Positive electrode material and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention relates to a positive electrode material and a preparation method thereof, a positive plate and a lithium ion battery. The positive electrode material comprises a core part and a coating layer located on the surface of the core part, the coating layer comprises a first coating layer and a second coating layer, and the first coating layer is located between the core part and the second coating layer; the first coating layer is an ion conductor coating layer, and the second coating layer is a carbon coating layer; the core part is LiMnxAlyTizO4, x + y + z = 2, x is greater than or equal to 1.8 and less than or equal to 1.925, y is greater than or equal to 0.025 and less than or equal to 0.15, and z is greater than or equal to 0.025 and less than or equal to 0.15. High-valence ions are introduced into the manganese-based material for co-doping, manganese dissolution and a Jahn-Teller effect are inhibited, the surface of the material is protected by adopting double coating layers, the interface stability is maintained, and meanwhile, an ion / electron transmission channel is maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery materials, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery. BACKGROUND

[0002] In recent years, lithium ion batteries have gradually been favored by people due to their high energy density, good cycle performance, environmental friendliness and other advantages, and are widely used in electric vehicles, digital, electric tools and other fields. The positive electrode material in the lithium ion battery plays a decisive role in the performance of the battery, so the research on the positive electrode material has become one of the main research and development directions.

[0003] Lithium manganate (LiMn2O4) has become one of the important positive electrode materials due to its high energy, high discharge voltage, high safety and environmental protection. However, the Jahn-Teller effect causes the lattice distortion of manganese-based materials during charging and discharging, resulting in capacity attenuation and cycle performance degradation of the battery, so that the battery performance cannot meet the expected performance. The traditional technology dopes metal ions Ti 4+ , Al 3+ on the surface of the material to enhance the structural stability, but Ti 4+ increases the charge transfer impedance and reduces the conductivity of the material, affecting the rate charge-discharge performance. The non-electrochemical active ion Al 3+ doping leads to a decrease in electronic conductivity of the material, which needs to rely on the compensation of the conductive agent, and the distribution of the doping element is uneven, part of which exists on the surface, which brings structural defects, and then causes a side reaction with the electrolyte, resulting in a decrease in interface stability. SUMMARY

[0004] To solve the above technical problems, the present application provides a positive electrode material, a preparation method thereof, a positive electrode sheet and a lithium ion battery.

[0005] The first aspect of the present application provides a positive electrode material, which comprises:

[0006] a core part and a coating layer located on the surface of the core part;

[0007] The coating layer comprises a first coating layer and a second coating layer, and the first coating layer is located between the core part and the second coating layer;

[0008] The first coating layer is an ion conductor coating layer, and the second coating layer is a carbon coating layer;

[0009] The molecular formula of the core part is LiMn x Al y Ti z O4, wherein x+y+z=2, 1.8≤x≤1.925, 0.025≤y≤0.15 and 0.025≤z≤0.15.

[0010] In some embodiments, LiMn x Al y Ti z Al 3+ and Ti 4+ accounts for 3.75%~10% of the total content of Mn, Al, and Ti; the molar ratio of Al 3+ and Ti 4+ is (0.5~3):(0.5~3).

[0011] In some embodiments, the thickness of the ion conductor coating layer is 3nm~20nm; the thickness of the carbon coating layer is 2nm~10nm.

[0012] In some embodiments, the ion conductor coating layer is Li3PO4.

[0013] The second aspect of the present application provides a preparation method of a positive electrode material, comprising the following steps:

[0014] S1, weighing a lithium source, a manganese source, an aluminum source, and a titanium source according to a proportion to provide raw materials;

[0015] S2, mixing the raw materials with a first solvent and a second solvent respectively according to the material properties, and then mixing with a complexing agent and a pH adjuster to form a solution, and filtering and drying to prepare a precursor;

[0016] S3, mixing the precursor with a third solvent and a surfactant, and stirring to prepare a sol;

[0017] S4, sequentially performing gel treatment and calcination treatment on the sol to prepare an aluminum-titanium doped spinel lithium manganate;

[0018] S5, forming an ion conductor coating layer on the surface of the aluminum-titanium doped spinel lithium manganate;

[0019] S6, forming a carbon coating layer on the surface of the ion conductor coating layer.

[0020] In some embodiments, when the raw materials are inorganic salt materials, the first homogeneous solution is formed by dissolving in a first solvent, and the first solvent is water; when the raw materials are organic salt materials, the second homogeneous solution is formed by dissolving in a second solvent, and the second solvent is an alcohol solvent.

[0021] In some embodiments, the concentration of the first homogeneous solution and the second homogeneous solution formed is 0.4 mol / L~1mol / L.

