A positive electrode material, a preparation method thereof, an electrochemical device, and an electronic device

Abstract

The application provides a positive electrode material and a preparation method thereof, an electrochemical device and an electronic equipment, and particularly relates to the technical field of batteries. 1+x M 1‑x O2, wherein 0 3+ and Zr 4+ , the anion includes F ‑ , and the alkali metal ion includes Na + . The application can effectively improve the problems of low first coulomb efficiency, serious voltage attenuation and poor safety of the lithium-rich layered positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of battery 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 new energy technologies, the market has placed more stringent demands on the energy density of lithium-ion batteries. Lithium-rich layered cathode materials, with their theoretical specific capacity far exceeding that of traditional ternary cathode materials, have become one of the core research directions for improving the energy density of lithium-ion batteries, demonstrating broad application potential in high-energy-density power batteries and energy storage.

[0003] However, current lithium-rich layered cathode materials still suffer from a series of technical defects in practical applications: during the first charge and discharge process, irreversible oxygen loss and severe side reactions at the electrolyte-cathode interface easily occur on the material surface, resulting in a large number of lithium ions failing to reversibly intercalate and deintercalate during the first charge, leading to an initial coulombic efficiency of less than 80%; during cycling, transition metal ions (such as Ni)... 2+ Mn 3+ Migration triggers Li / Ni mixing and continuous loss of lattice oxygen, inducing a phase transformation from layered phase to spinel / rock salt phase, which in turn blocks Li... + The channel further reduces diffusion efficiency, and the microcracks in the electrode particles exacerbate electrolyte side reactions, leading to poor cycle stability and severe voltage decay; it also results in poor safety, low lattice oxygen binding energy, easy detachment and oxidation of the electrolyte at high temperatures, and the release of transition metal ions (such as Mn) during cycling. 2+ The catalytic decomposition of the electrolyte generates flammable and explosive substances, which together trigger the risk of thermal runaway. These defects limit the industrial application of lithium-rich layered cathode materials in fields such as electric vehicles and large-scale energy storage.

[0004] Therefore, there is an urgent need to develop a lithium-rich layered oxide cathode material that can simultaneously address the aforementioned multidimensional defects in order to further promote the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0005] This invention provides a cathode material and its preparation method, an electrochemical device, and an electronic device to solve the technical problems of low initial coulombic efficiency, severe voltage decay, and poor safety of lithium-rich layered oxides.

[0006] To achieve the above and other related objectives, the present invention provides a cathode material comprising: a core and a protective layer, wherein the core has the chemical formula Li. 1+x M 1-xO2, where 0 < x ≤ 0.2, and M is selected from one or more of Ni, Co, and Mn; the protective layer covers the surface of the core, and the main structure of the protective layer is integrally and continuously distributed with the crystal structure of the core, and the protective layer is doped with cations, anions, and alkali metal ions; wherein, the cations and anions are distributed in a doping concentration gradient from the inside to the outside along the thickness direction of the protective layer, and the alkali metal ions are doped on the surface layer of the protective layer; the cations include B 3+ and Zr 4+ The anion includes F - The alkali metal ions include Na + .

[0007] In one embodiment of the present invention, the B 3+ The doping gradient coefficient is 0.1~0.5 at% µm. -1 The B 3+ The atomic percentage of the outermost layer of the protective layer is 0.5~3 at%; wherein the outermost layer refers to the region of the protective layer that extends from the outside to the inside along the thickness direction of 0~0.1 μm.

[0008] In one embodiment of the present invention, the Zr 4+ The doping gradient coefficient is 0.05~0.3 at% µm. -1 The Zr 4+ The atomic percentage of the outermost layer of the protective layer is 0.2~2 at%.

[0009] In one embodiment of the present invention, the F - The doping gradient coefficient is 0.2~1 at% µm -1 The F - The atomic percentage of the outermost layer of the protective layer is 2-10 at%.

[0010] In one embodiment of the present invention, the Na + The atomic percentage of the outermost layer of the protective layer is 0.8~5 at%.

[0011] In one embodiment of the present invention, the thickness of the protective layer is 1~5 μm, and / or, the Na + The doping depth in the protective layer is in the range of 0~50nm extending inward from the outer surface of the protective layer.

[0012] In one embodiment of the present invention, the particle size distribution D50 of the positive electrode material is 5~15 µm.

[0013] The present invention also provides a method for preparing a cathode material, the method comprising the following steps:

[0014] Precursor co-precipitation: Prepare a salt solution containing transition metal elements according to the chemical formula of the cathode material, add a cation source and an anion source to the salt solution, adjust the pH value and temperature to carry out co-precipitation, and obtain the doped precursor;

[0015] Gradient diffusion sintering: The doped precursor is mixed with a lithium source and then subjected to gradient diffusion sintering to obtain an intermediate doped with cations and anions.

