Positive electrode material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention provides a positive electrode material and a preparation method thereof, an electrochemical device and electronic equipment, and particularly relates to the technical field of battery materials. The positive electrode material comprises an inner core and a shell, wherein the inner core is selected from active substances capable of reversibly embedding and removing lithium ions; the surface of the inner core is coated with the shell, the material of the shell comprises Li4Ti5-xMxO12, x is more than 0 and less than or equal to 0.3, and M comprises one or more of V, Ta and Nb. The transition metal element doped lithium titanate shell is constructed on the surface of the common positive electrode active material, so that the cycle performance of the positive electrode active material can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, and in particular to a positive electrode material, a preparation method thereof, an electrochemical device and an electronic device. BACKGROUND

[0002] Lithium ion batteries (LIBs) have been widely applied in portable electronic devices, electric vehicles, large-scale energy storage systems and other fields as the most core electrochemical energy storage technology. The dominant position of lithium ion batteries is due to their excellent comprehensive performance: extremely high energy density lays the foundation for long endurance of equipment, excellent cycle life guarantees long-term use economy, strong rate capability enables it to support fast charging and high power discharging, no memory effect realizes the convenience of charging as needed, low self-discharge rate ensures the persistence of power, and high working voltage improves the system energy conversion efficiency. Although challenges still exist in the pursuit of higher energy density, faster charging speed, longer life and absolute safety, lithium ion batteries have become the core power to promote the electrification of transportation and the transformation of clean energy, and the technological breakthrough is of great significance to the construction of future energy system.

[0003] With the rapid development of electric vehicles and large-scale energy storage, the market has put forward higher requirements for the fast charging capability, cycle life and safety of lithium ion batteries. The positive active materials of the mainstream lithium ion batteries, such as lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganate and ternary materials, have their own unique advantages, but in the long-term cycle process, they all have common problems that cannot be avoided: transition metals in the positive active material are prone to dissolution, and severe side reactions are prone to occur between the material surface and the electrolyte. These two problems directly lead to the attenuation of battery rate performance and the shortening of cycle life, which seriously restricts the application expansion of lithium ion batteries in fast charging scenarios and long-term service requirements.

[0004] Therefore, it is urgent to provide a new material structure to improve the problems of transition metal dissolution and side reactions, so as to meet the urgent needs of high-end markets for high power density and ultra-long cycle life of lithium ion batteries. SUMMARY

[0005] In view of the above shortcomings of the prior art, the present application provides a positive electrode material, a preparation method thereof, an electrochemical device and an electronic device to improve the technical problems of transition metal dissolution and side reactions in the positive electrode material.

[0006] To achieve the above object and other related objects, the present application provides a positive electrode material, which comprises: an inner core and an outer shell, the inner core is selected from active substances capable of reversible intercalation and deintercalation of lithium ions; the outer shell is coated on the surface of the inner core, and the material of the outer shell comprises Li4Ti 5-x Mx O 12 wherein 0 < x ≤ 0.3, M comprises one or more of V, Ta, Nb.

[0007] In an embodiment of the present application, the mass of the core is 80% to 88% of the total mass of the positive electrode material, and the mass of the shell is 12% to 20% of the total mass of the positive electrode material.

[0008] In an embodiment of the present application, the thickness of the shell is 500 nm to 1000 nm.

[0009] In an embodiment of the present application, the particle size of the core is 10000 nm to 20000 nm.

[0010] In an embodiment of the present application, the core comprises one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt aluminate, and lithium nickel cobalt manganate.

[0011] The present application also provides a preparation method of the positive electrode material, characterized by comprising the following steps: Core pretreatment: the core material is mixed with a solvent and then subjected to ball milling to obtain a core slurry; Shell precursor configuration: a lithium source, a titanium source, and a doping source are weighed according to the stoichiometric ratio of the shell material, dissolved in a solvent to obtain a shell precursor slurry; Blending: the core slurry and the shell precursor slurry are mixed and stirred to enable the shell precursor to be adsorbed on the surface of the core material, thereby obtaining a positive electrode material precursor; Heat treatment: the positive electrode material precursor is subjected to heat treatment to obtain a positive electrode material.

[0012] In an embodiment of the present application, the step of shell precursor configuration comprises: the lithium source, the titanium source, and the doping source are dispersed into the solvent respectively, stirred until completely dissolved, and then the lithium source solution, the titanium source solution, and the doping source solution are mixed; wherein the lithium source comprises lithium acetate, the titanium source comprises tetrabutyl titanate, and the doping source comprises one or more of organic acid salt, inorganic acid salt, oxide, and hydroxide of a doping element, and the doping element comprises one or more of vanadium, tantalum, and niobium.

[0013] In an embodiment of the present application, the step of blending comprises: after the core slurry and the shell precursor slurry are mixed, stirring in a water bath, wherein the water bath temperature is 50 to 80℃, and the stirring time is 5 to 8 hours.

[0014] In an embodiment of the present application, the heat treatment temperature is 600℃ to 900℃, the heat treatment time is 1 hour to 10 hours, and the heating rate is 1℃ / min to 20℃ / min.

[0015] The application also provides an electrochemical device comprising the positive electrode material or the positive electrode material prepared by the preparation method.

[0016] The application also provides an electronic device comprising the electrochemical device.

[0017] The application has the following beneficial effects: the positive electrode material of the application has a core-shell structure, with a commonly used positive electrode active material as the core and a transition metal doped lithium titanate (LTMO) as the shell. The LTMO shell layer has excellent ion conductivity and three-dimensional diffusion channels, which provide an efficient path for the migration of lithium ions at the interface of the positive electrode active material particles, thereby greatly reducing the interface impedance. At the same time, the LTMO shell layer acts as a stable physical barrier, which can effectively isolate the direct contact between the core active material and the electrolyte, inhibit the side reactions (such as transition metal dissolution and electrolyte oxidation) under high temperature and high voltage, thereby significantly enhancing the cycle stability and storage life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application. It is to be understood that the drawings are only schematic and that they do not necessarily represent a limiting embodiment of the application. For the purpose of explanation and clearness, elements in the drawings have not necessarily been drawn to scale. The same reference numbers in different drawings represent the same or similar elements.

