Method for preparing sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule thermal method and obtained positive electrode material

Abstract

The invention discloses a method for one-step preparation of a sodium-nitrogen-sulfur doped cobalt-free lithium-rich layered positive electrode material based on a Joule thermal method and the obtained positive electrode material, and belongs to the technical field of battery materials. Sodium saccharin containing three elements of NaNS is introduced through a one-step method, the modified lithium-rich layered material with excellent cycle performance is obtained through a Joule heat method, the 0.1 C discharge specific capacity of the prepared material is about 296.1 mAh / g, the 100-time cycle capacity retention rate under the 1C multiplying power is higher than 97%, and the electrical performance is remarkably improved. Therefore, the cobalt-free lithium-rich layered material with three doped atoms can be obtained in one step in the material preparation process, meanwhile, the material can be prepared in dozens of seconds by utilizing a Joule thermal method, and the preparation method is simple and convenient and facilitates industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on a Joule heat method, and the obtained positive electrode material. Background Art

[0002] With the development of the low-altitude economy, drones and low-altitude electric aircraft will have an increasing demand for high energy density and long-endurance power batteries. Secondary batteries mainly include lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium-ion batteries and sodium-ion batteries. Among them, lithium-ion batteries have been widely used in 3C electronic products, new energy vehicles and large-scale energy storage fields due to their high energy density and long cycle performance. However, the current commercial lithium-ion batteries are mainly lithium cobalt oxide, ternary materials and lithium iron phosphate. The energy density of the above lithium-ion batteries is far from meeting the endurance requirements of drones and electric aircraft in the low-altitude economy. Therefore, the development of lithium-ion batteries with high energy density and long cycle performance has become a consensus in the field.

[0003] According to Faraday's law, the specific discharge capacity of lithium ions is proportional to the number of lithium ions that can migrate in the positive electrode material. Among the many lithium ion positive electrode materials, lithium-rich layered materials have the largest number of lithium ions, so they have a high specific discharge capacity (>250mAh·g -1 ). At the same time, the voltage range of lithium-rich layered materials is 2.0-4.8V (vs Li + / Li), according to the energy density calculation company, the energy density of lithium-ion batteries composed of lithium-rich layered materials as positive electrodes and lithium metal as responsible components is as high as 900Wh / kg. Therefore, lithium-rich layered materials can meet the needs of low-altitude economy for high-energy-density power batteries.

[0004] Although lithium-rich layered materials have high energy density, the rapid decay of voltage and capacity seriously restricts their industrial application. The research results show that in the first charging process, the Li-O-Li structure in the material crystal structure is used to maintain the charge balance of the system, and the oxygen ions are oxidized to oxygen and escape from the crystal structure. At the same time, the Mn 4+ Migration to lithium vacancies causes the crystal structure to transform from layered to spinel. Therefore, the content of Li-O-Li configuration in lithium-rich layered materials directly affects the electrochemical stability.

[0005] Element doping has a significant effect on improving the crystal structure and electrochemical stability of lithium-rich layered materials. Traditional doping elements include single doping and double doping, and only a few literature reports on multi-element doping. Chinese patent application CN202311418791.5 discloses a lithium-rich manganese-based positive electrode material modified by anion and cation co-doping and a preparation method. Ammonium fluoride and sodium dodecylbenzene sulfonate are used to coat the surface of the lithium-rich layered material, and then low-temperature calcination is used to achieve F / S / Na doping. The above preparation method requires the introduction of different raw materials, which are achieved through coating and sintering. It has the disadvantages of complex preparation process and long sintering time. At the same time, this process affects the electrochemical properties of the material to a certain extent. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered material based on a Joule heat method in one step. Na / N / S can be introduced into the cobalt-free lithium-rich layered material by introducing a single chemical. At the same time, the material can be prepared in tens of seconds using the Joule heat method. The prepared positive electrode material can improve the electrochemical performance of the battery. The preparation method is simple and convenient for industrial application.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0008] A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method comprises the following steps:

