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 a matrix and a coating layer, wherein the matrix is selected from active substances capable of reversibly embedding and removing lithium ions; the surface of the matrix is uniformly coated with the coating layer, the material of the coating layer comprises lithium titanate, and the relative standard deviation RSD of the mass fraction of the titanium element in the coating layer is less than 5%. According to the invention, the uniformly coated lithium titanate coating layer is constructed on the surface of the common positive electrode active material in situ, so that the cycle performance of the positive electrode active material can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a cathode material and its preparation method, an electrochemical device, and an electronic device. Background Technology

[0002] With the rapid development of electric vehicles and large-scale energy storage, the market has placed higher demands on the overall performance of lithium-ion batteries. Among the core components of lithium-ion batteries, the cathode material directly determines the upper limit of the battery's energy density, while the interfacial stability between the cathode material and the electrolyte determines the battery's energy output efficiency, cycle life, and safety margin.

[0003] Currently, mainstream lithium-ion battery cathode materials, whether high-energy-density layered transition metal oxides or high-safety olivine-structured polyanionic materials, all face severe interfacial challenges: during high-voltage charging and discharging, side reactions between the active material and the electrolyte continuously consume active lithium, induce transition metal dissolution, lead to a surge in interfacial impedance, and accelerate capacity decay. This common problem severely restricts the battery's fast-charging capability and service life.

[0004] To address the aforementioned interface stability issues, interface engineering technology has become a key research direction in the field of cathode materials. Among these, the core-shell structure construction strategy, which achieves physical isolation and chemical protection between the active material and the electrolyte, suppressing interfacial side reactions at the source, is widely recognized as a highly feasible interface stabilization solution. However, most existing coatings suffer from problems such as unevenness, lack of density, and weak adhesion to the substrate. These coatings are prone to microscopic defects (such as microcracks), pores, or isolated island-like distributions, making it impossible to construct a continuous and complete protective interface. This non-ideal coating structure not only fails to effectively prevent electrolyte corrosion but may also hinder the smooth transport of lithium ions, and even degrade the battery's rate performance due to excessive interfacial impedance. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a positive electrode material and its preparation method, an electrochemical device and an electronic device, so as to improve the technical problem that the existing coating layer cannot effectively block the interfacial side reactions caused by the electrolyte and the active material.

[0006] To achieve the above and other related objectives, the present invention provides a cathode material comprising: a substrate and a coating layer, wherein the substrate is selected from an active material capable of reversibly inserting and extracting lithium ions, the coating layer uniformly coats the surface of the substrate, the material of the coating layer includes lithium titanate, and the relative standard deviation (RSD) of the mass fraction of titanium in the coating layer is <5%.

[0007] In one embodiment of the present invention, the relative standard deviation (RSD) of the thickness of the coating layer is <5%.

[0008] In one embodiment of the present invention, the thickness of the coating layer is 120~280nm.

[0009] In one embodiment of the present invention, the matrix 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.

[0010] This invention also provides a method for preparing a positive electrode material, characterized by comprising the following steps: Matrix pretreatment: The matrix material is dispersed in a solvent, and the pH value of the system is adjusted to below the isoelectric point of the matrix material, so that the surface of the matrix material is positively charged, and a matrix suspension is obtained; Preparation of coating precursor: Titanium source and lithium source are dissolved in solvent according to the stoichiometric ratio of coating material, and chelating agent is added and mixed and stirred to obtain coating precursor solution; Electrostatic adsorption: The coating precursor solution is added to the matrix suspension, the system is kept in an acidic environment, and the coating precursor is spontaneously adsorbed onto the surface of the matrix particles by electrostatic attraction to form a molecular-level precursor layer. After aging and stirring, the cathode material precursor is obtained. Heat treatment: The cathode material precursor is heat-treated in an inert atmosphere to transform the molecular-level precursor layer into a crystalline coating layer, thereby obtaining the cathode material.

[0011] In one embodiment of the present invention, in the matrix pretreatment step, the pH value of the system is 2.5~3.5; and the matrix suspension is placed in a water bath environment at 40~60℃ and stirred at a constant temperature for 1~3 hours, with the stirring rate controlled at 400~800rpm, so as to maintain the surface charge stability of the matrix material.

[0012] In one embodiment of the present invention, the lithium source includes one or more of lithium acetate and lithium nitrate.

[0013] In one embodiment of the present invention, the titanium source includes one or more of tetrabutyl titanate and tetraisopropyl titanate.

[0014] In one embodiment of the present invention, the chelating agent includes one or more of glacial acetic acid, acetylacetone, citric acid, and tartaric acid.

[0015] In one embodiment of the present invention, the electrostatic adsorption step includes: adding the coating precursor solution dropwise to the matrix suspension in a water bath environment of 40℃~60℃; controlling the stirring speed at 400~800 rpm during the dropwise addition process, and maintaining the pH value of the reaction system at 2.8~3.2; and using the mass of the matrix in the matrix suspension as a reference, making the ratio of the mass of the matrix to the theoretical mass of the coating layer formed by the subsequent process of the coating precursor 1:(0.06~0.2); and / or, the aging and stirring treatment time is 4~6 hours.

[0016] In one embodiment of the present invention, the heat treatment step includes: maintaining at 200~300°C for 2~3 hours, then raising the temperature to 600~800°C and maintaining for 4~6 hours.

[0017] The present invention also provides an electrochemical device, the electrochemical device comprising the above-described positive electrode material, or comprising a positive electrode material prepared by the above-described preparation method.

[0018] The present invention also provides an electronic device comprising the electrochemical device described above.

[0019] The beneficial effects of the present invention are as follows: The present invention uses a commonly used positive electrode active material as a substrate and constructs a lithium titanate coating layer on its surface. The relative standard deviation (RSD) of the mass fraction of titanium in the coating layer is less than 5%, which indicates that the coating layer has extremely high uniformity in elemental composition and spatial distribution. This achieves uniform coating of the surface of the positive electrode active material and ensures the consistency of the coating layer function at the microscopic level. This highly uniform coating structure ensures that the volume expansion / contraction stress caused by lithium-ion insertion / extraction is evenly distributed during the charging and discharging process, preventing cracking of the coating layer or pulverization of active material particles due to localized stress concentration. This effectively maintains the integrity of the electrode structure and the continuity of the coating layer's protective function. Furthermore, the uniformity of elemental distribution ensures consistent ion conduction efficiency and electron transport performance throughout the coating layer. The migration rate of lithium ions within the electrode tends to be uniform, preventing conduction bottlenecks caused by uneven local coating. This significantly improves the synergy and stability of ion transport. On this basis, the coating layer effectively isolates the internal positive electrode active material from direct contact with the electrolyte, suppressing interfacial side reactions and transition metal dissolution, thereby significantly improving the material's cycle life and high-temperature stability. On the other hand, the coating layer provides an efficient transport channel for lithium ions and electrons, reducing interfacial impedance and significantly improving its fast-charging performance. Ultimately, without sacrificing the inherent advantages of the internal positive electrode active material, it breaks through the bottlenecks in rate capability and lifespan, meeting the application requirements of next-generation high-performance lithium-ion batteries in electric vehicles, large-scale energy storage, and other fields.

