Cobalt-free lithium-rich manganese-based positive electrode material and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a cobalt-free lithium-rich manganese-based positive electrode material, a preparation method thereof, a positive plate and a lithium ion battery. The preparation method comprises the following steps: mixing a lithium source, a nickel-manganese precursor and a dopant, and performing first sintering to obtain an REE-doped intermediate material; doping elements in the dopant at least comprise Ce and La elements, and further comprise at least one of Sc, Y and Dy elements; and mixing the intermediate material with a fluorine-containing organic matter, and carrying out second sintering to obtain the cobalt-free lithium-rich manganese-based positive electrode material with the F / C coating layer, the fluorine-containing organic matter comprises at least one of polytetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene oxide and hexafluoropropylene. According to the method, the first-circle charge-discharge efficiency and charge-discharge specific capacity of the cobalt-free lithium-rich manganese-based positive electrode material can be improved, the voltage attenuation is remarkably reduced, and the cycle performance is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a cobalt-free lithium-rich manganese-based positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are particularly important in modern social power equipment and have an important strategic position in the fields of electric vehicles, portable electronic devices, energy storage, etc. With the increasing demand of the downstream battery industry for power batteries, the demand for the next generation of high-voltage high-capacity batteries is urgent. As a core component of the next generation of lithium ion batteries, the performance of lithium-rich manganese-based positive electrode active material has a direct impact on the performance of the next generation of lithium ion batteries.

[0003] Among them, the cobalt-free lithium-rich manganese-based positive electrode material is a branch of lithium-rich manganese-based positive electrode material. Since it does not use cobalt element, it has the advantages of environmental friendliness, non-toxicity and low price. However, the most important disadvantage of the current cobalt-free lithium-rich manganese-based positive electrode material is that the voltage decay is serious with the increase of charge and discharge cycles, thereby affecting the capacity of the material.

[0004] Therefore, it is necessary to provide a cobalt-free lithium-rich manganese-based positive electrode material with high capacity, stable structure and low voltage decay.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a preparation method of a cobalt-free lithium-rich manganese-based positive electrode material, which can improve the first circle charge and discharge efficiency and specific capacity of the cobalt-free lithium-rich manganese-based positive electrode material, and significantly reduce the voltage decay and improve the cycle performance. Specifically, the F element in the cobalt-free lithium-rich manganese-based positive electrode material can improve the stability of the lattice oxygen, so that the cycle stability is improved, the voltage decay in the cycle process is improved, and the particle structure is stabilized by the F / C coating layer. In addition, the f-orbital electrons of the doped elements can interact with the electrons and orbits of Ni, Mn and O to produce a more stable electronic structure, so that the overall electronic structure of the material is more stable, and the voltage decay is reduced; at the same time, the oxygen vacancies produced by the solid solution (such as CeLaO 2-x Solid solution) formed by the dopant can be used as an anchor point for F element during coating, and the concentration of oxygen vacancies in the solid solution can be further changed by the incorporation of doped elements, and the change in the concentration of oxygen vacancies will in turn change the coating effect of F / C, thereby improving the electrochemical performance of the battery.

[0007] The second object of the present application is to provide a cobalt-free lithium-rich manganese-based positive electrode material with high first-cycle specific discharge capacity, slow voltage attenuation, high capacity retention rate and good cycle performance.

[0008] The third object of the present application is to provide a positive electrode sheet, and a battery prepared using the positive electrode sheet can significantly reduce voltage attenuation after cycle charging and discharging.

[0009] The fourth object of the present application is to provide a lithium ion battery with high first-cycle specific discharge capacity, slow voltage attenuation, high capacity retention rate and excellent cycle performance.

[0010] In order to achieve the above objects of the present application, the following technical solutions are adopted:

[0011] The present application first provides a preparation method of a cobalt-free lithium-rich manganese-based positive electrode material, comprising the following steps: mixing a lithium source, a nickel-manganese precursor and a dopant, and then performing first sintering to obtain an REE-doped intermediate material; the dopant contains at least Ce and La elements, and further contains at least one of Sc, Y and Dy elements; the intermediate material is mixed with a fluorine-containing organic matter, and then second sintering is performed to obtain the cobalt-free lithium-rich manganese-based positive electrode material with a F / C coating layer; the fluorine-containing organic matter includes at least one of polytetrafluoroethylene, trifluorochloroethylene, hexafluoroisopropylene oxide and hexafluoropropylene.

