A lithium-rich manganese-based cathode material and its preparation method

Abstract

This invention discloses a lithium-rich manganese-based cathode material in which phosphorus is uniformly distributed. The preparation method includes: segmented pre-sintering of a manganese-based binary carbonate precursor under an oxygen-containing atmosphere to obtain a manganese-based binary oxide; impregnation of the manganese-based binary oxide in a phosphate solution, followed by mixing with a lithium source and an additive containing M1, and primary sintering under an oxygen-containing atmosphere; washing the primary sintering product with water, adding an additive containing M2, and then performing a secondary sintering under an oxygen-containing atmosphere to obtain the lithium-rich manganese-based cathode material. In this invention, phosphorus is uniformly distributed in the lithium-rich manganese-based cathode material, which improves the material's energy density while maintaining its performance. This invention directly performs segmented low-temperature pre-sintering of the manganese-based binary carbonate precursor, which can pre-remove carbon dioxide from the material, improve the internal structure of the material, reduce the porosity, and improve the material's cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, and in particular to a lithium carbonate-rich manganese-based cathode material and its preparation method. Background Technology

[0002] High energy density and low cost are the two main directions for the development of lithium-ion batteries. In terms of energy density, the mainstream ternary cathode materials are prone to structural decomposition and phase transitions under high voltage. Therefore, increasing the nickel content is the general development direction to improve the specific capacity and energy density of the materials. However, high-nickel ternary cathode materials are sensitive to moisture, have poor storage performance under normal conditions, and the problem of residual lithium on the surface makes the materials prone to deterioration. At the same time, gas generation and interfacial side reactions are prone to occur during the electrochemical reaction, which may lead to a deterioration in the electrochemical performance of the materials and cause safety issues. In terms of cost, due to the persistently high prices of nickel and cobalt resources, the cost of traditional lithium cobalt oxide and ternary cathode materials is continuously increasing. Lithium-rich manganese-based cathode materials, due to their unique composite layered phase structure, can not only be used in high-voltage systems, but also have a discharge specific capacity far exceeding that of ternary and lithium iron phosphate cathode materials. They are considered an ideal choice for achieving high energy density next-generation lithium battery cathode materials. At the same time, lithium-rich manganese-based cathode materials have a high lithium excess coefficient, but lower nickel content and higher manganese content in the composition, resulting in lower material costs than current medium-nickel ternary materials, giving them a significant cost advantage.

[0003] Based on the type of cathode material precursor, lithium-rich manganese-based cathode materials can currently be classified into various systems such as carbonate, hydroxide, and oxalate. Among them, carbonate-based lithium-rich manganese-based materials have relatively higher specific capacity and energy density. The synthesis method of carbonate-based lithium-rich manganese-based cathode materials usually involves mixing manganese-based carbonate precursors with lithium sources and then sintering them to obtain lithium-rich manganese-based cathode materials. However, due to the characteristics of the precursors and the high lithium excess coefficient, the reaction is violent during the mixing and sintering of lithium sources and precursors, resulting in severe carbon dioxide gas production. This leads to a large number of internal pores in the sintered cathode material and unstable performance. Stepwise sintering and the introduction of additives are effective means to reduce gas production and improve material performance. For example, patent document CN102820463A discloses that manganese-based precursors are mixed with lithium sources and pre-sintered at 400-600℃ in one step, and then calcined at 800-950℃ to obtain lithium-rich manganese-based cathode materials. Another example is patent document CN111082041A, which discloses that manganese-based precursors are mixed with a portion of lithium sources and pre-sintered at 280-650℃ in one step, and then calcined with the remaining lithium sources and additives at 650-900℃ to obtain lithium-rich manganese-based cathode materials. However, current stepwise sintering technologies mix manganese-based precursors with lithium sources for stepwise sintering, which cannot separate the gas generation from the thermal decomposition of the precursors from the gas generation from the reaction with the lithium sources. During the pre-sintering stage, the precursors will still generate gas rapidly inside, causing the cathode material to form an internal porous structure, which is not conducive to the material's energy density. On the other hand, the material needs to be mixed with lithium salts multiple times during stepwise sintering, and the tempering treatment after sintering usually requires dry mixing with additives again, making the mixing process cumbersome. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a lithium-rich manganese-based cathode material and its preparation method.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A lithium-rich manganese-based cathode material is disclosed, wherein the secondary particles of the lithium-rich manganese-based cathode material are spherical, and phosphorus is uniformly distributed within the spherical lithium-rich manganese-based cathode material. Viewed in its tangential section, in the circular region extending outward from the center of the cathode material particle to a distance of 1 / 3r (i.e., 0 ≤ L < 1 / 3r), the phosphorus content accounts for 8% to 14% of the phosphorus content in the tangential section; in the annular region extending outward from the center of the cathode material particle to a distance of 1 / 3r to 2 / 3r (i.e., 1 / 3r ≤ L < 2 / 3r), the phosphorus content is... The phosphorus content accounts for 30% to 36% of the phosphorus content in the tangential section; in the annular region of the cathode material particle from 2 / 3r to r distance outward from the center, i.e., the annular region of 2 / 3r≤L≤r, the phosphorus content accounts for 53% to 59% of the phosphorus content in the tangential section, where r is the radius of the tangential section of the cathode material particle, and L is the distance from the center of the tangential section of the cathode material particle. The tangential section of the lithium-rich manganese-based cathode material refers to the circular section passing through the center of the sphere after cutting the spherical cathode material particle.

