CN112599783A

CN112599783A - Selenium-doped lithium-rich manganese-based positive electrode material and preparation method and application thereof

Info

Publication number: CN112599783A
Application number: CN202110242324.6A
Authority: CN
Inventors: 纪效波; 陈军; 侯红帅; 邹国强
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2021-03-05
Filing date: 2021-03-05
Publication date: 2021-04-02
Anticipated expiration: 2041-03-05
Also published as: CN112599783B

Abstract

The invention provides a selenium-doped lithium-rich manganese-based positive electrode material and a preparation method and application thereofHas a general formula of mLi₂MnO_3‑δSe_2δ/3•(1‑m)LiTMO_2‑δSe_2δ/3Wherein TM is at least one of Ni, Co and Mn, m is more than or equal to 0.2 and less than or equal to 0.8, and delta is more than 0 and less than 2; the selenium content in the positive electrode material is 0-5% by mass. The positive electrode material has good lattice stability and electrode/electrolyte interface stability, can inhibit lattice oxygen loss in a circulation process, can inhibit electrolyte decomposition, relieves capacity attenuation and voltage drop of the lithium-rich manganese-based positive electrode material in the circulation process, and effectively overcomes the problems of poor rate capability and the like of the conventional positive electrode material. The preparation method is simple and easy to popularize.

Description

Selenium-doped lithium-rich manganese-based positive electrode material and preparation method and application thereof

Technical Field

The invention relates to the field of preparation of lithium-rich manganese-based cathode materials, in particular to a selenium-doped lithium-rich manganese-based cathode material and a preparation method and application thereof.

Background

With the development of society, clean and efficient energy storage and conversion are the research hotspots in the energy field. The lithium ion battery as a novel secondary power supply has the advantages of high specific energy, no memory effect, long cycle life, small environmental pollution and the like, and injects fresh blood for the vigorous development of an energy network. The lithium ion electric automobile is an important component in a new energy automobile family, and the high-energy-density lithium ion power battery is used as the heart of the electric automobile, so that the problem of mileage anxiety in the field of electric automobiles can be effectively solved. In recent years, the demand of lithium ion power batteries has increased explosively, and high energy density positive electrode materials have received much attention from researchers as a key part of lithium ion power batteries.

The lithium-rich manganese-based positive electrode material has higher specific capacity (-250 mAh g) under the coupling action of redox of transition metal cations and oxygen anions^-1) Is one of the most potential next generation high energy density lithium ion battery positive electrode materials. Oxyanion Redox Inclusion of reversible Redox (O) in bulk^2-→O_n ^{- 2}) And irreversible lattice oxygen loss (O) from the surface^2-→O₂). However, irreversible lattice oxygen loss induces irreversible transition metal migration and lattice distortion during cycling, which ultimately leads to problems such as capacity fade of the positive electrode material, drop of discharge voltage, and slow kinetics of the electrochemical reaction process. Furthermore, Ni⁴⁺Has higher activity in a high-voltage charging state, induces the side reaction of an electrode/electrolyte interface to occur, and leads the transition metal on the surface of the electrode to be dissolved, irreversibly transferred and structurally distorted. The synergistic effect of electrode/electrolyte interface side reactions and irreversible lattice oxygen loss can exacerbate the capacity fade, discharge voltage drop and reaction kinetics retardation of the positive electrode material. Therefore, the biggest challenge is to not only induce the redox of oxygen anions, but also to stabilize the structural changes and lattice oxygen loss caused by the redox process.