[0020] Furthermore, this invention also provides a preparation method adapted to the above-mentioned cathode material. This method precisely controls the pH value of the reaction system to make the surface of the matrix material particles strongly positively charged, while simultaneously hydrolyzing the titanium source to generate negatively charged titanate ions. Due to the strong electrostatic attraction between the positive and negative charges, carbonate ions are spontaneously and directionally adsorbed onto the entire surface of the matrix material particles, achieving uniform molecular-level spreading and dense adsorption. Subsequently, through heat treatment, the precursor is transformed in situ on the particle surface, ultimately forming an ultrathin, continuous, defect-free, and tightly bonded lithium titanate nanocoating layer on the matrix material surface. The lithium titanate nanocoating layer formed by this method, combined with its inherently high lithium-ion diffusion coefficient, provides a complete and low-impedance migration path for lithium ions, synergistically achieving a dual improvement in both rate performance and fast-charging capability.

[0021] The electrostatic self-assembly method of this invention has significant process advantages over existing preparation methods: First, it ensures that the coating layer precursor reacts in situ only on the substrate surface, avoiding raw material waste caused by bulk precipitation and improving the utilization rate of titanium source; Second, the process parameters are easy to control and have excellent reproducibility; Third, it is compatible with existing cathode material mass production equipment, and can achieve large-scale production without additional modifications, laying a solid foundation for technology transfer. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0023] In the attached diagram: Figure 1 This is a schematic diagram of the structure of a positive electrode material provided in an embodiment of the present invention; Figure 2 This is an EDS distribution diagram of titanium in the coating layer of a cathode material provided in an embodiment of the present invention; Figure 3 This is a flowchart of a method for preparing a cathode material according to an embodiment of the present invention; Figure 4 This is a schematic diagram of a method for preparing a cathode material according to an embodiment of the present invention.

[0024] Figure label: 1. Substrate; 2. Coating layer; 21. Coating precursor; 3. Cathode material. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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; LiNix Co y Al 1-x-y Materials such as O2 (NCA) and other high-energy-density layered transition metal oxides (such as NCM, NCA, etc.) or high-safety olivine-type polyanionic materials (such as LFP, LMFP, etc.) all face severe interface challenges: during high-voltage charging and discharging, the side reactions between the active material and the electrolyte will continuously consume active lithium, induce the dissolution of transition metals, and lead to a surge in interfacial impedance and accelerated capacity decay.

[0032] To address these issues, surface coating is a common technique in existing technologies. However, while traditional physical mixing or sol-gel methods can achieve coating, they often suffer from uneven, non-dense coating layers and weak adhesion to the substrate. These methods struggle to achieve precise control at the molecular or nanoscale, resulting in coating layers with widespread defects, pores, or isolated island-like distributions, failing to form a continuous and complete protective layer. This non-ideal coating structure not only fails to effectively prevent direct contact between the electrolyte and the positive electrode active material, making it difficult to suppress transition metal dissolution and side reactions; it may also hinder the smooth transport of lithium ions due to structural discontinuities or excessive porosity, and even significantly degrade the battery's rate performance (especially fast charging performance) due to a substantial increase in interfacial charge transport impedance.

[0033] Based on this, the present invention provides a cathode material, a method for preparing the cathode material, an electrochemical device comprising the cathode material, and an electronic device comprising the electrochemical device. By constructing a uniformly coated lithium titanate layer on the surface of commonly used cathode active materials, the advantages of cathode active materials can be retained while overcoming their rate capability and lifespan bottlenecks, thus meeting the application requirements of high-performance lithium-ion batteries.

[0034] Please see Figure 1 The cathode material 3 of the present invention includes a substrate 1 and a coating layer 2. The substrate 1 serves as the active component, undertakes the main energy storage function, provides high reversible capacity and a stable working voltage platform, and ensures the high energy density characteristics of the cathode material. The coating layer 2 serves as a high-speed ion conductor and a physical protective barrier.

[0035] The substrate 1 is selected from active materials capable of reversibly inserting and extracting lithium ions, including but not limited to commonly used cathode active materials. In some embodiments, the substrate 1 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. For example, the substrate 1 can be lithium iron phosphate, or lithium manganese iron phosphate, or lithium cobalt oxide, or lithium nickel cobalt manganese oxide, etc. It should be noted that the ratio of nickel, cobalt, and manganese elements in the lithium nickel cobalt manganese oxide ternary material is not limited and any ratio suitable for lithium-ion batteries can be used. For example, lithium nickel cobalt manganese oxide can be LiNi. 0.5 Co0.2 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 aluminum oxide ternary material is not limited; any ratio suitable for lithium-ion batteries can be used. For example, lithium nickel cobalt aluminum oxide can be LiNi... 0.7 Co 0.25 Al 0.05 O2, or LiNi 0.8 Co 0.15 Al 0.05 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 involving element ratios, such as lithium manganese iron phosphate, do not have restrictions on the ratio of manganese and iron, as long as they can be used in lithium-ion batteries. They will not be listed here one by one.

[0036] Those skilled in the art will understand that the material of the substrate 1 can also be a doped positive electrode active material, that is, doping the materials listed above with appropriate amounts of other elements. There are no restrictions on the doping elements; conventional doping elements can be selected as needed, such as Al, Zr, Cr, Zn, Bi, La, Ti, Mg, etc. These doping elements can be used for single doping, such as Al doping, Zr doping, Mg doping, etc.; or they can be used for combined doping, such as Al and Zr combined doping, Ti and La combined doping, etc.

[0037] In some embodiments, the particle size d of a single particle in the matrix 1 is 10000nm~20000nm (10μm~20μm). For example, d can be 10000nm, 13000nm, 15000nm, 18000nm or 20000nm, etc.

[0038] The coating layer 2 is uniformly coated on the surface of the substrate 1. In this application, the material of the coating layer 2 includes Li4Ti5O. 12(LTO) and the relative standard deviation (RSD) of the mass fraction of titanium in the coating layer is <5%, for example, RSD can be 4%, 3%, 2%, 1%, etc. The three-dimensional tunnel crystal structure of LTO gives it excellent ionic conductivity and three-dimensional diffusion channels, providing an efficient path for the migration of lithium ions at the interface of cathode material particles, thereby significantly reducing interface impedance and significantly improving the fast charging capability of the material; and LTO is electrochemically inert at the working potential of substrate 1 (cathode active material) (3.0~4.2V), and does not undergo redox reactions or side reactions with electrolyte under high voltage and high temperature (≤60℃) conditions. Therefore, the LTO coating layer is a stable physical barrier, effectively isolating the core of the cathode active material 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 cycle life and high temperature stability of the battery.

[0039] Furthermore, titanium is a characteristic element of lithium titanate, a coating material, and its elemental distribution can be used to characterize the distribution of the lithium titanate coating layer. (See [link to relevant documentation]). Figure 2 , Figure 2 The image shows the distribution of titanium in the cathode material obtained by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) in one embodiment of the present invention. As can be seen from the image, titanium is uniformly distributed on the surface of the cathode material particles, proving that the lithium titanate coating layer is uniformly distributed.

[0040] Furthermore, the relative standard deviation (RSD) of the titanium mass fraction in the coating layer can accurately reflect the relative concentration of titanium distribution, thereby quantifying the coating uniformity. The smaller the RSD of the titanium mass fraction in the coating layer, the more uniform the titanium distribution, and the better the coating quality. In this invention, the RSD of the titanium mass fraction in the coating layer is <5%, indicating that the coating layer is continuous and dense, without obvious thin areas or exposed points. The aforementioned relative standard deviation of the titanium mass fraction was determined by SEM-EDS characterization technology to detect the titanium (Ti) mass fraction in the coating layer, and then calculated according to the formula: RSD = (σ / μ) × 100%, where σ = (σ is the standard deviation, x) i (where μ represents the titanium content at a single detection point, n is the number of detection points, and μ is the average mass fraction of titanium across the n detection points).