[0019] In the drawings: Figure 1 Structure schematic diagram of the positive electrode material provided by an embodiment of the application; Figure 2 Flowchart of the preparation method of the positive electrode material provided by an embodiment of the application.

[0020] Reference numerals: 1, shell; 2, core. DETAILED DESCRIPTION

[0021] The above description is only some embodiments of the application. Those skilled in the art can easily understand other advantages and effects of the application from the above description. The application can also be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the application. The following embodiments and features in the embodiments can be combined with each other without conflict.

[0022] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0023] 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0024] The terms or phrases used in this article have the following meanings: In this article, the terms "multiple," "various," and "multiple times" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0025] In this document, terms such as “preferred,” “ideal,” “further,” “even more,” and “particularly” are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0026] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0027] Currently, the mainstream positive electrode active materials for lithium-ion batteries include lithium iron phosphate (LiFePO4, abbreviated as LFP) and lithium manganese iron phosphate (LiMn). x Fe 1-x PO4 (LMFP), lithium cobalt oxide (LiCoO2, LCO), lithium manganese oxide (LiMn2O4, LMO), and ternary materials (LiNi) x Co y Mn 1-x-y O2, abbreviated as NCM; LiNi x Co y Al 1-x-y While materials such as O2 (NCA) and others possess unique advantages, such as the safety and stability of lithium iron phosphate and the high energy density of ternary materials, they all share common and unavoidable problems during long-term cyclic use: the transition metals in the positive electrode active material are prone to dissolution, and severe side reactions easily occur between the material surface and the electrolyte.

[0028] To improve the above problems, the prior art often uses modification methods such as element doping and carbon coating for optimization. However, with the continuous improvement of performance requirements, the limitations of such traditional modification methods are increasingly prominent, and they can only alleviate the problems from the surface or locally, and cannot fundamentally break through the core technical bottlenecks of slow ion migration dynamics and internal transition metal dissolution.

[0029] Based on this, the present application provides a kind of positive electrode material, the preparation method of the positive electrode material, the electrochemical device comprising the positive electrode material, and the electronic equipment comprising the electrochemical device. By constructing transition metal element doped lithium titanate shell on the surface of commonly used positive electrode active material, the problems of slow ion migration dynamics and internal transition metal dissolution can be fundamentally solved while retaining the advantages of core positive electrode active material.

[0030] Please refer to Figure 1 The positive electrode material of the present application comprises a core 2 and a shell 1, wherein the core 2 is the active component in the positive electrode material, which undertakes the main energy storage function, provides high reversible capacity and stable working voltage platform, and ensures the high energy density characteristics of the positive electrode material, and the shell 1 serves as a high-speed ion conductor and a physical protection barrier.

[0031] The core 2 is selected from active substances capable of reversible intercalation and deintercalation of lithium ions, including but not limited to commonly used positive electrode active materials. In some embodiments, the core 2 comprises one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt aluminate, lithium nickel cobalt manganate, for example, the core 2 can be lithium iron phosphate, or lithium manganese iron phosphate, or lithium cobaltate, or lithium nickel cobalt manganate, etc. It should be noted that the ratio of nickel, cobalt and manganese elements in the lithium nickel cobalt manganate ternary material is not limited, and any ratio that can be used for lithium ion batteries can be used, for example, the lithium nickel cobalt manganate can be LiNi 0.5 Co 0.2 Mn 0.3 O2, or LiNi 0.6 Co 0.1 Mn 0.3 O2, or LiNi 0.8 Co 0.1 Mn 0.1 O2, or LiNi 0.9 Co 0.05 Mn 0.05 O2, etc. Similarly, the ratio of nickel, cobalt and aluminum elements in the lithium nickel cobalt aluminate ternary material is not limited, and any ratio that can be used for lithium ion batteries can be used, for example, the lithium nickel cobalt aluminate can be LiNi 0.7 Co 0.25 Al 0.05 O2, or LiNi 0.8 Co 0.15 Al0.05 O2, or LiNi 0.85 Co 0.1 Al 0.05 O2, or LiNi 0.9 Co 0.05 Al 0.05 O2, etc. Other materials involve element ratios, such as the ratio of manganese and iron in lithium manganese iron phosphate is not limited, as long as it can be used in lithium ion batteries, and will not be listed here.

[0032] Those skilled in the art can understand that the core 2 can also be a doped positive electrode active material, that is, a proper amount of other elements is doped in the above-mentioned listed materials, wherein the doping elements are not limited, and conventional doping elements can be selected according to needs, for example, Al, Zr, Cr, Zn, Bi, La, Ti, Mg, etc. These doping elements can be singly doped, for example, Al doping, Zr doping, Mg doping, etc. They can also be combined doping, for example, Al and Zr combined doping, Ti and La combined doping, etc.

[0033] The shell 1 is wrapped on the surface of the core 2, and the material of the shell 1 in the application includes Li4Ti 5-x M x O 12 (LTMO), wherein 0 < x ≤ 0.3, M includes one or more of V, Ta, Nb. That is, M elements are doped in LTO (Li4Ti5O 12 , lithium titanate), and x represents the doping amount of M elements in Li4Ti5O 12 . Exemplarily, M can be V elements, or Ta elements, or Nb elements, and M can also be a combination of V and Ta doping, or a combination of Ta and Nb doping. The doping amount x of M can be 0.05, 0.1, 0.2 or 0.3, etc.