[0022] In some embodiments, the step of preparing the sol comprises at least one of the following features (1)~(2):

[0023] (1) the concentration of the precursor in the third solvent is 0.01 g / mL to 0.15 g / mL;

[0024] (2) the mass of the surfactant is 1% to 3% of the mass of the precursor.

[0025] The third aspect of the present application provides a positive electrode sheet comprising the positive electrode material provided by the first aspect of the present application or comprising the positive electrode material prepared by the preparation method provided by the second aspect of the present application.

[0026] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode sheet provided by the third aspect of the present application.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] By introducing high-valence ion co-doping into the manganese-based material, Ti 4+ and Al 3+ occupy Mn 4+ and Mn 3+ sites, respectively, and the two co-dope, have a structural synergistic stabilization effect, reduce the risk of phase change, and optimize the lattice parameters and bond energy, inhibit manganese dissolution and Jahn-Teller effect, specifically:

[0029] The ionic radius of Ti 4+ (0.0605 nm) is slightly larger than that of Mn 4+ (0.053 nm), and moderate doping can increase the lattice parameters and alleviate the volume change during charging and discharging. Specifically, after Ti 4+ substitutes Mn 4+ , the Jahn-Teller distortion effect of Mn 3+ is inhibited by the strong stability of Ti-O bond, thereby improving the structural stability; the strong Ti-O bond of Ti 4+ stabilizes the crystal framework and reduces the dissolution of manganese during charging and discharging; at the same time, after Ti 4+ doping, to maintain charge balance, part of Mn 3+ is oxidized to Mn 4+ , thereby reducing the overall Mn 3+ concentration, improving the average valence of manganese, and inhibiting Jahn-Teller distortion; in addition, after Ti 4+ partially substitutes Mn 4+ , the stability of Mn-O bond is enhanced, the dissolution of Mn 3+ is reduced, and thus the deposition of manganese in the negative electrode is inhibited.

[0030] After Al 3+ substitutes Mn 3+ , the dissolution of Mn 3+The content of Al is increased, so as to inhibit lattice distortion, improve cycle stability, and reduce oxygen release at high temperature, thereby enhancing stability.

[0031] The present application adopts a double-layer coating structure to protect the material surface, maintain interface stability, and maintain ion / electron transmission channels. Specifically, the inner layer is an ion conductor coating layer, which improves the ion conductivity of the doped Ti 4+ and increases the charge transfer impedance, improves the rate charge-discharge performance, and maintains the ion transmission channel. The outer layer is a carbon coating layer, which improves the problem of reduced electronic conductivity caused by the doped Al 3+ . At the same time, the double-layer coating structure improves the problem of interface stability decline caused by uneven distribution of the doped elements, partial presence on the surface, and possible structural defects, and further side reactions with the electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the embodiments or the related art description will be briefly introduced. Obviously, the drawings in the following description only constitute some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0033] Figure 1 It is a schematic diagram of the preparation method of the positive electrode material in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The reference of the embodiments of the present application will be provided in detail, and one or more embodiments are described below. Each embodiment is provided as an explanation rather than a limitation of the present application. Actually, it is obvious for those skilled in the art that various modifications and changes can be made to the present application without departing from the scope or spirit of the present application. For example, the features described or illustrated as part of one embodiment can be used in another embodiment to produce further embodiments.

[0035] Therefore, it is intended that the present application cover such modifications and changes as fall within the scope of the appended claims and their equivalents. Other objects, features, and aspects of the present application are disclosed in or are obvious from the following detailed description. Those skilled in the art will appreciate that the discussion herein is a description of exemplary embodiments only and is not intended to limit the broader aspects of the present application.

[0036] In the present application, the technical features described in an open manner include both the closed technical solutions consisting of the listed features and the open technical solutions containing the listed features.

[0037] In the present application, if a numerical interval is involved, the numerical interval is considered to be continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value of the range, unless otherwise specified. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0038] In the present application, if a numerical interval is involved, the numerical interval is considered to be continuous and includes the minimum value and the maximum value of the range and each value between the minimum value and the maximum value of the range, unless otherwise specified. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0039] If not particularly specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0040] If not particularly specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0041] If not particularly specified, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method further comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0042] If not particularly specified, "including" and "containing" mentioned in the present application means open type, and can also be closed type. For example, "including" and "containing" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0043] The first aspect of the present application provides a positive electrode material, which comprises a core part and a coating layer located on the surface of the core part.

[0044] The coating layer comprises a first coating layer and a second coating layer, and the first coating layer is located between the core part and the second coating layer.

