Coated positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the field of positive electrode materials, and particularly relates to a coated positive electrode material as well as a preparation method and application thereof. The coated positive electrode material comprises a matrix inner core and a coating layer located on at least part of the surface of the matrix inner core, the matrix inner core has the following composition: Li1 + 2x [(MnaNibCoc) 1-yMy] 1-xO2, x is more than or equal to 0.05 and less than or equal to 0.15, y is more than or equal to 0.01 and less than or equal to 0.05, a is more than or equal to 0.5 and less than 1.0, b is more than 0.1 and less than 0.5, c is more than 0.1 and less than 0.5, and a + b + c = 1; m is a group IIA metal element, a group IIIA metal element and a group IVB metal element; the material of the coating layer comprises Li3PO4 and LiF; the coated positive electrode material is high in specific capacity, high in first cycle efficiency, good in rate capability and good in cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a coated cathode material, its preparation method, and its application. Background Technology

[0002] The rapid development of large-scale energy storage technology has placed higher demands on the energy density, cycle stability, and safety of lithium-ion batteries. Lithium-rich manganese-based cathode materials have become ideal candidate materials due to their high theoretical specific capacity, low cost, and abundant manganese resources. However, this material has the following three shortcomings:

[0003] 1. Large irreversible capacity loss during the first charge: During the first charge, the Li2MnO3 phase undergoes oxygen migration and lattice reconstruction, releasing oxygen and forming an irreversible surface structure, which reduces the reversibility of the lithium-ion insertion / extraction process;

[0004] 2. Poor cycle stability: The dissolution of manganese causes loss of active materials, which reduces the charge and discharge capacity of the battery and thus affects the cycle stability of the battery; in addition, the layered structure transforms into spinel / rock salt phase, blocking the lithium ion diffusion channels, and the cycle stability of the battery decreases after long-term charge and discharge.

[0005] 3. Insufficient rate performance: Low electronic conductivity prevents electrons from flowing quickly, which limits the current during battery charging or discharging, thus affecting its rate performance. It also reduces the ion diffusion rate, preventing lithium ions from reaching the electrode surface or penetrating deep into the electrode material in time, thus limiting high-current charging and discharging performance and affecting its rate performance. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects of existing cathode materials, such as low specific capacity, low initial cycle efficiency, insufficient rate performance and poor cycle stability, thereby providing a coated cathode material, its preparation method and application.

[0007] Therefore, the present invention provides the following technical solution:

[0008] The first aspect of this invention protects a coated cathode material, wherein the coated cathode material comprises a substrate core and a coating layer located on at least a portion of the surface of the substrate core; the substrate core has the following composition: Li 1+2x [(Mn a Ni b Co c ) 1-y M y ] 1-x O2, 0.05≤x≤0.15, 0.01≤y≤0.05, 0.5≤a<1.0, 0.1<b<0.5, 0.1<c<0.5, a+b+c=1; M is a metal element of Group IIA, Group IIIA, or Group IVB;

[0009] The coating material includes Li3PO4 and LiF.

[0010] In some optional embodiments, the molar ratio of Li3PO4 to LiF in the coating layer is (1-3):1, and optionally (2-3):1.

[0011] In some alternative embodiments, M includes at least one of Mg, Al, Zr, and Ti; optionally, M includes at least one of Mg and Al.

[0012] In some alternative embodiments, the average particle size of the matrix core is 10-15 μm, and the thickness of the coating layer is 5-20 nm, optionally 10-20 nm.

[0013] A second aspect of this invention protects a method for preparing the aforementioned coated cathode material, wherein the preparation method includes the following steps:

[0014] S1, Synthesis of doped cathode material precursor;

[0015] S2, prepare a composite coating solution containing Li3PO4 and LiF;

[0016] S3, the doped cathode material precursor is mixed with the lithium source and sintered for the first time to obtain a sintered material. The composite coating liquid is mixed with the sintered material and sintered for the second time to obtain the coated cathode material.

[0017] In this invention, the first sintering and the second sintering are carried out independently in an oxygen environment. The heating rate of the first sintering and the second sintering is a conventional heating rate in the art, typically and non-limitingly, the heating rate is 2-5℃ / min.