[0034] LTMO retains the three-dimensional tunnel crystal structure of LTO, has excellent ion conductivity and three-dimensional diffusion channel, provides an efficient path for the migration of lithium ions at the grain boundary of the positive electrode material, thereby greatly reducing the interface impedance and significantly improving the fast charging capacity and low temperature performance of the material. After doping Nb on the basis of LTO, on the one hand, Nb 5+ substitutes Ti 4+ , which produces excess positive charge, and the material will induce part of Ti 4+ to be reduced to Ti 3+This process increases the concentration of electron carriers, significantly improving the intrinsic electronic conductivity of the material; and after Nb doping, the d orbital electrons are shifted, causing the number of energy bands near the Fermi surface to increase, which is beneficial for electron transfer, thereby significantly enhancing the electronic conductivity. In addition, Nb doping can reduce the original LTO electron transition energy barrier from 0.75 eV to 0.62 eV, reducing the energy threshold for electrons to be excited from the valence band to the conduction band, making the electron transition process more likely to occur, thereby further optimizing the conductive performance of the material. On the other hand, since the ionic radius of Nb 5+ is generally larger than that of Ti 4+ , its incorporation can strengthen the lattice like a "rivet" through strong Nb-O bonds, effectively suppressing lattice distortion and volume change during the cycle process, thereby enhancing structural stability. V doping focuses on valence regulation, and doping V in LTO, V 5+ will replace Ti 4+ in the lattice, in order to maintain charge balance, this substitution process will induce the reduction of adjacent Ti 4+ to form Ti 3 + The formation of Ti 3+ introduces additional free electrons, thereby significantly improving the electronic conductivity of the material and improving the electrode reaction kinetics, allowing it to maintain high capacity at high rates. The enhancement effect of Ta doping is focused on the rivet effect: Ta is an element with a large atomic mass. The introduction of large mass Ta atoms in the lattice, like "rivets", anchor the surrounding lattice atoms, effectively suppressing atomic thermal vibration amplitude and displacement deviation under high temperature environment, significantly enhancing lattice rigidity and structural integrity. This effect can effectively suppress phase transition and lattice distortion during the cycle process, significantly improving the cycle life and thermal stability of the material.

[0035] In addition, LTMO is electrochemically inert at the working potential of the core 2 (positive active material) (3.0~4.2V), and does not undergo redox reactions or side reactions with the electrolyte under high pressure and high temperature (≤60℃) conditions. The LTMO shell acts as a stable physical barrier, effectively isolating the positive active material core from direct contact with the electrolyte, suppressing side reactions (such as transition metal dissolution and electrolyte oxidation) under high temperature and high voltage, thereby significantly enhancing the high-temperature cycle stability and storage life of the battery.

[0036] In some embodiments, the mass of the inner core 2 is 80% to 88% of the total mass of the positive electrode material, for example, 80%, 84%, 88%, etc., based on the total mass of the positive electrode material as the mass reference; the mass of the shell 1 is 12% to 20% of the total mass of the positive electrode material, for example, 12%, 16%, 20%, etc., based on the total mass of the positive electrode material as the mass reference. The mass ratio of the shell 1 is controlled at a very low level under the premise of meeting the functional requirements, thereby maximizing the high-voltage platform and high-energy density core advantages of the inner core 1, and the LTMO shell 1 can act as a certain physical protection layer to improve the cycle life of the battery.

[0037] Further, the single particle size D of the inner core 2 is 10,000 nm to 20,000 nm (10 μm to 20 μm). For example, D can be 10,000 nm, 13,000 nm, 15,000 nm, 18,000 nm, or 20,000 nm, etc. Under the coating ratio in the above mass range, the thickness T of the shell 1 coated on the surface of the inner core 2 is 500 nm to 1,000 nm. For example, T can be 500 nm, 800 nm, or 1,000 nm. Precise control of the thickness of the shell 1 at the nanoscale can ensure that the functional mass ratio is extremely small, thereby maximizing the high-voltage platform and high-energy density advantages of the inner core. If the mass ratio of the shell 1 in the positive electrode material is less than 12%, the shell 1 cannot be uniformly coated on the surface of the particles of the inner core 2, the shell 1 is discontinuously coated, cracks or holes appear on the surface of the material, and the performance improvement effect is poor due to the inability to construct an efficient ion channel network; if the mass ratio of the shell 1 in the positive electrode material is greater than 20%, the shell 1 formed on the surface of the inner core 2 is too thick, the thick shell 1 hinders ion migration, increases the interface impedance, and since the shell 1 itself does not contribute to the capacity, a mass ratio that is too large reduces the overall energy density of the positive electrode material.

[0038] In the present application, the morphology of the positive electrode material, the particle size of the inner core 2, and the coating thickness of the shell 1 can be observed by a scanning electron microscope-energy spectrometer (SEM-EDS).

[0039] In the present application, the morphology of the positive electrode material, the particle size of the inner core 2, and the coating thickness of the shell 1 can be observed by a scanning electron microscope-energy spectrometer (SEM-EDS).

[0040] Please refer to Figure 2The application further provides a preparation method of the positive electrode material, which comprises the following steps: S1, the core material is mixed with a solvent and then subjected to ball milling treatment to obtain a core slurry; S2, a lithium source, a titanium source and a doping source are weighed according to the stoichiometric ratio of the shell material and dissolved in a solvent to obtain a shell precursor slurry; S3, the core slurry and the shell precursor slurry are mixed and stirred, so that the shell precursor is adsorbed on the surface of the core material to obtain a positive electrode material precursor; S4, the positive electrode material precursor is subjected to heat treatment to obtain the positive electrode material.

[0041] Specifically, the core material in step S1 is selected from active substances capable of reversible intercalation and deintercalation of lithium ions, including but not limited to commonly used positive electrode active materials. In some embodiments, the core material includes one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt aluminum acid, lithium nickel cobalt manganate, which can be the above-mentioned listed materials, or can be doped with conventional elements within the above-mentioned listed materials, which will not be described here. The core material in this step can be obtained by general commercial means, or can be prepared by conventional methods in the art, such as hydrothermal method, which is not specifically limited here. In some embodiments, the particle size D of the core material is 10000nm-20000nm, which can balance the design of energy density, charge transport efficiency, processing performance and cycle stability.

