CN114597368A - Surface sulfur-doped lithium-rich manganese-based layered material with lithium sulfate protective layer - Google Patents

Surface sulfur-doped lithium-rich manganese-based layered material with lithium sulfate protective layer Download PDF

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CN114597368A
CN114597368A CN202210253380.4A CN202210253380A CN114597368A CN 114597368 A CN114597368 A CN 114597368A CN 202210253380 A CN202210253380 A CN 202210253380A CN 114597368 A CN114597368 A CN 114597368A
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lithium
rich manganese
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sulfur
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CN114597368B (en
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陈来
苏岳锋
赵佳雨
李宁
董锦洋
郝佳男
李文博
卢赟
曹端云
黄擎
吴锋
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Beijing Institute of Technology BIT
Chongqing Innovation Center of Beijing University of Technology
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Chongqing Innovation Center of Beijing University of Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a lithium-rich manganese-based layered material with a sulfur-doped surface and a lithium sulfate protective layer, and belongs to the technical field of lithium ion batteries. The material takes a lithium-rich manganese-based layered material as a matrix, sulfur is doped on the surface of the matrix and lithium sulfate is coated on the surface of the matrix, a sulfur simple substance and the lithium-rich manganese-based layered material are mixed and then calcined in an oxygen atmosphere, and by controlling the oxygen flow, the heating rate, the calcination temperature and the calcination time, on one hand, sulfur enters the matrix and is doped on the surface layer of the matrix, on the other hand, sulfur also reacts with oxygen to generate sulfur dioxide, and the sulfur dioxide reacts with residual alkali on the surface of the lithium-rich manganese-based layered material to generate a lithium sulfate coating in situ. The material has good electrochemical performance.

Description

Surface sulfur-doped lithium-rich manganese-based layered material with lithium sulfate protective layer
Technical Field
The invention relates to a lithium-rich manganese-based layered material with a sulfur-doped surface and a lithium sulfate protective layer, and belongs to the technical field of lithium ion batteries.
Background
In a lithium ion battery, a lithium-rich manganese-based layered material is obtained due to the ultrahigh specific discharge capacity (more than 250mAh/g), and becomes a research hotspot of a positive electrode material. However, since the lithium-rich manganese-based layered material has a severe irreversible oxygen release, which may cause a structural transformation and a discharge plateau decay, in practical use, the material needs to be modified to reduce oxygen loss and phase transition.
At present, element doping is carried out in a more common modification method, and S element is a common dopant due to the similar characteristic of O element. For example, in the method for preparing a sulfur anion doped lithium-rich cathode material disclosed in chinese patent application CN106229502A, lithium sulfide is added at the stage of precursor lithium mixing, and sulfur doping is achieved by subsequent high temperature of 900 ℃. However, in the method, lithium sulfide is easy to absorb water in the air to generate water, which explains the highly toxic hydrogen sulfide gas, and harms the environment and the human health, and the melting point of lithium sulfide is above 900 ℃, so that the doping temperature is too high, and the energy cost is increased; meanwhile, sulfur in the final material is bulk-doped, so that the suppression of surface side reactions is less, and partial capacity loss is brought along by the replacement of the bulk doping with respect to oxygen. Further, as disclosed in chinese patent application CN111697208A, in the modified lithium ion battery positive electrode material and the preparation method thereof, sulfur vapor is formed by heating elemental sulfur or a sulfur-containing material, and the material is treated. The concentration of sulfur vapor is high, the process operation is too complex, and the requirement on equipment is high; the capacity and stability of the final material still remains to be further improved.
Disclosure of Invention
In view of the above, the present invention provides a lithium-rich manganese-based layered material with a surface sulfur-doped and lithium sulfate protective layer.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a lithium-rich manganese-based layered material with a sulfur-doped surface and a lithium sulfate protective layer is prepared by the following method, wherein the method comprises the following steps:
(1) grinding and uniformly dispersing elemental sulfur powder in absolute ethyl alcohol, then adding a lithium-rich manganese-based layered material, ultrasonically dispersing uniformly, heating, stirring and evaporating to dryness, and drying in vacuum to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.01: 1-0.1: 1;
(2) and calcining the intermediate product at 200-300 ℃ for 4-8 h at the temperature of 6-12 ℃/min under the oxygen atmosphere in the tubular furnace at the oxygen flow rate of 60-200 mL/min to obtain the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer.