The Chinese patent application with the application publication number of CN 110492095A (with the application number of 201910747712.2) discloses a doping modification method of a lithium-rich manganese-based positive electrode material of a lithium ion battery, wherein the lithium-rich manganese-based positive electrode material in the embodiment is Li [ Li ] in_0.2Mn_0.53Ni_0.13Co_0.13Sn_0.01]O₂. The specific modification steps are as follows: (1) adding 1 mol/L of chloride salt solution of nickel, cobalt, manganese and tin, precipitant sodium carbonate solution and ammonia water into a reactor respectively, controlling the pH value in the precipitation process to be 8.0, the precipitation temperature to be 55 ℃, stirring speed to be 800 r/min, aging time to be 6 h, standing for 24 h, washing for multiple times, and drying in vacuum for 8 h at 90 ℃ to obtain a corresponding carbonate precursor; (2) grinding the obtained carbonate precursor and lithium hydroxide monohydrate with the mass excess coefficient of 5% for 0.5 h, calcining in a tubular furnace in an air atmosphere, heating to 450 ℃ at the heating rate of 3 ℃/min, keeping the temperature for 5h, then continuously heating to 850 ℃, keeping the temperature for 12 h, and naturally cooling to obtain the lithium-rich manganese-based positive electrode material. The method adopts the traditional coprecipitation method to realize lattice doping, and can improve the stability of the crystal structure to a certain extent; however, the prepared cathode material can directly contact with the electrolyte in the circulation process, and side reactions occurring at an electrode/electrolyte interface can further induce lattice oxygen loss and transition metal dissolution and migration, so that the capacity attenuation and voltage drop of the lithium-rich manganese-based cathode material in the circulation process are accelerated.

The invention discloses a preparation method of an anion co-doped lithium-rich manganese-based solid solution cathode material, which is disclosed by Chinese patent application with application publication number CN 109860509A (application number CN201910033472. X). in the invention, soluble metal salt and soluble phosphate are dissolved in secondary deionized water to prepare a mixture solution; the polymer was dissolved in absolute ethanol to make an anhydrous-polymer solution. And uniformly mixing the polymer solution and the mixture solution, and preparing a precursor by using an electrostatic spinning device. And finally, uniformly mixing the obtained precursor and fluoride according to a molar ratio, and roasting in an oxygen environment to obtain the anion co-doped lithium-rich manganese-based solid solution cathode material. The method realizes phosphate radical doping in the preparation process of the precursor, and carries out fluorine ion gradient doping through high-temperature induction in the roasting process, so that lattice oxygen loss and interface side reaction can be relieved to a certain extent, but the stability of fluorine ions is poor, trace water molecules exist in the electrolyte, the interface side reaction is serious in the long-cycle charging and discharging process, the decomposition of the electrolyte can be caused, and the lithium-rich manganese-based positive electrode material has obvious capacity attenuation and voltage drop in the long-cycle process.

Therefore, the search for a suitable dopant doping modified lithium-rich manganese-based cathode material is crucial to improving the capacity fading and voltage drop during the cycling process of the lithium-rich manganese-based cathode material.

Disclosure of Invention

Aiming at the defects of the lithium-rich manganese-based cathode material in the prior art, one of the purposes of the invention is to provide a selenium anion doped modified lithium-rich manganese-based cathode material which has good lattice stability and electrode/electrolyte interface stability, the cathode material can inhibit lattice oxygen loss in the circulation process and can inhibit electrolyte decomposition, thereby relieving capacity attenuation and voltage reduction of the lithium-rich manganese-based cathode material in the circulation process, and effectively overcoming the problems of poor rate capability, serious capacity and voltage attenuation in the circulation process and the like of the conventional cathode material.

In order to achieve the purpose, the technical scheme of the invention is as follows:

selenium is distributed in the layered lithium-rich manganese-based positive electrode material in the form of anions, and the chemical structure of the selenium-doped layered lithium-rich manganese-based positive electrode materialHas a general formula of mLi₂MnO_3-δSe_2δ/3•(1-m)LiTMO_2-δSe_2δ/3Wherein TM is at least one element of Ni, Co and Mn, m is more than or equal to 0.2 and less than or equal to 0.8, and delta is more than 0 and less than or equal to 2; the selenium content in the positive electrode material is 0-5% by mass.

In some embodiments, the selenium is uniformly distributed in the layered lithium-rich manganese-based positive electrode material.