[0042] Due to the weak interactions such as van der Waals force, hydrogen bond and electrostatic attraction on the surface of the core material particles, the particles spontaneously aggregate to form a loose agglomerate structure (also known as soft agglomeration) during drying, storage or dispersion. The particles inside the agglomerate cannot fully contact with the coating material (i.e. the shell), resulting in uneven thickness of the coating layer and local absence of coating; the agglomerate is prone to form voids or cracks after the electrode is rolled, increasing the resistance of lithium ion transport. Therefore, before coating the shell on the surface of the core material particles, step S1 is performed to pretreat the core, a certain amount of core material is mixed with a solvent, and then dispersed by ball milling process to effectively break the soft agglomeration structure of the core material, obtaining a highly dispersed, uniform and stable core slurry. The solvent in this step is not specifically limited and can be selected according to the type of core material. It should be noted that the solvent should be matched with the polarity of the core material surface, the surface tension should be moderate, it can penetrate the soft agglomeration gap between the core particles, reduce the van der Waals force and hydrogen bond interaction between the particles, and cooperate with ball milling to achieve efficient dispersion; it does not react with the core material and does not destroy the structure, and it is suitable for subsequent processes. Exemplarily, when the core material is LFP, the solvent can be selected from anhydrous ethanol or deionized water; when the core material is NCM, the solvent can be selected from anhydrous ethanol, isopropyl alcohol, etc.

[0043] Step S2, i.e. shell precursor configuration, the shell material includes Li4Ti 5-x M x O 12 , wherein 0 < x ≤ 0.3, M includes one or more of V, Ta, Nb. When configuring the shell precursor, according to the stoichiometric ratio of the shell material, first measure the lithium source, titanium source and M doping source, wherein the lithium source and the titanium source need to have good solubility and be able to participate in the reaction at a lower temperature, and the by-products are harmless or volatile. Illustratively, the lithium source is lithium acetate, and the titanium source is tetrabutyl titanate, etc. The M doping source includes one or more of organic acid salt, inorganic acid salt, oxide, hydroxide containing a doping element, and the doping element includes one or more of vanadium (V), tantalum (Ta), and niobium (Nb), i.e. the M doping source can select an organic acid salt containing a doping element, or an inorganic acid salt containing a doping element, or an oxide containing a doping element, or a hydroxide containing a doping element, or a combination of these materials, etc. And the doping element can be V, or Ta, or Nb, or several combinations of these three elements, etc. Illustratively, the doping element is Nb, the M doping source is a niobium source, and the niobium source is selected from niobium pentachloride (NbCl5), niobium nitrate (Nb (NO3)5), di-niobium pentoxide (Nb2O5), niobium alcoholate (such as niobium ethoxide Nb(OC2H5)5), etc.; the doping element is Ta, and the M doping source is a tantalum source, and the tantalum source is selected from tantalum chloride (TaCl5), di-tantalum pentoxide (Ta2O5), tantalum alcoholate (such as isopropyl tantalum Ta(O-iPr)5), etc.; the doping element is V, and the M doping source is a vanadium source, and the vanadium source is selected from di-vanadium pentoxide (V2O5), vanadium nitrate (V (NO3)3), vanadyl sulfate (VOSO4 3H2O), etc. Then, the measured materials are respectively dispersed into corresponding solvents according to the reactivity and solubility, fully stirred until completely dissolved, to obtain a lithium source solution, a titanium source solution and a doping source solution, and then the three are mixed uniformly to obtain a shell precursor slurry. Here, the types of solvents are not limited, as long as the above raw materials are completely dissolved, for example, lithium acetate is dispersed into deionized water, niobium source niobium pentachloride and titanium source tetrabutyl titanate are dispersed into anhydrous ethanol, etc. The specific ratio between the solvent and each raw material is not specially limited, as long as all the raw materials are completely dissolved.

[0044] It should be noted that steps S1 and S2 are not sequential, and S1 can be performed first, followed by S2; or S2 can be performed first, followed by S1; or S1 and S2 can be performed simultaneously. The mass of the core material in step S1 and the amount of each raw material of the shell precursor in step S2 are converted according to the mass percentage of the core and the shell in the prepared positive electrode material.

[0045] Step S3, i.e. blending, the shell precursor slurry obtained in step S2 is added dropwise into the core slurry obtained in step S1, and mixed and stirred, so that the shell precursor is uniformly adsorbed on the particle surface of the core material, to obtain the positive electrode material precursor.

[0046] In some embodiments, in order to enable the shell precursor to be better adsorbed on the particle surface of the core material, it is necessary to provide sufficient reaction temperature and time, therefore, step S3 is constant temperature stirring in a water bath for a period of time, for example, the water bath temperature is 50-80°C, for example, it can be 50°C, 60°C, 70°C or 80°C, etc., and the stirring time is 5-8 hours, for example, it can be 5 hours, 6 hours, 7 hours or 8 hours, etc.

[0047] Further, after the positive electrode material precursor is generated in step S3, in order to better perform the subsequent heat treatment, it further includes drying treatment of the positive electrode material precursor, and the drying treatment mode is not limited, and a conventional drying mode in the art can be used, for example, drying in an oven, the drying treatment temperature is 60-80°C, for example, 60°C, 70°C, 80°C, etc., and the drying time is 12-24 hours, for example, 12 hours, 18 hours, 24 hours, etc.

[0048] Step S4, i.e. the heat treatment step, the positive electrode material precursor obtained in step S3 is loaded into a sintering container for high-temperature calcination, so as to convert the shell precursor into the three-dimensional tunnel type crystal structure of the target LTMO at high temperature.

[0049] In some optional embodiments, the temperature in the heat treatment step is 600-900°C, for example, 600°C, 700°C, 800°C, 850°C or 900°C, etc., and the heat treatment time is 1-10 hours, for example, 1 hour, 5 hours, 8 hours or 10 hours, etc. The heat treatment process is carried out in an inert atmosphere, and the temperature rising rate of the heat treatment step is 1-20°C / min, for example, 1°C / min, 5°C / min, 10°C / min, 15°C / min or 20°C / min, etc.

[0050] After that, in order to better perform the subsequent positive electrode slurry preparation of the obtained positive electrode material, the positive electrode material obtained in step S4 needs to be post-treated, so that the material is better dispersed, and the post-treatment mode includes but is not limited to grinding. The grinding time is changed according to the mass of the positive electrode material, for example, 100g of positive electrode material needs to be ground for 4 hours, and as the mass of the positive electrode material increases, the grinding time is appropriately increased.