[0009] (1) dissolving a soluble nickel source and a soluble manganese source in a solvent to form a solution A;

[0010] (2) dissolving a soluble carbonate in an aqueous solution to prepare a precipitant solution B;

[0011] (3) quickly pouring solution B into solution A to form a suspension, sealing the suspension and placing it in a reaction vessel for hydrothermal reaction, filtering, washing and drying after the reaction to obtain product 1;

[0012] (4) placing product 1, saccharin sodium and lithium salt in an agate mortar and mixing evenly;

[0013] (5) placing the mixture in a Joule heat reactor, setting the sintering temperature and heating rate, and obtaining a sodium, nitrogen, and sulfur-doped cobalt-free lithium-rich layered positive electrode material.

[0014] Furthermore, the solvent in step (1) is a mixed solution of water and ethanol, the volume ratio of ethanol to water is 4:1, the soluble manganese source is MnSO4·H2O, the soluble nickel source is NiSO4·6H2O, the molar ratio thereof is 3:1, and the molar concentration of solution A is 0.1-0.5 mol / L.

[0015] Furthermore, the soluble carbonate in step (2) is one or more of ammonium carbonate, sodium carbonate, and potassium carbonate, and the molar concentration of the precipitant B is 0.5-1 mol / L. The precipitant is a soluble carbonate.

[0016] Furthermore, the molar ratio of the precipitant to the metal salt in step (3) is (1-3):1; the hydrothermal reaction temperature in step (3) is 140-210°C, and the reaction time is 6-15h.

[0017] Furthermore, in step (4), the molar ratio of the transition metal element, the lithium element and saccharin sodium is 1:(1.312-1.475):(0.025-0.1875).

[0018] Furthermore, the lithium salt in step (4) is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium oxide, and the molecular formula of sodium saccharin is: C7H4NNaO3S·2H2O.

[0019] Furthermore, the lithium salt in step (4) is one or more of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate.

[0020] Furthermore, in step (5), the sintering temperature is 800-1400°C, the sintering time is 10-40s, the heating rate is 200-500°C / s, and after the reaction is completed, a sodium, nitrogen and sulfur-doped cobalt-free lithium-rich layered positive electrode material is obtained, and the sintering atmosphere is air, nitrogen or a mixture of the two.

[0021] Furthermore, the sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered cathode material was prepared with the formula: Li 1.2- x Na x Mn 0.6 Ni 0.2 O 2-2x N x S x ,0 <x<0.15。

[0022] All raw materials of the present invention are commercially available, and the Joule heat reactor used can be a commercially available device.

[0023] Beneficial effects:

[0024] In the present invention, saccharin sodium contains three elements, Na\N\S. By adding this chemical reagent in the preparation process of cobalt-free lithium-rich layered materials, sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered materials can be obtained in one step. The sodium ions replace lithium ions, which can reduce the number of Li-O-Li configurations in the lithium-rich layered materials, and can play a role in supporting the crystal structure when lithium ions are released during the charging process; since nitrogen ions and sulfur ions have larger ionic radius and smaller electronegativity than oxygen ions, partial nitrogen ions and sulfur ions replace oxygen ions, which can reduce the degree of oxygen ion oxidation and oxygen release, thereby improving the crystal stability and electrochemical cycle performance of lithium-rich layered materials. Compared with step-by-step doping, one-step doping is more uniform in element doping, better in effect, and the electrochemical performance of the resulting material is more stable.

[0025] The use of Joule heating method can shorten the sintering time and improve the process efficiency, but more importantly, the experimental temperature can be quickly raised and lowered within a few seconds. The sintering process can form lattice defects on the surface of the material, which is beneficial to improve the stability of the material's crystal structure.