[0045] The first coating layer is an ion conductor coating layer, and the second coating layer is a carbon coating layer.

[0046] The molecular formula of the core part is LiMn x Al y Ti zO4, wherein x+y+z=2, 1.8≤x≤1.925, 0.025≤y≤0.15, 0.025≤z≤0.15.

[0047] The application introduces high-valence ion co-doping into the manganese-based material, Ti 4+ and Al 3+ occupy Mn 4+ and Mn 3+ sites respectively, both of which co-dope, have structural synergistic stabilization effect, reduce the risk of phase transition, optimize the lattice parameters and bond energy, inhibit manganese dissolution and Jahn-Teller effect, specifically:

[0048] The ionic radius of Ti 4+ (0.0605 nm) is slightly larger than that of Mn 4+ (0.053 nm), and moderate doping can increase the lattice parameters and relieve the volume change during charging and discharging. Specifically, after Ti 4+ substitutes Mn 4+ , the Jahn-Teller distortion effect of Mn 3+ is inhibited by the strong stability of Ti-O bond, thereby improving the structural stability; the strong Ti-O bond of Ti 4+ stabilizes the crystal framework and reduces the dissolution of manganese during charging and discharging; at the same time, after Ti 4+ doping, to maintain charge balance, part of Mn 3+ is oxidized to Mn 4+ , thereby reducing the overall Mn 3+ concentration, improving the average valence of manganese, and inhibiting Jahn-Teller distortion; in addition, after Ti 4+ partially substitutes Mn 4+ , the stability of Mn-O bond is enhanced, the dissolution of Mn 3+ is reduced, and thus the deposition of manganese in the negative electrode is inhibited.

[0049] After Al 3+ substitutes Mn 3+ , the content of Mn 3+ is reduced, thereby inhibiting lattice distortion and improving cycle stability; the Al-O bond energy is stronger than the Mn-O bond energy, which can reduce the oxygen release of the material at high temperature and enhance the stability.

[0050] The application uses a double-layer coating structure to protect the material surface, maintain the interface stability, and maintain the ion / electron transmission channel. Specifically, the inner layer is an ion conductor coating layer, which improves the problem of increased charge transfer impedance caused by doping Ti 4+ , improves the rate charging and discharging performance, and maintains the ion transmission channel. The outer layer is a carbon coating layer, which improves the doping of Al 3+This leads to a decrease in electronic conductivity. Simultaneously, the use of a double-layer coating structure mitigates the problem of uneven dopant distribution, where some dopants remain on the surface, potentially causing structural defects and subsequent side reactions with the electrolyte, leading to decreased interfacial stability.

[0051] In some embodiments, the core material is LiMn x Al y Ti z Al in O4 3+ With Ti 4+ It accounts for 3.75%~10% of the total content of Mn, Al, and Ti; Al 3+ With Ti 4+ The molar ratio is (0.5~3):(0.5~3).

[0052] In some embodiments, Al in the core material 3+ With Ti 4+ The percentage of Mn, Al, and Ti in the total content can be selected as 3.75%, 5%, 6%, 7%, 8%, 9%, 10%, etc.; Al 3+ With Ti 4+ The molar ratio can be selected from 0.5:1, 1:1, 2:1, 3:1, 1:0.5, 1:2, 1:3, etc. Specific values ​​are not limited here and can be selected according to the actual situation.

[0053] In some embodiments, the thickness of the ion conductor coating layer is 3 nm to 20 nm; the thickness of the carbon coating layer is 2 nm to 10 nm.

[0054] In some embodiments, the thickness of the ion conductor coating layer can be selected from 3nm, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, etc.; the thickness of the carbon coating layer can be selected from 2nm, 5nm, 8nm, 10nm, etc. Specific values ​​are not limited here and can be selected according to the actual situation.

[0055] In some embodiments, the ion conductor coating material is Li3PO4.

[0056] like Figure 1 As shown, a second aspect of this application provides a method for preparing a cathode material, comprising the following steps:

[0057] S1. Weigh the lithium source, manganese source, aluminum source and titanium source in proportion to provide raw materials.

[0058] S2. The raw materials are mixed with the first solvent and the second solvent according to their material properties, and then mixed with the complexing agent and pH adjuster to form a solution. After filtration and drying, the precursor is prepared.

[0059] S3, mixing the precursor with a third solvent and a surfactant, stirring to prepare a sol.

[0060] S4, sequentially performing gel treatment and calcination treatment on the sol to prepare aluminum titanium doped spinel lithium manganate.

[0061] S5, forming an ion conductor coating layer on the surface of the aluminum titanium doped spinel lithium manganate.

