CN116143199A - Surface-coated layered oxide, preparation method thereof, positive plate, sodium ion battery and electric equipment - Google Patents

Surface-coated layered oxide, preparation method thereof, positive plate, sodium ion battery and electric equipment Download PDF

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CN116143199A
CN116143199A CN202310434242.0A CN202310434242A CN116143199A CN 116143199 A CN116143199 A CN 116143199A CN 202310434242 A CN202310434242 A CN 202310434242A CN 116143199 A CN116143199 A CN 116143199A
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layered oxide
tmo
powder
sodium
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CN116143199B (en
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江柯成
王迪
张继宗
蒋绮雯
董丰恺
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Jiangsu Zenio New Energy Battery Technologies Co Ltd
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Abstract

The invention discloses a method for preparing surface-coated layered oxide, which comprises the following stepsThe method comprises the following steps: s1, preparing layered oxide Na y TMO 2 The powder is exposed to the air environment with the humidity more than or equal to 30 percent; s2, treating the layered oxide Na treated by the step S1 y TMO 2 Powder and TiO 2 Ball milling and mixing nanometer powder; s3, sintering the mixture obtained in the step S2 to obtain the surface-coated layered oxide. The invention also discloses the surface-coated layered oxide prepared by the method, a positive plate, a sodium ion battery and electric equipment. The surface-coated layered oxide provided by the invention can improve the defect of poor air stability of the layered oxide, and improves the cycle performance and the multiplying power performance of the layered oxide material.

Description

Surface-coated layered oxide, preparation method thereof, positive plate, sodium ion battery and electric equipment
Technical Field
The invention relates to the technical field of sodium ion batteries, in particular to a surface-coated layered oxide, a preparation method thereof, a positive plate, a sodium ion battery and electric equipment.
Background
Among various positive electrode materials of sodium ion batteries, O3-phase layered oxides have received attention because they can provide sufficient sodium in a full battery, have high electrochemical activity, have high theoretical specific capacities, and are easy to synthesize. However, the O3 phase layered oxide material has poor air stability and unstable structure, resulting in a certain influence on the cycle performance and rate performance of the material.
Therefore, how to improve the structural stability of the O3-phase layered oxide, and further improve the cycle performance and the rate performance of the battery becomes one of the key problems in the related art of sodium ion batteries.
Disclosure of Invention
The invention aims to solve the technical problem of providing a surface-coated layered oxide, which can improve the air stability of the layered oxide and improve the multiplying power performance and the cycle stability of the layered oxide material.
In order to solve the technical problems, the invention provides the following technical scheme:
the first aspect of the present invention provides a method for preparing a surface-coated layered oxide, comprising the steps of:
s1, layered oxide Na y TMO 2 The powder is exposed to the air environment with the humidity more than or equal to 30 percent;
s2, the layered oxide Na treated in the step S1 y TMO 2 Powder and TiO 2 Ball milling and mixing nanometer powder;
s3, sintering the mixture obtained in the step S2 to obtain the surface-coated layered oxide;
in the step S1, y is more than 0.8 and less than or equal to 1, and TM is one or more selected from Ti, V, cr, mn, fe, co, ni, cu, zn, li, B, mg, al, K, ca, zr, nb, sn.
Further, in step S1: the Na is y TMO 2 Is NaNi i Fe j Mn k M m O 2 M is one or more of Li, B, mg, al, K, ca, co, V, cr, cu, zn, zr, nb and Sn; wherein: 0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i+j+k+m=1;
and/or the layered oxide Na y TMO 2 The powder is exposed to the air environment with the humidity of more than or equal to 30 percent for 24-36 hours.
Further, in step S1, the layered oxide NaNi i Fe j Mn k M m O 2 The preparation method of (2) comprises the following steps:
a. precursor Ni i Fe j Mn k M m (OH) 2 Ball-milling and mixing with a sodium source;
b. pre-sintering the mixture obtained in the step a, and then performing solid-phase sintering to obtain the layered oxide NaNi i Fe j Mn k M m O 2 ；
Wherein: in the step a, the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate and sodium nitrate;
and/or in the step b, the temperature of the presintering is 200-550 ℃, and the presintering time is 1-8 hours; the temperature of the solid phase sintering is 750-1100 ℃, and the time of the solid phase sintering is 4-20 h.
Further, in step S2: the TiO 2 Nano powderThe addition amount of the powder is the layered oxide Na y TMO 2 0.4-0.8 wt% of the weight of the material;
and/or the rotation speed of the ball milling is 300-600 r/min, and the ball milling time is 2-7 h.
Further, in step S3: the sintering treatment temperature is 600-800 ℃, and the sintering treatment time is 0.5-3.5 h.
In a second aspect, the present invention provides a surface-coated layered oxide comprising layered oxide Na y TMO 2 Located in the layered oxide Na y TMO 2 Na of surface 4 Ti 5 O 12 A cladding layer, wherein: y is more than 0.8 and less than or equal to 1, and TM is one or more selected from Ti, V, cr, mn, fe, co, ni, cu, zn, li, B, mg, al, K, ca, zr, nb, sn.
Further, the Na y TMO 2 Is NaNi i Fe j Mn k M m O 2 M is one or more of Li, B, mg, al, K, ca, co, V, cr, cu, zn, zr, nb and Sn; wherein: 0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i+j+k+m=1;
and/or the layered oxide Na y TMO 2 The particle diameter D50 of the particles is 7-12 mu m;
and/or, the Na 4 Ti 5 O 12 The thickness of the coating layer is 5-20 nm.