[0006] Preferably, the lithium-rich manganese-based cathode material described above has the general chemical formula Li. 1+ x Ni a Mn b M1 c M2 d P e O 2+x Where 0.2≤x<0.6, 0<a<0.5, 0.5<b<0.98, 0<c≤0.02, 0<d≤0.02, 0≤e≤0.02, M1 is one or more of Zr, Ti, Nb, and Co, and M2 is one or more of Al, Co, and Nb, and M1 and M2 have different chemical elements; Further preferred values ​​are: 0.25≤x≤0.45, 0.3≤a≤0.4, 0.58≤b≤0.96, 0.001≤c≤0.01, 0.002≤d≤0.01, and 0.001≤e≤0.01.

[0007] As a general inventive concept, this invention also provides a method for preparing a lithium-rich manganese-based cathode material, comprising the following steps: (1) The manganese-based binary carbonate precursor was pre-sintered in a segmented manner under an oxygen-containing atmosphere to obtain manganese-based binary oxides; (2) The manganese-based binary oxide obtained in step (1) is added to a phosphate solution for impregnation treatment; (3) The impregnated manganese-based binary oxide, lithium source and M1 additive are mixed and sintered in an oxygen atmosphere to obtain a sintered product; wherein M1 is selected from one or more of Zr, Ti, Nb and Co. (4) The first sintering product obtained in step (3) is washed with water and mixed with additive containing M2. Then, it is sintered again under an oxygen atmosphere to obtain lithium-rich manganese-based cathode material. M2 is selected from one or more of Al, Co and Nb, and M1 and M2 have different chemical elements.

[0008] In the above preparation method, preferably, in step (2), the phosphate solution is one or more of diammonium hydrogen phosphate aqueous solution, diammonium dihydrogen phosphate aqueous solution, and lithium titanium aluminum phosphate aqueous solution; the phosphorus element in the phosphate solution accounts for 0.05~2% of the molar content of the manganese-based binary carbonate precursor, more preferably 0.01~1%.

[0009] In the above preparation method, preferably, in step (2), the immersion treatment time is 0.5~2h.

[0010] In the above-mentioned preparation method, preferably, in step (1), the segmented pre-sintering is divided into 2 to 5 segments, the pre-sintering temperature is 100 to 550°C, the temperature difference between each segment is 30 to 120°C and increases gradually, the pre-sintering time for each segment is 1 to 6 hours, and the heating rate is 0.1 to 5°C / min. More preferably, the segmented pre-sintering is divided into 3 to 4 segments, the pre-sintering temperature is 200 to 450°C, the temperature difference between each segment is 40 to 110°C and increases gradually, the pre-sintering time for each segment is 2 to 4 hours, and the heating rate is 0.25 to 3°C / min.

[0011] In the above preparation method, preferably, in step (3), the primary sintering temperature is 750~1050℃, the primary sintering time is 3~12h, and the heating rate is 0.1~5℃ / min. More preferably, the primary sintering temperature is 850~1000℃, the primary sintering time is 4~10h, and the heating rate is 0.25~3℃ / min; even more preferably, the primary sintering temperature is 900~950℃, the primary sintering time is 5~8h, and the heating rate is 1~2.5℃ / min.

[0012] In the above preparation method, preferably, in step (3), the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium fluoride, lithium sulfate and lithium nitrate, and the M1-containing additive is one or more of zirconium oxide, titanium oxide, niobium pentoxide and cobalt hydroxide.

[0013] In the above preparation method, preferably, the molar ratio of the lithium source to the manganese-based binary oxide is (1.2~1.6):1, more preferably (1.25~1.45):1; the metal element in the M1-containing additive accounts for 0.05~2% of the molar content of the primary sintering product, more preferably 0.2~1%.