[0051] The preparation method of the present application can in-situ coat a uniform, dense and firm LTMO shell on the surface of the core material particles, thereby obtaining a core-shell structured positive electrode material. The LTMO shell as a stable physical barrier can effectively isolate the direct contact between the positive electrode material core and the electrolyte, inhibit the side reaction under high temperature and high voltage, at the same time, the LTMO has excellent ionic conductivity and three-dimensional diffusion channel, providing an efficient path for the migration of lithium ions at the interface of the positive electrode material particles, thereby greatly reducing the interface impedance and significantly improving the fast charging capacity and low temperature performance of the material.

[0052] The positive electrode material of the present application can also be prepared by other conventional preparation methods in the art, as long as the corresponding core-shell structured positive electrode material can be obtained.

[0053] The present application also provides an electrochemical device comprising the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.

[0054] In an embodiment, the electrochemical device comprises a lithium ion battery, which can be a liquid lithium ion battery (electrolyte is a non-aqueous electrolyte) or a solid-state lithium ion battery (electrolyte is a solid-state electrolyte), which is not limited herein.

[0055] The structure of the liquid lithium ion battery is described in detail as follows: the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a non-aqueous electrolyte and a separator.

[0056] The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector. The positive electrode current collector is selected from materials with excellent electrical conductivity and mechanical strength, such as aluminum foil or carbon-coated aluminum foil, etc. The positive electrode current collector has two surfaces arranged in opposite directions along its thickness direction, and the positive electrode active material layer can be arranged on one side of the surface of the positive electrode current collector or on both sides of the surface. The positive electrode active material layer comprises the above-mentioned positive electrode material, a positive electrode conductive agent and a positive electrode binder. The positive electrode binder comprises any one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, polyamide, polyacrylonitrile, polyacrylate, polyvinyl ether, polymethyl methacrylate, ethylene-propylene-diene terpolymer, polyhexafluoropropylene, etc. Exemplarily, the positive electrode binder can be polyvinylidene fluoride, or polytetrafluoroethylene, etc. The positive electrode conductive agent includes but is not limited to one or more of conductive carbon black (SP), acetylene black, carbon nanotube, carbon fiber, graphite, etc. Exemplarily, the conductive agent is conductive carbon black; or a combination of carbon fiber and conductive carbon black; or a combination of carbon nanotube and graphene, etc.

[0057] The preparation process of the positive electrode sheet is exemplified as follows: first, the positive electrode material, the positive electrode conductive agent, and the positive electrode binder are mixed and stirred uniformly in a solvent such as N-methyl pyrrolidone (NMP) according to the set ratio to form a positive electrode slurry, then the positive electrode slurry is coated on the positive electrode current collector, and after processes such as drying, rolling, and sheet cutting, the positive electrode sheet is obtained. The ratio of the positive electrode material, the conductive agent, and the binder can be set according to the conventional settings in the art, and is not specifically limited here.

[0058] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector. The negative electrode current collector is made of a material with good electrical conductivity and mechanical strength, such as copper foil or carbon-coated copper foil, and has two surfaces arranged in opposite directions along its thickness. The negative electrode active material layer can be arranged on one side surface of the negative electrode current collector or on both side surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a thickening agent. The specific types of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the thickening agent are not specifically limited here, and materials known in the art that can be used in lithium ion batteries can be used, and the selection can be made according to actual needs by those skilled in the art.

[0059] Exemplarily, the negative electrode active material includes but is not limited to soft carbon, hard carbon, artificial graphite, natural graphite, silicon-based materials (such as silicon, silicon oxide, silicon-carbon composite), etc., which can be used alone or in combination. For example, the negative electrode active material is artificial graphite or a combination of artificial graphite and silicon-carbon composite. The negative electrode conductive agent is selected from one or more of acetylene black, conductive carbon black (Super P), carbon fiber (VGCF), carbon nanotube (CNT), Ketjen black, and graphite powder, such as acetylene black, or conductive carbon black, or a combination of carbon fiber and carbon nanotube, etc. The negative electrode binder is selected from any one or a combination of several in any proportion of polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and styrene butadiene rubber; for example, it can be styrene butadiene rubber, polyacrylic acid, etc.; and the thickening agent is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0060] The preparation process of the negative electrode sheet is exemplified as follows: first, the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the thickening agent are mixed and stirred uniformly in a solvent such as deionized water according to the set ratio to form a negative electrode slurry, then the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying, rolling, and sheet cutting, the negative electrode sheet is obtained.

[0061] The separator is arranged between the positive electrode tab and the negative electrode tab, for separating the positive electrode tab and the negative electrode tab, preventing short circuit inside the battery, and enabling lithium ions to move between the positive electrode and the negative electrode, so as to realize the charging and discharging process of the battery. The separator needs to have excellent electrochemical stability, mechanical strength and thermal stability. For example, the separator can be a porous film such as a polyethylene (PE) film, a polypropylene (PP) film or a multi-layer composite film (such as a PP / PE / PP film) and the like. A functional layer can also be coated on the above-mentioned porous film. The functional layer can be arranged on any one side or both sides of the porous film. The functional layer includes a ceramic coating and / or a polymer adhesive layer. The ceramic coating includes but is not limited to ceramic materials such as aluminum oxide (Al2O3) and silicon oxide (SiO2), and polymer adhesives such as polyvinylidene fluoride (PVDF) and aramid. The specific types and proportions of the above-mentioned materials can be selected by those skilled in the art according to the performance requirements of the battery. The polymer adhesive layer can be a PVDF and aramid adhesive layer.

[0062] The non-aqueous electrolyte plays a role in conducting lithium ions during the charging and discharging process of the battery. The non-aqueous electrolyte includes an organic solvent and a lithium salt. The lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorobis(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodiphosphate (LiDFOP) and lithium tetrafluorodiphosphate (LiTFOP). Further, the lithium salt is preferably lithium hexafluorophosphate or a combination of lithium hexafluorophosphate and other lithium salts, for example, a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide. The organic solvent can be selected from one or more of carbonates (such as one or more of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC and ethyl methyl carbonate EMC), carboxylic acid esters (such as ethyl acetate and ethyl propionate), ethers (such as 1,3-dioxolane DOL and dimethoxyethane DME) and sulfones (such as sulfolane).