In a third aspect, the present invention provides a positive electrode sheet comprising the surface-coated layered oxide prepared by the aforementioned preparation method, or comprising the aforementioned surface-coated layered oxide.
According to a fourth aspect of the invention, there is provided a sodium ion battery comprising the positive electrode sheet described above.
In a fifth aspect, the invention provides an electric device, which comprises the sodium ion battery.
Compared with the prior art, the invention has the beneficial effects that:
1. in the surface-coated layered oxide of the present invention, layered oxide Na y TMO 2 Has Na on the surface 4 Ti 5 O 12 A dense coating layer which on the one hand hinders the material from being mixed with H in the air 2 O、CO 2 O and O 2 The reaction occurs, so that the air stability of the material is greatly improved; on the other hand, the structural change of the layered oxide material caused by sodium ion deintercalation in the circulation process is inhibited, and the structural stability of the material in the circulation process is improved.
2. In the surface-coated layered oxide of the present invention, na 4 Ti 5 O 12 The existence of the compact coating layer prevents the material from being in direct contact with the electrolyte to a certain extent, ensures the stability of the material interface and improves the cycle performance of the layered oxide material.
3. The surface-coated layered oxide of the present invention, ti during sintering 4+ The sodium ions can diffuse into the bulk phase of the material at high temperature to form bulk phase doping, so that the interlayer spacing of the material is enlarged, the diffusion capacity of the sodium ions in the material is improved, and the rate capability of the material is improved; and Ti is 4+ The ionic compound is high-valence ions, and the electronic conductivity of the material can be improved by doping the high-valence ions, so that the rate capability of the material is further improved; in addition, ti 4+ The doping into the material can also play a role in stabilizing the structure, so that the cycling stability of the material can also be improved.
4. In the sintering process, the surface coating and doping process can be completed in one step, and the method is simple and convenient for large-scale application.
Drawings
FIG. 1 is an X-ray diffraction pattern (XRD) of O3 phase layered oxide materials prepared in example 4, comparative example 1 and comparative example 4 after three days of exposure to an air atmosphere having a humidity of 55%;
FIG. 2 is a Transmission Electron Microscope (TEM) image of the O3-phase layered oxide material prepared in example 1;
fig. 3 a-d are lattice spacing diagrams of the O3 phase layered oxide materials prepared in example 4, comparative example 1, comparative example 2 and comparative example 4, respectively, under high power transmission electron microscopy.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
The invention provides a coating modification method for layered oxide, which comprises coating Na on the surface of layered oxide 4 Ti 5 O 12 The compact coating layer improves the structural stability of the layered oxide and improves the cycle performance and the multiplying power performance of the material.
Specifically, the invention provides a surface-coated layered oxide, which comprises layered oxide Na y TMO 2 Located in the layered oxide Na y TMO 2 Na of surface 4 Ti 5 O 12 A cladding layer, wherein: y is more than 0.8 and less than or equal to 1, and TM is one or more selected from Ti, V, cr, mn, fe, co, ni, cu, zn, li, B, mg, al, K, ca, zr, nb, sn.
In the present invention, layered oxide Na y TMO 2 Is an O3 phase layered oxide, where 0.8 < y.ltoreq.1, e.g. y=0.9, 1, etc. The O3 phase layered oxide has the common problems of poor multiplying power performance, poor cycle performance and the like due to unstable structure.
In the invention, the O3 phase layered oxide Na y TMO 2 The particles may be used in the form of particles of any shape, such as spheres, flakes or irregular particles. Furthermore, the O3 phase layered oxide particles may be in the form of primary particles or secondary particles. The size of the O3 phase layered oxide particles may be any size commonly used in the art. Preferably, the layered oxide Na y TMO 2 The secondary particles of (2) have a particle diameter D50 of 7 to 12 μm, for example, 7, 8, 9, 10, 11, 12 μm, etc.
In the present invention, O3 phase layered oxide Na y TMO 2 The surface is formed with a dense water-insoluble coating layer Na 4 Ti 5 O 12 The presence of such a coatingOn the one hand hinder the material from being mixed with H in the air 2 O、CO 2 O and O 2 The air stability of the layered oxide material is greatly improved by the reaction; on the other hand inhibit the O3 phase layered oxide Na y T M O 2 The structural change caused by sodium ion deintercalation in the circulation process improves the structural stability of the material in the circulation process; in addition, na 4 Ti 5 O 12 The compact coating layer also avoids direct contact between the material and the electrolyte to a certain extent, ensures the interface stability of the material and improves the cycle performance of the material. In the present invention, na 4 Ti 5 O 12 The thickness of the coating layer is preferably 5 to 20nm, for example, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20nm, etc.
In a preferred embodiment of the invention, the O3 phase layered oxide Na y TMO 2 Is NaNi i Fe j Mn k M m O 2 Wherein M is one or more of Li, B, mg, al, K, ca, co, V, cr, cu, zn, zr, nb and Sn; 0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i+j+k+m=1. For example, i=0.1, 0.2, 0.3, 0.4, or j=0.1, 0.2, 0.3, 0.4, 0.5, or k=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or m=0.1, 0.2, etc.