[0014] In the above preparation method, preferably, in step (4), the M2-containing additive is one or more of aluminum sulfate, cobalt sulfate, cobalt nitrate, niobium oxalate, and ammonium niobium oxalate; the metal element in the M2-containing additive accounts for 0.05~2% of the molar content of the lithium-rich manganese-based cathode material.

[0015] The preferred preparation method described above includes the following specific operation process in step (4): adding the first sintering product to water and mixing to form a mixed slurry; then adding the M2 additive to the mixed slurry and stirring to mix; washing with water and then filtering to remove water and drying; and sintering.

[0016] In the above preparation method, preferably, the secondary sintering temperature is 250~700℃, more preferably 300~650℃, and most preferably 350~600℃; the secondary sintering time is 1~7h, more preferably 2~5h; and the heating rate is preferably 0.1~5℃ / min, more preferably 0.25~4℃ / min, and most preferably 0.5~3.5℃ / min.

[0017] In the above preparation method, preferably, the oxygen-containing atmosphere is an air atmosphere or a pure oxygen atmosphere.

[0018] Compared with the prior art, the advantages of the present invention are as follows: (1) In the lithium-rich manganese-based cathode material of the present invention, phosphorus element is uniformly distributed in the spherical lithium-rich manganese-based cathode material, which can improve the material cycle performance and increase the material energy density.

[0019] (2) The present invention directly performs segmented low-temperature pre-sintering treatment on manganese-based carbonate precursor, which can remove carbon dioxide in the material in advance, improve the internal structure of the material, reduce the porosity of the material, and facilitate the utilization of the material's energy density.

[0020] (3) In this invention, the manganese-based carbonate precursor is directly subjected to segmented low-temperature pre-sintering treatment, so that the precursor after removing carbonate is no longer sensitive to alkaline solution environment. While maintaining the original nickel and manganese content, the phosphate can be more uniformly introduced into the material surface and interior through impregnation doping. From the tangential section of the material, the content distribution ratio of phosphate in different regions inside the material is closer to the ratio of the region area. When phosphate is doped into the crystal structure of the material, it can promote the crystal structure transformation of the surface of lithium-rich manganese-based material, maintain the structure of close packing of lattice oxygen, and improve the material cycle performance while also increasing the material energy density.

[0021] (4) In the preparation process of lithium-rich manganese-based cathode material, the present invention introduces metal elements with small ionic radii. During the sintering process, metal elements with small ionic radii can enter the nickel-manganese-lithium layered crystal structure to form doped crystals. The stronger metal-O bond energy makes the doped crystal have a better stabilizing effect on lattice oxygen. Furthermore, the addition of metal elements with small ionic radii and phosphate ions has a synergistic effect on the formation of stable lithium-rich manganese crystal structure during the sintering process. It further fixes the bulk lattice oxygen, inhibits the gas generation caused by oxygen desorption, promotes the growth of primary particles of lithium-rich manganese-based cathode material, reduces the internal pore shrinkage of the material, and further reduces the porosity of the material.

[0022] (5) In the water washing stage of preparing lithium-rich manganese-based cathode materials, the present invention performs wet coating and mixing treatment, which is more conducive to the more uniform entry of metal-containing additives into the surface and interior of the material compared with the traditional dry mixing method, and reduces the additional mixing process. Attached Figure Description

[0023] Figure 1 These are cross-sectional SEM images and phosphorus intensity distribution images of the lithium-rich manganese-based cathode materials prepared in Comparative Example 2 and Example 3 of this invention.

[0024] Figure 2 This is a cross-sectional SEM image of the lithium-rich manganese-based cathode material prepared in Comparative Example 1 of this invention.

[0025] Figure 3 This is a cross-sectional SEM image of the lithium-rich manganese-based cathode material prepared in Example 1 of this invention.

[0026] Figure 4 This is a cross-sectional SEM image of the lithium-rich manganese-based cathode material prepared in Example 5 of this invention.

[0027] Figure 5 This refers to the cycle capacity retention performance of the lithium-rich manganese-based cathode materials prepared in Examples 1, 3 and Comparative Example 1 of this invention at a rate of 0.33C.

[0028] Figure 6 This refers to the retention performance of the lithium-rich manganese-based cathode material prepared in Examples 1, 3 and Comparative Example 1 of this invention at a 0.33C rate during cycling. Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all reagents and raw materials used in this invention are commercially available products or products that can be prepared by known methods.