[0041] In some embodiments, the thickness of the coating layer 2 is 120~280 nm, and exemplaryly, it can be 120 nm, 160 nm, 200 nm, 220 nm, 240 nm, or 280 nm. Uniform coating at the nanoscale ensures that its mass percentage is extremely small, thereby maximizing the preservation of the high voltage plateau and high energy density advantages of the substrate 1 material, and preventing the excessively thick coating layer 2 from hindering ion migration and increasing interfacial impedance. Furthermore, the relative deviation (RSD) of the thickness of the coating layer 2 is <5%. For example, the relative deviation (RSD) of the coating layer thickness can be 4%, 3%, 2%, or 1%, etc. The smaller the relative deviation (RSD) of the thickness of the coating layer 2, the smaller the thickness fluctuation of the coating layer 2 on the surface of the positive electrode active material particles, the less obvious the "protrusions," "depressions," or locally thin areas, and the better the thickness uniformity. This ensures that the barrier effect between the electrolyte and the substrate 1 material is consistent, effectively avoiding side reactions such as transition metal dissolution and lattice oxygen precipitation caused by local thin areas, and reducing the risk of interface impedance surge. The thickness of the coating layer of this invention can be characterized by SEM-EDS: first, the boundary region between the substrate 1 and the coating layer 2 is determined by surface scanning, and the thickness of the coating layer = (diameter of the coating layer - diameter of the substrate) / 2; then, it is calculated according to the formula: RSD = (σ / μ) × 100%, where σ = (σ is the standard deviation, x) i (where μ is the thickness of a single detection point, n is the number of detection points, and μ is the average thickness of the n detection points).

[0042] This invention constructs a uniform lithium titanate coating layer on the surface of the positive electrode active material particles. On the one hand, this effectively isolates the internal positive electrode active material from direct contact with the electrolyte, suppresses interfacial side reactions and transition metal dissolution, thereby significantly improving the material's cycle life and high-temperature stability. On the other hand, this coating layer provides an efficient transport channel for lithium ions and electrons, reduces interfacial impedance, and significantly improves its fast-charging performance. Ultimately, without sacrificing the inherent advantages of the internal positive electrode active material, this invention improves its rate capability and cycle life.

[0043] Please see Figure 3 and Figure 4 The present invention also provides a method for preparing the above-mentioned cathode material, the method comprising the following steps: S1. Disperse the matrix material in a solvent and adjust the pH of the system to below the isoelectric point of the matrix material, so that the surface of the matrix material is positively charged, to obtain a matrix suspension; S2. Dissolve the titanium source and lithium source in a solvent according to the stoichiometric ratio of the coating material, and add a chelating agent to mix and stir to obtain a coating precursor solution; S3. Add the coating precursor solution to the matrix suspension, maintain the system in an acidic environment, and use electrostatic attraction to make the coating precursor spontaneously adsorb onto the surface of the matrix particles to form a molecular-level precursor layer. After aging and stirring, the cathode material precursor is obtained. S4. Heat-treat the cathode material precursor in an inert atmosphere to transform the molecular-level precursor layer into a crystalline coating layer, thereby obtaining the cathode material.

[0044] Specifically, the matrix material in step S1 is selected from active materials capable of reversibly inserting and extracting lithium ions, including but not limited to commonly used cathode active materials. In some embodiments, the matrix material 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. These materials can be those listed above, or they can be doped with conventional elements, which will not be elaborated here. The matrix material in this step can be obtained through general commercial means or prepared using conventional methods in the art, such as hydrothermal methods, without specific limitations. In some embodiments, the particle size d of the matrix material is 10000 nm to 20000 nm. Within this particle size range, the energy density, charge transport efficiency, processing performance, and cycle stability can be balanced.

[0045] Step S1 involves pretreating the matrix material to impart a positive charge to its surface. The specific process is as follows: First, the matrix material is dispersed in a suitable solvent to ensure the matrix particles are uniformly suspended in the solvent. The type of solvent is not limited and can be selected based on the type of matrix material. It should be noted that the solvent does not react with the matrix material, does not damage its structure, and is compatible with subsequent processes. Furthermore, the solvent can penetrate the soft agglomerates between the matrix particles, reducing van der Waals forces and hydrogen bonds between particles, thus dispersing the soft agglomerates through stirring. For example, if the matrix material is LFP, the solvent can be anhydrous ethanol or deionized water; if the matrix material is NCM, the solvent can be anhydrous ethanol, isopropanol, etc. The ratio of solvent to matrix material is not limited, as long as it can disperse the matrix material. For example, the mass ratio of solvent to matrix material can be 1:(1~3), such as 1:1, 1:2, or 1:3, etc. The dispersion methods for the matrix material include, but are not limited to, ultrasonic treatment, magnetic stirring, etc. Then, the reaction system was transferred to a constant-temperature reactor, and the pH of the reaction system was adjusted by adding acid until the pH was adjusted below the isoelectric point (IEP) of the matrix material, so that the particle surface of matrix 1 material was positively charged (e.g., ...). Figure 4 (As shown). The aforementioned constant-temperature reactor is, for example, a water bath at 40~60℃. After adding acid, stirring is carried out continuously for 1~3 hours, with the stirring rate controlled at 400~800 rpm. For example, the water bath temperature can be 40℃, 50℃, or 60℃, etc., the stirring time can be 1 hour, 2 hours, or 3 hours, etc., and the stirring rate can be 400 rpm, 600 rpm, or 800 rpm, etc. It should be noted that: the isoelectric point (IEP) refers to the state at which the net surface charge of a specific substance (such as cathode material particles) is zero at a certain pH value. At this time, the total positive and negative charges of the particles are equal, and the whole is electrically neutral. When the pH value of the system is lower than the IEP, the particle surface carries a positive charge; when the pH value is higher than the IEP, the surface carries a negative charge.

[0046] The pH value of the reaction system in step S1 is 2.5~3.5, for example, it can be 2.5, 3.0 or 3.5, etc., and the specific value can be selected according to the type of matrix 1 material. The acid used to adjust the pH value can be dilute nitric acid, acetic acid, oxalic acid or other acids that do not affect the material structure and the reaction system. For example, the concentration of dilute nitric acid can be 0.1 mol / L; or acetic acid, or oxalic acid, etc.

[0047] Step S2 involves configuring the coating precursor, with the coating material being Li4Ti5O. 12 When preparing the coating precursor, the lithium source, titanium source, and chelating agent are first measured according to the stoichiometric ratio of the coating material. The lithium and titanium sources must have good solubility, be able to participate in the reaction at a low temperature, and produce harmless or volatile byproducts. For example, the lithium source is selected from lithium acetate (LiOAc·2H2O), lithium nitrate (LiNO3), or a combination of two lithium sources; the titanium source is selected from tetrabutyl titanate (TBOT), tetraisopropyl titanate (TTIP), or a combination of two titanium sources; the chelating agent is selected from one or more of glacial acetic acid (CH3COOH), acetylacetone (C5H8O2), citric acid (C6H8O7), and tartaric acid (C4H6O6), such as glacial acetic acid, citric acid, tartaric acid, or a combination of acetylacetone and glacial acetic acid, etc. The molar ratio of the effective functional group providing lone pair electrons in the chelating agent to the titanium source is controlled at 2:1.

[0048] Then, the weighed lithium source and titanium source are dispersed into their respective solvents according to their reactivity and compatibility, and stirred thoroughly until completely dissolved to obtain lithium source solution and titanium source solution. These two solutions are then mixed, and a chelating agent is added and stirred until homogeneous to obtain the coated precursor solution. There are no restrictions on the type of solvent, as long as the raw materials are completely dissolved. For example, lithium acetate can be dispersed in deionized water, and titanium source in anhydrous ethanol. The specific ratio between the solvent and each raw material is not particularly limited; the key is to ensure complete dissolution of all raw materials.