The invention also discloses a preparation method of the surface-coated layered oxide, which comprises the following steps:
s1, layered oxide Na y TMO 2 Exposing the powder to an air atmosphere with humidity of more than or equal to 30%;
s2, the layered oxide Na treated in the step S1 y TMO 2 Powder and TiO 2 Ball milling and mixing nanometer powder;
s3, sintering the mixture obtained in the step S2 to obtain the surface-coated layered oxide;
in the above step S1, na y TMO 2 Is an O3 phase layered oxide, wherein: y is more than 0.8 and less than or equal to 1, and TM is one or more selected from Ti, V, cr, mn, fe, co, ni, cu, zn, li, B, mg, al, K, ca, zr, nb, sn.
In the above step S1, the layered oxide Na y TMO 2 The powder may be prepared by methods conventional in the art, such as solid phase sintering.
In a preferred embodiment, the O3 phase layered oxide Na y TMO 2 Is NaNi i Fe j Mn k M m O 2 Wherein M is one or more of Li, B, mg, al, K, ca, co, V, cr, cu, zn, zr, nb and Sn; 0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i+j+k+m=1. For example, i=0.1, 0.2, 0.3, 0.4, or j=0.1, 0.2, 0.3, 0.4, 0.5, or k=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or m=0.1, 0.2, etc.
For layered oxide Na y TMO 2 The powder can be prepared by sintering sodium source and metal source with a certain molar ratio. With NaNi i Fe j Mn k M m O 2 For example, the powder may be prepared by the steps of:
a. precursor source Ni i Fe j Mn k M m (OH) 2 Ball-milling and mixing with a sodium source;
b. pre-sintering the mixture obtained in the step a, and then performing solid-phase sintering to obtain the layered oxide NaNi i Fe j Mn k M m O 2 。
In the step a, the sodium source may be a commonly used sodium-containing compound, including but not limited to one or more selected from sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate, and sodium nitrate. The sodium source is relative to the precursor source Ni i Fe j Mn k M m (OH) 2 Excess is required, for example 5%, 6%, 7%, 8% excess, etc.
In the step a, the precursor source Ni i Fe j Mn k M m (OH) 2 Mixing with sodium source preferably by ball milling, not only can refine the particles of raw materials, but also can lead the precursor source Ni i Fe j Mn k M m (OH) 2 And more evenly mixed with the sodium source. The rotation speed of the ball mill is preferably300 to 800r/min, for example 300, 400, 500, 600, 700, 800 r/min; the ball milling time is preferably 0.5 to 5 hours, for example 0.5, 1, 2, 3, 4, 5 hours, etc.
In the step b, the mixture is presintered in a sintering furnace (such as a muffle furnace), wherein the presintering temperature is preferably 200-550 ℃, such as 200, 250, 300, 350, 400, 450, 500, 550 ℃, etc.; the pre-sintering time is preferably 1 to 8 hours, for example 1, 2, 3, 4, 5, 6, 7, 8 hours, etc. After the pre-sintering is finished, the temperature is raised again to carry out solid-phase sintering. The temperature rise rate is 1-10 ℃/min, such as 1, 2, 3, 4, 5, 6, 8, 10 ℃/min, etc. The solid phase sintering temperature is preferably 750-1100 ℃, such as 750, 800, 850, 900, 950, 1000, 1050, 1100 ℃, etc.; the solid phase sintering time is 4-20 hours, for example, 4, 5, 6, 8, 10, 12, 15, 16, 18, 20 hours and the like.
After solid phase sintering, the layered oxide NaNi is obtained i Fe j Mn k M m O 2 . The sintered product is further ground to obtain black NaNi i Fe j Mn k M m O 2 And (3) powder.
In the above step S1, the layered oxide Na y TMO 2 The powder needs to be exposed to a humid air environment for a period of time, the purpose of this step being: in moist air, layered oxide Na y TMO 2 The powder will react with H in the air 2 O、CO 2 O and O 2 React to generate Na on the surface 2 CO 3 、NaOH、NaHCO 3 Etc., thereby making it easier to react with TiO in subsequent steps 2 React to generate more complete Na 4 Ti 5 O 12 And a coating layer. In the above-mentioned moist air environment, the air humidity is preferably not less than 30%, for example, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, etc. The exposure time can be adjusted according to the air humidity so that Na y TMO 2 Powder and H in air 2 O、CO 2 O and O 2 The reaction is fully performed. In some embodiments, the exposure time may be 1 to 36 hours, preferably 24 to 36 hours, such as 1, 2, 4, 8, 12, 16, 24, 30, 36 hours, etc.
In the above step S2, tiO 2 The addition amount of the nano powder is preferably layered oxide Na y TMO 2 The mass of the catalyst is 0.4wt% to 0.8wt%, for example, 0.4wt%, 0.5 wt%, 0.6wt%, 0.7 wt%, 0.8wt%, etc. During mixing, the materials are preferably mixed by adopting a ball milling mode, the rotation speed of the ball milling is preferably 300-600 r/min, such as 300, 400, 500, 600r/min and the like, and the time of the ball milling is preferably 2-7 h, such as 2, 3, 4, 5, 6, 7h and the like.
In the step S3, the solid powder mixture after ball milling is placed in a sintering furnace (such as a muffle furnace), and the temperature is raised to perform sintering treatment. Wherein the temperature rising rate is 1-10 ℃/min, such as 1, 2, 3, 4, 5, 6, 8, 10 ℃/min, etc.
In the step S3, ti is added during sintering 4+ The high-temperature diffusion of the material into the bulk phase of the O3 phase layered material forms bulk phase doping, and the interlayer spacing of the material is enlarged, so that the diffusion capacity of sodium ions in the material is improved, and the rate capability of the material is improved; next, ti 4+ The material can be doped with the material to play a role in stabilizing the structure, so that double insurance is performed for improving the cycle stability of the material; again, ti 4+ The O3 phase layered material is doped with high-valence ions, so that the electronic conductivity of the material can be improved, and the rate capability of the material is further improved.