[0026] In summary, the sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered material prepared by the one-step Joule heat method in the present invention has a 0.1C discharge specific capacity of about 296.1 mAh / g, and a 100-cycle capacity retention rate at a 1C rate of more than 97%, and the electrical performance is significantly improved. Therefore, the present invention can obtain three types of cobalt-free lithium-rich layered materials doped with atoms in one step during the material preparation process, and the material can be prepared in tens of seconds using the Joule heat method. The preparation method is simple and convenient for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the XRD pattern of Example 2 of the present invention;

[0028] Figure 2 is an EDS-mapping diagram of Example 2 of the present invention;

[0029] Figure 3 This is the charge and discharge curve of the material in Example 2 of the present invention at a rate of 0.1C;

[0030] Figure 4 The graph is a cycle performance diagram of the positive electrode materials of all embodiments and comparative examples of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with specific embodiments, but is not limited thereto.

[0032] Example 1

[0033] A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method comprises the following steps:

[0034] Step 1. According to the transition metal ion Mn:Ni molar ratio of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.0483g of ammonium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above suspension in a reactor and seal it with stirring for hydrothermal reaction, the hydrothermal reaction temperature is 140℃, and the reaction time is 6h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0035] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0g), according to the molar ratio of transition metal element, lithium element and sodium saccharin 1:1.475:0.025, weigh 1.312g lithium acetate and 0.0531g sodium saccharin, use an agate mortar to mix the above substances evenly, place the mixture in a Joule heat reactor, and under the protection of nitrogen and air mixed gas, heat it to 800℃ at a heating rate of 200℃ / s and keep it for 40s. After the reaction is completed, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.18 Na 0.02 Mn 0.6 Ni 0.2 O 1.96 N 0.02 S 0.02 .

[0036] Example 2

[0037] A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method comprises the following steps:

[0038] Step 1. According to the transition metal ion Mn:Ni molar ratio of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.156g of sodium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above suspension in a reactor and seal it with stirring for hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the reaction time is 12h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0039] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0g), according to the molar ratio of transition metal element, lithium element and sodium saccharin 1:1.4375:0.0625, weigh 0.4837g lithium carbonate and 0.1376g sodium saccharin, use an agate mortar to mix the above substances evenly, place the mixture in a Joule heat reactor, and under the protection of nitrogen and air mixture, heat it to 950℃ at a heating rate of 200℃ / s and keep it for 20s. After the reaction is completed, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.15 Na 0.05 Mn 0.6 Ni 0.2 O 1.9 N 0.05 S 0.05 .

[0040] Figure 1 This is the XRD spectrum of the cobalt-free lithium-rich layered material prepared in Example 2. It can be seen from the figure that the material is consistent with the α-NaFeO2 structure, and the 21-23o peak is the characteristic peak of the LiMn6 superlattice, indicating that the introduction of Na\N\S does not change the crystal structure of the lithium-rich layered material, and no impurity phase exists. Figure 3 The charge and discharge curves of the prepared material at a rate of 0.1C have two platforms. The charge capacity is 326.0mAh / g, the discharge capacity is 296.1mAh / g, and the discharge curve has a platform at 2.75V. This platform is due to the introduction of sodium into the lithium site to produce a spinel phase. The first coulomb efficiency of the material can reach 90.78%, which also shows that the introduction of Na\N\S improves the first coulomb efficiency of lithium-rich materials. Figure 2This is the ESD-mapping spectrum of the positive electrode material obtained in Example 2. It can be seen from the figure that there is a small amount of Na / N / S in the modified material, indicating that the lithium-rich layered material is successfully introduced through this method.

[0041] Example 3

[0042] A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method comprises the following steps:

[0043] Step 1. According to the transition metal ion Mn:Ni molar ratio of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.1563g of sodium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above suspension in a reactor and seal it with stirring for hydrothermal reaction, the hydrothermal reaction temperature is 180℃, and the reaction time is 12h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0044] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0g), according to the molar ratio of transition metal element, lithium element and sodium saccharin 1:1.375:0.125, weigh 0.826g lithium nitrate and 0.266g sodium saccharin, use an agate mortar to mix the above substances evenly, place the mixture in a Joule heat reactor, and under the protection of nitrogen and air mixed gas, heat it to 950℃ at a heating rate of 300℃ / s and keep it for 20s. After the reaction is completed, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.1 Na 0.1 Mn 0.6 Ni 0.2 O 1.8 N 0.1 S 0.1 .