[0032] The phosphorus distribution ratio of the cathode material in the following embodiments and comparative examples was obtained through the following characterization and calculation methods: The cathode material particles were cross-sectionally cut using an argon ion beam to obtain a smooth-surfaced sample. Electron microscopy was used to obtain electron micrographs of the argon-polished cross-sectional morphology of individual particles and the phosphorus content at each point in the particle. The radius of the tangential cross-section of the cathode material particle was denoted as r, and L was the distance from the center of the tangential cross-section of the cathode material particle. The circular region extending outward from the center of the tangential cross-section of the cathode material particle to a distance of 1 / 3r (i.e., 0 ≤ L < 1 / 3r) was denoted as R1. The annular region extending from 1 / 3r to 2 / 3r (i.e., 1 / 3r ≤ L < 2 / 3r) was denoted as R1. The annular region is denoted as R2, and the annular region from 2 / 3r to r, i.e., the annular region where 2 / 3r≤L≤r, is denoted as R3. The area ratio of the three regions is calculated mathematically as R1:R2:R3=11:33:56. The proportion of phosphorus content in regions R1, R2, and R3 to the total phosphorus content in the entire tangential cross-section region (R1+R2+R3) is calculated and denoted as the phosphorus distribution ratio of R1, R2, and R3. The tangential cross-section of lithium-rich manganese-based cathode material refers to the circular cross-section through the center of the sphere after cutting the spherical particles of the cathode material. The viewing angle of the image is perpendicular to the circular cross-section, and there is no difference between the circular area shown in the image and the actual area due to oblique shooting.

[0033] The average porosity of the cathode material in the following examples and comparative examples was obtained through the following characterization and calculation methods: the cathode material particles were cross-sectionally cut using an argon ion beam to obtain a sample with a smooth surface. The argon ion polished cross-sectional morphology of a single particle was obtained by field emission scanning electron microscopy, and the internal porosity of the particles was observed and calculated. The total area of ​​pores in the particles / the cross-sectional area of ​​the particles was recorded as the porosity of a single particle. The average porosity of a single particle in ten different regions was statistically analyzed and recorded as the average porosity.

[0034] Electrochemical performance testing: The cathode material was prepared into a lithium-ion power battery and its performance was tested. The charge-discharge cycle settings were as follows: (1) The pre-activation charge-discharge cutoff voltage was 2.0-4.65V and the charge-discharge current was 0.1C (1C=230mA / g); (2) The first charge-discharge cutoff voltage was 2.5-4.4V and the charge-discharge current was 0.1C (1C=230mA / g); (3) The second to fifth charge-discharge cutoff voltage was 2.5-4.4V and the charge-discharge current was 0.33C (1C=230mA / g).

[0035] Example 1: A method for preparing a lithium-rich manganese-based cathode material according to the present invention includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was sintered in three stages under an air atmosphere. First, it was heated to 330°C at a heating rate of 1°C / min and held for 2 hours. Then, it was heated to 410°C at a heating rate of 1°C / min and held for 2 hours. Finally, it was heated to 475°C at a heating rate of 1°C / min and held for 3 hours to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0036] (2) Place the oxide obtained in step (1) into a stirred tank, and weigh the deionized aqueous solution of lithium titanium aluminum phosphate according to the element mass of 0.8% of P molar content in the first sintering product and pour it into the tank. Stir for 1 hour, separate the impregnated material by vacuum filtration, and finally place the impregnated material in a vacuum oven to dry it to obtain the pretreated precursor raw material.

[0037] (3) Weigh lithium carbonate according to the molar ratio of the pretreated precursor raw material obtained in step (2) to lithium of 1:1.35. At the same time, weigh cobalt hydroxide according to the element mass of 0.5% of Co molar amount in the primary sintering product. Then, place the oxide, lithium carbonate and cobalt hydroxide in a high-speed mixer for mixing. After mixing, heat to 905℃ under an oxygen atmosphere at a heating rate of 1.67℃ / min for primary sintering. Hold the primary sintering temperature for 8 hours to obtain the primary sintering product Li. 1.35 Ni 0.3 3Mn 0.66 Co 0.005 P 0.008 O 2.35 .

[0038] (4) The primary sintering product was placed in a stirred tank and deionized water was added and stirred to form a slurry. Aluminum sulfate was weighed according to the elemental mass of 0.63% Al molar content in the finished lithium-rich manganese-based cathode material, and added to the slurry. After stirring, deionized water was added for washing. The washed material was separated by vacuum filtration. Finally, the washed material was placed in a vacuum oven to dry, and the dried product was obtained. The dried product was placed in an air atmosphere and heated to 500℃ at a heating rate of 0.83℃ / min for secondary sintering. The temperature was held for 4 hours to obtain Li. 1.35 Ni 0.33 Mn 0.66 Co 0.005 P 0.008 Al 0.0063 O 2.35 Positive electrode material.