[0012] Further, the molar ratio of lithium elements in the lithium source, nickel elements in the nickel-manganese precursor, manganese elements in the nickel-manganese precursor and doping elements in the dopant is 1.1-1.5:0.2-0.4:0.6-0.8:0.001-0.04.

[0013] Further, the molar ratio of doping elements in the intermediate material to fluorine elements in the fluorine-containing organic matter is 1:0.01-100.

[0014] Further, the lithium source includes at least one of Li2CO3, LiOH and LiCl.

[0015] Further, the nickel-manganese precursor includes a nickel-manganese carbonate precursor and / or a nickel-manganese hydroxide precursor.

[0016] Further, the temperature of the first sintering is 600-1000℃, the holding time is 8-20h, and the heating rate is 1-5℃ / min.

[0017] Further, the temperature of the second sintering is 300-700℃, the holding time is 3-8h, and the heating rate is 1-5℃ / min.

[0018] The application further provides a cobalt-free lithium-rich manganese-based positive electrode material prepared by the preparation method of the cobalt-free lithium-rich manganese-based positive electrode material.

[0019] The application further provides a positive electrode sheet comprising the cobalt-free lithium-rich manganese-based positive electrode material.

[0020] The application further provides a lithium ion battery comprising the positive electrode sheet.

[0021] Compared with the prior art, the application has the beneficial effects that the preparation method of the cobalt-free lithium-rich manganese-based positive electrode material can improve the first cycle charge-discharge efficiency and charge-discharge specific capacity of the cobalt-free lithium-rich manganese-based positive electrode material, significantly reduces the voltage attenuation, and significantly improves the cycle performance. Specifically, the F element in the cobalt-free lithium-rich manganese-based positive electrode material can improve the stability of the lattice oxygen, so that the cycle stability is improved, the voltage attenuation in the cycle process is improved, and the F / C coating layer can stabilize the particle structure. In addition, the f-orbital electrons of the doped elements can interact with the electrons and orbits of Ni, Mn and O to produce a more stable electronic structure, so that the overall electronic structure of the material is more stable, and the voltage attenuation is reduced; at the same time, the oxygen vacancies generated by the solid solution (such as CeLaO 2-x formed by CeO2 and La2O3) can be used as the anchor point of the F element during coating, and the concentration of the oxygen vacancies in the solid solution can be further changed by the incorporation of the doped elements, and the change in the concentration of the oxygen vacancies will in turn change the coating effect of F / C, thereby ultimately improving the electrochemical performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 SEM image of the cobalt-free lithium-rich manganese-based positive electrode material prepared by Example 1 provided by the application;

[0024] Figure 2 SEM image of the cobalt-free lithium-rich manganese-based positive electrode material prepared by Comparative Example 3 provided by the application;

[0025] Figure 3 First cycle charge-discharge diagram of the battery prepared by the cobalt-free lithium-rich manganese-based positive electrode materials of Example 1 and Comparative Examples 1-3 provided by the application;

[0026] Figure 4The long cycle diagram of the first 200 cycles of the battery prepared from the cobalt-free lithium-rich manganese-based positive electrode material of Example 1 and Comparative Examples 1-3 provided by the present application;

[0027] Figure 5 The median voltage diagram of the first 200 cycles of the battery prepared from the cobalt-free lithium-rich manganese-based positive electrode material of Example 1 and Comparative Examples 1-3 provided by the present application. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased on the market.

[0029] If not specifically stated, in the present application, "first aspect", "second aspect", "third aspect", "fourth aspect" and the like are only used for description purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth" and the like only serve the purpose of non-exhaustive enumeration and description, and should be understood as not constituting a closed limitation on the quantity.

[0030] If not specifically stated, the "includes" and "contains" mentioned in the present application mean open-ended, and can also be closed. For example, the "includes" and "contains" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0031] If not specifically stated, in the present application, "one or more" or "at least one" means any one, any two or any two or more of the listed items. Among them, "several" means any two or more.