[0049] Furthermore, the pH of the reaction system in step S2 is controlled to be 3.0~4.5, for example, it can be 3.0, 4.0 or 4.5, etc. An acidic environment facilitates the hydrolysis of the titanium source, forming a negatively charged coated precursor 21 (titanium ion). See [link to relevant documentation]. Figure 4 Furthermore, to avoid the titanium source from undergoing violent hydrolysis due to high temperature, step S2 is carried out under relatively mild conditions, such as constant temperature water bath stirring, with the stirring rate controlled at 400~800 rpm, for example, 400 rpm, 600 rpm or 800 rpm, etc.

[0050] It should be noted that steps S1 and S2 are not sequential; S1 can be executed first, followed by S2; or S2 can be executed first, followed by S1; or S1 and S2 can be executed simultaneously. The mass of the matrix material in step S1 and the amount of each raw material in the coating precursor in step S2 are adjusted according to the coating thickness of the coating layer in the cathode material to be prepared.

[0051] In some alternative implementations, the mass of the matrix in the matrix suspension is used as a reference, and the ratio of the mass of the matrix to the theoretical mass of the coating layer formed by the subsequent process of the coating precursor is 1:(0.06~0.2). For example, it can be 1:0.06, 1:0.1, 1:0.15 or 1:0.2, etc.

[0052] Step S3 is electrostatic adsorption. In a water bath environment, the negatively charged precursor solution is slowly added dropwise to the positively charged matrix suspension to maintain an acidic environment. Electrostatic attraction is used to make the coated precursor 21 spontaneously, uniformly and firmly adsorbed on the surface of the matrix 1 material particles to form a molecular-level precursor layer.

[0053] In some embodiments, the water bath temperature in step S3 is 40°C to 60°C, the dropping rate is 0.4 L / min, and the stirring speed is controlled at 400 to 800 rpm. For example, the water bath temperature can be 40°C, 50°C, or 60°C, and the stirring speed can be 400 rpm, 600 rpm, or 800 rpm.

[0054] The acidic environment in step S3 has a pH of 2.8 to 3.2, such as 2.8, 3.0, or 3.2. Maintaining this acidic environment requires the addition of an acidic solvent, such as dilute nitric acid. The acidic environment can be monitored using an online pH meter or by checking the pH value of the reaction system at appropriate intervals. After the addition is complete, maintain the water bath temperature and stirring rate constant, and continue the reaction for 4 to 6 hours (i.e., aging), such as 4, 5, or 6 hours. After aging, the cathode material precursor is obtained.

[0055] Furthermore, after the cathode material precursor is generated in step S3, in order to better carry out subsequent heat treatment, the cathode material precursor is also dried. The drying method is not limited and can adopt conventional drying methods in the art, such as drying in an oven. The drying temperature is 60~80℃, such as 60℃, 70℃, 80℃, etc.; the drying time is 12~24 hours, such as 12 hours, 18 hours, 24 hours, etc.

[0056] Step S4 is the heat treatment step, in which the cathode material precursor obtained in step S3 is placed into a sintering container and calcined at high temperature under an inert atmosphere to transform the molecular-level precursor layer into a crystalline coating layer, thereby obtaining the cathode material.

[0057] In some alternative embodiments, the temperature in the heat treatment step is 600°C to 800°C, for example, 600°C, 700°C, or 800°C, etc.; the heat treatment time is 4 to 6 hours, for example, 4 hours, 5 hours, or 6 hours, etc.; and the heating rate in the heat treatment step is 1 to 10°C / min, for example, 1°C / min, 5°C / min, 8°C / min, or 10°C / min, etc.

[0058] Preferably, the heat treatment can be carried out in stages. For example, it can be maintained at a low temperature (200~300℃) for 2~3 hours to fully remove the solvent, and then the temperature can be raised to 600~800℃ for high-temperature calcination. For example, the temperature of the low-temperature stage can be 200℃, 250℃ or 300℃, and the time can be 2 hours, 2.5 hours or 3 hours, etc. After heat treatment, allow it to cool naturally to room temperature. Subsequently, to better prepare the cathode material for subsequent cathode slurry preparation, post-processing is required to improve material dispersion. Post-processing methods include, but are not limited to, grinding. After grinding and sieving, cathode material meeting the application requirements can be obtained.

[0059] This invention achieves precise and uniform construction of the coating layer at the nanoscale through electrostatic self-assembly technology. This method precisely controls the pH value of the reaction system to imbue the surface of the internal positive electrode active material particles with a strong positive charge, while simultaneously hydrolyzing the titanium source to generate negatively charged titanate ions. Due to the strong electrostatic attraction between the positive and negative charges, carbonate ions are spontaneously and directionally adsorbed onto the entire surface of the positive electrode active material particles, achieving uniform molecular-level spreading and dense adsorption. Subsequently, through heat treatment, the precursor is transformed in situ on the particle surface, ultimately forming an ultrathin, continuous, defect-free, and tightly bonded lithium titanate nanocoating layer on the surface of the positive electrode active material. The lithium titanate nanocoating layer formed by this method, combined with its inherently high lithium-ion diffusion coefficient, provides a complete and low-impedance migration path for lithium ions, synergistically achieving a dual improvement in both rate performance and fast-charging capability.

[0060] This strong electrostatic adsorption ensures that the coating precursor reacts in situ only on the substrate surface, avoiding raw material waste caused by bulk precipitation and improving the utilization rate of titanium source; moreover, the process parameters are easy to control and the process reproducibility is good, laying a solid foundation for large-scale production.

[0061] The present invention also provides an electrochemical device comprising the above-described positive electrode material or a positive electrode material prepared by the above-described preparation method.

[0062] In one embodiment, the electrochemical device includes a lithium-ion battery, which can be a liquid lithium-ion battery (with a non-aqueous electrolyte) or a solid lithium-ion battery (with a solid electrolyte), and there is no limitation herein.

[0063] The following is a detailed description of the structure of a liquid lithium-ion battery, taking it as an example: A lithium-ion battery includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator.

[0064] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive current collector is made of a material possessing both excellent conductivity and mechanical strength, such as aluminum foil or carbon-coated aluminum foil. The positive current collector has two surfaces disposed opposite to each other along its thickness direction. The positive active material layer can be disposed on one surface of the positive current collector or on both surfaces. The positive active material layer includes the positive electrode material, positive conductive agent, and positive binder described above. The positive binder includes any one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, polyamide, polyacrylonitrile, polyacrylate, polyethylene ether, polymethyl methacrylate, ethylene-propylene-diene terpolymer, and polyhexafluoropropylene. For example, the positive 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 nanotubes, carbon fibers, and graphene. For example, the conductive agent is conductive carbon black; or a combination of carbon fibers and conductive carbon black; or a combination of carbon nanotubes and graphene, etc.

[0065] The preparation process of the positive electrode sheet is exemplified as follows: First, the positive electrode material, positive electrode conductive agent, and positive electrode binder are mixed and stirred evenly in a solvent such as N-methylpyrrolidone (NMP) according to a set ratio to form a positive electrode slurry. Then, the positive electrode slurry is coated onto the positive electrode current collector. After drying, rolling, and cutting, the positive electrode sheet is obtained. The ratio of the positive electrode material, positive electrode conductive agent, and positive electrode binder can refer to the conventional settings in this field and is not specifically limited here.