[0039] Example 2: A method for preparing a lithium-rich manganese-based cathode material according to the present invention includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was sintered in three stages under an air atmosphere. First, it was heated to 325°C at a heating rate of 1°C / min and held for 2 hours. Then, it was heated to 375°C at a heating rate of 1°C / min and held for 2 hours. Finally, it was heated to 440°C at a heating rate of 1°C / min and held for 3 hours to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0040] (2) Place the oxide obtained in step (1) into a stirred tank, and weigh the deionized aqueous solution of ammonium dihydrogen phosphate according to the element mass of 0.5% of P molar content in the first sintering product and pour it into the tank. Stir for 1 hour, separate the impregnated material by vacuum filtration, and finally place the impregnated material in a vacuum oven to dry it to obtain the pretreated precursor raw material.

[0041] (3) Weigh lithium carbonate in a molar ratio of 1:1.35 to the pretreated precursor obtained in step (2). Weigh cobalt hydroxide according to the element mass of 0.5% Co molar content in the primary sintering product and niobium pentoxide according to the element mass of 0.64% Nb molar content in the primary sintering product. Mix the oxides, lithium carbonate, cobalt hydroxide and niobium pentoxide in a high-speed mixer. After mixing, heat to 905℃ at a heating rate of 1.67℃ / min under an oxygen atmosphere and sinter for 8 hours to obtain the primary sintering product Li. 1.35 Ni 0.33 Mn 0.66 Co 0.005 Nb 0.0064 P 0.005 O 2.35 .

[0042] (4) Place the first sintering product in a stirred tank and pour in deionized water. Stir to form a slurry. Weigh aluminum sulfate according to the element mass of 0.63% Al molar content in the finished lithium-rich manganese-based cathode material, pour it into the slurry, continue stirring, and then pour in deionized water for washing. Vacuum filter to separate the washed material, and finally place the washed material in a vacuum oven to dry it to obtain a dried product. Place the dried product in an air atmosphere and heat it to 500℃ at a heating rate of 0.83℃ / min. Hold it at this temperature for 4 hours to obtain Li. 1.35 Ni 0.33 Mn 0.66 Co 0.005 Nb 0.0064 P 0.005 Al 0.0063 O 2.35 Positive electrode material.

[0043] Example 3: A method for preparing a lithium-rich manganese-based cathode material according to the present invention includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was sintered in an air atmosphere in four stages. First, it was heated to 260℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Then, it was heated to 310℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Next, it was heated to 375℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Finally, it was heated to 430℃ at a heating rate of 1.05℃ / min and held for 3.2 h to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0044] (2) Place the oxide obtained in step (1) in a stirred tank, and weigh the deionized aqueous solution of diammonium hydrogen phosphate according to the element mass containing 0.67% P molar amount in the first sintering product. Pour it into the tank and stir for 1 hour. Vacuum filter to separate the impregnated material. Finally, place the impregnated material in a vacuum oven to dry it to obtain the pretreated precursor raw material.

[0045] (3) Weigh lithium hydroxide at a molar ratio of 1:1.32 to the pretreated precursor obtained in step (2), and weigh niobium pentoxide according to the element mass of 0.32% Nb molar content in the primary sintering product. Place the pretreated precursor, lithium hydroxide, and niobium pentoxide in a high-speed mixer for mixing. After mixing, heat to 930°C at a heating rate of 1.67°C / min under an oxygen atmosphere and sinter at high temperature for 8 hours to obtain the primary sintering product Li. 1.32 Ni 0.33 Mn 0.66 Nb0.0032 P 0.0067 O 2.32 .

[0046] (4) Place the first sintering product in a stirred tank and pour in deionized water to form a slurry. Weigh aluminum sulfate according to the elemental mass of 1.25% Al molar content in the finished lithium-rich manganese-based cathode material and pour it into the slurry. Continue stirring and then pour in deionized water to wash. Vacuum filter to separate the washed material. Finally, place the washed material in a vacuum oven to dry and obtain the dried product. Place the dried product in an air atmosphere and heat it to 500℃ at a heating rate of 3℃ / min. Sinter at high temperature for 4 hours to obtain Li. 1.32 Ni 0.33 Mn 0.66 Nb 0.0032 Al 0.0125 P 0.0067 O 2.32 Positive electrode material.