[0063] In some optional embodiments, the non-aqueous electrolyte further includes functional additives, such as film-forming additives (such as vinylene carbonate VC and fluoroethylene carbonate FEC), flame-retardant additives (such as phosphate esters), overcharge protection additives (such as biphenyls) and additives for improving high and low temperature performance. The specific additives can be added according to actual needs.

[0064] Battery assembly: the prepared positive electrode sheet, separator and negative electrode sheet are placed in sequence, the separator is placed between the positive and negative electrode sheets to play a role of isolation, and a bare battery cell is obtained by winding or stacking. The bare battery cell is assembled into a battery shell, and the water content is less than 450 ppm after sufficient baking. After the processes of liquid injection, formation, sealing and inspection, a lithium ion battery is obtained.

[0065] In other embodiments, the lithium ion battery is a solid-state lithium ion battery, and the electrolyte of the solid-state lithium ion battery is solid. Common solid-state electrolytes include oxide solid-state electrolytes, halide solid-state electrolytes, sulfide solid-state electrolytes, etc., which will not be described here. Those skilled in the art can select according to actual production needs.

[0066] It should be noted that the structures not described in detail in the above lithium ion battery can be set according to the prior art, and will not be described here.

[0067] The present application also provides an electronic device comprising the above lithium ion battery. The lithium ion battery can be used in the form of a single battery, a battery module or a battery pack for the electronic device to provide power.

[0068] In some embodiments, the electronic device includes but is not limited to a mobile phone, a tablet, a notebook computer, an electric toy, an electric car, a new energy vehicle, a ship, a spacecraft, etc. Among them, the electric toy can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric plane toys, etc. The spacecraft can include airplanes, rockets, space shuttles and spaceships, etc. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle or an extended range vehicle, etc.

[0069] The technical solutions of the present application will be described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the instruments used in the examples are commercially available.

[0070] Example 1 This embodiment provides a positive electrode material, which comprises a core and a shell. The core is a commercial carbon-free LiFePO4, and the shell material is Li4Ti 4.8 Nb 0.2 O 12 The mass of the shell is 12% of the total mass of the positive electrode material.

[0071] The preparation method of the above positive electrode material is as follows: Step one: commercial carbon-free LiFePO4 and anhydrous ethanol are added to a ball mill tank, and ball milling is carried out at a speed of 300 rpm for 2 hours to obtain a core slurry.

[0072] Step two: disperse lithium acetate into deionized water, disperse niobium pentachloride and tetrabutyl titanate into anhydrous ethanol solution, stir until completely dissolved, then slowly drop the lithium source solution into the solution containing the titanium source and transition metal source, continue stirring to obtain a uniform LTMO precursor slurry.

[0073] Step three: slowly add the LTMO precursor slurry into the inner core slurry under a 60℃ water bath, continue stirring for 6 hours, then transfer to a 80℃ oven to dry for 24 hours after the solvent is volatilized, to obtain the positive electrode material precursor.

[0074] Step four: place the positive electrode material precursor into a tube furnace in an argon atmosphere at 700℃ (the heating rate is 10℃ / min), keep the temperature for 4 hours, and then take out the positive electrode material after natural cooling and grind for 4 hours.

[0075] The embodiment also provides a lithium ion battery, and the specific composition of the lithium ion battery is as follows: Preparation of the positive electrode sheet: The above positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.5:1.5, added into an N-methyl pyrrolidone (NMP) solvent, and fully stirred and dispersed to obtain a positive electrode slurry; the positive electrode slurry is coated on an aluminum foil, and then subjected to drying, rolling, slitting, die cutting and other processes to obtain the positive electrode sheet.

[0076] Preparation of the negative electrode sheet: The artificial graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC-Na) and styrene butadiene rubber (SBR) are mixed in a mass ratio of 95.8:0.6:1.4:2.2, added into deionized water, and fully stirred and dispersed to obtain a negative electrode slurry; the negative electrode slurry is coated on a copper foil, and then subjected to drying, rolling, slitting, die cutting and other processes to obtain the negative electrode sheet.

[0077] Preparation of the electrolyte: The ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are quantitatively mixed in an equal volume ratio to prepare a composite organic solvent. Then, the lithium hexafluorophosphate (LiPF6) that is fully dried is dissolved in the mixed solvent, and the concentration is adjusted to 1 mol / L to obtain the target electrolyte.

[0078] Preparation of the separator: The polyethylene (PE) porous film is used as the separator; the thickness is 11 μm, the air permeability is 180-300 s / 100 mL, and the porosity is 40%-45%.

[0079] Battery assembly: The positive electrode sheet, the separator and the negative electrode sheet are assembled into an electric core through a lamination process, and are packaged with an aluminum plastic film. After being fully dried, the electrolyte is injected, and then the processes of standing immersion, formation, aging and the like are sequentially completed, so as to finally obtain a lithium ion battery (i.e. a soft package battery, and the designed capacity is 1 Ah).

[0080] Example 2 The difference between this example and Example 1 is that the mass of the shell is 16% of the total mass of the positive electrode material.

[0081] Example 3 The difference between this example and Example 1 is that the mass of the shell is 20% of the total mass of the positive electrode material.

[0082] Example 4 The difference between this example and Example 1 is that the mass of the shell is 9% of the total mass of the positive electrode material.

[0083] Example 5 The difference between this example and Example 1 is that the mass of the shell is 25% of the total mass of the positive electrode material.

[0084] Example 6 The difference between this example and Example 1 is that the shell material is Li4Ti 4.7 Nb 0.3 O 12 .

[0085] Example 7 The difference between this example and Example 1 is that the shell material is Li4Ti 4.9 Nb 0.1 O 12 .

[0086] Example 8 The difference between this example and Example 1 is that the shell material is Li4Ti 4.8 Ta 0.2 O 12 .