In the above step S3, the sintering temperature and time need to be controlled within a certain range. If the sintering time is too long and the temperature is too high, ti is accelerated 4+ Into the bulk structure of the material, resulting in Ti 4+ Not fully with layered oxide Na y TMO 2 Surface generation of Na 2 CO 3 、NaOH、NaHCO 3 The substances react fully to form complete Na 4 Ti 5 O 12 Coating, in turn, results in residual Na on the surface of the material 2 CO 3 、NaOH、NaHCO 3 NaO is generated by the substances at high temperature, and after the temperature is reduced, the substances continue to react with H in the air 2 O、CO 2 O and O 2 Reactions occur, affecting the air stability of the material. In the present invention, the sintering treatment temperature is preferably controlled to 600 to 800 ℃, for example 600, 650,700. 750, 800 ℃, etc.; the sintering time is preferably controlled to 0.5 to 3.5 hours, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5 hours, etc.
In a preferred embodiment of the present invention, the humidity of the environmental conditions is controlled to be 5% or less in the process of synthesizing the above surface-coated layered oxide, because: (1) Certain raw materials (such as sodium carbonate) are easy to absorb water, and the weighing precision is affected; (2) The layered oxide is sensitive to water, is easy to react with water carbon dioxide and oxygen in the air, so that sodium is separated out, and the material is subjected to phase change when serious; (3) Ensure strict experimental conditions, prevent humidity interference and make the experiment not have contrast.
On the basis of the surface-coated layered oxide, the invention also provides a sodium ion battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the diaphragm is arranged to isolate the positive plate from the negative plate.
In the sodium ion battery, the positive plate can be prepared by adopting a common plate preparation process in the field. The preparation method is as follows: mixing the surface-coated layered oxide, the conductive agent and the binder to prepare slurry, coating the slurry on at least one side surface of the positive electrode current collector, and drying and tabletting to obtain the positive electrode plate.
In the preparation method of the positive plate, the type and the content of the conductive agent are not particularly limited, and can be selected according to actual requirements. In some embodiments, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, acetylene black, graphene, ketjen black, carbon nanofibers, and the like. It will be appreciated that other conductive agents capable of performing the functions of the present application may be selected as desired without limitation without departing from the spirit of the present application.
In the preparation method of the positive plate, the types and the content of the binder are not particularly limited, and can be selected according to actual requirements. In some embodiments, the binder includes at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene butadiene rubber, sodium alginate, chitosan, polyethylene glycol, guar gum, and the like.
The type of the positive electrode current collector is not particularly limited, and may be selected according to practical requirements, for example, the positive electrode current collector may be an aluminum foil, a nickel foil or a polymer conductive film, and preferably the positive electrode current collector is an aluminum foil.
In the sodium ion battery, the type of separator is not particularly limited, and any separator material used in conventional batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, nonwoven fabric, multilayer composite films thereof, and modified separators such as ceramic modification and PVDF modification of the separator may be used.
In the sodium ion battery, the electrolyte can be one or more of organic liquid electrolyte, organic solid electrolyte, solid ceramic electrolyte and gel electrolyte. Preferably, the electrolyte is an organic liquid electrolyte obtained by dissolving sodium salt in a nonaqueous organic solvent; wherein the sodium salt may comprise sodium difluorophosphate (NaPO) 2 F 2 ) Sodium hexafluorophosphate (NaPF) 6 ) One or more of sodium bis (fluorosulfonyl) imide (NaFSI), sodium bis (trifluoromethanesulfonyl) imide (naftsi), and sodium difluoro (NaDFOB) oxalato borate (NaDFOB). The nonaqueous organic solvent may include one or more of cyclic carbonate, chain carbonate, and carboxylate. Wherein the cyclic carbonate can be selected from one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), butylene carbonate and gamma-butyrolactone; the chain carbonate may be selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl Propyl Carbonate (MPC), methyl Acetate (MA), ethyl Acetate (EA), and Ethyl Propionate (EP).
In some embodiments, a certain amount of additives may also be added to the organic liquid electrolyte. The additive may include one or more of Vinylene Carbonate (VC), vinyl carbonate (VEC), vinyl sulfate (DTD), ethylene Sulfite (ES), methylene Methane Disulfonate (MMDS), 1, 3-Propane Sultone (PS), propylene sultone (PES), propylene sulfate (TMS), trimethylsilyl phosphate (TMSP), trimethylsilyl borate (TMSB), fluoroethylene carbonate (FEC).
The invention further provides electric equipment which comprises the sodium ion battery.
In some embodiments, the powered device of the present invention includes, but is not limited to, a backup power source, a motor, an electric car, an electric motorcycle, a moped, a bicycle, an electric tool, a household large-scale battery, and the like.
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
The experimental methods used in the following examples are conventional methods unless otherwise specified, and materials, reagents, etc. used, unless otherwise specified, are commercially available.
In the examples below, the symbol "@" represents cladding, na 4 Ti 5 O 12 @NaNi 0.1 Fe 0.2 Mn 0.6 Mg 0.1 O 2 The layered oxide material represents Na 4 Ti 5 O 12 Coating on NaNi 0.1 Fe 0.2 Mn 0.6 Mg 0.1 O 2 The surface of the layered oxide.