Another object of the present invention is to provide a method for preparing a selenium-doped lithium-rich manganese-based positive electrode material according to any of the above embodiments, wherein the method has simple process steps and low raw material cost, and is beneficial to large-scale popularization and production, and the method includes the following steps:

s1, preparing a mixed material: according to the formula Li [ Li ]_xMn_yNi_zCo_1-x-y-z]O₂The theoretical calculated ratio is Mn_yNi_zCo_1-x-y-zThe transition metal oxide precursor is mixed with lithium source to obtain Li_xMn_yNi_zCo_1-x-y-z]O₂A mixture precursor of (a); wherein x =0.2, z is more than 0.1 and less than y and less than 0.8;

s2, lithiation and solid solution: placing the mixture precursor obtained in the step S1 into calcining equipment for calcining, and uniformly grinding a calcined product to obtain a lithium-rich manganese-based positive electrode material;

s3, selenizing and doping: uniformly mixing the lithium-rich manganese-based positive electrode material obtained in the step S2 with selenium powder to obtain a mixed material, and then placing the mixed material into a calcining device for selenization to obtain a selenized lithium-rich manganese-based positive electrode material;

s4, selenylation post-treatment: and (4) dispersing the lithium-rich manganese selenide positive electrode material obtained in the step (S3) in a carbon disulfide solution, washing off residual selenium powder on the surface, filtering, washing with alcohol, and drying in vacuum to obtain the selenium-doped lithium-rich manganese-based positive electrode material.

As a preferable scheme, the transition metal oxide precursor material in step S1 is at least one of transition metal carbonate, transition metal oxalate and transition metal hydroxide; the transition metal includes at least one of Ni, Co, and Mn.

As a preferable scheme, the lithium source in step S1 is a lithium source commonly used in the process of preparing a cathode material, and includes, but is not limited to, at least one of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, lithium nitrate, and lithium acetate.

Preferably, the mass excess coefficient of the lithium source in step S1 is 3-10%. Wherein the mass excess coefficient of the lithium source is measured by taking the theoretical mass of the lithium source required for completely converting the transition metal oxide precursor material into the corresponding solid solution as 100%, and the mass excess coefficient is 3-10%.

As a preferable scheme, the material mixing time in the step S1 is 0.5-1 h.

As a preferable mode, in step S2, the calcination is performed in an oxidizing atmosphere, and the calcination is performed in two stages: the first stage of calcination is calcination at 500-700 ℃ for 5-10 h, and the second stage of calcination is calcination at 800-900 ℃ for 10-15 h. The first stage of calcination mainly aims at decomposing the lithium source into oxides to facilitate the solid solution reaction of the second stage of calcination, the second stage of calcination aims at fully carrying out the solid solution reaction of the precursors and the decomposition products of the lithium source while decomposing the precursors into the oxides, and a tubular furnace or a shaft furnace is adopted for calcination. The flow of oxygen in the calcining process is controlled to be 0.5-2 m³And h, wherein the temperature rise speed in the calcining process is 3-10 ℃/min. And after the calcination is finished, cooling in a natural cooling mode.

As a preferable scheme, in the step S3, the material mixing time is 1-5 h, the selenization atmosphere is an inert atmosphere, the gas flow is 1-20 mL/min, and the inert atmosphere can prevent the selenium from being oxidized.

As a preferable scheme, in step S3, the selenization time is 5-10 h, and sufficient selenization time can ensure that selenium is uniformly distributed in the lithium-rich manganese-based positive electrode material.

As a preferable scheme, in the step S3, the selenization temperature is 500-900 ℃, the heating rate is 1-5 ℃/min, and the high-temperature selenization can ensure that selenium is uniformly distributed in the lithium-rich manganese-based positive electrode material.

As a preferable scheme, in step S4, the selenized lithium-rich manganese-based positive electrode material needs to be washed with a carbon disulfide solution to remove residual selenium powder on the surface of the lithium-rich manganese-based positive electrode, the washing adopts stirring washing, the washing solution/solid ratio is 5-10 mL/g, the stirring rotation speed is 300-.

Preferably, in step S4, the number of alcohol suction filtration and washing is 1-5.

Preferably, in the step S4, the drying temperature is 100-150 ℃, and the drying time is 6-12 h.

The invention also aims to provide a positive pole piece, which comprises the selenium-doped lithium-rich manganese-based positive pole material prepared by the preparation method of any one of the above embodiments or the selenium-doped lithium-rich manganese-based positive pole material prepared by the preparation method of any one of the above embodiments.