[0045] Example 4

[0046] A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method comprises the following steps:

[0047] Step 1. According to the transition metal ion Mn:Ni molar ratio of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.508g of potassium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above mixture in a sealed reactor, and place it in a stirred hydrothermal reactor to react at 210℃ for 15h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0048] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0g), according to the molar ratio of transition metal element, lithium element and sodium saccharin 1:1.312:0.1875, weigh 0.480g lithium hydroxide and 0.398g sodium saccharin, use an agate mortar to mix the above substances evenly, place the mixture in a Joule heat reactor, and under the protection of nitrogen and air mixed gas, heat it to 1400℃ at a heating rate of 500℃ / s and keep it for 10s. After the reaction is completed, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.05 Na 0.15 Mn 0.6 Ni 0.2 O 1.7 N 0.15 S 0.15 .

[0049] Comparative Example 1

[0050] A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method comprises the following steps:

[0051] Step 1. According to the transition metal ion Mn:Ni molar ratio of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.445g of sodium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above suspension in a reactor and seal it with stirring for hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the time is 12h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn0.75 Ni 0.25 CO3.

[0052] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0g), weigh 0.045g sodium acetate, 0.0174g sulfur powder, 0.0327g urea, and 0.4837g lithium carbonate, use an agate mortar to mix the above raw materials evenly, place the mixture in a Joule heat reactor, and heat it to 950℃ at a heating rate of 200℃ / s in a nitrogen and air atmosphere for 20s. After the reaction is completed, take out the sample and grind it to obtain a cobalt-free lithium-rich layered material Li 1.15 Na 0.05 Mn 0.6 Ni 0.2 O 1.9 N 0.05 S 0.05 .

[0053] In this comparative example, except for changing the doping method of N / S / Na elements, that is, not using saccharin sodium, sodium acetate, sulfur powder, and urea are used as doping raw materials for doping modification, and the remaining raw materials and preparation methods are the same as those in Example 2.

[0054] Comparative Example 2

[0055] A method for preparing a sodium, nitrogen and sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step, comprising the following steps:

[0056] Step 1. According to the transition metal ion Mn:Ni molar ratio of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.1563g of sodium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above suspension in a reactor and seal it with stirring for hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the reaction time is 12h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0057] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25CO3 (1.0 g), according to the molar ratio of transition metal element, lithium element and sodium saccharin 1:1.4375:0.0625, weigh 0.4837 g lithium carbonate and 0.1376 g sodium saccharin, use an agate mortar to mix the above substances evenly, place the mixture in a muffle furnace, and keep it at 900 ° C for 15 hours. After the calcination is completed, wait for the temperature to drop to 100 ° C, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.15 Na 0.05 Mn 0.6 Ni 0.2 O 1.9 N 0.05 S 0.05 .

[0058] Compared with Example 2, this comparative example adopts the same raw materials and preparation method as Example 2 except that the final sintering method is changed, that is, the conventional sintering method of lithium-rich layered materials is adopted.

[0059] Comparative Example 3

[0060] A cobalt-free lithium-rich layered material and a method thereof based on the Joule method, comprising the following steps:

[0061] Step 1. According to the molar ratio of transition metal ions Mn:Ni of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.445g of sodium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Pour solution B quickly into solution A to form a suspension, place the above mixture in a sealed reactor and stir for hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the reaction time is 12h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0062] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0 g), according to the molar ratio of transition metal elements to lithium elements of 1:1.5, weigh 0.505 g Li2CO3, use an agate mortar to mix the two evenly, place the mixture in a Joule heat reactor, and heat it to 950°C in an air atmosphere at a heating rate of 200°C / s and keep it for 20s. After the reaction is completed, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.2 Mn 0.6 Ni 0.2 O2.