[0047] Example 4: A method for preparing a lithium-rich manganese-based cathode material according to the present invention includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was sintered in four stages under an air atmosphere. First, it was heated to 210℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Then, it was heated to 280℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Next, it was heated to 380℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Finally, it was heated to 450℃ at a heating rate of 1.05℃ / min and held for 3.2 h to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0048] (2) Place the oxide obtained in step (1) into a stirred tank, and weigh out the deionized aqueous solution of diammonium hydrogen phosphate according to the element mass containing 0.3% P molar amount in the first sintering product and pour it into the tank. Stir for 1 hour, separate the impregnated material by vacuum filtration, and finally place the impregnated material in a vacuum oven to dry it to obtain the pretreated precursor raw material.

[0049] (3) Weigh lithium hydroxide at a molar ratio of 1:1.30 with the pretreated precursor raw material obtained in step (2), and weigh cobalt hydroxide according to the element mass containing 0.5% Co molar amount in the primary sintering product. Place the oxide, lithium hydroxide and cobalt hydroxide in a high-speed mixer for mixing. After mixing, heat to 930℃ in air at a heating rate of 1.5℃ / min and sinter for 8 hours to obtain the primary sintering product Li. 1.30 Ni 0.33 Mn0.66 Co 0.005 P 0.003 O 2.30 .

[0050] (4) Place the first sintering product in a stirred tank, pour in deionized water and stir to form a slurry. Weigh niobium oxalate according to the element mass of 0.32% Nb molar content in the finished lithium-rich manganese-based cathode material and pour it into the slurry. Continue stirring and then pour in deionized water to wash. Vacuum filter to separate the washed material. Finally, place the washed material in a vacuum oven to dry and obtain the dried product. Place the dried product in an air atmosphere and heat it to 500℃ at a heating rate of 3℃ / min. Hold it at this temperature for 4 hours to obtain Li. 1.30 Ni 0.33 Mn 0.66 Co 0.005 Nb 0.0032 P 0.003 O 2.30 Positive electrode material.

[0051] Example 5: A method for preparing a lithium-rich manganese-based cathode material according to the present invention includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was sintered in four stages under an air atmosphere. First, it was heated to 220℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Then, it was heated to 320℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Next, it was heated to 345℃ at a heating rate of 1.05℃ / min and held for 2.4 h. Finally, it was heated to 445℃ at a heating rate of 1.05℃ / min and held for 3.2 h to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0052] (2) Place the oxide obtained in step (1) into a stirred tank, and weigh the deionized aqueous solution of lithium titanium aluminum phosphate according to the element mass of 0.1% of P molar content in the first sintering product and pour it into the tank. Stir for 1 hour, separate the impregnated material by vacuum filtration, and finally place the impregnated material in a vacuum oven to dry it to obtain the pretreated precursor raw material.

[0053] (3) Weigh lithium carbonate at a molar ratio of 1:1.28 with the pretreated precursor raw material obtained in step (2), and weigh niobium pentoxide according to the element mass of 0.32% Nb molar content in the primary sintering product. Place the oxide, lithium carbonate and niobium pentoxide in a high-speed mixer for mixing. After mixing, heat to 930℃ at a heating rate of 1.5℃ / min under air atmosphere, and sinter for 8 hours to obtain the primary sintering product Li. 1.28 Ni0.33 Mn 0.66 Nb 0.0032 Ti 0.00 1Al 0.001 P 0.001 O 2.28 .

[0054] (4) Place the sintering product obtained in step (3) into a stirred tank and pour in deionized water to stir and form a slurry. Weigh aluminum sulfate according to the element mass of Al molar content in the finished cathode material of 0.53% and pour it into the slurry. Continue stirring and then pour in deionized water to wash. Vacuum filter to separate the washed material. Finally, place the washed material in a vacuum oven to dry and obtain a dried product. Place the dried product in an air atmosphere and heat it to 500℃ at a heating rate of 0.83℃ / min. Hold it at this temperature for 4 hours to obtain Li. 1.28 Ni 0.33 Mn 0.66 Nb 0.0032 Ti 0.001 Al 0.0063 P 0.001 O 2.28 Positive electrode material.

[0055] Comparative Example 1: The preparation method of the lithium-rich manganese-based cathode material in this comparative example includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was heated to 500℃ in air at a heating rate of 1℃ / min and sintered at that temperature for 6 hours to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0056] (2) Weigh lithium carbonate in a molar ratio of 1:1.35 to the oxide obtained in step (1), and weigh cobalt hydroxide according to the element mass of 0.5% Co molar content in the primary sintering product. Place the oxide, lithium carbonate and cobalt hydroxide in a high-speed mixer for mixing. After mixing, heat to 905℃ in an oxygen atmosphere at a heating rate of 1.67℃ / min, and sinter for 8 hours to obtain the primary sintering product Li. 1.35 Ni 0.33 Mn 0.66 Co 0.005 O 2.35 .