[0066] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. The negative current collector is made of a material with excellent conductivity and mechanical strength, such as copper foil or carbon-coated copper foil. The negative current collector has two surfaces arranged opposite to each other along its thickness direction. The negative active material layer can be disposed on one surface or both surfaces of the negative current collector. The negative active material layer includes a negative active material, a negative conductive agent, a negative binder, and a thickener. The specific types of the negative active material, negative conductive agent, negative binder, and thickener are not specifically limited here; materials known in the art for use in lithium-ion batteries can be used, and those skilled in the art can select them according to actual needs.

[0067] For example, the negative electrode active material includes, but is not limited to, soft carbon, hard carbon, artificial graphite, natural graphite, and silicon-based materials (such as silicon, silicon oxide, and silicon-carbon composites). These materials can be used alone or in combination. For example, the negative electrode active material may be artificial graphite, or a combination of artificial graphite and silicon-carbon composites. The negative electrode conductive agent is selected from one or more of acetylene black, conductive carbon black (Super P), carbon fiber (VGCF), carbon nanotubes (CNTs), Ketjen black, and graphene. For example, it may be acetylene black, conductive carbon black, or a combination of carbon fiber and carbon nanotubes, etc. The negative electrode binder is selected from any one of polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and styrene-butadiene rubber, or a combination of several mixed in any proportion; for example, it may be styrene-butadiene rubber, polyacrylic acid, etc. The thickener is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0068] The preparation process of the negative electrode sheet is as follows: First, the negative electrode active material, negative electrode conductive agent, negative electrode binder and thickener are mixed and stirred evenly 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. After drying, rolling, cutting and other processes, the negative electrode sheet is obtained.

[0069] A separator is positioned between the positive and negative electrodes to separate them, preventing short circuits within the battery and allowing lithium ions to move between them for charging and discharging. The separator must possess excellent electrochemical stability, mechanical strength, and thermal stability. For example, the separator can be a porous membrane such as polyethylene (PE), polypropylene (PP), or a multilayer composite membrane (e.g., PP / PE / PP). A functional layer can also be coated onto the porous membrane, located on either side or both sides. This functional layer includes a ceramic coating and / or a polymer binder. The ceramic coating includes, but is not limited to, ceramic materials such as alumina (Al2O3) and silicon oxide (SiO2), and polymer binders such as polyvinylidene fluoride (PVDF) and aramid fiber. The specific types and proportions can be selected by those skilled in the art based on battery performance requirements. The polymer binder can be a PVDF and aramid fiber binder.

[0070] Non-aqueous electrolytes play a role in conducting lithium ions during battery charging and discharging. Non-aqueous electrolytes include organic solvents and lithium salts. The lithium salt can be selected from one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Further, lithium hexafluorophosphate or a combination of lithium hexafluorophosphate and other lithium salts with superior overall performance is selected, such as a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. The organic solvent can be selected from one or more of the following: carbonates (such as 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 ethylene glycol dimethyl ether DME), and sulfones (such as sulfolane).

[0071] In some optional embodiments, the non-aqueous electrolyte also includes functional additives, such as film-forming additives (e.g., vinylene carbonate VC, fluoroethylene carbonate FEC, etc.), flame-retardant additives (e.g., phosphate esters), overcharge protection additives (e.g., biphenyls), and additives to improve high and low temperature performance. Specific additives can be added according to actual needs.

[0072] Battery assembly: The prepared positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cells are obtained by winding or stacking. The bare cells are then installed into the battery casing and thoroughly baked until the water content is below 450 ppm. After liquid injection, formation, sealing, and inspection, a lithium-ion battery is obtained.

[0073] In other embodiments, the lithium-ion battery is a solid-state lithium-ion battery. The electrolyte of the solid-state lithium-ion battery is solid. Common solid electrolytes include oxide solid electrolytes, halide solid electrolytes, sulfide solid electrolytes, etc., which will not be elaborated here. Those skilled in the art can choose according to actual production needs.

[0074] It should be noted that the structures not described in detail in the above lithium-ion batteries can all be set up with reference to existing technologies, and will not be elaborated here.

[0075] The present invention also provides an electronic device comprising the above-mentioned lithium-ion battery, which can be used in the form of a single cell, a battery module, or a battery pack to power the electronic device.

[0076] In some embodiments, electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.

[0077] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0078] Example 1 This embodiment provides a cathode material, which includes a substrate and a coating layer. The substrate material is carbon-free LiFePO4, and the coating layer material is Li4Ti5O. 12 .

[0079] The preparation method of the above-mentioned cathode material is as follows: (1) Matrix pretreatment: Carbon-free LiFePO4 powder was dispersed in anhydrous ethanol and ultrasonically treated for 1 hour to ensure uniform suspension of particles. The suspension was then transferred to a water bath at 50°C, and 0.1 mol / L dilute nitric acid solution was slowly added at a stirring rate of 500 rpm to adjust the pH of the system to 3.0. The mixture was kept at a constant temperature and stirred for 1 hour to fully protonate the surface of the LiFePO4 particles, forming a stable positively charged surface, thus obtaining the LFP suspension.

[0080] (2) Preparation of coating precursor: Titanium source and lithium source are dissolved in anhydrous ethanol and deionized water respectively according to stoichiometric ratio. Then, the titanium source solution and lithium source solution are mixed evenly, and glacial acetic acid is added as a chelating agent. After magnetic stirring for 1 hour, a clear mixed solution is formed. The titanium source is tetrabutyl titanate, and the lithium source is lithium acetate dihydrate. The mass ratio of the lithium source to the titanium source is 1:4.5. The molar ratio of the effective functional group providing lone pair electrons in the chelating agent to the titanium source is 2:1. The titanium source forms negatively charged titanate clusters under the action of acidic environment and chelating agent. The ratio of the mass of the matrix to the theoretical mass of the coating layer formed by the subsequent process of coating precursor is 1:0.15. (3) Electrostatic adsorption: Under constant temperature of 50℃, the reactor was placed on a heat-collecting constant temperature magnetic stirrer, and the stirring rate was maintained at 500 rpm. The precursor solution from step (2) was uniformly added to the LFP suspension from step (1) over 2 hours using a peristaltic pump. During this period, the liquid level was kept stable, and there was no local high concentration. During the coating process, the pH value of the reaction system was kept within the range of 3.00±0.20 by real-time monitoring of the pH control system. When the pH value deviated from the range of 3.00±0.20, it was precisely adjusted by an automatic titration unit equipped with 0.1 mol / L dilute nitric acid solution, and the amount added each time was controlled within 0.5 mol. After the addition was completed, the constant temperature of 50℃ and the stirring rate of 500 rpm were maintained, and the reaction continued for 4 h. The entire coating process was carried out under nitrogen protection, and a reflux condenser was installed on the top of the reactor to control the solvent loss rate within 2%. After the reaction was completed, the system temperature was immediately lowered to 25℃ to terminate the reaction.

[0081] (4) Heat treatment: The material obtained in step (3) is dried and transferred to a constant temperature forced-air drying oven. It is dried at 80°C for 24 hours to obtain powder. The dried powder is evenly spread in an alumina crucible and placed in the central temperature zone of a tube furnace. High-purity argon gas is introduced and the air is vented for 0.5 hours to ensure that the air is completely vented. Then, the temperature is increased from room temperature to 350°C at a heating rate of 5°C / min and held at this temperature for 2 hours to allow the organic matter to fully decompose and volatilize. Then, the temperature is increased to 650°C at the same heating rate and held for 4 hours to carry out the crystallization reaction. After the reaction is completed, the heating is stopped and the furnace is cooled to room temperature under continuous argon protection. Finally, the sintered product is processed by an air jet mill and passed through a standard sieve to obtain the final cathode material.

[0082] Example 2 The difference between this embodiment and embodiment 1 is that in step (3), the pH of the reaction system is controlled to be 4.00 ± 0.20.