1. XRD test method
Grinding the prepared powder material, transferring to a glass sheet object stage, and transferring to an X-ray diffractometer for scanning test, wherein the scanning range is 10-80 degrees, and the scanning speed is 5 degrees/min.
2. TEM test method
And (3) grinding the prepared powder uniformly, performing ultrasonic treatment on the material by using absolute ethyl alcohol as a dispersing agent, dripping the dispersed material on a transmission electron microscope carrier net by using a dropper, and observing.
3. Assembling and testing of button cell
Exposing the anode material for 3 days in an environment with humidity of more than or equal to 55%, grinding the anode material, the conductive agent Super P and the binder PVDF uniformly according to a mass ratio of 9:0.5:0.5, adding a proper amount of NMP to prepare slurry, uniformly coating the slurry on the pretreated aluminum foil, drying the aluminum foil in a blast drying box at 80 ℃ for 1h, and drying the aluminum foil in a vacuum drying box at 120 ℃ for 12h; then cutting into 14mm round positive plates by a cutting machine. Sodium metal sheets with the diameter of 14mm and the thickness of 0.2mm are used as a negative electrode, 0.1mol/L sodium perchlorate solution is used as electrolyte (the solvent is a mixed solvent formed by ethylene carbonate and dimethyl carbonate according to the volume ratio of 1:1), whatman GF/F glass fibers with the diameter of 16mm are used as a diaphragm, and the CR2032 button cell is assembled in a glove box filled with high-purity argon.
The assembled CR2032 coin cell was tested for charge and discharge at a current density of 0.1C using a constant current charge and discharge mode. The test items include: the first charge and discharge, rate capability and 1C charge and discharge capacity retention rate of 100 circles of the material in the sodium ion battery.
The first-circle charge and discharge testing method comprises the following steps: placing the button cell on a Wuhan blue electric cell tester (CT 2001A), and testing the charge and discharge capacity of the button cell at the first circle by adopting the multiplying power of 0.1C, wherein the charge and discharge voltage range is 2.0-4.0V;
the multiplying power performance testing method comprises the following steps: placing the button cell on a Wuhan blue electric cell tester (CT 2001A), wherein the charging and discharging voltage ranges from 2.0V to 4.0V, and activating the first circle by adopting a multiplying power of 0.1C for 3 weeks; performing charge and discharge test for 5 weeks by adopting a 1C multiplying power from the 4 th week, wherein the average value of each circle of charge and discharge of the 1C multiplying power in the period is recorded as 1C discharge capacity; performing charge and discharge test for 5 weeks by adopting a 2C multiplying power from the 9 th week, wherein the average value of each circle of charge and discharge of the 2C multiplying power in the period is recorded as 2C discharge capacity; performing charge and discharge test for 5 weeks by using a 5C rate from the 14 th week, wherein the average value of each circle of charge and discharge of the 5C rate in the period is recorded as 5C discharge capacity;
1C method for testing capacity retention rate of 100 circles of charging and discharging: and placing the button cell on a Wuhan blue electric cell tester (CT 2001A), activating the button cell for 3 weeks by adopting a multiplying power of 0.1C, performing charge-discharge cycle for 100 circles by adopting a multiplying power of 1C from 4 weeks, and recording that the charge and discharge capacity of the 100 th circle are respectively C0 and C1, wherein C1/C0 is 100% of the capacity retention rate of 1C, and the charge-discharge voltage range is 2.0-4.0V.
Example 1
(1) Ni is added with 0.1 Fe 0.2 Mn 0.6 Mg 0.1 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 300r/min according to the molar ratio of 1:1.06, and ball milling for 2 hours to fully mix the precursor and the sodium acetate; placing the mixed powder in a muffle furnace, presintering for 3h at 200 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 800 ℃, carrying out high-temperature solid-phase sintering for 10h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.1 Fe 0.2 Mn 0.6 Mg 0.1 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.1 Fe 0.2 Mn 0.6 Mg 0.1 O 2 Exposing the black powder of (2) in an environment with the air humidity of more than or equal to 30 percent for 24 hours; then NaNi is added 0.1 Fe 0.2 Mn 0.6 Mg 0.1 O 2 Black powder and TiO 0.4wt% of powder mass 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then placing the powder into a muffle furnace with the temperature rising rate of 3 ℃/min, and sintering at 650 ℃ for 3.5h. Cooling along with the furnace to obtain Na 4 Ti 5 O 12 @ NaNi 0.1 Fe 0.2 Mn 0.6 Mg 0.1 O 2 Layered oxide materials.
Example 2
(1) Ni is added with 0.2 Fe 0.3 Mn 0.45 Al 0.05 (OH) 2 Placing the precursor and sodium carbonate in a ball milling tank with the rotating speed of 700r/min according to the molar ratio of 1:0.503, and ball milling for 0.5h to fully mix the precursor and the sodium carbonate; placing the mixed powder in a muffle furnace, presintering for 2h at 300 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 850 ℃, carrying out high-temperature solid-phase sintering for 15h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.2 Fe 0.3 Mn 0.45 Al 0.05 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.2 Fe 0.3 Mn 0.45 Al 0.05 O 2 Exposing the black powder of (2) for 36 hours in an environment with the air humidity of more than or equal to 30%; then NaNi is added 0.2 Fe 0.3 Mn 0.45 Al 0.05 O 2 Black powder and 0.55wt% TiO based on the mass of the powder 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then the mixture is placed in a muffle furnace with the temperature rising rate of 5 ℃/min, and sintered for 2.5 hours at the temperature of 750 ℃. Cooling along with the furnace to obtain Na 4 Ti 5 O 12 @ NaNi 0.2 Fe 0.3 Mn 0.45 Al 0.05 O 2 Layered oxide materials.