[0032] In the first aspect, the present application provides a preparation method of a low-voltage drop cobalt-free lithium-rich manganese-based positive electrode material, comprising the following steps:

[0033] The lithium source, the nickel-manganese precursor and the dopant are added into a mixer to be mixed sufficiently to obtain a uniform mixed powder, and then the mixed powder is subjected to first sintering to obtain an REE-doped intermediate material after cooling. The dopant contains at least Ce (cerium) and La (lanthanum) elements, and further contains at least one of Sc (scandium), Y (yttrium) and Dy (dysprosium).

[0034] That is, the intermediate material is doped with at least the rare earth elements Ce and La, and further doped with at least one of the rare earth elements Sc, Y and Dy.

[0035] Subsequently, the intermediate material is mixed with a fluorine-containing organic matter to be uniformly mixed, and then subjected to second sintering to obtain the cobalt-free lithium-rich manganese-based positive electrode material with a F / C coating layer after cooling. The fluorine-containing organic matter includes at least one of polytetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene oxide and hexafluoropropylene.

[0036] That is, the coating layer contains fluorine elements and carbon elements, and at least partially coats the REE-doped intermediate material.

[0037] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided by the application can solve the problem of voltage attenuation, improve the discharge specific capacity of the cobalt-free lithium-rich manganese-based positive electrode material, reduce voltage attenuation and improve the cycle performance.

[0038] Specifically, the F element in the cobalt-free lithium-rich manganese-based positive electrode material can improve the stability of lattice oxygen, so that the cycle stability is improved, the voltage attenuation in the cycle process is improved, and the F / C coating layer can stabilize the particle structure. In addition, the f-orbital electrons of the rich dopant elements can interact with the electrons and orbits of Ni, Mn and O to produce a more stable electronic structure, so that the overall electronic structure of the material is more stable, and the voltage attenuation is reduced; at the same time, the oxygen vacancies produced by the solid solution (such as CeLaO 2-x formed by CeO2 and La2O3) can be used as the anchor point of F element during coating, and the concentration of oxygen vacancies in the solid solution can be further changed by the doping of dopant elements, and the change of the concentration of oxygen vacancies will in turn change the coating effect of F / C, so as to finally improve the electrochemical performance of the battery.

[0039] In the application, F should have three different positions in the structure: (1) F occupies O; (2) F does not occupy O, but extends and bonds as a surface transition metal ion; (3) F does not bond with the positive electrode material, but together with C forms a FC coating layer to wrap the surface of the positive electrode material, which can prevent the direct contact between the electrolyte and the positive electrode during charging and discharging, and can alleviate the excessive decomposition and consumption of the electrolyte composition.

[0040] In some embodiments, the molar ratio of lithium element in the lithium source, nickel element in the nickel-manganese precursor, manganese element in the nickel-manganese precursor, and doping element in the dopant (referring to the total molar amount of all doping elements) is 1.1-1.5 (for example, 1.1, 1.2, 1.3, 1.4, or 1.5): 0.2-0.4 (for example, 0.2, 0.25, 0.3, 0.35, or 0.4): 0.6-0.8 (for example, 0.6, 0.65, 0.7, 0.75, or 0.8): 0.001-0.04 (for example, 0.001, 0.003, 0.005, 0.008, 0.01, 0.02, 0.03, or 0.04). Controlling the molar ratio within this range is conducive to forming a material with a certain O vacancy CeLaO 2-x Solid solution ability, not too much O vacancy, resulting in partial structure collapse of the material crystal; or too little is not effective.

[0041] In some embodiments, the molar ratio of doping element in the intermediate material (referring to the total molar amount of all doping elements) to fluorine element in the fluorine-containing organic matter is 1:0.01-100, including but not limited to any one of the point values of 1:0.01, 1:0.05, 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:3, 1:5, 1:8, 1:10, 1:20, 1:30, 1:40, 1:50, 1:70, 1:80, 1:100 or a range value between any two of them.

[0042] In some embodiments, the lithium source is a raw material providing lithium element, including at least one of lithium-containing compounds, such as Li2CO3, LiOH, and LiCl.