In the step (1):
preferably, the lithium-rich manganese-based layered material is Li1.2Mn0.6Ni0.2O2。
Preferably, the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.03: 1-0.06: 1.
Preferably, the vacuum drying temperature is 60-120 ℃, and the drying time is 10-12 h.
In the step (2):
preferably, the heating rate during calcination is 8 ℃/min to 10 ℃/min.
Preferably, the oxygen flow rate is 80mL/min to 150 mL/min.
Advantageous effects
The invention provides a lithium-rich manganese-based layered material with a sulfur-doped surface and a lithium sulfate protective layer, wherein the lithium sulfate protective layer on the surface in the material can improve the stability of an electrode material, can relieve the side reaction of an electrode and electrolyte, improve the stability of an interface, and can increase the ion transmission of the interface, thereby being beneficial to improving the rate capability; the S doped on the surface is beneficial to the lithium ion extraction, the multiplying power performance and the discharge capacity are improved, and meanwhile, the introduction of the S can also increase O2The released energy barrier can relieve irreversible oxygen release in circulation and improve the circulation stability; the S atoms doped into the lattice can also serve to anchor the cladding layer.
The invention provides a lithium-rich manganese-based layered material with a surface sulfur-doped and lithium sulfate protective layer, which is prepared by mixing a sulfur simple substance with the lithium-rich manganese-based layered material, calcining the mixture in an oxygen atmosphere, and controlling oxygen flow, heating rate, calcining temperature and time, wherein on one hand, sulfur enters a matrix and is doped on the surface layer of the matrix, on the other hand, sulfur also reacts with oxygen to generate sulfur dioxide, and the sulfur dioxide reacts with residual alkali on the surface of the lithium-rich manganese-based layered material to generate a lithium sulfate coating layer in situ; the proper oxygen flow rate and higher temperature rise rate can reduce sulfur loss, and the method only needs trace amount of sulfur to greatly improve the electrochemical performance of the material.
Drawings
FIG. 1 is an X-ray diffraction (XRD) pattern of the materials described in examples 1-4.
FIG. 2 is a Scanning Electron Microscope (SEM) image of the material described in example 1.
Fig. 3 is a SEM image of the material described in example 2.
Fig. 4 is an SEM image of the material described in example 3.
FIG. 5 is an SEM image of the material of example 4.
Fig. 6 is a graph of discharge capacity of the assembled batteries of example 1 and comparative example 1 at 30C and 1C for 50 cycles.
Fig. 7 is an alternating current impedance (EIS) graph of the assembled batteries of example 2 and comparative example 1.
Fig. 8 is a first cycle capacity differential curve at 0.1C rate for the assembled cells of example 3 and comparative example 1.
FIG. 9 is an X-ray photoelectron spectroscopy (XPS) plot of the material described in example 4.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
In the following examples:
(1) XRD test: the instrument used was Rigaku Ultima IV-185, Japan.
(2) SEM test, energy spectroscopy (EDS): the instrument used was FEI Quanta, the netherlands.
(3) XPS test: the instrument used was ULVAC-PHI, Japan.
(4) Inductively coupled plasma emission spectroscopy (ICP-OES) test: the instrument used was AgilentICPOES730, usa.
(5) Assembling the battery: mixing the active material prepared in the embodiment or the comparative example with acetylene black and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1, adding N-methyl pyrrolidone (NMP) to grind into slurry, coating the slurry on an aluminum foil by a scraper, drying and cutting into pieces to prepare a positive plate; then assembling the cell into a CR2025 button type half cell in an argon glove box (water is less than 0.01ppm, oxygen is less than 0.01ppm), wherein the positive electrode is the positive plate, the counter electrode is a lithium plate, the diaphragm is Celgard 2500, the electrolyte is dimethyl carbonate, diethyl carbonate and ethyl carbonate which are in a volume ratio of 1:1:1 as solvents, and 1mol/L LiPF6Is a solution prepared from solute.
(6) And (3) testing the battery performance: a LAND CT 2001A tester was used, purchased from blue-ray electronics, Inc., Wuhan; the charge and discharge cycle was continued for 2 weeks at 30 ℃ in a voltage interval of 2.0V to 4.8V with 0.1C (1C: 250mA/g), and for 50 weeks with 1C in a voltage interval of 2.0V to 4.6V.
(7) And (3) testing alternating current impedance: an electrochemical workstation model CHI604D was used, purchased from chenhua instruments ltd.