[0087] Example 9 The difference between this example and Example 1 is that the shell material is Li4Ti 4.8 V 0.2 O 12 .

[0088] Example 10 The difference between this example and Example 1 is that the core is a commercial carbon-free LiFe 0.6 Mn 0.4 PO4.

[0089] Example 11 The difference between this embodiment and embodiment 1 is that the core is doped lithium iron phosphate, LiFe 0.8 Al 0.2 PO4.

[0090] Example 12 The difference between this embodiment and embodiment 1 is that the core is commercial LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0091] Example 13 The difference between this embodiment and embodiment 1 is that the core is commercial LiCoO2.

[0092] Comparative Example 1 The difference between this comparative example and embodiment 1 is that no shell is provided on the surface of the core.

[0093] Comparative Example 2 The difference between this comparative example and embodiment 1 is that the shell material is Li4Ti5O 12 .

[0094] Comparative Example 3 The difference between this comparative example and embodiment 1 is that the shell material is Li4Ti 4.5 Nb 0.5 O 12 .

[0095] Comparative Example 4 The difference between this comparative example and embodiment 1 is that the shell material is Li4Ti 4.8 Mg 0.2 O 12 .

[0096] Comparative Example 5 The difference between this comparative example and embodiment 12 is that no shell is provided on the surface of the core.

[0097] Comparative Example 6 The difference between this comparative example and embodiment 13 is that no shell is provided on the surface of the core.

[0098] The positive electrode materials prepared in the above embodiments and comparative examples were tested as follows, and the test results are shown in Table 1: (1) Shell thickness test: First, use the scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) to scan the surface of the positive electrode material particles of each example and the comparative example, and determine the core region and shell region of a single particle according to the specific elements of the core and shell (for example, the core is Fe element, and the shell is M element, such as Nb element). Use image analysis software (such as Image J) to outline the minimum circumscribed circle that can contain the specific element of the shell of a single particle, and outline the core region boundary with the Fe element distribution area (the closed line may be approximately circular or irregular in shape), and outline the shell region boundary with the Nb element distribution area; Then take the center of the minimum circumscribed circle as the center, and select 10 points on the core region boundary at 10 equal angles (i.e. interval angle 36°), along the radial direction of the minimum circumscribed circle, respectively calculate the distance (d1, d2, …, d 10 ) from the 10 points on the core region boundary to the shell region boundary, and calculate the average value, then the thickness of the shell T = (d1+d2+…d 10 ) / 10.

[0099] (2) Test of doping amount of doping elements in the shell: After the positive electrode material of each example and the comparative example is prepared into a sample, test it by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer), obtain the mass fraction of each element, and then obtain the doping percentage of M element by the mass fraction of M element doping element / the mass fraction of Ti element. In order to ensure accuracy, 5 samples need to be measured at the same time, and the average value of the doping amount is taken as the final result.

[0100] The applicant assembles the positive electrode material of each example and the comparative example in a CR2032 type button half battery (design capacity is 3 mAh). The positive electrode sheet, electrolyte and separator in the battery are as follows: the positive electrode sheet and electrolyte in each example and the comparative example, and the negative electrode is a metal lithium sheet. Then use the CR2032 type button half battery to test the first coulomb efficiency of each example and the comparative example, and the test results are shown in Table 1, and the test method is as follows: (1) First coulomb efficiency Under the condition of constant temperature at 25°C, first charge to the battery cut-off voltage (3.75V for lithium iron phosphate battery, 4.3V for lithium nickel manganese cobalt ternary battery, and 4.5V for lithium cobalt oxide battery) at a current of 1mA, then constant voltage charge to 0.015mA at the battery cut-off voltage, and then discharge to the battery cut-off voltage (2.5V for lithium iron phosphate battery, 3.0V for lithium nickel manganese cobalt ternary battery, and 2.8V for lithium cobalt oxide battery) at a current of 1mA. Calculate the first coulomb efficiency according to the following formula: Initial coulombic efficiency = first discharge capacity / first charge capacity x 100%; The applicant carried out cycle performance tests on the soft package batteries of each embodiment and the comparative examples, and the test results are shown in Table 1. The test method is as follows: (2) Cycle performance test First, 2 weeks of cycle activation were carried out at 0.33C rate in the rated voltage range (for lithium iron phosphate battery: 2.0V~3.8V; for lithium nickel cobalt manganese ternary battery: 2.8V~4.4V; for lithium cobalt oxide battery: 2.5V~4.2V). Then, the cycle performance test was carried out, and the charging and discharging program was switched to: constant current charging to the battery charging cut-off voltage (for lithium iron phosphate battery: 3.8V; for lithium nickel cobalt manganese ternary battery: 4.4V; for lithium cobalt oxide battery: 4.2V), and then constant voltage charging to 0.05C. Then, cycle test was carried out by discharging at 1C to the battery discharge cut-off voltage (for lithium iron phosphate battery: 2.0V; for lithium nickel cobalt manganese ternary battery: 2.8V; for lithium cobalt oxide battery: 2.5V). The test was terminated when the cycle reached 80% SOH, and the corresponding cycle number was the cycle performance of the battery. The definition of 80% SOH is that the ratio of the discharge capacity of the battery after cycling to the discharge capacity of the first cycle is equal to or lower than 80% for the first time.

[0101] Table 1: Parameters and test results of examples 1-13 and comparative examples 1-6

[0102] From Table 1, it can be seen that: Examples 1-5 keep other conditions unchanged, and adjust the ratio of Li4Ti 4.8 Nb 0.2 O 12 shell in the positive electrode material, thereby adjusting the thickness of the shell. The test results show that: when the mass ratio of the Li4Ti 4.8 Nb 0.2 O 12 shell in the positive electrode material is 12%~20%, the initial efficiency and cycle performance of the battery are better; if the mass ratio of the shell in the positive electrode material is too low, it may not be uniformly coated on the surface of the core particles, resulting in cracks or holes on the surface of the material, and the performance improvement effect is poor due to the inability to build an efficient ion channel network; if the mass ratio of the shell in the positive electrode material is too high, the shell formed on the surface of the core is too thick, and the thick shell will hinder ion migration, increase the interface impedance, and because the shell does not contribute to the capacity, a too high mass ratio will reduce the overall energy density of the positive electrode material.