[0043] In some embodiments, the nickel-manganese precursor includes a nickel-manganese carbonate precursor and / or a nickel-manganese hydroxide precursor.

[0044] In some embodiments, the dopant is a compound containing doping elements, such as an oxide, a carbonate, or a hydroxide, but is not limited thereto.

[0045] In some embodiments, the temperature of the first sintering is 600-1000°C, including but not limited to any one of the point values of 600°C, 700°C, 800°C, 900°C, 1000°C or a range value between any two of them.

[0046] In some embodiments, the holding time of the first sintering is 8-20h, including but not limited to any one of the point values of 8h, 10h, 12h, 15h, 18h, 20h or a range value between any two of them.

[0047] In some specific embodiments, the temperature of the second sintering is 300-700 DEG C, including but not limited to any one of 300 DEG C, 400 DEG C, 500 DEG C, 600 DEG C, 700 DEG C, or a range value between any two of them.

[0048] In some specific embodiments, the temperature of the second sintering is 300-700 DEG C, including but not limited to any one of 300 DEG C, 400 DEG C, 500 DEG C, 600 DEG C, 700 DEG C, or a range value between any two of them.

[0049] In some specific embodiments, the temperature of the second sintering is 300-700 DEG C, including but not limited to any one of 300 DEG C, 400 DEG C, 500 DEG C, 600 DEG C, 700 DEG C, or a range value between any two of them.

[0050] In some specific embodiments, the temperature of the second sintering is 300-700 DEG C, including but not limited to any one of 300 DEG C, 400 DEG C, 500 DEG C, 600 DEG C, 700 DEG C, or a range value between any two of them.

[0051] The present application does not make specific limitations on the cooling method, for example, the natural cooling method can be used for cooling, or a certain cooling rate can be used to achieve the cooling effect.

[0052] The present application does not make specific limitations on the mixing method, as long as the raw materials are uniformly mixed. For example, the high-speed mixer can be used for mixing; preferably, the rotation speed of the high-speed mixer is 800-1400 r / min, the mixing time is 30-60 min, and the mixing temperature is 10-80 DEG C.

[0053] In the second aspect, the present application provides a cobalt-free lithium-rich manganese-based positive electrode material, which is prepared by the above method.

[0054] The battery prepared by using the cobalt-free lithium-rich manganese-based positive electrode material can significantly reduce the voltage decay after the cycle charging and discharging.

[0055] In the third aspect, the present application provides a positive electrode sheet, which comprises the above cobalt-free lithium-rich manganese-based positive electrode material.

[0056] The positive electrode sheet uses the above cobalt-free lithium-rich manganese-based positive electrode material as the positive electrode active material, which can effectively improve the cycle performance of the battery.

[0057] In the fourth aspect, the present application provides a lithium ion battery, which comprises the above positive electrode sheet.

[0058] The lithium ion battery has high first circle discharge specific capacity, slow voltage decay, high capacity retention rate, and excellent cycle performance.

[0059] In some specific embodiments, the lithium ion battery has a discharge specific capacity of 200-260 mAh·g -1 after 200 cycles at a current density of 1C, the working voltage attenuation of the lithium ion battery before and after cycling is significantly reduced, and the capacity retention rate can reach 86.84%.

[0060] In some specific embodiments, the lithium ion battery prepared by using the above-mentioned cobalt-free lithium-rich manganese-based positive electrode material can be prepared by any conventional method. For example, the cobalt-free lithium-rich manganese-based positive electrode material, a conductive agent, and a binder are mixed in a certain mass ratio, and then N-methyl pyrrolidone is added to prepare a uniform slurry. Then, the slurry is coated on an aluminum foil to form a positive electrode sheet with a certain thickness, and then the positive electrode sheet is dried in a vacuum for a certain period of time to obtain a positive electrode sheet. Then, the positive electrode sheet, a lithium sheet, and a battery electrolyte are subjected to a tabletting and standing process in a glove box to obtain a 2032 button cell. Preferably, the conductive agent can be one or more of acetylene black, conductive carbon black, Super-P, or Ketjen black; and the binder can be one or more of polyvinylidene fluoride, polyacrylic acid, and sodium alginate. The thickness of the coated positive electrode sheet is not limited, for example, the coating thickness is 15-25 microns. In addition, the electrolyte can be a carbonate electrolyte with a volume ratio of 3:7 of ethylene carbonate and methyl ethyl carbonate, a concentration of 1 mol / L, or other commonly used lithium ion battery electrolytes in the art.