[0018] In this invention, before the second sintering, the process further includes drying to remove excess coating liquid. Typically, but not limited to, the drying is carried out by evaporation at a temperature of 60-80°C.

[0019] In some alternative embodiments, the conditions for the second sintering include a temperature of 300-400°C and a time of 1-3 hours.

[0020] In some alternative embodiments, the conditions for the second sintering include a temperature of 320-380°C.

[0021] In some optional embodiments, step S1, the synthesis of the doped cathode material precursor includes the following steps: mixing manganese source, nickel source, cobalt source, M source with water to obtain a metal salt solution, performing a co-precipitation reaction, washing, drying, and obtaining the synthesized doped cathode material precursor.

[0022] In this invention, the coprecipitation reaction is carried out by adding an alkaline solution to adjust the pH to 10-11. The alkaline solution is a conventional solution in the art, typically and non-limitingly, a sodium hydroxide solution with a concentration of 5-10 mol / L.

[0023] In some alternative embodiments, the concentration of metal ions in the metal salt solution is 1-2 mol / L.

[0024] In some alternative embodiments, the conditions for the coprecipitation reaction include: a temperature of 60-80°C, a pH of 10-11, and a time of 8-12 hours.

[0025] In some alternative embodiments, the drying conditions include a temperature of 80-100°C and a time of 12-16 hours.

[0026] In some alternative embodiments, the first sintering includes a first calcination and a second calcination.

[0027] In some alternative embodiments, the conditions for the first calcination include: a temperature of 400-500°C and a time of 2-4 hours.

[0028] In some alternative embodiments, the conditions for the second calcination include a temperature of 800-900°C and a time of 8-12 hours.

[0029] In some alternative embodiments, in step S2, the total concentration of Li3PO4 and LiF in the composite coating solution is 0.01-0.03 g / mL.

[0030] In this invention, the solvent of the Li3PO4 and LiF composite coating solution is a conventional solvent in the art, typically and non-limitingly, including ethanol and water in a volume ratio of 1:(1-2). After adding Li3PO4 and LiF to the solvent, it can be sonicated for 30-60 minutes to make Li3PO4 and LiF more uniformly dispersed. The molar ratio of Li3PO4 and LiF has been defined in the first aspect of this invention and will not be repeated here.

[0031] In some alternative embodiments, the ratio of the amount of the synthesized doped cathode material precursor to the Li3PO4 and LiF composite coating solution is (3-12):1 g / mL.

[0032] In this invention, the lithium source is a conventional lithium source in the art, typically including at least one of lithium carbonate and lithium hydroxide, without limitation; the amount of the doped cathode material precursor and the lithium source is adjusted according to the requirements of the final matrix core composition.

[0033] In this invention, the Li3PO4 and LiF composite coating liquid is mixed with a calcined material and then sonicated for 30-60 minutes.

[0034] A third aspect of this invention protects a secondary battery, wherein the secondary battery comprises the aforementioned coated positive electrode material or the coated positive electrode material prepared by the aforementioned preparation method.

[0035] In this invention, the additives and binders are conventional materials in the art. Typically, without limitation, the additives include at least one of conductive carbon black (Super P), graphite, and carbon nanotubes; the binders include at least one of polyvinylidene fluoride (PVDF) and carboxymethyl cellulose (CMC); the mass ratio of the coated cathode material, additives, and binders is (80-85):(10-12):(5-9).

[0036] The technical solution of this invention has the following advantages:

[0037] 1. This invention provides a coated cathode material, wherein the coated cathode material comprises a substrate core and a coating layer located on at least a portion of the surface of the substrate core; the substrate core has the following composition: Li 1+2x [(Mn a Ni b Co c ) 1-y M y ] 1-x O2, 0.05≤x≤0.15, 0.01≤y≤0.05, 0.5≤a<1.0, 0.1<b<0.5, 0.1<c<0.5, a+b+c=1; M is a metal element of Group IIA, Group IIIA, or Group IVB; the coating material includes Li3PO4 and LiF; lithium excess design (x=0.05-0.15) improves specific capacity; doping with metal element M can improve electronic conductivity, LiF has high interfacial energy and preferentially adsorbs at oxygen vacancy defects on the substrate surface, inhibiting further loss of lattice oxygen and reducing irreversible oxygen release during the first charge; the PO bond of Li3PO4 can stabilize the surface transition metal ions and inhibit cation migration and layered structure transformation to spinel phase caused by oxygen loss during charging; the coated cathode material of this invention has high specific capacity, high first cycle efficiency, good rate performance, and good cycle stability.