[0063] In this comparative example, the lithium-rich layered material is prepared without using sodium saccharin for modification.

[0064] Comparative Example 4

[0065] A cobalt-free lithium-rich layered material and a method thereof, comprising the following steps:

[0066] Step 1. According to the molar ratio of transition metal ions Mn:Ni of 0.75:0.25 (calculated based on the total amount of transition metal ions of 9mmol), weigh 1.135g of MnSO4·H2O and 0.588g of NiSO4·6H2O respectively, add the above raw materials to 50mL of solvent to prepare solution A, the solvent is a mixed solution of water and ethanol, wherein the volume ratio of ethanol to water is 40mL:10mL. Weigh 1.445g of sodium carbonate and dissolve it in 25mL of distilled water to prepare solution B. Quickly pour solution B into solution A to form a suspension, place the above suspension in a reactor and seal it with stirring for hydrothermal reaction, the hydrothermal reaction temperature is 200℃, and the reaction time is 12h. After the reaction is completed, wait until the temperature drops to room temperature, filter the product, wash it with water, and dry it to obtain the product 1Mn 0.75 Ni 0.25 CO3.

[0067] Step 2. Weigh a certain amount of product 1Mn 0.75 Ni 0.25 CO3 (1.0 g), according to the ratio of transition metal elements to lithium elements of 1:1.5, weigh 0.505 g Li2CO3, use an agate mortar to mix the two evenly, place the mixture in a muffle furnace, and keep it at 900 ° C for 15 h. After the calcination, wait for the temperature to drop to 100 ° C, take out the sample and grind it to obtain the cobalt-free lithium-rich layered material Li 1.2 Mn 0.6 Ni 0.2 O2.

[0068] In this comparative example, on the one hand, no sodium saccharin was added for modification, and at the same time, a common heating method was used to prepare the cobalt-free lithium-rich layered material.

[0069] Performance Testing

[0070] The samples obtained in the examples and comparative examples were used as active materials. The active materials, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) were mixed uniformly at a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added to form a slurry and coated on an aluminum sheet. The slurry was vacuum dried at 120°C for 10 hours and then vacuum dried at 120°C for 12 hours to be used as a working electrode. The metal lithium sheet was used as the negative electrode, and 1 mol·L -1A mixed solution of LiPF6 ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DEC) (volume ratio of 1:1:1) was used as the electrolyte, and Celgard 2500 was used as the diaphragm to make a CR2032 button cell in an argon-filled glove box. The battery charge and discharge cycle performance was tested in the 2.0-4.8V electrochemical window using the BlueHe battery test system.

[0071] The test results are as follows:

[0072] Table 1 Comparison of electrochemical performance of button cells assembled

[0073] Material Discharge capacity (0.1C) Cycle performance (1C, 100 cycles) Cycle performance (1C, 200 cycles) Example 1 290.6mAh / g 94.77％ 87.65％ Example 2 296.1mAh / g 97.67％ 91.35％ Example 3 292.4mAh / g 94.92％ 88.48％ Example 4 286.2mAh / g 93.02％ 87.60％ Comparative Example 1 260.3mAh / g 82.04％ 73.71％ Comparative Example 2 267.9mAh / g 84.38％ 73.81％ Comparative Example 3 260.3mAh / g 80.04％ 72.13％ Comparative Example 4 252.1mAh / g 78.23％ 69.05％