[0061] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. The specific conditions not specified in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained by purchase.

[0062] Example 1

[0063] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in this embodiment includes the following steps:

[0064] (1) Li2CO3, Ni 0.25 Mn 0.75CO3 (nickel-manganese precursor), CeO2, La(OH)3, Y2O3 are weighed according to the element molar ratio of Li:Ni:Mn:Ce:La:Y = 1.13:0.215:0.645:0.005:0.003:0.002 (i.e. the molar ratio of lithium element in the lithium source, nickel element in the nickel-manganese precursor, manganese element in the nickel-manganese precursor, and doping elements in the dopant is 1.13:0.215:0.645:0.01), and mixed uniformly at 70°C and a rotation speed of 900 r / min, to obtain a uniform mixture.

[0065] (2) The uniform mixture obtained in step (1) is heated to 800°C at a heating rate of 4°C / min in an air atmosphere for first sintering, and after holding for 10h, it is naturally cooled to room temperature to obtain a Ce-La-Y co-doped intermediate material.

[0066] (3) The intermediate material obtained in step (2) is weighed with polytetrafluoroethylene according to a molar ratio of doping elements (i.e. the sum of the molar amounts of Ce, La, and Y) to fluorine element of 1:4, and mixed at a rotation speed of 900 r / min for 50 min; then heated to 700°C at a heating rate of 4°C / min in an air atmosphere for second sintering, and after holding for 5h, it is naturally cooled to room temperature to obtain a cobalt-free lithium-rich manganese-based positive electrode material with a F / C coating layer.

[0067] The chemical formula of the cobalt-free lithium-rich manganese-based positive electrode material prepared in this example is Li 1.13 Ni 0.215 Mn 0.645 Ce 0.005 La 0.003 Y 0.002 O 1.99 F 0.01 @FC, and the particle size D50 is 9.2 μm.

[0068] Figure 1 The SEM image of the cobalt-free lithium-rich manganese-based positive electrode material prepared in this example is shown.

[0069] Example 2

[0070] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in this example is basically the same as that in Example 1, except that in step (1), Y2O3 is replaced by Sc(NO3)3, and the element molar ratio of Li:Ni:Mn:Ce:La:Sc is still 1.13:0.215:0.645:0.005:0.003:0.002.

[0071] Example 3

[0072] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), Y2O3 is replaced by Dy(NO3)3, and the element molar ratio of Li:Ni:Mn:Ce:La:Dy is still 1.13:0.215:0.645:0.005:0.003:0.002.

[0073] Embodiment 4

[0074] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), Y2O3 is replaced by a mixture of Y2O3 and Dy(NO3)3, and the element molar ratio of Li:Ni:Mn:Ce:La:Y:Dy is still 1.13:0.215:0.645:0.005:0.003:0.001:0.001.

[0075] Embodiment 5

[0076] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), the element molar ratio of Li:Ni:Mn:Ce:La:Y is replaced by 1.19:0.2:0.6:0.005:0.003:0.002.

[0077] Embodiment 6

[0078] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (1), the element molar ratio of Li:Ni:Mn:Ce:La:Y is replaced by 1.13:0.21:0.63:0.01:0.01:0.01 (i.e., the molar ratio of lithium element in the lithium source, nickel element in the nickel-manganese precursor, manganese element in the nickel-manganese precursor, and doping element in the dopant is 1.13:0.21:0.63:0.03).

[0079] Embodiment 7

[0080] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (3), polytetrafluoroethylene is replaced by trifluorochloroethylene, and the molar ratio of the doping element (i.e., the sum of the molar amounts of Ce, La, and Y) to fluorine element is still 1:4.

[0081] Embodiment 8

[0082] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in the embodiment is basically the same as that in Embodiment 1, except that in step (3), the molar ratio of the doping element (i.e., the sum of the molar amounts of Ce, La, and Y) to fluorine element is replaced by 10:1.