The fourth objective of the present invention is to provide a battery, which includes the above-mentioned positive electrode plate.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the selenium-doped lithium-rich manganese-based positive electrode material provided by the invention, selenium is distributed in a layered lithium-rich manganese-based positive electrode material in an anion form, selenium anions are doped under a high potential to inhibit excessive oxidation of lattice oxygen and relieve loss of the lattice oxygen, and selenium can also eliminate superoxide radicals generated in the oxidation process of the lattice oxygen and relieve decomposition of electrolyte caused by the superoxide radicals, so that capacity attenuation and voltage drop of the lithium-rich manganese-based positive electrode material in a circulating process are finally synergistically inhibited.

(2) The selenium-doped lithium-rich manganese-based positive electrode material provided by the invention can synchronously obtain multiple modification advantages, and the selenium-modified lithium-rich manganese-based positive electrode material is used for electrochemical performance tests of lithium ion batteries, and the results show that after the material is cycled for 200 times under the current density of 2-4.8V and 1C (1C =250 mA/g), the capacity retention rate is as high as 100%, and the discharge voltage drop is only 0.39V, which indicates that the material provided by the invention has excellent specific discharge capacity retention rate and excellent average discharge voltage stability as the positive electrode material of the lithium ion batteries.

(3) The preparation process of the selenium-doped lithium-rich manganese-based positive electrode material provided by the invention is simple, is easy to popularize, and is a method for effectively inhibiting capacity attenuation and voltage drop of the lithium-rich manganese-based positive electrode material in a circulation process.

Drawings

FIG. 1 is a scanning electron micrograph of a sample (LRM) obtained in example 1, wherein b is an enlarged view of a;

FIG. 2 is a scanning electron micrograph of a sample (Se-LRM) obtained in example 2, wherein b is an enlarged view of a;

FIG. 3 is a schematic view of a spherical aberration electron microscope of the sample obtained in example 2;

FIG. 4 is an X-ray absorption spectrum of a sample obtained in example 2;

FIG. 5 is an X-ray diffraction pattern of the samples obtained in example 1 and example 2;

FIG. 6 is electron paramagnetic resonance spectra of samples obtained in example 1 and example 2;

FIG. 7 is a first charge-discharge curve of samples obtained in examples 1 and 2;

FIG. 8 is a discharge medium voltage curve of 200 cycles at a current density of 1C for the samples obtained in examples 1 and 2;

FIG. 9 is a graph of mass to capacity for 200 cycles at a current density of 1C for samples from example 1 and example 2;

FIG. 10 is a graph of energy density of 200 cycles at a current density of 1C for samples obtained in examples 1 and 2;

FIG. 11 is a plot of the overpotential for 200 cycles at a current density of 1C for the samples obtained in examples 1 and 2.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.

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 purity of the high purity oxygen used in the following examples was 99.99%; the inert atmosphere adopts nitrogen or argon with the purity of 99.99 percent; the precursor was a commercially available carbonate complex (Mn)_0.672Ni_0.164Co_0.164CO₃) The raw materials or chemical agents used in the examples of the present invention are obtained by conventional commercial methods unless otherwise specified.

The invention aims to provide a selenium-doped lithium-rich manganese-based positive electrode material, wherein selenium is distributed in a layered lithium-rich manganese-based positive electrode material in an anion form, and the chemical general formula of the selenium-doped layered lithium-rich manganese-based positive electrode material is mLi₂MnO_3-δSe_2δ/3•(1-m)LiTMO_2-δSe_2δ/3Wherein TM is at least one element of Ni, Co and Mn, m is more than or equal to 0.2 and less than or equal to 0.8, and delta is more than 0 and less than or equal to 2; the selenium content in the positive electrode material is 0-5% by mass. The anode material can inhibit lattice oxygen loss in the circulation process and can inhibit the decomposition of electrolyte, so that the capacity attenuation and voltage drop of the lithium-rich manganese-based anode material in the circulation process can be relieved, and the problems of poor rate performance, serious capacity and voltage attenuation in the circulation process and the like of the conventional anode material can be effectively solved.