[0062] S6, forming a carbon coating layer on the surface of the ion conductor coating layer.

[0063] In some embodiments, the lithium source includes but is not limited to one or more of lithium nitrate (LiNO3), lithium acetate (LiCH3COO).

[0064] In some embodiments, the manganese source includes but is not limited to one or more of manganese acetate (Mn(CH3COO)2), manganese sulfate (MnSO4), manganese nitrate (Mn(NO3)2).

[0065] In some embodiments, the aluminum source includes but is not limited to one or more of aluminum nitrate (Al(NO3)3), aluminum sulfate (Al2(SO4)3), aluminum isopropoxide (Al(O-iC3H7)3).

[0066] In some embodiments, the titanium source includes but is not limited to one or more of n-butyl titanate (C 16 H 36 O4Ti), titanium sulfate (Ti(SO4)2).

[0067] In some embodiments, the complexing agent includes but is not limited to one or more of citric acid, oxalic acid, acrylic acid.

[0068] In some embodiments, the pH value ranges from 1 to 3, preferably from 1.5 to 2.5.

[0069] In some embodiments, the pH value can be selected as 1, 2, 3, etc. The specific value is not limited herein and can be selected according to actual conditions.

[0070] It can be understood that the type of pH regulator is not particularly limited in the present application, and any known pH regulator capable of achieving the purpose of the present application can be applied to the present application without deviating from the overall inventive concept of the present application. The following is only exemplary, and the pH regulator is nitric acid.

[0071] In some embodiments, the first and second solvents include but are not limited to one or more of water, an alcohol solvent.

[0072] It can be understood that the water in the present application can be deionized water, ultrapure water or distilled water, and the alcohol in the present application can be anhydrous ethanol, methanol, isopropanol, n-butanol, ethylene glycol, glycerol and the like.

[0073] Step S2 comprises the following steps:

[0074] The raw materials and the first solvent and the second solvent are mixed to form a homogeneous solution.

[0075] The complexing agent and the pH adjusting agent are added to the homogeneous solution, and stirring treatment is performed for 30 min to 60 min to prepare a solution.

[0076] In some embodiments, the stirring time can be selected as 30 min, 40 min, 50 min, 60 min, etc. The specific value is not limited herein and can be selected according to the actual situation.

[0077] In step S2 of the present application, stirring treatment is used to stabilize the metal ion complex structure in the solution.

[0078] In some embodiments, when the raw material is an inorganic salt material, it is dissolved in the first solvent to form a first homogeneous solution, and the first solvent is water; when the raw material is an organic salt material, it is dissolved in the second solvent to form a second homogeneous solution, and the second solvent is an alcohol solvent.

[0079] For example, when the raw materials are lithium nitrate, manganese acetate, aluminum nitrate and n-butyl titanate, lithium nitrate, manganese acetate, aluminum nitrate and water are mixed to prepare a first homogeneous solution; n-butyl titanate and anhydrous ethanol are mixed to prepare a second homogeneous solution; and then the first homogeneous solution and the second homogeneous solution are mixed to prepare a homogeneous solution.

[0080] Optionally, the molar concentration of the raw material in the homogeneous solution is 0.4 mol / L to 1 mol / L, which can be selected as 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, etc. The specific value is not limited herein and can be selected according to the actual situation.

[0081] In some embodiments, the volume ratio of the complexing agent to the first solvent is 1:(1-3), which can be selected as 1:1, 1:2, 1:3, etc. The specific value is not limited herein and can be selected according to the actual situation.

[0082] In some embodiments, the drying temperature in step S2 is 70°C to 100°C, which can be selected as 70°C, 80°C, 90°C, 100°C, etc.; and the drying time is 6h to 12h, which can be selected as 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc. The specific value is not limited herein and can be selected according to the actual situation.

[0083] In some embodiments, in step S3, the third solvent is an alcohol solvent and is the same as the second solvent, which will not be repeated here.

[0084] In some embodiments, in step S3, the surfactant includes but is not limited to one or more of polyvinylpyrrolidone, polyethylene glycol.

[0085] In some embodiments, in step S3, the concentration of the precursor in the second solvent is 0.01 g / mL to 0.15 g / mL, which can be selected as 0.01 g / mL, 0.03 g / mL, 0.05 g / mL, 0.08 g / mL, 0.1 g / mL, 0.12 g / mL, 0.15 g / mL. The specific value is not limited here and can be selected according to the actual situation.

[0086] In some embodiments, in step S3, the mass of the surfactant is 1% to 3% of the mass of the precursor, which can be selected as 1%, 2%, 3%. The specific value is not limited here and can be selected according to the actual situation.