[0083] Example 3 The difference between this embodiment and embodiment 1 is that in step (3), the pH of the reaction system is controlled to be 1.00 ± 0.20.

[0084] Example 4 The difference between this embodiment and embodiment 1 is that in step (2), the coating precursor is prepared according to the ratio of the matrix mass to the theoretical mass of the coating layer formed by the subsequent process of the coating precursor, which is 1:0.06.

[0085] Example 5 The difference between this embodiment and embodiment 1 is that in step (2), the coating precursor is prepared according to the ratio of the matrix mass to the theoretical mass of the coating layer formed by the subsequent process of the coating precursor, which is 1:0.2.

[0086] Example 6 The difference between this embodiment and embodiment 1 is that the heat treatment temperature in step (4) is 600℃.

[0087] Example 7 The difference between this embodiment and embodiment 1 is that the heat treatment temperature in step (4) is 800℃.

[0088] Example 8 The difference between this embodiment and Embodiment 1 is that the substrate material in step (1) is doped lithium iron phosphate (LiFe). 0.8 Al 0.2 PO4.

[0089] Example 9 The difference between this embodiment and Embodiment 1 is that the matrix material in step (1) is LiNi. 0.5 Co 0.2 Mn 0.3 O2.

[0090] Example 10 The difference between this embodiment and embodiment 1 is that the matrix material in step (1) is LiCoO2.

[0091] Comparative Example 1 The difference between this comparative example and Example 1 is that: Comparative example 1 uses uncoated LiFePO4, and the same batch of LiFePO4 powder as Example 1 is used without any surface modification treatment.

[0092] Comparative Example 2 The preparation method of this comparative example differs from that of Example 1. The specific process is as follows: (1) Preparation of LTO precursor: Tetrabutyl titanate and lithium acetate dihydrate were dissolved together in anhydrous ethanol and stirred at 300 rpm for 2 hours using a magnetic stirrer to obtain a precursor mixture.

[0093] (2) Sol-gel coating: LFP was dispersed in anhydrous ethanol to form an LFP suspension. The LFP suspension was kept at a constant temperature of 25 °C and continuously stirred at 500 rpm. The precursor solution was poured into the suspension in one go using a glass funnel. Immediately after pouring, the solution changed from transparent to milky white, indicating that TBOT began to hydrolyze. The reaction system was kept open and the reaction was carried out at room temperature and relative humidity of 40%-60% for 6 hours.

[0094] (3) Heat treatment process The material obtained in step (2) above was dried and transferred to a constant temperature forced-air drying oven, where it was dried at 80 °C for 24 hours to obtain powder. The dried powder was evenly spread in an alumina crucible and placed in the central temperature zone of a tube furnace. High-purity argon gas was introduced and the air was vented for 0.5 hours to ensure complete air removal. Subsequently, the temperature was increased from room temperature to 650 °C at a heating rate of 5 °C / min and held for 6 hours. After the reaction was completed, heating was stopped, and the furnace was cooled to room temperature under continuous argon protection. Finally, the sintered product was processed by an air jet mill and passed through a standard sieve to obtain the final cathode material.

[0095] Comparative Example 3 The difference between this comparative example and Comparative Example 2 is that the matrix material in step (1) is LiNi. 0.5 Co 0.2 Mn 0.3 O2.

[0096] Comparative Example 4 The difference between this comparative example and comparative example 2 is that the matrix material in step (1) is LiCoO2.

[0097] Comparative Example 5 The difference between this embodiment and embodiment 1 is that in step (2), the coating precursor is prepared according to the ratio of the matrix mass to the theoretical mass of the coating layer formed by the subsequent process of the coating precursor, which is 1:0.03.

[0098] Comparative Example 6 The difference between this embodiment and embodiment 1 is that in step (2), the coating precursor is prepared according to the ratio of the matrix mass to the theoretical mass of the coating layer formed by the subsequent process of the coating precursor, which is 1:0.25.

[0099] Comparative Example 7 The difference between this embodiment and embodiment 1 is that the heat treatment temperature in step (4) is 900℃.

[0100] The cathode materials prepared in the above embodiments and comparative examples were tested as follows, and the test results are shown in Table 1: (1) Test of the mass fraction of titanium in the coating layer: First, the elemental distribution on the surface of the prepared cathode material particles was tested by SEM-EDS. Five 2*2μm regions were randomly selected on the same particle, and the Ti content in the region samples was recorded as a1, a2, a3, a4, and a5, respectively. The average value μ=(a1+a2+a3+a4+a5) / 5 and the standard deviation were calculated. The relative standard deviation (RSD) is calculated as (σ / μ) × 100%.

[0101] (2) Coating thickness test: First, the elemental distribution of the prepared cathode material particles is scanned using SEM-EDS. Specific elements of the matrix and coating are used. For example, if the active material is lithium iron phosphate, the specific element of the matrix is ​​selected as Fe, and the specific element of the coating is selected as Ti. The matrix region and coating region of a single particle are determined. The smallest circumcircle that can contain the specific elements of the coating of a single particle is delineated using the image analysis software of the instrument. The boundary of the matrix region is delineated with the Fe element distribution region (this closed line may be an approximate circle or an irregular shape). Using the Ti element distribution area as the delineation boundary of the coating region, and taking the center of the smallest circumscribed circle as the center point, five points are selected on the boundary of the matrix region at five equal angles (i.e., at 72° intervals). The boundary of the matrix region (i.e., at equal angles) is divided into five equal parts. The distances from these five equal points on the boundary of the matrix region to the boundary of the coating region are calculated along the radial direction of the smallest circumscribed circle and denoted as d1, d2, d3, d4, and d5, respectively. The average value μ = (d1 + d2 + d3 + d4 + d5) / 5 is calculated, and the standard deviation is calculated. The relative standard deviation (RSD) is calculated as (σ / μ) × 100%.

[0102] To verify the performance of the cathode material of this invention, the applicant assembled the cathode materials of each embodiment and comparative example into CR2032 coin cells and pouch cells, respectively. The CR2032 coin cells were used to test the initial coulombic efficiency, and the pouch cells were used to test the cycle performance. The specific battery composition is as follows: Preparation of the positive electrode sheet: The positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.5:1.5 and added to N-methylpyrrolidone (NMP) solvent. The mixture is stirred and dispersed to obtain a positive electrode slurry. The positive electrode slurry is coated onto aluminum foil and then dried, rolled, slit, and die-cut to obtain a positive electrode sheet.

[0103] Negative electrode: Lithium metal sheet.

[0104] Electrolyte preparation: A composite organic solvent was prepared by quantitatively mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in equal volume ratios. Then, thoroughly dried lithium hexafluorophosphate (LiPF6) was dissolved in this mixed solvent, and its concentration was adjusted to 1 mol / L to obtain the target electrolyte.

[0105] Preparation of the diaphragm: A porous polyethylene (PE) membrane is used as the diaphragm; the thickness is 11μm, the air permeability is 180~300s / 100mL and the porosity is 40%~45%.

[0106] Battery assembly: The positive electrode, separator and lithium metal sheet are assembled into a CR2032 button half cell (design capacity is 3.2mAh).

[0107] The positive electrode, electrolyte, and separator of the pouch battery are the same as those of the CR2032 button half-cell; the negative electrode is shown below: 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 to deionized water, and thoroughly stirred to disperse and mix to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, and the negative electrode sheet is obtained through processes such as drying, rolling, slitting, and die-cutting.