The preparation method comprises the following steps:

s1, mixing the precursor and a lithium source in a drying environment for 0.5-1 h, and uniformly mixing to obtain a mixture; wherein the mass excess coefficient of the lithium source is 3-10%; lithium sources are common lithium-containing compounds including, but not limited to, lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, lithium nitrate, and the like; the precursor can be replaced by carbonate, oxalate, acetate or hydroxide of nickel, cobalt and manganese with different proportions;

s2, placing the mixture obtained in the step S1 in a calcining device to be calcined in an oxygen atmosphere, and cooling the mixture to room temperature along with a furnace after calcining to obtain the lithium-rich manganese-based positive electrode material; the calcination adopts a two-stage calcination mode: the first stage of calcination is calcination at 500-700 ℃ for 5-10 h, and the second stage of calcination is calcination at 800-900 ℃ for 10-15 h; the calcining process adopts a tube furnace or a shaft furnace for calciningThe flow rate of oxygen in the process is controlled to be 0.5-2 m³H, the temperature rising speed in the calcining process is 3-10 ℃/min;

s3, mixing the lithium-rich manganese-based positive electrode material obtained in the step S2 and selenium powder for 1-5 hours, uniformly mixing, and placing the mixed material in a tube furnace for selenization to obtain a lithium-rich manganese-based selenide positive electrode material; the selenizing process is carried out under the protection of inert atmosphere, the flow rate of inert gas is controlled to be 1-10 mL/min, the selenizing temperature is 500-; the protective atmosphere can be at least one of argon and nitrogen;

s4, washing the lithium-rich manganese selenide-based positive electrode material obtained in the step S3 with a carbon disulfide solution, stirring and washing, wherein the washing liquid/solid ratio is 5-10 mL/g, the stirring speed is 300-600 r/min, the stirring time is 3-6 h, and after washing and filtering, the lithium-rich manganese selenide-based positive electrode material is subjected to suction filtration and washing with alcohol for 1-5 times.

S5, drying the lithium-rich manganese selenide-based positive electrode material washed in the step S4 in a vacuum drying oven to obtain a selenium-doped lithium-rich manganese-based positive electrode material final product; wherein the drying temperature is 100-150 ℃, and the drying time is 6-12 h.

In order that the invention may be fully understood, a more complete and detailed description of the invention is set forth below in connection with the appended drawings and the preferred embodiments, but the scope of the invention is not limited to the specific embodiments described below.

Unless otherwise defined, all terms of art used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various starting materials, reagents, equipment, and apparatuses and the like to which the present invention is applied are commercially available or prepared by the prior art.

Example 1

The preparation method of the lithium-rich manganese-based positive electrode material comprises the following steps:

(1) 2 g of the precursor Mn_0.672Ni_0.164Co_0.164CO₃With 1.02 g LiOH₂Placing O in agate mortar and drying in a ringMixing materials for 1 h in the environment to obtain a mixture precursor;

(2) and (2) transferring the uniformly mixed mixture precursor in the step (1) into a corundum ark, then placing the corundum ark into a tubular furnace in an oxygen atmosphere for calcination, wherein the calcination condition is that the temperature is raised to 500 ℃ at the speed of 5 ℃/min, the temperature is kept for 5h, then the temperature is raised to 900 ℃ at the speed of 5 ℃/min, the temperature is kept for 12 h, and the mixture is cooled to room temperature along with the furnace to obtain a lithium-rich manganese-based positive electrode material sample named as LRM.

Example 2

A preparation method of a selenium-doped lithium-rich manganese-based positive electrode material comprises the following steps:

s1, mixing 2 g of the lithium-rich manganese-based positive electrode material prepared in the

embodiment

1 and 20 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination condition is that the temperature is raised to 500 ℃ at a speed of 2 ℃/min, the temperature is kept for 5h, and the gas flow is 2 mL/min;

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium anion doped lithium-rich manganese-based positive electrode material named Se-LRM, wherein the mass fraction of selenium is 0.86% as shown by electron spectrum analysis.