[0038] 2. Further limiting the molar ratio of Li3PO4 and LiF in the coated cathode material of the present invention can further balance rigidity and toughness. The rigid material (Li3PO4) has small volume change during cycling, maintaining the overall framework of the coating layer; the tough material (LiF) alleviates the stress caused by volume change and reduces the risk of coating layer cracking; further improving the specific capacity, first cycle efficiency, rate performance and cycle stability of the coated cathode material.

[0039] 3. Further limiting the types of doping elements can enhance the stability of the crystal structure and reduce oxygen release and phase transition; further improve the specific capacity, first cycle efficiency, rate performance and cycle stability of the coated cathode material.

[0040] 4. Further limiting the second sintering conditions can further ensure that Li3PO4 and LiF form a uniform, dense and firmly bonded composite coating layer on the surface of the matrix core, thereby further improving the specific capacity, first cycle efficiency, rate performance and cycle stability of the coated cathode material.

[0041] 5. The first calcination (400-500℃) in the first sintering process can be pretreated at a low temperature to avoid violent reaction; the second calcination (800-900℃) is a high-temperature sintering process that can form a stable crystal structure. Detailed Implementation

[0042] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0044] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0045] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0046] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0048] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0049] The concentration of the sodium hydroxide solution is 10 mol / L.

[0050] Example 1

[0051] This embodiment provides a coated positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0052] Coated cathode material

[0053] S1. Synthesis of doped cathode material precursor: Manganese sulfate (MnSO4·H2O), nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and magnesium nitrate (Mg(NO3)2·6H2O) were added in stoichiometric ratio and mixed with 500 mL of deionized water to obtain a metal salt solution with a metal ion concentration of 2 mol / L. Co-precipitation reaction was carried out at 70℃, pH 10.5, and time for 10 h to obtain a precipitate. The precipitate was washed and dried at 90℃ for 14 h to obtain the synthesized doped cathode material precursor.

[0054] S2, Li3PO4 and LiF in a molar ratio of 1:1 are mixed with anhydrous ethanol and deionized water in a volume ratio of 1:1 and ultrasonically dispersed for 45 min to prepare a Li3PO4 and LiF composite coating solution, wherein the total concentration of Li3PO4 and LiF is 0.02 g / mL; the ratio of the amount of precursor used to synthesize the doped cathode material to the amount of Li3PO4 and LiF composite coating solution is 3:1 g / mL;

[0055] S3, the precursor of the synthesized doped cathode material is mixed with lithium carbonate in a certain molar ratio, and the first sintering is performed. In an oxygen atmosphere, the temperature is first increased to 450℃ at 2℃ / min and held for 3 hours, then increased to 850℃ at 2℃ / min and held for 10 hours. After cooling, the matrix core is obtained. The matrix core is composed of Li. 1.1 [(Mn 0.5 Ni 0.3 Co 0.2 ) 0.95 Mg 0.05 ] 0.95 O2; mix the matrix core and the Li3PO4 and LiF composite coating solution, ultrasonically disperse for 30 min, stir and evaporate the solvent at 65℃, and then sinter at 350℃ for 2 h at a rate of 2℃ / min to obtain the coated cathode material.

[0056] Secondary batteries

[0057] The prepared coated cathode material, Super P, and PVDF were mixed at a mass ratio of 83:10:7 to obtain a cathode mixture. The cathode mixture was then mixed with N-methylpyrrolidone (NMP) to form a slurry, wherein the ratio of cathode mixture to NMP was 2:1 (g / mL). The slurry was coated on aluminum foil with an areal density of 10 mg / cm³. 2 After drying, a positive electrode sheet is prepared. A negative electrode mixture is obtained by mixing graphite, binder (LA133), and carbon nanotubes (CNTs) in a mass ratio of 92:6:2. The negative electrode mixture and NMP are then coated onto copper foil in a ratio of 2:1 (g / mL), resulting in an areal density of 10 mg / cm³. 2 After drying, a negative electrode sheet is prepared; the electrolyte is a 1 mol / L LiPF6 ethylene carbonate (EC) and dimethyl carbonate (DMC) solution, wherein the volume ratio of EC to DMC is 1:1; the positive electrode sheet, separator (PE / PP composite membrane), negative electrode sheet and electrolyte are assembled into a 2025 type coin cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.