[0087] In some embodiments, in step S3, the stirring temperature is 60°C to 80°C and the stirring time is 2h to 4h.

[0088] In some embodiments, the stirring temperature can be selected as 60°C, 65°C, 70°C, 75°C, 80°C, etc.; the stirring time can be selected as 2h, 2.5h, 3h, 3.5h, 4h, etc. The specific value is not limited here and can be selected according to the actual situation.

[0089] The present application adds a surfactant in step S3 and performs stirring treatment on the solution to improve the dispersibility of the sol, thereby preparing a uniform sol system.

[0090] In some embodiments, step S4 is specifically as follows:

[0091] The sol is incubated at 80°C to 150°C for 10h to 30h to prepare a dry gel.

[0092] The dry gel is placed in an environment with a temperature of 25°C to 40°C and a humidity of 50% to 70% for 6h to 24h to prepare a porous dry gel.

[0093] In some embodiments, the dry gel incubation temperature can be selected from 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc.; the time can be selected from 10h, 15h, 20h, 25h, 30h, etc.; the porous dry gel temperature can be selected from 25℃, 30℃, 35℃, 40℃; the humidity can be selected from 50%, 60%, 70%; and the standing time can be selected from 6h, 10h, 15h, 20h, 24h, etc. The specific values are not limited herein and can be selected according to actual conditions.

[0094] It can be understood that the present application does not particularly limit the incubation device, and any device capable of achieving the incubation effect can be applied to the present application without departing from the overall inventive concept of the present application. By way of example only, the incubation device can be an oven.

[0095] The present application is beneficial to the evaporation of the solvent in the sol to form a dry gel by incubating the sol at a higher temperature. The porous dry gel with a three-dimensional network structure is prepared by treating the dry gel at a lower temperature and in a certain humidity environment to avoid cracking of the dry gel.

[0096] In some embodiments, the calcination treatment in step S4 includes a pre-burning stage and a crystallization stage, which are specifically as follows:

[0097] Pre-burning stage: incubation at 300℃-400℃ for 2h-6h. The organic matter and residual nitrate in the porous dry gel are decomposed.

[0098] In some embodiments, the pre-burning stage temperature can be selected from 300℃, 350℃, 400℃, etc.; and the time can be selected from 2h, 4h, 6h, etc. The specific values are not limited herein and can be selected according to actual conditions.

[0099] Crystallization stage: calcination at 600℃-750℃ in air for 6h-12h. Spinel-type aluminum-titanium-doped lithium manganate is prepared.

[0100] In some embodiments, the calcination temperature can be selected from 600℃, 650℃, 680℃, 700℃, 750℃, etc.; and the calcination time can be selected from 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc. The specific values are not limited herein and can be selected according to actual conditions.

[0101] In some embodiments, in step S5, the method for forming the ion conductor coating layer on the surface of the aluminum-titanium-doped spinel lithium manganate is atomic layer deposition (ALD) technology, dry coating method or wet chemical method.

[0102] It can be understood that the specific type of ion conductor coating layer is not particularly limited in the present application, and any known ion conductor coating layer capable of achieving the purpose of the present application can be applied to the present application without deviating from the overall inventive concept of the present application. The ion conductor coating layer is Li3PO4 coating layer as an example.

[0103] In a specific embodiment, a Li3PO4 coating layer is formed on the surface of aluminum-titanium-doped spinel lithium manganate by atomic layer deposition (ALD) technology.

[0104] Specifically, the aluminum-titanium-doped spinel lithium manganate material is operated in a fluidized bed or a rotary bed ALD system, lithium hexamethyldisilazide (LiHMDS) with high vapor pressure and reactivity is used as a lithium precursor, and trimethyl phosphate (MPO) or H3PO4 derivatives are alternately reacted with the lithium lithium precursor to form Li3PO4. The H3PO4 derivatives include but are not limited to one or more of pyrophosphoric acid (H4P2O7), polyphosphoric acid (H5P3O 10 ), and metaphosphoric acid (HPO3).

[0105] Reaction steps: each ALD cycle includes LiHMDS adsorption, inert gas purging, MPO or H3PO4 derivative reaction, and secondary purging. The number of cycles required is selected according to the actual required thickness of the ion conductor coating layer, and about 80 nm of ion conductor coating layer can be deposited per 100 cycles.

[0106] The deposition temperature is 250°C~350°C, which can ensure sufficient reaction of the precursors and avoid thermal decomposition of the material.

[0107] The reaction chamber is maintained at a low pressure (about 10 mBar) to facilitate the diffusion and surface adsorption of the precursors.