Example 3

s1, mixing 2 g of the lithium-rich manganese-based positive electrode material obtained in the

embodiment

1 and 20 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination condition is that the temperature is raised to 600 ℃ at a speed of 2 ℃/min, the temperature is kept for 5h, and the gas flow is 2 mL/min;

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material, wherein the mass fraction of selenium is 0.81% as shown by electron energy spectrum analysis.

Example 4

embodiment

1 and 20 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination conditions include that the temperature is raised to 700 ℃ at a speed of 2 ℃/min, the temperature is kept for 5h, and the gas flow is 2 mL/min;

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material, wherein the mass fraction of selenium is 0.82% as shown by electron energy spectrum analysis.

Example 5

embodiment

1 and 20 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination conditions include that the temperature is raised to 700 ℃ at a speed of 2 ℃/min, the temperature is kept for 6 h, and the gas flow is 2 mL/min;

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material, wherein the mass fraction of selenium is 0.77% as shown by electron energy spectrum analysis.

Example 6

s1, mixing 2 g of the lithium-rich manganese-based positive electrode material obtained in the example 1 and 20 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination conditions include that the temperature is raised to 700 ℃ at a speed of 2 ℃/min, the temperature is kept for 7 h, the gas flow is 2 mL/min,

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material, wherein the mass fraction of selenium is 0.85% as shown by electron energy spectrum analysis.

Example 7

embodiment

1 and 10 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination conditions include that the temperature is raised to 700 ℃ at a speed of 2 ℃/min, the temperature is kept for 7 h, and the gas flow is 2 mL/min;

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material, wherein the mass fraction of selenium is 0.54% as shown by electron energy spectrum analysis.

Example 8

embodiment

1 and 30 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination conditions include that the temperature is raised to 700 ℃ at a speed of 2 ℃/min, the temperature is kept for 7 h, and the gas flow is 2 mL/min;

and S2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material. The electron energy spectrum analysis shows that the mass fraction of selenium is 2.53%.

Example 9

embodiment

1 and 30 mg of commercial selenium powder for 2 h, transferring the uniformly mixed material into a corundum ark, and then placing the corundum ark into a tubular furnace in an argon atmosphere for calcination, wherein the calcination conditions include that the temperature is raised to 700 ℃ at a speed of 2 ℃/min, the temperature is kept for 7 h, and the gas flow is 5 mL/min;

s2, adding the sample calcined and sintered in the step S1 into 10mL of carbon disulfide solution for 500 r/min, stirring for 5h, carrying out suction filtration and washing on alcohol for 4 times, and carrying out vacuum drying at 120 ℃ for 12 h to obtain the selenium-doped lithium-rich manganese-based positive electrode material, wherein the mass fraction of selenium is 2.86% as shown by electron energy spectrum analysis.

The samples prepared in example 1 and example 2 were characterized and the results are shown in FIGS. 1-6:

fig. 1 is a scanning electron microscope image of a sample obtained in example 1, and it can be seen from fig. 1 that the obtained microsphere cathode material is formed by agglomeration of primary nanoparticles, the secondary particle size is about 10 μm, and the primary particle size is about 100 nm.

Fig. 2 is a scanning electron microscope image of the sample obtained in example 2, and it can be seen from fig. 2 that the surface of the secondary particle becomes rough after selenization, which is mainly caused by selenium anion doping.

FIG. 3 is a SEM image of a sample obtained in example 2, wherein the bright spots in a and the dark spots in b are uniform in size, indicating that both are transition metals, indicating that doped Se does not enter the transition metal layer and the lithium layer.

FIG. 4 shows the X-ray absorption spectrum of the sample obtained in example 2, and it can be seen from FIG. 4 that the absorption edge of the obtained sample Se is equal to that of the standard sample Ni₂Se₃The absorption edge goodness of fit of the medium Se is higher, which indicates that the valence state of the Se in the obtained sample is-3 and exists in the form of anions.