Example 3
(1) Ni is added with 0.3 Fe 0.1 Mn 0.5 Cu 0.05 Al 0.05 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 500r/min according to the molar ratio of 1:1.06, and ball milling for 1.5h to fully mix the precursor and the sodium acetate; placing the mixed powder in a muffle furnace, presintering for 2h at 300 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 800 ℃, carrying out high-temperature solid-phase sintering for 15h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.3 Fe 0.1 Mn 0.5 Cu 0.05 Al 0.05 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.3 Fe 0.1 Mn 0.5 Cu 0.05 Al 0.05 O 2 Exposing the black powder of (2) for 36 hours in an environment with the air humidity of more than or equal to 30%; then NaNi is added 0.3 Fe 0.1 Mn 0.5 Cu 0.05 Al 0.05 O 2 Black powder and 0.75wt% TiO based on the powder mass 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then placing the powder into a muffle furnace with the temperature rising rate of 5 ℃/min, and sintering for 2 hours at 800 ℃. Cooling along with the furnace to obtain Na 4 Ti 5 O 12 @ NaNi 0.3 Fe 0.1 Mn 0.5 Cu 0.05 Al 0.05 O 2 Layered oxide materials.
Example 4
(1) Ni is added with 0.15 Fe 0.25 Mn 0.55 Zr 0.05 (OH) 2 The precursor and sodium acetate are placed in a ball milling tank with the rotating speed of 300r/min according to the mol ratio of 1:1.06Ball milling for 2h to fully mix the materials; placing the mixed powder in a muffle furnace, presintering for 2h at 300 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 900 ℃, carrying out high-temperature solid-phase sintering for 12h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Exposing the black powder of (2) in an environment with the air humidity of more than or equal to 30 percent for 24 hours; then NaNi is added 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Black powder and TiO 0.6wt% of powder mass 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then the mixture is placed in a muffle furnace with the temperature rising rate of 3 ℃/min, and sintered for 2.5 hours at the temperature of 750 ℃. Cooling along with the furnace to obtain Na 4 Ti 5 O 12 @ NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Layered oxide materials.
Comparative example 1
Ni is added with 0.15 Fe 0.25 Mn 0.55 Zr 0.05 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 300r/min according to the molar ratio of 1:1.06, and ball milling for 2 hours to fully mix the precursor and the sodium acetate; placing the mixed powder in a muffle furnace, presintering for 2h at 300 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 900 ℃, carrying out high-temperature solid-phase sintering for 12h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Is a black powder of (a).
Comparative example 2
(1) Ni is added with 0.15 Fe 0.25 Mn 0.55 Zr 0.05 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 300r/min according to the molar ratio of 1:1.06, and ball milling for 2 hours to fully mix the precursor and the sodium acetate; placing the mixed powder in a muffle furnace, presintering at 300 ℃ for 2h at a heating rate of 5 ℃/min, then raising the temperature to 900 ℃, carrying out high-temperature solid-phase sintering for 12h, and naturally coolingBut grinding to obtain layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Exposing the black powder of (2) in an environment with the air humidity of more than or equal to 30 percent for 24 hours; then NaNi is added 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Black powder and TiO 0.2wt% of powder mass 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then the mixture is placed in a muffle furnace with the temperature rising rate of 3 ℃/min, and sintered for 2.5 hours at the temperature of 750 ℃. Cooling along with the furnace to obtain Na 4 Ti 5 O 12 @ NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Layered oxide materials.
Comparative example 3
(1) Ni is added with 0.15 Fe 0.25 Mn 0.55 Zr 0.05 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 300r/min according to the molar ratio of 1:1.06, and ball milling for 2 hours to fully mix the precursor and the sodium acetate; the mixed powder is placed in a muffle furnace to be presintered for 2 hours at the temperature of 300 ℃ at the heating rate of 5 ℃/min, then the temperature is increased to 900 ℃ to be sintered for 12 hours in a high-temperature solid phase, and the layered oxide material NaNi is obtained after natural cooling and grinding 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Exposing the black powder of (2) in an environment with the air humidity of more than or equal to 30 percent for 24 hours; then NaNi is added 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Black powder and TiO 1wt% of powder mass thereof 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then the mixture is placed in a muffle furnace with the temperature rising rate of 3 ℃/min, and sintered for 2.5 hours at the temperature of 750 ℃. Cooling along with the furnace to obtain Na 4 Ti 5 O 12 @ NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Layered oxide materials.
Comparative example 4
(1) Ni is added with 0.15 Fe 0.25 Mn 0.55 Zr 0.05 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 300r/min according to the molar ratio of 1:1.06, and ball milling for 2 hours to fully mix the precursor and the sodium acetate; placing the mixed powder in a muffle furnace, presintering for 2h at 300 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 900 ℃, carrying out high-temperature solid-phase sintering for 12h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Is a black powder of (a).
(2) The layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Exposing the black powder of (2) in an environment with the air humidity of more than or equal to 30 percent for 24 hours; then NaNi is added 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Black powder and TiO 4.5wt% based on the powder mass 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then placing the powder into a muffle furnace with the temperature rising rate of 3 ℃/min, and sintering for 12h at 900 ℃. Cooling along with the furnace to obtain NaNi doped with Ti element 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Layered oxide materials.