Example 1
(1) Grinding and dispersing elemental sulfur powder in absolute ethyl alcohol uniformly, and then adding a lithium-rich manganese-based layered material Li1.2Mn0.6Ni0.2O2After ultrasonic dispersion is uniform, heating to 70 ℃, stirring and evaporating to dryness, and vacuum drying at 80 ℃ for 12 hours to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.03: 1;
(2) and under the oxygen atmosphere in the tubular furnace, the oxygen flow rate is 80mL/min, the intermediate product is calcined at 270 ℃ for 8h, and the heating rate is 10 ℃/min, so that the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer is obtained.
The XRD test result of the material is shown in figure 1, and the characteristic peak position and LiNiO of the material2And Li2MnO3The characteristic peaks are consistent, no obvious miscellaneous peak is generated, and the lamellar structure is better.
The SEM test result of the material is shown in figure 2, the average particle size of the material is 100 nm-200 nm, and particles are attached to the surface of the material.
The EDS result of the material shows that S elements are distributed on the surface layer of the material. The ICP-OES results of the material showed that the content of the S element in the material was 0.0478 wt%.
XPS test results of the material show that the peak between 160eV and 164eV has a bond between S and TM (TM: transition metal), and the peak between 167eV and 170eV has SO4 2-(ii) a In combination with the EDS results, it was found that the surface layer of the material was doped with sulfur and coated with Li2SO4。
As shown in fig. 6, when the material is used as an active material, the first specific capacity of the assembled battery is 225.4mAh/g during cycling at 30 ℃ and 1C rate, the capacity after 50 cycles is 203mAh/g, and the capacity retention rate is 90.06%.
Example 2
(1) Grinding and dispersing elemental sulfur powder in absolute ethyl alcohol uniformly, and then adding a lithium-rich manganese-based layered material Li1.2Mn0.6Ni0.2O2After ultrasonic dispersion, heating to 70 ℃, stirring and evaporating to dryness, and vacuum drying at 80 DEG CDrying for 12h to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.03: 1;
(2) and under the oxygen atmosphere in the tubular furnace, the oxygen flow rate is 100mL/min, the intermediate product is calcined at 270 ℃ for 6h, and the heating rate is 7 ℃/min, so that the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer is obtained.
The XRD test result of the material is shown in figure 1, and the characteristic peak position and LiNiO of the material2And Li2MnO3The characteristic peaks are consistent, no obvious miscellaneous peak is generated, and the lamellar structure is better.
The SEM test result of the material is shown in figure 3, the average particle size of the material is 100 nm-200 nm, and particles are attached to the surface of the material.
The EDS result of the material shows that S elements are distributed on the surface layer of the material. The ICP-OES results of the material showed that the content of the S element in the material was 0.0382 wt%.
XPS test results of the material show that the peak between 160eV and 164eV has a bond between S and TM (TM is a transition metal), and the peak between 167eV and 170eV has SO4 2-(ii) a In combination with the EDS results, it was found that the surface layer of the material was doped with sulfur and coated with Li2SO4。
The material is used as an active material, the first cycle specific capacity of the assembled battery is 221.9mAh/g in the 1C multiplying power cycle process at 30 ℃, the capacity is 200.4mAh/g after 50 cycles, and the capacity retention rate is 90.31%.
EIS results for the assembled cell are shown in fig. 7, and the material in this example has a lower interfacial charge transfer resistance compared to comparative example 1; the material of the embodiment is favorable for interface ion transfer, thereby reducing impedance.
Example 3
(1) Grinding and dispersing elemental sulfur powder in absolute ethyl alcohol uniformly, and then adding a lithium-rich manganese-based layered material Li1.2Mn0.6Ni0.2O2After ultrasonic dispersion is uniform, heating to 70 ℃, stirring and evaporating to dryness, and vacuum drying at 80 ℃ for 12 hours to obtain an intermediate product(ii) a Wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.03: 1;
(2) and calcining the intermediate product at 270 ℃ for 8h at the temperature rise rate of 10 ℃/min under the oxygen atmosphere in the tubular furnace at the oxygen flow rate of 80mL/min to obtain the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer.
The XRD test result of the material is shown in figure 1, and the characteristic peak position and LiNiO of the material2And Li2MnO3The characteristic peaks are consistent, no obvious miscellaneous peak is generated, and the lamellar structure is better.
The SEM test result of the material is shown in figure 4, the average particle size of the material is 100 nm-150 nm, and particles are attached to the surface of the material.
The EDS result of the material shows that S elements are distributed on the surface layer of the material. The ICP-OES result of the material shows that the content of the S element in the material is 0.0412 wt%.