FIG. 5 shows X-ray diffraction patterns of samples obtained in examples 1 and 2, and it can be seen from FIG. 5 that the obtained samples all have a layered structure, and the corresponding space group is R-3m, and the space group corresponding to a diffraction peak of a superlattice in the range of 20 to 25 ℃ is C2/m (Li 2/m)₂MnO₃). In addition, as shown in fig. 5, the X-ray diffraction peak intensity of the sample obtained in example 2 is significantly increased from that of the sample obtained in example 1, and this phenomenon indicates that the selenium anion doping can fill up the oxygen vacancy and improve the crystallinity of the crystal.

FIG. 6 shows EPR patterns of the samples obtained in examples 1 and 2, and it can be seen from FIG. 6 that oxygen vacancies are significantly reduced in the sample after doping with selenium anions, indicating that selenium enters the oxygen vacancies. The selenium anion doping can relieve lattice oxygen loss, and meanwhile, selenium can eliminate superoxide radical generated in the lattice oxygen oxidation process and inhibit the decomposition of electrolyte, and the series of characteristics are favorable for relieving the capacity attenuation and voltage drop of the material serving as the lithium ion battery anode material in the circulation process.

The samples obtained in example 1 and example 2 were used as a positive electrode material of a lithium ion battery to prepare a positive electrode sheet. The concrete mode is as follows: mixing the prepared anode material powder with acetylene black (a conductive agent) and polyvinylidene fluoride (PVDF, a binder) according to a mass ratio of 8:1:1, dropwise adding a proper amount of N-methylpyrrolidone (NMP) serving as a dispersing agent, and grinding into slurry; and then uniformly coating the slurry on an aluminum foil, carrying out vacuum drying at 120 ℃ for 12 h, and transferring the aluminum foil into an argon atmosphere glove box for later use.

The half-cells were assembled in an argon atmosphere glove box. The lithium metal is used as a counter electrode, LiPF 6/ethylene carbonate (EC: DMC: DEC =1:1: 1) is used as an electrolyte, a CR2016 type button cell is assembled, charging and discharging are carried out by using a constant current charging and discharging mode, a first-turn charging and discharging curve under the current density of 0.1C (1C =250 mA/g) is shown in figure 7, the first-turn discharging capacities are 277.7 (LRM) and 293.5 (Se-LRM) mAh/g respectively, and the corresponding coulombic efficiencies are 88.2% (LRM) and 94.3% (Se-LRM) respectively. As can be seen from fig. 7, the first coulombic efficiency of the modified lithium-rich manganese-based positive electrode material is significantly improved, which indicates that the oxygen loss of the selenium-doped lithium-rich manganese-based positive electrode material in the charging process is significantly suppressed.

Fig. 8 is a voltage drop curve of the batteries made of the positive electrode material samples obtained in examples 1 and 2 after cycling 200 times at a current density of 1C, and it can be seen from fig. 8 that the positive electrode material sample modified by selenium doping has good voltage stability characteristics in the cycling process, and the voltage drop of the unmodified positive electrode material after cycling 200 times is 0.47V, which is significantly higher than the voltage drop (0.33V) of example 2, indicating that the lithium-rich manganese-based positive electrode material modified by selenium doping can effectively inhibit the voltage drop of the electrode material in the cycling process.

Fig. 9 is a discharge specific capacity change curve of the positive electrode material samples obtained in example 1 and example 2 after 200 cycles at a current density of 1C, and as can be seen from fig. 9, the capacity retention rate of the positive electrode material sample obtained in example 2 after 200 cycles is as high as 100%, while the discharge capacity retention rate of the positive electrode material sample obtained in example 1 after 200 cycles is only 52.6%, which indicates that the selenium-doped modified lithium-rich manganese-based positive electrode material can effectively inhibit capacity fading of the electrode material during the cycling process.

Fig. 10 is a graph showing the energy density change curves of the positive electrode material samples obtained in examples 1 and 2 after 200 cycles at a current density of 1C, and it can be seen from fig. 10 that the cycle retention rate of the energy density of the positive electrode material sample obtained in example 2 after 200 cycles is 92.5%, which is significantly higher than the cycle retention rate of the energy density of the positive electrode material sample obtained in example 1 (only 45.6%).