[0103] Example 1, Example 6~7 and Comparative Example 3, under the premise of keeping other conditions unchanged, the doping amount of Nb in the shell material is regulated, and the test results show that when the doping molar amount of Nb in the shell satisfies 0 < x < 0.3, the first coulombic efficiency and the cycle performance of the battery are better, and when x = 0.2, the comprehensive effect is optimal, because: if the doping amount of Nb is low, the modification effect of LTO lattice is limited, and the effect of improving electronic conductivity and optimizing structural stability cannot be fully played, which leads to insignificant performance improvement; if the doping amount of Nb is high, excessive Nb 5+ occupies the site of Ti 4+ in the LTO lattice in disorder, which destroys the integrity of the lattice structure and hinders the migration channel of Li + and the transmission efficiency of electrons, ultimately leading to the deterioration of the electrochemical performance of the battery.

[0104] Example 1, Example 8~9 and Comparative Example 4, under the premise of keeping other conditions unchanged, the type of doping element in the shell material is regulated. The test results show that the performance of Nb-doped LTO shell, V-doped LTO shell and Ta-doped LTO shell in protecting the positive electrode material and delaying capacity decay is better than that of Mg-doped LTO shell. This is because Nb, V and Ta doping can form a more dense, more stable or higher ionic conductivity interface layer, thereby more effectively isolating the electrolyte side reaction and maintaining the structural integrity of the positive electrode material in long-term cycling.

[0105] Example 10 and Example 11 compared to Example 1, the doping element is introduced into the core, and from the test results, it can be seen that the cycle performance and first efficiency of the doped modified core material are also significantly improved.

[0106] Example 1 and Example 12, 13 compared to Comparative Example 1, Comparative Example 5 and Comparative Example 6 all set the LTMO shell, and by comparing the test results, it can be found that in terms of first efficiency, the first efficiency of the three batteries all reaches a high level. It shows that the Nb-doped LTO shell can be well compatible with various mainstream positive electrode materials and effectively improve or maintain their high first coulombic efficiency. The shell may form a stable interface, reduce the side reaction of various positive electrode materials with the electrolyte during the first charge and discharge process, thereby reducing the irreversible loss of active lithium. In terms of cycle life, the three batteries (LFP: 4000 cycles, NCM523: 2500 cycles, LCO: 1200 cycles) all achieve cycle numbers far exceeding the conventional level (LFP: 1500 cycles, NCM523: 1500 cycles, LCO: 900 cycles). This result shows that the Nb-doped LTO coating layer can provide excellent interface protection for positive electrode materials with different properties, thereby significantly prolonging the cycle life.

[0107] The positive electrode material provided by the application takes a commonly used positive electrode active material as an inner core, takes a transition metal element doped lithium titanate (LTMO) as an outer shell, forms a positive electrode material with a core-shell structure, uses the excellent ion conductivity and three-dimensional diffusion channel of the LTMO shell to provide an efficient path for the migration of lithium ions at the interface of the positive electrode active material particles, thereby greatly reducing the interface impedance. At the same time, the LTMO shell, as a stable physical barrier, can effectively isolate the direct contact of the inner core active material and the electrolyte, inhibit the side reactions (such as transition metal dissolution and electrolyte oxidation) under high temperature and high voltage, thereby significantly enhancing the cycle stability and storage life of the battery. Therefore, the application effectively overcomes some practical problems in the prior art, thereby having high utilization value and use significance.

[0108] The above examples only illustrate the principles and effects of the application, and are not used to limit the application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the application should be covered by the claims of the application.

Claims

1. A positive electrode material, characterized in that, include: The core is selected from an active material capable of reversibly inserting and extracting lithium ions; An outer shell, covering the surface of the core, wherein the outer shell material includes Li4Ti 5-x M x O 12 Where 0 < x ≤ 0.3, and M includes one or more of V, Ta, and Nb.

2. The cathode material according to claim 1, characterized in that, The mass of the core is 80% to 88% of the total mass of the cathode material, and the mass of the outer shell is 12% to 20% of the total mass of the cathode material.

3. The cathode material according to claim 1, characterized in that, The thickness of the outer shell is 500nm~1000nm; and / or the particle size of the core is 10000nm~20000nm.

4. The cathode material according to claim 1, characterized in that, The core includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide.

5. A method for preparing the positive electrode material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Core pretreatment: The core material is mixed with a solvent and then ball-milled to obtain a core slurry; Shell precursor configuration: According to the stoichiometry of the shell material, the lithium source, titanium source, and doping source are measured and dissolved in a solvent to obtain the shell precursor slurry; Blending: The core slurry and the shell precursor slurry are mixed and stirred so that the shell precursor is adsorbed on the surface of the core material to obtain the cathode material precursor; Heat treatment: The cathode material precursor is heat treated to obtain the cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that, The steps for configuring the shell precursor include: first, dispersing the lithium source, the titanium source, and the dopant source separately in a solvent and stirring until completely dissolved; then mixing the lithium source solution, the titanium source solution, and the dopant source solution; wherein the lithium source includes lithium acetate, the titanium source includes tetrabutyl titanate, and the dopant source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides containing a dopant element, and the dopant element includes one or more of vanadium, tantalum, and niobium.

7. The method for preparing the cathode material according to claim 5, characterized in that, The blending step includes: mixing the core slurry with the shell precursor slurry, and then stirring in a water bath, wherein the water bath temperature is 50~80℃ and the stirring time is 5~8 hours.

8. The method for preparing the cathode material according to claim 5, characterized in that, The heat treatment temperature is 600℃~900℃, the time is 1 hour~10 hours, and the heating rate is 1℃ / min~20℃ / min.

9. An electrochemical device, characterized in that, It includes the cathode material according to any one of claims 1 to 4, or the cathode material prepared by any one of claims 5 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

Images