[0057] (3) The Li sintering product from the first sintering 1.35 Ni 0.33 Mn 0.66 Co 0.005 O 2.35The mixture was placed in a stirred tank and deionized water was added to form a slurry. Aluminum sulfate was weighed according to the elemental mass of 0.63% Al molar content in the finished lithium-rich manganese-based cathode material and added to the slurry. After continued stirring, deionized water was added for washing. The washed material was separated by vacuum filtration and finally dried in a vacuum oven to obtain a dried product. The dried product was placed in an air atmosphere and heated to 500℃ at a heating rate of 0.83℃ / min, and sintered at that temperature for 4 hours to obtain Li. 1.35 Ni 0.33 Mn 0.66 Co 0.005 Al 0.0063 O 2.35 Positive electrode material.

[0058] Comparative Example 2: The preparation method of the lithium-rich manganese-based cathode material in this comparative example includes the following steps: (1) Ni, a manganese-based binary carbonate precursor 0.34 Mn 0.66 CO3 was heated to 500℃ in air at a heating rate of 1℃ / min and sintered at that temperature for 6 hours to obtain an oxide with the general formula 0.34(NiMn)O3·0.16Mn2O3.

[0059] (2) Weigh lithium carbonate in a ratio of 1:1.35 with the oxide obtained in step (1), and weigh cobalt hydroxide according to the element mass of 0.5% Co molar content in the first sintering product. Place the weighed raw materials in a high-speed mixer for mixing. After mixing, heat to 905℃ at a heating rate of 1.67℃ / min under an oxygen atmosphere, and sinter for 8 hours to obtain Li 1.35 Ni 0.33 Mn 0.66 Co 0.005 O 2.35 .

[0060] (3) Li 1.35 Ni 0.33 Mn 0.66 Co 0.005 Nb 0.0032 O 2.35 The mixture was placed in a stirred tank and deionized water was added to form a slurry. Aluminum sulfate was weighed according to the elemental mass of 0.63% Al molar content in the finished cathode material, and diammonium hydrogen phosphate was weighed according to the elemental mass of 0.67% P molar content in the finished lithium-rich manganese-based cathode material. These were added to the slurry, and after continued stirring, deionized water was added for washing. The washed materials were separated by vacuum filtration. Finally, the washed materials were dried in a vacuum oven to obtain the dried product. The dried product was heated to 500℃ in air at a heating rate of 0.83℃ / min and sintered at that temperature for 4 hours to obtain Li. 1.35 Ni0.33 Mn 0.66 Co 0.005 Al 0.0063 P 0.0067 O 2.35 Positive electrode material.

[0061] The cross-sectional SEM images and phosphorus intensity distribution of the lithium-rich manganese-based cathode materials prepared in Comparative Examples 2 and 3 are shown below. Figure 1 As shown in the figure, the phosphorus element distribution in region R3 of Comparative Example 2 is uneven, with element enrichment in some areas near the surface of the cathode material particles. In contrast, the cathode material particles in Example 3, which were treated by impregnation, show no phosphorus element enrichment in regions R1, R2, and R3, and the elements are evenly distributed.

[0062] The cross-sectional SEM image of the lithium-rich manganese-based cathode material prepared in Comparative Example 1 is shown below. Figure 2 As shown, the cross-sectional SEM image of the lithium-rich manganese-based cathode material prepared in Example 1 is as follows. Figure 3 As shown, the cross-sectional SEM image of the lithium-rich manganese-based cathode material prepared in Example 5 is as follows. Figure 4 As shown. From Figure 2 , Figure 3 , Figure 4 The comparison shows that after the precursors in Examples 1 and 5 were subjected to segmented pre-sintering and phosphate impregnation treatment, the internal cracks of the particles were reduced and the porosity was decreased.

[0063] The cycle capacity retention and cycle energy density retention performance of the lithium-rich manganese-based cathode materials prepared in Comparative Example 1, Example 1, and Example 5 at a rate of 0.33C are shown in [reference needed]. Figure 5 and Figure 6 As shown. From Figure 5 and Figure 6 It can be seen that after the precursor segment pre-sintering and phosphate impregnation treatment, the capacity and energy density retention rates of Examples 1 and 5 are improved, and the energy density is also improved to a certain extent.