[0108] The pulse time of the precursors: the pulse time of the lithium source and the phosphorus source is set to 1s~2s respectively, and the purging time is matched to remove by-products.

[0109] In some embodiments, the method for forming a carbon coating layer on the surface of the ion conductor coating layer in step S6 is chemical vapor deposition (CVD), chemical liquid deposition, sputtering deposition, evaporation plating, DLC, spraying, or dipping.

[0110] In a specific embodiment, a carbon coating layer is formed on the surface of the ion conductor coating layer by chemical vapor deposition (CVD).

[0111] Specifically, the ion conductor coating layer is used as a growth substrate, acetylene (which can be efficiently decomposed at 300-450°C) is selected as a carbon source gas, and the flow rate of the carbon source gas is 50-500sccm; inert gas (Ar or He) is used as a carrier gas, and the flow rate is controlled at 20-200sccm; and the reaction chamber pressure is 1-50Torr.

[0112] The present application can improve the high valence Ti 4+ and Al 3+ co-doping in the lithium manganate material, respectively occupy Mn 4+ and Mn 3+ sites, have structural synergy, optimize lattice parameters and bond energy, and inhibit manganese dissolution and Jahn-Teller effect. At the same time, through the gradient coating of the double-layer coating layer, the technical problems brought by the co-doping of Ti 4+ and Al 3+ are improved, the material surface is protected, the interface stability is maintained, and the ion / electron transmission channel is maintained.

[0113] The third aspect of the present application provides a positive electrode sheet, which comprises the positive electrode material provided by the first aspect of the present application, or comprises the positive electrode material prepared by the preparation method provided by the second aspect of the present application.

[0114] It can be understood that the positive electrode sheet can further comprise other auxiliary materials or additives.

[0115] In some embodiments, the positive electrode sheet further comprises at least one of a conductive agent and a binder.

[0116] Further, the conductive agent can comprise one or more of conductive carbon black, acetylene black, carbon fiber, carbon nanotube and graphene. The binder can comprise polyvinylidene fluoride.

[0117] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode sheet provided by the third aspect of the present application.

[0118] In some embodiments, the lithium ion battery further comprises a negative electrode sheet, an electrolyte and a separator, the positive electrode sheet and the negative electrode sheet are oppositely and spacedly arranged, and the electrolyte and the separator are arranged between the positive electrode sheet and the negative electrode sheet.

[0119] Further, the present application also provides the following specific examples and comparative examples to further illustrate the specific implementation of the present application and its advantages.

[0120] Example 1

[0121] The raw materials are provided according to the stoichiometric ratio of lithium nitrate, manganese acetate, aluminum nitrate and titanium tetrabutoxide as 1:1.9:0.05:0.05. Among them, Al 3+ and Ti4+ The sum of the stoichiometric amounts accounts for 5% of the total content of Mn, Al, Ti 3+ The molar ratio of Al to Ti 4+ is 1:1.

[0122] Lithium nitrate, manganese acetate, aluminum nitrate and deionized water were mixed to form a first homogeneous solution of 0.5 mol / L, n-butyl titanate and anhydrous ethanol were mixed to form a second homogeneous solution of 0.5 mol / L, and the first and second homogeneous solutions were mixed to form a homogeneous solution. Citric acid (50% of the volume of the solvent) was added to the homogeneous solution; nitric acid was added dropwise to adjust the pH to 2.0, stirred for 35 min, filtered, and dried at 80°C for 10 h to prepare the precursor.

[0123] The precursor, anhydrous ethanol and PVP were mixed, stirred at 70°C for 3 h to prepare a sol. The concentration of the precursor in anhydrous ethanol was 0.08 g / mL, and the mass of PVP was 2% of the mass of the precursor.

[0124] The sol was placed in an oven at 120°C for 15 h to evaporate the solvent and form a dry gel; the standing temperature was adjusted to 30°C, the humidity was 60%, and the time was 12 h to prepare a porous dry gel.

[0125] The porous dry gel was incubated at 350°C for 4 h and calcined in an air atmosphere at 680°C for 10 h to form spinel LiMn 1.9 Al 0.05 Ti 0.05 O4.

[0126] A Li3PO4 coating layer was formed on the surface of the LiMn 1.9 Al 0.05 Ti 0.05 O4 by atomic layer deposition technology. Li3PO4 was generated by alternating reactions of LiHMDS and MPO, the deposition temperature was 300°C, the reaction cavity pressure was 10 mBar, the pulse times of LiHMDS and MPO were 1.5 s respectively, and the thickness of the Li3PO4 coating layer was 10 nm.