[0058] Example 2

[0059] This embodiment provides a coated positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0060] Coated cathode material

[0061] S1, Synthesis of doped cathode material precursor: Manganese nitrate, nickel nitrate, cobalt nitrate and aluminum nitrate were added in stoichiometric ratio and mixed with 500 mL of deionized water to obtain a metal salt solution with a metal ion concentration of 1 mol / L. Co-precipitation reaction was carried out at 60℃, pH 11 and time 12 h to obtain a precipitate. The precipitate was washed and dried at 100℃ for 12 h to obtain the synthesized doped cathode material precursor.

[0062] S2, Li3PO4 and LiF in a molar ratio of 3:1 were mixed with anhydrous ethanol and deionized water in a volume ratio of 1:1 and ultrasonically dispersed for 45 min to prepare a Li3PO4 and LiF composite coating solution, wherein the total concentration of Li3PO4 and LiF was 0.03 g / mL; the ratio of the amount of precursor used to synthesize the doped cathode material to the amount of Li3PO4 and LiF composite coating solution was 5:1 g / mL;

[0063] S3, the precursor of the synthesized doped cathode material is mixed with lithium carbonate in a certain molar ratio, and the first sintering is performed. In an oxygen atmosphere, the temperature is first increased to 500℃ at 5℃ / min and held for 2 hours, then increased to 900℃ at 5℃ / min and held for 8 hours. After cooling, the matrix core is obtained. The matrix core is composed of Li. 1.3 [(Mn 0.6 Ni 0.2 Co 0.2 ) 0.95 Al 0.05 ] 0.85 O2; mix the matrix core and the Li3PO4 and LiF composite coating solution, ultrasonically disperse for 60 min, stir and evaporate the solvent at 75℃, and then sinter at 400℃ for 1 h at a rate of 5℃ / min to obtain the coated cathode material.

[0064] Secondary batteries

[0065] The prepared coated cathode material, Super P, and PVDF were mixed at a mass ratio of 83:10:7 to obtain a cathode mixture. The cathode mixture was then mixed with N-methylpyrrolidone (NMP) to form a slurry, wherein the ratio of cathode mixture to NMP was 2:1 (g / mL). The slurry was coated on aluminum foil with an areal density of 10 mg / cm³. 2 After drying, a positive electrode sheet is prepared. A negative electrode mixture is obtained by mixing graphite, binder (LA133), and carbon nanotubes (CNTs) in a mass ratio of 92:6:2. The negative electrode mixture and NMP are then coated onto copper foil in a ratio of 2:1 (g / mL), resulting in an areal density of 10 mg / cm³. 2After drying, a negative electrode sheet is prepared; the electrolyte is a 1 mol / L LiPF6 ethylene carbonate (EC) and dimethyl carbonate (DMC) solution, wherein the volume ratio of EC to DMC is 1:1; the positive electrode sheet, separator (PE / PP composite membrane), negative electrode sheet and electrolyte are assembled into a 2025 type coin cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.

[0066] Example 3

[0067] This embodiment provides a coated positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0068] The method is the same as in Example 1, except that in step S2, the molar ratio of Li3PO4 to LiF is 2:1.

[0069] Example 4

[0070] This embodiment provides a coated positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0071] The method is the same as in Example 1, except that in step S2, the molar ratio of Li3PO4 to LiF is 3:1.

[0072] Example 5

[0073] This embodiment provides a coated positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0074] The method is the same as in Example 1, except that in step S1, magnesium nitrate is replaced with zirconium chloride, and the composition of the matrix core is Li. 1.1 [(Mn 0.5 Ni 0.3 Co 0.2 ) 0.95 Zr 0.05 ] 0.95 O2.

[0075] Example 6

[0076] This embodiment provides a coated positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0077] The method is the same as in Example 1, except that in step S3, the temperature of the second sintering is 300°C.