XPS test results of the material show that the peak between 160eV and 164eV has a bond between S and TM (TM: transition metal), and the peak between 167eV and 170eV has SO4 2-(ii) a In combination with the EDS results, it was found that the surface layer of the material was doped with sulfur and coated with Li2SO4。
The material is used as an active material, the first cycle specific capacity of the assembled battery is 212.4mAh/g in the 1C multiplying power cycle process at 30 ℃, the capacity is 206.7mAh/g after 50 cycles, and the capacity retention rate is 97.31%.
The first cycle capacity differential curve at 0.1C rate of the assembled cell is shown in fig. 8, and the oxidation reduction peak intensity of the material described in this example has a significant effect compared to comparative example 1. In the dQ/dV diagram, the substantially uniform shape of the curves indicates that the materials undergo the same redox reaction. The strong oxidation peak with a voltage of about 4.5V is considered to be caused by the irreversible release of oxygen anions, and it can be seen from the figure that the peak position of the treated material is slightly biased to the high voltage direction, and the peak intensity is obviously reduced, which indicates that the material described in this example has a significant alleviation phenomenon on the oxygen release, increases the reaction potential and reduces the reaction amount, and is beneficial to the cycle stability of the material.
Example 4
(1) Grinding and dispersing elemental sulfur powder in absolute ethyl alcohol uniformly, and then adding a lithium-rich manganese-based layered material Li1.2Mn0.6Ni0.2O2After ultrasonic dispersion is uniform, heating to 70 ℃, stirring and evaporating to dryness, and vacuum drying at 80 ℃ for 12 hours to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.06: 1;
(2) and under the oxygen atmosphere in the tubular furnace, the oxygen flow rate is 100mL/min, the intermediate product is calcined at 270 ℃ for 6h, and the heating rate is 7 ℃/min, so that the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer is obtained.
The XRD test result of the material is shown in figure 1, and the characteristic peak position and LiNiO of the material2And Li2MnO3The characteristic peaks are consistent, no obvious miscellaneous peak is generated, and the lamellar structure is better.
The SEM test result of the material is shown in fig. 5, the average particle size of the material is 100nm to 200nm, and particles are attached to the surface of the material.
The EDS result of the material shows that S elements are distributed on the surface layer of the material. The ICP-OES result of the material shows that the content of the S element in the material is 0.0747 wt%.
The XPS test result of the material is shown in FIG. 9, the peak at 160eV-164eV has a bond between S and TM (TM: transition metal), and the peak at 167eV-170eV has SO4 2-(ii) a In combination with the EDS results, it was found that the surface layer of the material was doped with sulfur and coated with Li2SO4。
The material is used as an active material, and the first cycle specific capacity of the assembled battery is 227.7mAh/g, the capacity is 205.4mAh/g after 50 cycles, and the capacity retention rate is 90.22% in the 1C rate cycle process at 30 ℃.
Comparative example 1
Weighing lithium acetate, manganese acetate and nickel acetate according to a molar ratio of 1.2:0.6:0.2, and adding distilled water for dissolving to obtain a mixed salt solution; then, citric acid solution is added dropwise into the mixed salt solution, and then ammonia water is usedAdjusting the pH value to 7.8 to obtain a mixed solution; heating to gel at 80 ℃, vacuum drying at 80 ℃ for 40h, placing in a muffle furnace under oxygen atmosphere, firstly heating to 500 ℃ for calcining for 6h, then heating to 800 ℃ for calcining for 14h to obtain the Li rich in lithium manganese-based layered material1.2Mn0.6Ni0.2O2(ii) a Wherein the molar ratio of the citric acid to the transition metal ions is 1: 1; the heating rate during calcination is 5 ℃/min.
XRD test results of the material show that the characteristic peak position of the material and LiNiO2And Li2MnO3The characteristic peaks are consistent, no obvious miscellaneous peak is generated, and the lamellar structure is better.
As shown in fig. 6, the first specific discharge capacity of the assembled battery at 30 ℃ and 0.1C was 283.9mAh/g, using the material as an active material. In the 1C multiplying power circulation process, the first-cycle specific capacity is 175.4mAh/g, the capacity is 126.2mAh/g after 50-cycle circulation, and the retention rate is 71.95%.