Fig. 11 is a polarization curve of the positive electrode material samples obtained in examples 1 and 2 after cycling 200 times at a current density of 1C, and it can be seen from fig. 11 that the polarization of the positive electrode material sample obtained in example 2 is significantly lower than that of example 1, indicating that the positive electrode material sample doped with selenium anions has higher structural stability during long cycling.

It should be noted that, in the above embodiments, only the precursor is disclosed as Mn_0.672Ni_0.164Co_0.164CO₃The prepared selenium-doped lithium-rich manganese-based cathode material is prepared, but the invention is not limited to the precursor with the structure, and the method is suitable for all the cathode materials with the chemical general formula of mLi₂MnO₃•(1-m)LiTMO₂The lithium-rich manganese-based positive electrode material is characterized in that TM is at least one element of Ni, Co and Mn, and m is more than or equal to 0.2 and less than or equal to 0.8.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The selenium-doped lithium-rich manganese-based positive electrode material is characterized in that selenium is distributed in the layered lithium-rich manganese-based positive electrode material in an anion form, and the chemical general formula of the selenium-doped layered lithium-rich manganese-based positive electrode material is mLi₂MnO_3-δSe_2δ/3•(1-m)LiTMO_2-δSe_2δ/3Wherein TM is at least one element of Ni, Co and Mn, m is more than or equal to 0.2 and less than or equal to 0.8, and delta is more than 0 and less than or equal to 2; the selenium content in the positive electrode material is 0-5% by mass.

2. The selenium-doped lithium-rich manganese-based positive electrode material of claim 1, wherein the selenium is uniformly distributed in the layered lithium-rich manganese-based positive electrode material.

3. The method for preparing the selenium-doped lithium-rich manganese-based positive electrode material as claimed in claim 1 or 2, comprising the steps of:

s1, preparing a mixed material: according to the formula Li [ Li ]_xMn_yNi_zCo_1-x-y-z]O₂The theoretical calculation ratio is MnyNi_zCo_1-x-y-zThe transition metal oxide precursor is mixed with lithium source to obtain Li_xMn_yNizCo_1-x-y-z]O₂Wherein x =0.2, 0.1 < z < y < 0.8;

s2, lithiation and solid solution: calcining the mixture precursor obtained in the step S1, and uniformly grinding the calcined product to obtain the lithium-rich manganese-based positive electrode material;

s3, selenizing and doping: uniformly mixing the lithium-rich manganese-based positive electrode material obtained in the step S2 with selenium powder to obtain a uniform mixed material, and selenizing the uniform mixed material to obtain a selenized lithium-rich manganese-based positive electrode material;

s4, selenylation post-treatment: and (4) dispersing the lithium-rich manganese selenide-based positive electrode material obtained in the step (S3) in a carbon disulfide solution for washing, filtering, washing with alcohol, and drying to obtain the selenium-doped lithium-rich manganese-based positive electrode material.

4. The method of claim 3, wherein in step S1, the precursor of the transition metal oxide is at least one of carbonate, hydroxide and acetate; and/or the lithium source is at least one of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, lithium acetate and lithium nitrate.

5. The method of claim 3, wherein in step S1, the mass excess coefficient of the lithium source is 3% -10%.

6. The method for preparing the selenium-doped lithium-rich manganese-based positive electrode material according to claim 3, wherein the step S2 comprises calcining in an oxidizing atmosphere in two stages, wherein the first stage calcination is performed at 500-700 ℃ for 5-10 h, and the second stage calcination is performed at 800-900 ℃ for 10-15 h.

7. The method for preparing the selenium-doped lithium-rich manganese-based positive electrode material according to claim 3, wherein selenization is performed in step S3 under an inert atmosphere, and the flow rate of gas is 5-10 mL/min.

8. The method for preparing the selenium-doped lithium-rich manganese-based positive electrode material according to claim 3, wherein in the step S3, the selenization temperature is 500-900 ℃, and the temperature rise rate is 1-5 ℃/min.

9. The positive pole piece is characterized by comprising the selenium-doped lithium-rich manganese-based positive pole material in the claim 1 or 2 or the lithium-rich manganese-based positive pole material prepared by the preparation method in any one of the claims 3 to 7.

10. A battery comprising the positive electrode sheet according to claim 9.