[0127] An amorphous carbon coating layer was formed on the surface of the Li3PO4 coating layer by chemical vapor deposition technology. The carbon source gas was acetylene, the acetylene gas flow was 200 sccm, the carrier gas was argon, the argon flow was 100 sccm, the reaction chamber pressure was 25 Torr, the reaction time was 5 h, and the thickness of the amorphous carbon coating layer was 5 nm.

[0128] Example 2

[0129] The preparation methods of this example and Example 1 are basically the same, the main difference is that the thickness of the Li3PO4 coating layer in Example 2 is 3 nm.

[0130] Example 3

[0131] This example and the preparation method of Example 1 are basically the same, the main difference is that the thickness of the Li3PO4coating layer in Example 3 is 20 nm.

[0132] Example 4

[0133] This example and the preparation method of Example 1 are basically the same, the main difference is that the thickness of the carbon coating layer in Example 4 is 2 nm.

[0134] Example 5

[0135] This example and the preparation method of Example 1 are basically the same, the main difference is that the thickness of the carbon coating layer in Example 5 is 10 nm.

[0136] Example 6

[0137] This example and the preparation method of Example 1 are basically the same, the main difference is that the sum of the stoichiometry of Al 3+ and Ti 4+ in the raw material accounts for 3.75% of the total content of Mn, Al, Ti, and the molar ratio of Al 3+ to Ti 4+ is 1:2.

[0138] Example 7

[0139] This example and the preparation method of Example 1 are basically the same, the main difference is that the sum of the stoichiometry of Al 3+ and Ti 4+ in the raw material accounts for 10% of the total content of Mn, Al, Ti, and the molar ratio of Al 3+ to Ti 4+ is 3:1.

[0140] Example 8

[0141] This example and the preparation method of Example 1 are basically the same, the main difference is that the sum of the stoichiometry of Al 3+ and Ti 4+ in the raw material accounts for 3.75% of the total content of Mn, Al, Ti, and the molar ratio of Al 3+ to Ti 4+ is 2:1.

[0142] Example 9

[0143] This example and the preparation method of Example 1 are basically the same, the main difference is that the sum of the stoichiometry of Al 3+ and Ti 4+ in the raw material accounts for 10% of the total content of Mn, Al, Ti, and the molar ratio of Al3+ with Ti 4+ in a molar ratio of 1:3.

[0144] Comparative Example 1

[0145] The preparation of this comparative example and Example 1 are basically the same, the main difference is that Comparative Example 1 does not dope lithium manganate, and does not perform coating treatment of ion conductor coating layer and carbon coating layer.

[0146] Comparative Example 2

[0147] The preparation of this comparative example and Example 1 are basically the same, the main difference is that Comparative Example 2 does not perform coating treatment of ion conductor coating layer and carbon coating layer.

[0148] Comparative Example 3

[0149] The preparation of this comparative example and Example 1 are basically the same, the main difference is that Comparative Example 3 only dopes Al 3+ and does not perform coating treatment, the stoichiometric amount of Al 3+ accounts for 2.5% of the total content of Mn, Al and Ti.

[0150] Comparative Example 4

[0151] The preparation of this comparative example and Example 1 are basically the same, the main difference is that Comparative Example 4 only dopes Ti 4+ and does not perform coating treatment, the stoichiometric amount of Ti 4+ accounts for 2.5% of the total content of Mn, Al and Ti.

[0152] Comparative Example 5

[0153] The preparation of this comparative example and Example 1 are basically the same, the main difference is that Comparative Example 5 does not perform coating treatment of carbon coating layer.

[0154] Comparative Example 6

[0155] The preparation of this comparative example and Example 1 are basically the same, the main difference is that Comparative Example 6 does not perform coating treatment of ion conductor coating layer.

[0156] Test Example

[0157] The lithium ion batteries further prepared from the positive electrode materials of Examples 1-9 and Comparative Examples 1-6 are subjected to relevant performance tests, and the test results are shown in Table 1 below.

[0158] The positive electrode materials prepared in each embodiment and comparative example were used as positive electrode active materials. They were mixed and dispersed in N-methylpyrrolidone at a mass ratio of positive electrode active material: conductive carbon black: polyvinylidene fluoride = 97:2:1 to form a slurry. The slurry was coated onto aluminum foil, dried, and cut into sheets to serve as positive electrode sheets. Using lithium metal as the counter electrode, polypropylene as the separator, and 1 mol / L LiPF6 dissolved in a 1:1 volume ratio EC / DMC mixed solvent as the electrolyte, half-cells were assembled in an argon-filled glove box.