Comparative example 2
(1) Grinding and dispersing elemental sulfur powder in absolute ethyl alcohol uniformly, and then adding a lithium-rich manganese-based layered material Li1.2Mn0.6Ni0.2O2After ultrasonic dispersion is uniform, heating to 70 ℃, stirring and evaporating to dryness, and vacuum drying at 80 ℃ for 12 hours to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.2: 1;
(2) and under the oxygen atmosphere in the tubular furnace, the oxygen flow rate is 100mL/min, the intermediate product is calcined at 270 ℃ for 6h, and the heating rate is 7 ℃/min, so that the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer is obtained.
By using the material as an active material, the first cycle specific capacity of the assembled battery is 152.3mAh/g in the 1C multiplying power cycle process at 30 ℃, the capacity is only remained 41.5mAh/g after 50 cycles, and the capacity retention rate is 27.25%.
Comparative example 3
(1) Grinding and dispersing elemental sulfur powder in absolute ethyl alcohol uniformly, and then adding a lithium-rich manganese-based layered material Li1.2Mn0.6Ni0.2O2After ultrasonic dispersion is uniform, heating toStirring and evaporating at 70 ℃ to dryness, and vacuum drying at 80 ℃ for 12h to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.06: 1;
(2) and calcining the intermediate product at 270 ℃ for 6h at the temperature rise rate of 3 ℃/min under the oxygen atmosphere in the tubular furnace at the oxygen flow rate of 300mL/min to obtain the lithium-rich manganese-based layered material with the surface sulfur-doped lithium sulfate protective layer.
The ICP-OES result of the material shows that the content of the S element in the material is less than 0.01 wt%.
The material is used as an active material, and the first cycle specific capacity of the assembled battery is 176.8mAh/g in the 1C multiplying power cycle process at 30 ℃, the capacity is 119.7mAh/g after 50 cycles, and the retention rate is 67.70%.
In summary, the invention includes but is not limited to the above embodiments, and any equivalent replacement or local modification made under the spirit and principle of the invention should be considered as being within the protection scope of the invention.

Claims (7)

1. A surface sulfur-doped lithium-rich manganese-based layered material with a lithium sulfate protective layer is characterized in that: the material is prepared by the following method, and the method comprises the following steps:
(1) grinding and uniformly dispersing elemental sulfur powder in absolute ethyl alcohol, then adding a lithium-rich manganese-based layered material, ultrasonically dispersing uniformly, heating, stirring and evaporating to dryness, and drying in vacuum to obtain an intermediate product; wherein the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.01: 1-0.1: 1;
(2) and under the oxygen atmosphere in the tubular furnace, the flow rate of oxygen is 60 mL/min-200 mL/min, the intermediate product is calcined for 4 h-8 h at the temperature of 200-300 ℃, and the heating rate is 6 ℃/min-12 ℃/min, so that the lithium-rich manganese-based layered material with the surface sulfur doped and the lithium sulfate protective layer is obtained.
2. The lithium-rich manganese-based layered material with surface sulfur doping and lithium sulfate protective layer as claimed in claim 1, wherein: in the step (1), the lithium-rich manganese-based layered material is Li1.2Mn0.6Ni0.2O2。
3. The lithium-rich manganese-based layered material with surface sulfur doping and lithium sulfate protective layer as claimed in claim 1, wherein: in the step (1), the molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.03: 1-0.06: 1.
4. The lithium-rich manganese-based layered material with surface sulfur doping and lithium sulfate protective layer as claimed in claim 1, wherein: in the step (1), the vacuum drying temperature is 60-120 ℃, and the drying time is 10-12 h.
5. The lithium-rich manganese-based layered material with surface sulfur doping and lithium sulfate protective layer as claimed in claim 1, wherein: in the step (2), the temperature rise rate during calcination is 8-10 ℃/min.
6. The lithium-rich manganese-based layered material with sulfur-doped surface and a protective layer of lithium sulfate according to claim 1, wherein: in the step (2), the flow rate of the oxygen is 80mL/min to 150 mL/min.
7. The lithium-rich manganese-based layered material with surface sulfur doping and lithium sulfate protective layer as claimed in claim 1, wherein: in the step (1): the lithium-rich manganese-based layered material is Li1.2Mn0.6Ni0.2O2(ii) a The molar ratio of the elemental sulfur powder to the lithium-rich manganese-based positive electrode material is 0.03: 1-0.06: 1; the vacuum drying temperature is 60-120 ℃, and the drying time is 10-12 h; in the step (2): the heating rate is 8-10 ℃/min during calcination; the flow rate of the oxygen is 80mL/min to 150 mL/min.
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