[0108] Assembly of the pouch battery: The positive electrode, separator, and negative electrode are assembled into a bare cell using a stacking process, and then encapsulated with an aluminum-plastic film. After thorough drying, the electrolyte is injected, followed by a series of processes including static soaking, formation, and aging, ultimately producing a pouch battery (designed capacity of 1Ah).

[0109] The performance of the materials in each embodiment and comparative example was tested using assembled button half-cells and pouch cells. The test results are shown in Table 1. The test methods are as follows: (1) First Coulomb efficiency test: First, charge the battery at a constant current of 1 / 3C until it reaches the battery charging cutoff voltage (3.75V for lithium iron phosphate batteries, 4.3V for lithium nickel cobalt manganese ternary batteries, and 4.5V for lithium cobalt oxide batteries). Then, charge it at a constant voltage of the battery charging cutoff voltage until it reaches 0.015mA. Finally, discharge it at a constant current of 1 / 3C until it reaches the battery discharging cutoff voltage (2.5V for lithium iron phosphate batteries, 3.0V for lithium nickel cobalt manganese ternary batteries, and 2.8V for lithium cobalt oxide batteries). Calculate the initial coulombic efficiency using the following formula: Initial coulombic efficiency = first week discharge capacity / first week charge capacity × 100%.

[0110] (2) Cyclic performance test: First, perform a 2-week cycle activation at a 0.33C rate within the rated voltage range (2.0V~3.8V for lithium iron phosphate batteries; 2.8V~4.4V for nickel-cobalt-manganese ternary batteries; 2.5V~4.2V for lithium cobalt oxide batteries). Then, conduct cycle performance testing, specifically switching the charge / discharge program to: The battery was charged at a constant current of 0.5C to the charging cutoff voltage (3.8V for lithium iron phosphate batteries, 4.4V for lithium nickel cobalt manganese oxide batteries, and 4.2V for lithium cobalt oxide batteries), then charged at a constant voltage to 0.05C. Next, it was discharged at a constant current of 1C to the discharging cutoff voltage (2.0V for lithium iron phosphate batteries, 2.8V for lithium nickel cobalt manganese oxide ternary batteries, and 2.5V for lithium cobalt oxide batteries) for cycle testing. The test was terminated when the battery reached 80% SOH (State of Harmonic Drive). The corresponding number of cycles represents the battery's cycle performance. 80% SOH is defined as the ratio of the battery's discharge capacity after one cycle to its discharge capacity in the first cycle being equal to or less than 80% for the first time.

[0111] Table 1: Parameters and test results of Examples 1-10 and Comparative Examples 1-7

[0112] Table 2 Electrochemical performance of Examples 1-10 and Comparative Examples 1-7

[0113] As can be seen from Tables 1 and 2: In Examples 1-3, while keeping other conditions constant, adjusting the pH of the reaction system can form coatings of varying thicknesses, leading to differences in the electrochemical properties of the materials. Studies show that when the pH of the reaction system deviates from 3.0 (the optimal pH), the surface charge density of both the substrate LFP and the coating LTO increases significantly. For polymer chains or nanoparticles carrying the same charge, after adsorption onto the LFP surface, a strong electrostatic repulsion force is generated within them. This repulsion force forces the molecular chains to extend as much as possible to lower the energy barrier of the system, thereby forming a thicker adsorption layer, which macroscopically manifests as an increase in the thickness of the LTO coating.

[0114] The test results of Examples 1-3 show that the relative standard deviation (RSD) of the LTO coating thickness is less than 5%, and the RSD of the Ti content in the coating is also less than 5%, confirming that the electrostatic self-assembly synthesis process used in this application can prepare LTO coatings with excellent uniformity. Further comparison shows that the initial coulombic efficiency (97.4%) and cycle life (3400 cycles) of Example 1 are significantly improved compared to Examples 2 and 3, indicating that the overall performance of the material is optimal when the thickness of the LTO coating is 200 nm. This demonstrates that a uniform and appropriately thick LTO coating can more effectively suppress interfacial side reactions, structural distortion of the matrix material, and dissolution of transition metal ions during cycling, while optimizing lithium ion diffusion efficiency, thereby improving the electrochemical performance of the material. In Examples 1, 4-5 and Comparative Examples 5 and 6, while keeping other conditions consistent, the amount of coating layer precursor raw material was adjusted according to the mass ratio of the matrix to the coating layer. The test results show that the coating thickness gradually increases with the increase of the amount of precursor raw materials used in the coating layer. Further analysis shows that the relative standard deviation (RSD) of the coating layer thickness and the relative standard deviation (RSD) of the Ti element mass fraction in the coating layer are significantly different: when the mass ratio of the matrix to the coating layer is maintained in the range of 1:(0.06~0.2), the RSD of the coating layer thickness and the RSD of the Ti element mass fraction in the coating layer are both <5%, indicating that the coating layer prepared within this ratio range has good uniformity and can give full play to the coating protection and performance optimization functions, resulting in the best improvement effect on the electrochemical performance of the material. When the mass ratio of the matrix to the coating layer is lower than the lower limit or higher than the upper limit of this range, the uniformity of the obtained coating layer decreases significantly (RSD>5%), and a continuous and dense effective protective layer cannot be formed, thus leading to an unsatisfactory improvement effect on the electrochemical performance of the material.

[0115] In Examples 1, 6-7, and Comparative Example 7, under the premise of keeping other conditions consistent, the temperature during heat treatment was adjusted. The test results showed that when the heat treatment temperature was controlled within the range of 600-800℃, the coating layer could form a dense and uniform protective layer with a strong bond to the substrate interface, possessing both excellent ion transport performance and mechanical stability, resulting in a better coating effect and outstanding electrochemical performance of the corresponding material. However, when the heat treatment temperature exceeded 800℃, the high temperature accelerated the abnormal growth of the coating layer grains, leading to uneven grain size, increased intergranular voids and grain boundary defects, and structural defects such as cracks and pores appearing in the originally dense coating layer. These defects would damage the integrity of the coating layer, making it easier for the electrolyte to penetrate to the core-shell interface, triggering interfacial side reactions (such as the dissolution of transition metal ions and electrolyte decomposition), and significantly deteriorating the coating effect.

[0116] Compared to Example 1, Examples 8-10 changed the matrix material. The test results show that the electrostatic self-assembly process of this application has good universality and is applicable to a variety of positive electrode active material systems. It can prepare LTO coating layers with uniform thickness and composition. The relative standard deviation of Ti element mass fraction and the relative standard deviation of coating layer thickness in all samples are less than 5%, which confirms the stability and reliability of the process.

[0117] Under the same process conditions, the coating thickness and Ti content of NCM@LTO and LCO@LTO composite materials differ somewhat from those of LFP@LTO. The core reasons are: 1) The original particle sizes (such as particle size and particle size distribution) of the matrix particles of different cathode active materials are inherently different; 2) Under the reaction pH environment specified in this application, the surface charge density and charge distribution of LFP, NCM, and LCO are different, resulting in slight differences in the electrostatic interaction strength between them and the LTO coating precursor, which in turn affects the adsorption amount and deposition density of the precursor. Despite the above differences, the coating thickness of the three composite cathode materials is within a suitable range that can effectively play a protective and performance optimization role, and the coating effect is not lost due to the change of matrix material.

[0118] The comparative test results of Example 1 and Comparative Example 1 show that the electrochemical performance of the LFP matrix material is significantly improved after constructing a uniform and dense LTO coating layer by electrostatic self-assembly. Compared with the pure LFP material in Comparative Example 1, the initial coulombic efficiency of Example 1 increased from 95.0% to 97.4%, and the cycle life increased from 1500 cycles to 3400 cycles (an extension of approximately 2-3 times). This fully demonstrates that the LTO coating layer can effectively suppress the interfacial side reactions between LFP and the electrolyte, reduce the loss of active lithium, and its stable interfacial structure significantly delays capacity decay.