[0083] Example 9

[0084] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in this example is basically the same as that in Example 1, except that in step (2), the uniformly mixed material is heated to 700℃ at a heating rate of 2℃ / min for first sintering and heat preservation for 18h.

[0085] Example 10

[0086] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in this example is basically the same as that in Example 1, except that in step (3), the temperature is increased to 400℃ at a heating rate of 3℃ / min for second sintering and heat preservation for 8h.

[0087] Comparative Example 1

[0088] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in this example is basically the same as that in Example 1, except that in step (1), the dopant is CeO2 and La(OH)3 (i.e., Y2O3 is not added), and the element molar ratio of Li:Ni:Mn:Ce:La is 1.13:0.215:0.645:0.006:0.004.

[0089] Comparative Example 2

[0090] The preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided in this example is basically the same as that in Example 1, except that in step (1), CeO2, La(OH)3 and Y2O3 are not added (i.e., no dopant is added).

[0091] Comparative Example 3

[0092] The cobalt-free lithium-rich manganese-based positive electrode material provided in this example is Li 1.13 Ni 0.22 Mn 0.65 O2.

[0093] Figure 2 The SEM image of the cobalt-free lithium-rich manganese-based positive electrode material prepared in this example is shown.

[0094] By comparison Figure 1 and Figure 2 It can be seen that the surface of the cobalt-free lithium-rich manganese-based positive electrode material of Example 1 is relatively uniform, and the surface roughness increases slightly, which is due to the fact that after the second sintering, the F in the polytetrafluoroethylene can form bonds with metal elements by adhering to oxygen vacancy sites or directly replacing part of O, so that the F / C coating layer can be uniformly distributed, and the in-situ carbonized part can enhance the structural strength of the material, while increasing the surface roughness.

[0095] Experimental Example

[0096] The cobalt-free lithium-rich manganese-based positive electrode material prepared in each example and each comparative example was used as a positive electrode active material, and a lithium ion battery was prepared according to the following method: the positive electrode active material, the conductive agent Super-P and the binder polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, and N-methyl pyrrolidone was added to prepare a uniform positive electrode slurry; then the positive electrode slurry was coated on an aluminum foil (coating thickness was 20 microns) and dried under vacuum to obtain a positive electrode sheet; then the positive electrode sheet, lithium sheet and electrolyte were subjected to sheet pressing and standing processes in a glove box to prepare a 2032 button cell, wherein the electrolyte was a carbonate electrolyte with a concentration of 1 mol / L, which was prepared by mixing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7. Then the performance of each battery was tested, wherein the charge-discharge voltage range was 2.5V-4.6V, the test temperature was 25°C, and the cycle performance of the battery was tested at a rate of 1C after 3 weeks of 0.33C cycle. The test results are shown in Tables 1 and 2.

[0097] Table 1: First circle charge-discharge capacity and first circle charge-discharge efficiency results

[0098]

[0099]

[0100] Table 2: 200th circle charge-discharge capacity, capacity retention rate and median voltage results

[0101]

[0102] wherein, Figure 3 is the first circle charge-discharge diagram of the battery prepared by the cobalt-free lithium-rich manganese-based positive electrode material of Example 1 and Comparative Examples 1-3, respectively; Figure 4 is the first 200 circle long cycle diagram of the battery prepared by the cobalt-free lithium-rich manganese-based positive electrode material of Example 1 and Comparative Examples 1-3, respectively; Figure 5 is the first 200 circle median voltage diagram of the battery prepared by the cobalt-free lithium-rich manganese-based positive electrode material of Example 1 and Comparative Examples 1-3, respectively.

[0103] It can be seen from Figures 3 to 5 and Tables 1 and 2 that, compared with Comparative Example 3, Comparative Example 2 can improve the first circle charge-discharge efficiency due to the F / C coating layer, which may be because the SEI process generated by the first charge-discharge is optimized; at the same time, the capacity retention rate of Comparative Example 2 is significantly improved, which is because the presence of F improves the stability of lattice oxygen, and C makes the surface structure more stable, and the two synergistically improve the cycle stability.