Comparative example 5
(1) Ni is added with 0.15 Fe 0.25 Mn 0.55 Zr 0.05 (OH) 2 Placing the precursor and sodium acetate in a ball milling tank with the rotating speed of 300r/min according to the molar ratio of 1:1.06, and ball milling for 2 hours to fully mix the precursor and the sodium acetate; placing the mixed powder in a muffle furnace, presintering for 2h at 300 ℃ at a heating rate of 5 ℃/min, then raising the temperature to 900 ℃, carrying out high-temperature solid-phase sintering for 12h, and naturally cooling and grinding to obtain the layered oxide material NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Is a black powder of (a).
(2) NaNi is processed by 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Black powder and powder thereofTiO 0.6wt% 2 Placing the nano powder into a ball milling tank, and ball milling for 7 hours at the rotating speed of 300/min to uniformly mix; then placing the powder into a muffle furnace with the temperature rising rate of 3 ℃/min, and sintering at 550 ℃ for 8 hours. Cooling with furnace to obtain TiO 2 @NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 Layered oxide materials.
Characterization of materials
Characterization tests are performed below for the O3 phase layered oxide materials prepared in the examples and comparative examples.
FIG. 1 is an X-ray diffraction pattern of the O3 phase layered oxide materials prepared in example 4, comparative example 1 and comparative example 4 after being exposed to an air atmosphere having a humidity of 55% for three days. As can be seen from the figures, the materials prepared in comparative examples 1 and 4 show characteristic peaks of new phases in XRD diffractograms after three days of exposure to air, whereas the material prepared in example 4 has no characteristic peaks of new phases. This shows that the material prepared in example 4 has better structural stability in air.
Fig. 2 is a transmission electron microscope image of the material prepared in example 1. As can be seen from FIG. 2, the surface of the layered oxide is coated with Na 4 Ti 5 O 12 A coating layer; it can be seen from FIG. 3 that while coating, there is a part of Ti 4+ Doping is into the lattice of the layered oxide material.
Fig. 3 a-d are high power transmission electron micrographs of the O3 phase layered oxide materials prepared in example 4, comparative example 1, comparative example 2 and comparative example 4, respectively. As can be seen from FIG. 3, the interlayer spacing of the material of example 4 is increased compared to that of comparative example 1 because of Ti at high temperature 4+ The material can diffuse into the bulk phase of the O3 phase layered material to form bulk phase doping, so that the interlayer spacing of the material is enlarged; while the interlayer spacing of the material of comparative example 2 was unchanged from that of comparative example 1, indicating that in comparative example 2, ti 4+ Is not doped into the material and therefore the interlayer spacing is not enlarged. In comparative example 4, the interlayer spacing of the material was increased, indicating Ti 4+ Into the bulk phase of the layered oxide.
Electrochemical performance test
The results of the electrochemical tests of examples 1 to 4 and comparative examples 1 to 5 are shown in Table 1.
TABLE 1
Group of Whether new phases form after 3 days of exposure to the environment 0.1C first-turn discharge capacity mAh/g 1C discharge capacity mAh/g 2C discharge capacity mAh/g 5C discharge capacity mAh/g 1C 100 cycles capacity retention%
Example 1 Whether or not 131.23 122.37 113.7 100.3 95.3
Example 2 Whether or not 133.65 126.34 118.95 104.23 94.1
Example 3 Whether or not 137.32 129.54 121.22 110.1 92.3
Example 4 Whether or not 135.61 127.72 120.34 111.11 94.8
Comparative example 1 Is that 137.79 125.25 111.74 100.25 78.6
Comparative example 2 Whether or not 134.52 123.38 116.69 107.31 86.4
Comparative example 3 Whether or not 124.69 115.12 105.11 98.86 91.6
Comparative example 4 Is that 127.46 117.3 111.25 94.33 84.4
Comparative example 5 Is that 134.1 125.1 116.5 105.3 90.5
Examples 1-4, which employ the surface coating method provided by the invention, have excellent air stability, and after the material is exposed to an environment with an air humidity of 55% for 3 days, the XRD pattern of the material shows no new phase generation, which indicates that the material prepared by the method has excellent air stability in air. In addition, the material prepared by the method has excellent rate performance and cycle stability.
Comparative example 1 has the same layered oxide material as example 4, but does not employ the surface coating method provided by the present invention. The material of comparative example 1 was exposed to an atmosphere with an air humidity of 55% for 3 days, and the XRD diffraction peak was shifted and a new diffraction peak was generated, indicating that the air stability of the material without surface coating was poor. And the rate performance and the cycle stability of the material prepared in comparative example 1 are greatly different from those of example 4. This isThe Ti prepared by the surface coating method provided by the invention is shown 4+ Na doped into the surface phase 4 Ti 5 O 12 @NaNi 0.15 Fe 0.25 Mn 0.55 Zr 0.05 O 2 The material can improve the air stability, the multiplying power performance and the circulation stability of the material.
Comparative example 2 with lower TiO content 2 Surface coating was performed to improve both rate performance and capacity retention compared to the material of comparative example 1, but Ti in comparative example 2 4+ Does not dope the material, is simply Na 4 Ti 5 O 12 The coating layer improves the electrochemical performance; thus, comparative example 2 was limited in rate performance and capacity retention compared to example 4.