[0078] Comparative Example 1

[0079] This comparative example provides a positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0080] The method is the same as in Example 1, except that step S2 is not included. In step S3, the precursor of the synthesized doped cathode material is mixed with lithium carbonate in a molar ratio and subjected to a first sintering. The temperature is first raised to 500°C at 5°C / min and held for 2 hours in an oxygen atmosphere, and then raised to 900°C at 5°C / min and held for 8 hours. After cooling, the cathode material is obtained.

[0081] Comparative Example 2

[0082] This comparative example provides a positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0083] The method is the same as in Example 1, except that the coating material is only Li3PO4, and in step S2, LiF is replaced with an equal mass of Li3PO4.

[0084] Comparative Example 3

[0085] This comparative example provides a positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0086] The method is the same as in Example 1, except that the coating material is only LiF, and in step S2, Li3PO4 is replaced with an equal mass of LiF.

[0087] Comparative Example 4

[0088] This comparative example provides a positive electrode material and a secondary battery, the preparation method of which includes the following steps:

[0089] S1, Synthesis of doped cathode material precursor: Manganese sulfate, nickel sulfate, cobalt sulfate and magnesium nitrate were added in stoichiometric ratio and mixed with 500 mL of deionized water to obtain a metal salt solution with a metal ion concentration of 2 mol / L. Co-precipitation reaction was carried out at 70℃, pH 10.5 and time 10 h to obtain a precipitate. The precipitate was washed and dried at 90℃ for 14 h to obtain the synthesized doped cathode material precursor.

[0090] S2, Li3PO4 and LiF in a molar ratio of 1:1 are mixed with anhydrous ethanol and deionized water in a volume ratio of 1:1 and ultrasonically dispersed for 45 min to prepare a Li3PO4 and LiF composite coating solution, wherein the total concentration of Li3PO4 and LiF is 0.02 g / mL; the ratio of the amount of precursor used to synthesize the doped cathode material to the amount of Li3PO4 and LiF composite coating solution is 3:1 g / mL;

[0091] S3, the precursor of the synthesized doped cathode material is mixed with lithium carbonate in a certain molar ratio, and the first sintering is performed. In an oxygen atmosphere, the temperature is first increased to 450℃ at 2℃ / min and held for 3 hours, then increased to 850℃ at 2℃ / min and held for 10 hours. After cooling, the matrix core is obtained. The matrix core is composed of Li. 0.9[(Mn 0.5 Ni 0.3 Co 0.2 ) 0.97 Mg 0.03 ] 0.9 O2; mix the matrix core and the Li3PO4 and LiF composite coating solution, ultrasonically disperse for 30 min, stir and evaporate the solvent at 65℃, and then sinter at 350℃ for 2 h at a rate of 2℃ / min to obtain the coated cathode material.

[0092] The secondary battery was prepared according to the method described in Example 1.

[0093] Test case

[0094] (1) The average particle size of the matrix core was tested using a Malvern 3000 laser particle size analyzer, and the thickness of the coating layer was tested using a high-resolution transmission electron microscope.

[0095] The specific test results are shown in Table 1;

[0096] Table 1

[0097]

[0098]

[0099] (2) Charge the battery to 4.5V at a rate of 0.2C to obtain the initial charge capacity and initial charge specific capacity; then discharge it to 3V at a rate of 0.2C to obtain the initial discharge capacity and initial discharge specific capacity;

[0100] First cycle efficiency = (First discharge capacity / First charge capacity) × 100%;

[0101] At 25°C, the battery is charged to 4.5V at a rate of 1C and then discharged to 3V at a rate of 1C for 500 cycles. The 1C capacity retention rate is calculated as (discharge specific capacity in the 500th cycle / discharge specific capacity in the 1st cycle) × 100%.

[0102] At 25°C, the battery is charged to 4.5V at a rate of 5C and then discharged to 3V at a rate of 5C for 500 cycles. The 5C capacity retention rate is calculated as (discharge specific capacity in the 500th cycle / discharge specific capacity in the 1st cycle) × 100%.

[0103] See Table 2 for specific tests;

[0104] Table 2

[0105]

[0106] A comparison of the examples and comparative examples shows that the cathode material coated by the present invention has high specific capacity, high initial cycle efficiency, good rate performance, and good cycle stability.