[0074] It can be seen from the experimental data in Table 1 that the discharge specific capacity and cycle performance of Examples 1-4, which add sodium saccharin and use the Joule heat method, are better than those of Comparative Examples 1-2 in which the doping method and heating method are changed, and are also better than Comparative Examples 3-4. Among them, the electrochemical performance of Example 2 is the best, indicating that the addition of sodium saccharin to the lithium-rich material can improve the electrochemical performance of the battery. In addition, the discharge specific capacity and cycle performance of Examples 1-4 are better than those of Comparative Example 1. Compared with Comparative Example 1 in which the three atoms of sodium, nitrogen and sulfur are introduced into the lithium-rich material through three substances, it is shown that Examples 1-4 in which the three atoms of sodium, nitrogen and sulfur are added in one step can significantly improve the electrochemical performance of the battery. Comparative Example 2, in which the heating method is changed, adopts the long-term heating method of the muffle furnace commonly used in the preparation of layered materials. This conventional heating method is not conducive to the formation of lattice defects on the surface of the positive electrode material, and cannot effectively improve the crystal structure stability of the material. It can be seen that the one-step doping + Joule heat rapid heating method of the present invention is crucial to the formation of high-performance positive electrode materials, and the lack of one will weaken the effect.

[0075] It should be noted that the above embodiments are only partial embodiments of the preferred methods of implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material in one step based on Joule heat method, characterized in that: The following steps are involved: (1) dissolving a soluble nickel source and a soluble manganese source in a solvent to form a solution A; (2) dissolving a soluble carbonate in an aqueous solution to prepare a precipitant solution B; (3) quickly pouring solution B into solution A to form a suspension, sealing the suspension and placing it in a reaction vessel for hydrothermal reaction, filtering, washing and drying after the reaction to obtain product 1; (4) placing product 1, saccharin sodium and lithium salt in an agate mortar and mixing evenly; (5) placing the mixture in a Joule heat reactor, setting the sintering temperature and heating rate, and obtaining a sodium, nitrogen, and sulfur-doped cobalt-free lithium-rich layered positive electrode material.

2. The method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material based on Joule heat method in one step according to claim 1, characterized in that: The solvent in step (1) is a mixed solution of water and ethanol, the volume ratio of ethanol to water is 4:1; the soluble manganese source is MnSO4·H2O, the soluble nickel source is NiSO4·6H2O, the molar ratio of the soluble nickel source to the soluble manganese source is 3:1, and the molar concentration of solution A is 0.1-0.5 mol / L.

3. The method for preparing sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered positive electrode materials based on Joule heat method in one step according to claim 1, characterized in that: The soluble carbonate in step (2) is one or more of ammonium carbonate, sodium carbonate and potassium carbonate, and the molar concentration of the precipitant B is 0.5-1 mol / L.

4. The method for preparing a sodium-nitrogen-sulfur-doped cobalt-free lithium-rich layered positive electrode material based on Joule heat method in one step according to claim 1, characterized in that: The molar ratio of the precipitant to the metal salt in step (3) is (1-3):1; the hydrothermal reaction temperature in step (3) is 140-210°C, and the reaction time is 6-15h.

5. The method for preparing sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered positive electrode materials in one step based on Joule heat method according to claim 1, characterized in that: Step (4) The molar ratio of transition metal element, lithium element and saccharin sodium is 1:(1.312-1.475): (0.025-0.1875)。 6. The method for preparing sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered positive electrode materials based on Joule heat method in one step according to claim 1, characterized in that: The lithium salt in step (4) is one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate and lithium oxide. The molecular formula of sodium saccharin is: C7H4NNaO3S·2H2O.

7. The method for preparing sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered positive electrode materials based on Joule heat method in one step according to claim 1, characterized in that: In step (5), the sintering temperature is 800-1400° C., the sintering time is 10-40s, and the heating rate is 200-500° C. / s. After the reaction is completed, a sodium, nitrogen, and sulfur-doped cobalt-free lithium-rich layered positive electrode material is obtained. The sintering atmosphere is air, nitrogen, or a mixture of the two.

8. The method for preparing sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered materials in one step based on Joule heat method according to claim 1, characterized in that: The molecular formula of the product sodium, nitrogen and sulfur doped cobalt-free lithium-rich layered cathode material is: Li 1.2- x Na x Mn 0.6 Ni 0.2 O 2-2x N x S x ,0 <x<0.15。 9. A positive electrode material prepared according to any one of claims 1 to 8.

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