[0159] Capacity retention test

[0160] The batteries prepared in each embodiment and comparative example were charged at room temperature at 1C or a specified current to the termination voltage, with a cutoff current of 0.05C, and left to stand for 30 min; then discharged at 1C to the final discharge voltage, and the discharge capacity was recorded, followed by a 30 min resting period; the charge-discharge cycle was repeated 1000 times and the data were recorded.

[0161] Lattice constant test

[0162] The battery, after 1000 cycles, was disassembled, and the positive electrode material powder was scraped off. It was then cleaned and dried with anhydrous ethanol and measured using an XRD instrument. The X-rays selected were Cu-Kα (λ=0.15406nm) or Co-Kα (λ=0.17889nm), with the scanning range covering high exponential peaks, a step size of 0.005°, and a slow scan mode (0.02° / min). After obtaining the data, error correction and verification were performed.

[0163] Table 1

[0164] Capacity retention rate (%) for 1000 cycles Rate of change in lattice constant (%) Example 1 92.4 0.21 Example 2 86.1 0.27 Example 3 87.5 0.25 Example 4 86.8 0.26 Example 5 87.2 0.25 Example 6 87.6 0.25 Example 7 87.9 0.25 Example 8 88.1 0.24 Example 9 88.5 0.24 Comparative Example 1 68.0 0.50 Comparative Example 2 80.2 0.37 Comparative Example 3 81.9 0.35 Comparative Example 4 81.1 0.36 Comparative Example 5 77.0 0.42 Comparative Example 6 75.5 0.44

[0165] Compared with Comparative Examples 1-6, Examples 1-9 exhibit higher capacity retention and lower lattice constant change rate, indicating that doping and double-layer coating of lithium manganese oxide can improve the capacity and cycle life of the cathode material, while also enhancing the structural stability of the material.

[0166] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0167] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises: a core and a coating layer on the surface of the core; the coating layer comprises a first coating layer and a second coating layer, the first coating layer is between the core and the second coating layer; the first coating layer is an ion conductor coating layer, and the second coating layer is a carbon coating layer; The core has a molecular formula of LiMn x Al y Ti z O4, wherein x+y+z=2, 1.8≤x≤1.925, 0.025≤y≤0.15, 0.025≤z≤0.

15.

2. The positive electrode material of claim 1, wherein, The LiMn x Al y Ti z Al in O4 3+ With Ti 4+ It accounts for 3.75% to 10% of the total content of Mn, Al, and Ti; the Al 3+ With Ti 4+ The molar ratio is (0.5~3):(0.5~3).

3. The positive electrode material of claim 1, wherein, the thickness of the ion conductor coating layer is 3nm-20nm, and the thickness of the carbon coating layer is 2nm-10nm.

4. The positive electrode material of claim 1, wherein, The ion conductor coating layer is Li3PO4.

5. A method for producing a positive electrode material, characterized by, The method comprises the following steps: S1, weighing a lithium source, a manganese source, an aluminum source, and a titanium source in proportion to provide raw materials; S2, mixing the raw materials with a first solvent and a second solvent according to the material properties, and then mixing with a complexing agent and a pH adjuster to form a solution, filtering and drying to prepare a precursor; S3, mixing the precursor with a third solvent and a surfactant, stirring and treating to prepare a sol; S4, sequentially performing gel treatment and calcination treatment on the sol to prepare an aluminum-titanium doped spinel lithium manganate; S5, forming an ion conductor coating layer on the surface of the aluminum-titanium doped spinel lithium manganate; S6, forming a carbon coating layer on the surface of the ion conductor coating layer.

6. The method for preparing the cathode material according to claim 5, characterized in that, When the raw materials are inorganic salt materials, they are dissolved in the first solvent to form a first homogeneous solution, and the first solvent is water; when the raw materials are organic salt materials, they are dissolved in the second solvent to form a second homogeneous solution, and the second solvent is an alcohol solvent.

7. The method of claim 6, wherein the method further comprises a step of calcining the mixture at a temperature of 700-900°C for 5-20 hours. The concentration of the first homogeneous solution and the second homogeneous solution is 0.4mol / L-1mol / L.

8. The method for preparing the cathode material according to claim 5, characterized in that, The step of preparing the sol comprises at least one of the following features (1)-(2): (1) the concentration of the precursor in the third solvent is 0.01g / mL-0.15g / mL; (2) the mass of the surfactant is 1%-3% of the mass of the precursor.

9. A positive electrode sheet characterized by comprising: The positive electrode material comprises the positive electrode material prepared by the method of any one of claims 1-4 or the method of any one of claims 5-8.

10. A lithium-ion battery, characterized by, The positive electrode sheet comprises the positive electrode material of claim 9.

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