[0104] Further, compared with Comparative Example 3, Comparative Example 1 significantly improves the charge-discharge capacity and capacity retention of the material, improves the cycle stability of the battery, and reduces the voltage decay of the cobalt-free lithium-rich manganese-based positive electrode material due to the doping of Ce and La. This is because the rich f-orbital electrons of Ce and La elements can interact with the electrons and orbits of Ni, Mn and O, resulting in a more stable electronic structure, making the overall electronic structure of the material more stable, relieving the Jahn-Teller effect and reducing the voltage decay; since the ionic radius of Ce and La is larger than that of Mn, the doping of the two can widen the lattice spacing to provide a wider channel for lithium ion diffusion, which is beneficial to the rapid embedding and extraction of ions and improves the charge-discharge capacity. At the same time, the interaction of CeO2 and La2O3 can form CeLaO 2-x solid solution, which positively affects the subsequent F substitution of oxygen sites.

[0105] In addition, compared with Comparative Example 1, Example 1 changes the content of oxygen vacancies in CeO2-La2O3 by doping Y elements, because REE elements can change the formation process of CeLaO 2-x The change in the concentration of oxygen vacancies due to the formation process of the solid solution ultimately affects the coating effect of F / C, indicating that the prepared cobalt-free lithium-rich manganese-based positive electrode material with ultra-low pressure drop can further reduce the voltage decay, and the best voltage decay can reach 0.93 mV / cycle.

[0106] In summary, the preparation method of the cobalt-free lithium-rich manganese-based positive electrode material provided by the present application can improve the first charge-discharge efficiency and charge-discharge specific capacity of the cobalt-free lithium-rich manganese-based positive electrode material, and significantly reduce the voltage decay and significantly improve the cycle performance.

[0107] Although the present application has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit it; those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents without departing from the spirit and scope of the present application; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application; therefore, this means that all these replacements and modifications within the scope of the present application are included in the appended claims.

Claims

1. A method for preparing a cobalt-free, lithium-rich manganese-based cathode material, characterized in that, Includes the following steps: A lithium source, a nickel-manganese precursor, and a dopant are mixed and then subjected to a first sintering to obtain an REE-doped intermediate material; the dopant contains at least Ce and La elements, and also includes at least one of Sc, Y, and Dy elements; The intermediate material is mixed with a fluorinated organic compound and then subjected to a second sintering to obtain the cobalt-free lithium-rich manganese-based cathode material with an F / C coating layer; the fluorinated organic compound includes at least one of polytetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene oxide, and hexafluoropropylene.

2. The method for preparing the cobalt-free lithium-rich manganese-based cathode material according to claim 1, characterized in that, The molar ratio of lithium in the lithium source, nickel in the nickel-manganese precursor, manganese in the nickel-manganese precursor, and dopant in the dopant is 1.1–1.5: 0.2–0.4: 0.6–0.8: 0.001–0.

04.

3. The method for preparing the cobalt-free lithium-rich manganese-based cathode material according to claim 1, characterized in that, The molar ratio of the dopant element in the intermediate material to the fluorine element in the fluorine-containing organic compound is 1:0.01 to 100.

4. The method for preparing the cobalt-free lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The lithium source includes at least one of Li2CO3, LiOH, and LiCl.

5. The method for preparing the cobalt-free lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The nickel-manganese precursor includes nickel-manganese carbonate precursor and / or nickel-manganese hydroxide precursor.

6. The method for preparing the cobalt-free lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The first sintering temperature is 600-1000℃, the holding time is 8-20h, and the heating rate is 1-5℃ / min.

7. The method for preparing the cobalt-free lithium-rich manganese-based cathode material according to any one of claims 1 to 3, characterized in that, The second sintering temperature is 300–700℃, the holding time is 3–8h, and the heating rate is 1–5℃ / min.

8. A cobalt-free, lithium-rich manganese-based cathode material, characterized in that, It is prepared by the preparation method of cobalt-free lithium-rich manganese-based cathode material as described in any one of claims 1 to 7.

9. A positive electrode plate, characterized in that, Including the cobalt-free lithium-rich manganese-based cathode material as described in claim 8.

10. A lithium-ion battery, characterized in that, Includes the positive electrode as described in claim 9.

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