[0107] A comparison of Examples 1, 3, and 4 shows that further limiting the molar ratio of Li3PO4 to LiF in the coated cathode material of the present invention can further balance rigidity and toughness. Rigidity resists the small volume change during material cycling and maintains the overall framework of the coating layer; toughness alleviates the stress caused by volume change and reduces the risk of coating layer cracking; and further improves the specific capacity, first cycle efficiency, rate performance, and cycle stability of the coated cathode material.

[0108] A comparison of Examples 1 and 5 shows that further limiting the types of doping elements can enhance the stability of the crystal structure, reduce oxygen release and phase transition, and further improve the specific capacity, first cycle efficiency, rate performance and cycle stability of the coated cathode material.

[0109] A comparison of Examples 1 and 6 shows that further limiting the second sintering conditions can ensure that Li3PO4 and LiF form a uniform, dense and firmly bonded composite coating layer on the surface of the matrix core, further improving the specific capacity, first cycle efficiency, rate performance and cycle stability of the coated cathode material.

[0110] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A coated cathode material, characterized in that, The coated cathode material includes a matrix core and a coating layer located on at least a portion of the surface of the matrix core; the matrix core has the following composition: Li 1+2x [(Mn a Ni b Co c ) 1-y M y ] 1-x O2, 0.05≤x≤0.15, 0.01≤y≤0.05, 0.5≤a<1.0, 0.1<b<0.5, 0.1<c<0.5, a+b+c=1; M is a metal element of Group IIA, Group IIIA, or Group IVB; The coating material includes Li3PO4 and LiF.

2. The coated cathode material according to claim 1, characterized in that, The molar ratio of Li3PO4 to LiF in the coating layer is (1-3):1, and can be optionally (2-3):1; And / or, M includes at least one of Mg, Al, Zr, and Ti; optionally, M includes at least one of Mg and Al.

3. The coated cathode material according to claim 1 or 2, characterized in that, The average particle size of the matrix core is 10-15 μm, and the thickness of the coating layer is 5-20 nm.

4. A method for preparing the coated cathode material according to any one of claims 1-3, characterized in that, The preparation method includes the following steps: S1, Synthesis of doped cathode material precursor; S2, prepare a composite coating solution containing Li3PO4 and LiF; S3, the doped cathode material precursor is mixed with the lithium source and sintered for the first time to obtain a sintered material. The composite coating liquid is mixed with the sintered material and sintered for the second time to obtain the coated cathode material.

5. The preparation method according to claim 4, characterized in that, The conditions for the second sintering include: a temperature of 300-400℃ and a time of 1-3 hours; Optionally, the conditions for the second sintering include a temperature of 320-380°C.

6. The preparation method according to claim 4 or 5, characterized in that, In step S1, the synthesis of the doped cathode material precursor includes the following steps: mixing manganese source, nickel source, cobalt source, M source with water to obtain a metal salt solution, performing a co-precipitation reaction, washing, and drying to obtain the synthesized doped cathode material precursor.

7. The preparation method according to claim 6, characterized in that, The concentration of metal ions in the metal salt solution is 1-2 mol / L; Optionally, the conditions for the coprecipitation reaction include: a temperature of 60-80℃, a pH of 10-11, and a time of 8-12h; Optionally, the drying conditions include a temperature of 80-100°C and a time of 12-16 hours.

8. The preparation method according to any one of claims 4-7, characterized in that, The first sintering includes a first calcination and a second calcination; Optionally, the conditions for the first calcination include: a temperature of 400-500℃ and a time of 2-4 hours; Optionally, the conditions for the second calcination include: a temperature of 800-900℃ and a time of 8-12h.

9. The preparation method according to any one of claims 4-8, characterized in that, In step S2, the total concentration of Li3PO4 and LiF in the composite coating solution is 0.01-0.03 g / mL; And / or, the ratio of the amount of the precursor for synthesizing the doped cathode material to the Li3PO4 and LiF composite coating solution is (3-12):1 g / mL.

10. A secondary battery, characterized in that, The secondary battery includes the coated positive electrode material according to any one of claims 1-3 or the coated positive electrode material prepared by the preparation method according to any one of claims 4-9.

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