[0064] The electrochemical performance of the lithium-rich manganese-based cathode materials prepared in Examples 1-5 and Comparative Examples 1-2 is shown in Table 1 below.

[0065] Table 1. Electrochemical performance of lithium-rich manganese-based cathode materials in each embodiment and comparative example.

[0066] As shown in Table 1, in Examples 1-5, after segmented pre-sintering of the precursor and phosphate impregnation treatment, the particle porosity decreased, the cycle retention rate increased, and the energy density also improved to a certain extent. Furthermore, the phosphorus distribution ratio in regions R1, R2, and R3 of each example was basically consistent with the area ratio of each region, indicating that the phosphorus element was uniformly distributed inside the particles after phosphate impregnation treatment.

Claims

1. A lithium-rich manganese-based cathode material, characterized in that, The secondary particles of the lithium-rich manganese-based cathode material are spherical, and phosphorus is uniformly distributed in the spherical lithium-rich manganese-based cathode material. From its tangential cross-section, in the circular region of the cathode material particle extending outward from the center to 1 / 3r, the phosphorus content accounts for 8% to 14% of the phosphorus content in the tangential cross-section; in the annular region of the cathode material particle extending outward from 1 / 3r to 2 / 3r, the phosphorus content accounts for 30% to 36% of the phosphorus content in the tangential cross-section; in the annular region of the cathode material particle extending outward from 2 / 3r to r, the phosphorus content accounts for 53% to 59% of the phosphorus content in the tangential cross-section, where r is the radius of the tangential cross-section of the cathode material particle.

2. The lithium-rich manganese-based cathode material as described in claim 1, characterized in that, The general chemical formula of the lithium-rich manganese-based cathode material is Li. 1+x Ni a Mn b M1 c M2 d P e O 2+x Wherein, 0.2≤x<0.6, 0<a<0.5, 0.5<b<0.98, 0<c≤0.02, 0<d≤0.02, 0≤e≤0.02, M1 is selected from one or more of Zr, Ti, Nb, and Co, and M2 is selected from one or more of Al, Co, and Nb, and M1 and M2 have different chemical elements.

3. A method for preparing a lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: (1) The manganese-based binary carbonate precursor was pre-sintered in a segmented manner under an oxygen-containing atmosphere to obtain manganese-based binary oxides; (2) The manganese-based binary oxide obtained in step (1) is added to a phosphate solution for impregnation treatment; (3) The impregnated manganese-based binary oxide, lithium source and M1 additive are mixed and sintered in an oxygen atmosphere to obtain a sintered product; wherein M1 is selected from one or more of Zr, Ti, Nb and Co. (4) The first sintering product obtained in step (3) is washed with water and mixed with additive containing M2. Then, it is sintered again under an oxygen atmosphere to obtain lithium-rich manganese-based cathode material. M2 is selected from one or more of Al, Co and Nb, and M1 and M2 have different chemical elements.

4. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (2), the phosphate solution is one or more of diammonium hydrogen phosphate aqueous solution, diammonium dihydrogen phosphate aqueous solution, and lithium titanium aluminum phosphate aqueous solution; the phosphorus element in the phosphate solution accounts for 0.05~2% of the molar amount of the manganese-based binary carbonate precursor.

5. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (2), the immersion treatment time is 0.5~2h.

6. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (1), the segmented pre-sintering is divided into 2 to 5 sintering segments, the pre-sintering temperature is 100 to 550°C, the temperature difference between each pre-sintering segment is 30 to 120°C and increases gradually, the pre-sintering time of each segment is 1 to 6 hours, and the heating rate is 0.1 to 5°C / min.

7. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (3), the temperature of the first sintering is 750~1050℃ and the time of the first sintering is 3~12h.

8. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (3), the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium fluoride, lithium sulfate and lithium nitrate, and the M1-containing additive is one or more of zirconium oxide, titanium oxide, niobium pentoxide and cobalt hydroxide; the molar ratio of the lithium source to the manganese-based binary oxide is (1.2~1.6):1, and the metal element in the M1-containing additive accounts for 0.05~2% of the molar amount of the primary sintering product.

9. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (4), the M2-containing additive is one or more of aluminum sulfate, cobalt sulfate, cobalt nitrate, niobium oxalate, and ammonium niobium oxalate; the metal element in the M2-containing additive accounts for 0.05~2% of the molar amount of the lithium-rich manganese-based cathode material.

10. The method for preparing the lithium-rich manganese-based cathode material as described in claim 3, characterized in that, In step (4), the temperature of the secondary sintering is 250~700℃ and the time of the secondary sintering is 1~7h.

Images