Comparative example 3 with higher TiO content 2 The surface coating has improved rate performance and capacity retention compared with comparative example 1, but the discharge capacity of the material is greatly reduced, indicating excessive TiO 2 Surface coating is detrimental to the performance of the material. The reason for this is: on the one hand, too much TiO 2 The formed coating layer is too thick, so that the transmission of ions and electrons is affected; on the other hand, too much TiO 2 Can result in excessive non-electrochemical active ions Ti 4+ Doping of the precursor phase with these Ti 4+ It is difficult to perform the oxidation-reduction reaction. Thus, too much TiO 2 The gram capacity of the material is affected, and the electrochemical performance of the material is reduced.
Comparative example 4 has the same layered oxide material as example 4, except that the sintering time and temperature are increased, the rate performance and capacity retention of the material are improved to some extent relative to comparative example 1, but the first-turn discharge capacity of the material is significantly reduced relative to example 4, and a new phase is formed upon three days of exposure to air. Indicating that after the sintering temperature is increased and the sintering time is prolonged, ti 4+ All enter the bulk phase of the surface layer of the material without forming a coating on the surface of the material. Therefore, due to excessive Ti 4+ Into the bulk phase of the material, affecting the exertion of the reversible capacity of the material.
Comparative example 5 and example 4 toolWith the same layered oxide material, except that TiO is used 2 The layered oxide material was coated, and the capacity retention of the material was significantly improved as compared to comparative example 1, but the first-turn discharge capacity and rate performance of the material were slightly reduced as compared to example 4, and a new phase was formed after three days of exposure to air. Description of TiO 2 The coating material did not improve much the air stability and the electrochemical performance was not as pronounced as in example 4.
The test results show that the surface-coated modified O3-phase layered oxide provided by the invention not only improves the air stability of the O3-phase layered oxide material, but also improves the rate capability and the cycle stability of the material.
The above-described embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and modifications will occur to those skilled in the art based on the present invention, and are intended to be within the scope of the present invention. The protection scope of the invention is subject to the claims.

Claims (10)

1. A method for preparing a surface-coated layered oxide, comprising the steps of:
s1, layered oxide Na y TMO 2 The powder is exposed to the air environment with the humidity more than or equal to 30 percent;
s2, the layered oxide Na treated in the step S1 y TMO 2 Powder and TiO 2 Ball milling and mixing nanometer powder;
s3, sintering the mixture obtained in the step S2 to obtain the surface-coated layered oxide;
in the step S1, y is more than 0.8 and less than or equal to 1, and TM is one or more selected from Ti, V, cr, mn, fe, co, ni, cu, zn, li, B, mg, al, K, ca, zr, nb, sn.
2. The method for producing a surface-coated layered oxide according to claim 1, wherein in step S1: the Na is y TMO 2 Is NaNi i Fe j Mn k M m O 2 M is one or more of Li, B, mg, al, K, ca, co, V, cr, cu, zn, zr, nb and Sn; wherein: 0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i+j+k+m=1;
and/or the layered oxide Na y TMO 2 The powder is exposed to the air environment with the humidity of more than or equal to 30 percent for 24-36 hours.
3. The method for producing a surface-coated layered oxide according to claim 2, wherein in step S1, the layered oxide NaNi i Fe j Mn k M m O 2 The preparation method of (2) comprises the following steps:
a. precursor Ni i Fe j Mn k M m (OH) 2 Ball-milling and mixing with a sodium source;
b. pre-sintering the mixture obtained in the step a, and then performing solid-phase sintering to obtain the layered oxide NaNi i Fe j Mn k M m O 2 ；
Wherein: in the step a, the sodium source is selected from one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate and sodium nitrate;
and/or in the step b, the temperature of the presintering is 200-550 ℃, and the presintering time is 1-8 hours; the temperature of the solid phase sintering is 750-1100 ℃, and the time of the solid phase sintering is 4-20 h.
4. The method for producing a surface-coated layered oxide according to claim 1, wherein in step S2: the TiO 2 The addition amount of the nano powder is the layered oxide Na y TMO 2 0.4-0.8 wt% of the weight of the material;
and/or the rotation speed of the ball milling is 300-600 r/min, and the ball milling time is 2-7 h.
5. The method for producing a surface-coated layered oxide according to claim 1, wherein in step S3: the sintering treatment temperature is 600-800 ℃, and the sintering treatment time is 0.5-3.5 h.
6. A surface-coated layered oxide comprising a layered oxide Na y TMO 2 Located in the layered oxide Na y TMO 2 Na of surface 4 Ti 5 O 12 A cladding layer, wherein: y is more than 0.8 and less than or equal to 1, and TM is one or more selected from Ti, V, cr, mn, fe, co, ni, cu, zn, li, B, mg, al, K, ca, zr, nb, sn.
7. The surface-coated layered oxide of claim 6, wherein said Na y TMO 2 Is NaNi i Fe j Mn k M m O 2 M is one or more of Li, B, mg, al, K, ca, co, V, cr, cu, zn, zr, nb and Sn; wherein: 0<i≤0.4，0<j≤0.5，0<k≤0.6，0<m is less than or equal to 0.2, and i+j+k+m=1;
and/or the layered oxide Na y TMO 2 The particle diameter D50 of the particles is 7-12 mu m;
and/or, the Na 4 Ti 5 O 12 The thickness of the coating layer is 5-20 nm.
8. A positive electrode sheet comprising the surface-coated layered oxide produced by the production method according to any one of claims 1 to 5, or comprising the surface-coated layered oxide according to any one of claims 6 to 7.
9. A sodium ion battery comprising the positive electrode sheet of claim 8.
10. A powered device comprising the sodium ion battery of claim 9.
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