[0119] Comparative testing results of Examples 1 (LFP@LTO), 9 (NCM@LTO), and 10 (LCO@LTO) with the corresponding Comparative Examples 2-4 (using the traditional sol-gel method) show that the two coating processes have fundamental differences in coating quality and material electrochemical performance. The electrostatic self-assembly method has significant comprehensive advantages, specifically as follows: The LTO coating layer formed by the electrostatic self-assembly method has superior density and integrity, and can more effectively suppress interfacial side reactions between the cathode material and the electrolyte during the first charge-discharge process. Specifically, the sol-gel method has poor protective effect due to the inhomogeneity and defects in the coating layer, and cannot effectively prevent the irreversible consumption of active lithium. In contrast, the coating layer synthesized by the electrostatic self-assembly method can reduce the irreversible consumption of active lithium during the formation of the solid electrolyte interfacial film, reduce the degree of oxidative decomposition of the electrolyte, and thus improve the reversible insertion / extraction efficiency of lithium ions. In terms of cycling performance, materials prepared by the electrostatic self-assembly method (taking LFP@LTO as an example) can achieve a cycle life of 3400 cycles, while the cycle life of the same system material prepared by the sol-gel method is only 2200 cycles, with the former being more than 1.5 times that of the latter. This significant difference confirms the superiority of the two coating processes from a macroscopic performance perspective: the coating layer prepared by the sol-gel method not only has structural defects but also has weak interfacial bonding with the matrix. During long-term charge-discharge cycles, it is prone to failure phenomena such as coating layer detachment and cracking due to volume expansion and contraction and interfacial stress, resulting in a rapid decline in its protective effect with increasing cycle count. On the other hand, the LTO coating layer synthesized by the electrostatic self-assembly method forms a stable interface with strong interaction with the matrix. On the one hand, it can effectively inhibit the dissolution of transition metal ions and avoid ion-catalyzed electrolyte decomposition; on the other hand, it can reduce lattice distortion and structural degradation of the electrode material and alleviate the generation of cracks in matrix particles during cycling, thereby significantly slowing down the capacity decay rate. This significant improvement in cycle stability demonstrates that the electrostatic self-assembly method not only solves the technical pain points of "incomplete protection and short lifespan" of the traditional sol-gel coating method, but also shows great potential in extending the service life of power batteries and improving battery reliability, providing key technical support for the research and development of long-cycle, high-stability power batteries.

[0120] Furthermore, Examples 1, 9, and 10, and their corresponding Comparative Examples 2-4, exhibited significant differences in the mass fraction of Ti in the coating layer and the uniformity of the coating layer thickness. The RSD of the coating layer thickness and the RSD of the mass fraction of Ti in the coating layer of Examples 1, 9, and 10 were all less than 5%, indicating that the coating layer was uniformly distributed. In contrast, the RSD of the coating layer thickness and the RSD of the mass fraction of Ti in the coating layer of Comparative Examples 2-4 were much greater than 5%. These data indicate that the LTO coating layer prepared by the sol-gel method has poor uniformity and cannot achieve a good coating effect, which is also the reason for the performance differences.

[0121] The cathode material provided by this invention uses a commonly used cathode active material as a substrate, with a lithium titanate coating layer constructed on its surface. The relative standard deviation (RSD) of the titanium mass fraction at different locations in this coating layer is less than 5%, exhibiting uniform coating. This uniform coating layer effectively isolates the internal cathode active material from direct contact with the electrolyte, suppressing interfacial side reactions and transition metal dissolution, thereby significantly improving the material's cycle life and high-temperature stability. Furthermore, this coating layer provides an efficient transport channel for lithium ions and electrons, reducing interfacial impedance and significantly improving its fast-charging performance. Ultimately, without sacrificing the inherent advantages of the internal cathode active material, it overcomes the bottlenecks in rate capability and lifespan, meeting the application requirements of next-generation high-performance lithium-ion batteries in electric vehicles, large-scale energy storage, and other fields. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0122] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A positive electrode material, characterized in that, The positive electrode material comprises: a substrate selected from active materials capable of reversibly intercalating and deintercalating lithium ions; a coating layer uniformly coated on the surface of the substrate, wherein the material of the coating layer comprises lithium titanate, and the relative standard deviation RSD of the mass fraction of titanium element in the coating layer is less than 5%.

2. The positive electrode material of claim 1, wherein, The relative standard deviation RSD of the thickness of the coating layer is less than 5%.

3. The positive electrode material of claim 1, wherein, The thickness of the coating layer is 120-280 nm; and / or The substrate comprises one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium cobaltate, lithium manganate, lithium nickel cobalt aluminum phosphate, and lithium nickel cobalt manganate.

4. A method for producing the positive electrode material according to any one of claims 1 to 3, characterized by, The method comprises the following steps: substrate pretreatment: dispersing the substrate material in a solvent and adjusting the pH value of the system to below the isoelectric point of the substrate material to make the surface of the substrate material positively charged, thereby obtaining a substrate suspension; coating precursor preparation: dissolving a titanium source and a lithium source in a solvent according to the stoichiometric ratio of the coating material, adding a chelating agent, and mixing and stirring to obtain a coating precursor solution; electrostatic adsorption: adding the coating precursor solution to the substrate suspension, maintaining the system in an acidic environment, and using electrostatic attraction to make the coating precursor spontaneously adsorb to the surface of the substrate particles to form a molecular-level precursor layer, and then performing aging and stirring treatment to obtain a positive electrode material precursor; heat treatment: performing heat treatment on the positive electrode material precursor in an inert atmosphere to convert the molecular-level precursor layer into a crystallized coating layer, thereby obtaining a positive electrode material.

5. The method for preparing the cathode material according to claim 4, characterized in that, In the substrate pretreatment step, the pH value of the system is 2.5-3.5; and the substrate suspension is placed in a water bath environment at 40-60°C for constant temperature stirring for 1-3 hours, and the stirring rate is controlled to be 400-800 rpm to maintain the stability of the surface charge of the substrate material.

6. The method for preparing the cathode material according to claim 4, characterized in that, One or more of the following: The lithium source comprises one or more of lithium acetate and lithium nitrate; The titanium source comprises one or more of tetrabutyl titanate and tetraisopropyl titanate; The chelating agent comprises one or more of glacial acetic acid, acetylacetone, citric acid, and tartaric acid.

7. The method of claim 4, wherein the method further comprises a step of calcining the mixture at a temperature of 700-900°C for 1-10 hours. The electrostatic adsorption step comprises: adding the coating precursor solution dropwise to the substrate suspension in a water bath environment at 40-60°C; controlling the stirring speed to be 400-800 rpm during the dropwise addition, and maintaining the pH value of the reaction system to be 2.8-3.2; and taking the mass of the substrate in the substrate suspension as the basis, the ratio of the mass of the substrate to the theoretical mass of the coating layer formed by the subsequent process conversion of the coating precursor is 1:(0.06-0.2); and / or the aging and stirring treatment time is 4-6 hours.

8. The method of claim 4, wherein the method further comprises a step of adding a lithium source to the mixture. The heat treatment step comprises: maintaining at 200-300°C for 2-3 hours, then increasing the temperature to 600-800°C and maintaining for 4-6 hours.

9. An electrochemical device, characterized by, The positive electrode material comprises any one of the positive electrode materials according to claims 1-3, or is prepared by any one of the preparation methods according to claims 4-8.

10. An electronic device, comprising: The electrochemical device comprises the positive electrode material according to claim 9.

Images