are: heat treatment is carried out for 15-18 h at 900+/-10 ℃.
10. Use of a surface-coated ceria sodium-electrical layered transition metal oxide positive electrode material according to any one of claims 1-2 in a sodium ion battery.
CN202311182661.6A 2023-09-14 2023-09-14 Sodium-electricity layered transition metal oxide positive electrode material coated with cerium oxide on surface and preparation method thereof Pending CN117038854A (en)

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