[0016] Surface modification: A sodium source is introduced into the intermediate to form sodium enrichment on the surface of the intermediate, thereby obtaining the cathode material.

[0017] In one embodiment of the present invention, the gradient diffusion sintering includes:

[0018] The first sintering is carried out at a temperature of 650~750℃ for 2~6 hours to form an interface layer rich in doped ions;

[0019] The second sintering is carried out at a temperature of 780~850℃ for 10~20 hours to drive the diffusion of dopant ions in the interface layer to form a smooth dopant concentration gradient.

[0020] In one embodiment of the present invention, the surface modification includes: introducing sodium source vapor into the intermediate body at 450~600°C under an inert atmosphere and maintaining it for 30 minutes.

[0021] In one embodiment of the present invention, the pH value of the precursor co-precipitation is 9.5~11, and the temperature is 40~60℃.

[0022] In one embodiment of the present invention, the transition metal element is selected from one or more of Ni, Co, and Mn, and the salt solution containing the transition metal element includes any one of sulfate solution, nitrate solution, acetate solution, and chloride solution.

[0023] In one embodiment of the present invention, the lithium source includes one or more of lithium carbonate and lithium hydroxide.

[0024] In one embodiment of the present invention, the cation source includes a boron source and a zirconium source, wherein the boron source includes one or more of boric acid, ammonium borate, and sodium borate, and the zirconium source includes one or more of zirconium sulfate and zirconium tetrachloride.

[0025] In one embodiment of the present invention, the anion source includes a fluorine source, which includes one or more of ammonium fluoride and hydrogen fluoride.

[0026] In one embodiment of the present invention, the sodium source includes one or more of sodium fluoride and sodium carbonate.

[0027] The present invention also provides an electrochemical device comprising: the positive electrode material described in any one of the above claims, or the positive electrode material prepared by the above preparation method.

[0028] The present invention also provides an electronic device comprising the above-described electrochemical device.

[0029] The beneficial effects of this invention: The positive electrode material proposed in this invention, through in-situ construction of B on the surface of a lithium-rich layered positive electrode material... 3+ / Zr 4+ Dications and F - Cooperative gradient and Na + The multidimensional protective layer enriched on the surface enhances the material's performance from the aspects of structural stability, interface protection, and ion transport.

[0030] B 3+ and Zr 4+ First, synergy is achieved in terms of the stability of the main structure, B 3+ By suppressing the release of oxygen from the lattice, a stable oxygen foundation is established for the layered structure, while Zr 4+ Zr suppresses lithium / nickel mixing by supporting the layered framework. 4+ The skeletal support can strengthen B 3+ A stable oxygen environment helps both slow down voltage decay and structural degradation, while also effectively resisting lattice stress caused by repeated ion insertion / extraction, reducing the generation and propagation of microcracks, and laying a structural foundation for improving the material's cycle life.

[0031] F - On the one hand, a dense and stable metal fluoride layer is formed by enriching and reacting with transition metal ions on the material surface. This physical barrier can passivate the surface activity of the positive electrode, inhibiting the oxidative decomposition of the electrolyte and reducing the dissolution of transition metal ions, thereby constructing a more stable positive electrode-electrolyte interface (CEI). On the other hand, F - Within the crystal lattice, it can induce electron cloud reconstruction of surrounding metal cations (M), enhancing the MO bond strength, which is similar to B. 3+ The inhibition of lattice oxygen release forms a dual guarantee of bond energy and oxygen stability, which together inhibits the irreversible phase transformation from layered phase to spinel / rock salt phase.

[0032] Na enriched in the outermost layer + Then with F - B 3+ Zr 4+ The constructed inner layer of protection forms a collaborative protection system, Na + It can efficiently capture HF acid generated by trace amounts of water in the electrolyte, preventing HF from attacking the cathode material and causing metal ion dissolution. Simultaneously, Na... +By altering the interfacial surface energy and charge distribution, it is beneficial to form a thin and stable CEI layer. This CEI layer not only reduces interfacial impedance but also minimizes the impact of interfacial byproducts on Li. + Blockage of the conduction channel simultaneously improves the rate performance and initial coulombic efficiency of the material.

[0033] In conclusion, B 3+ / Zr 4+ / F - / Na + Through multi-dimensional synergy of structural stability, interface protection, environmental adaptation, and ion conduction, the material's cycle life, safety, and initial coulombic efficiency were simultaneously optimized. Attached Figure Description

[0034] 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.

[0035] In the attached diagram:

[0036] Figure 1 This is a schematic diagram of a method for preparing a cathode material according to an embodiment of the present invention. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The terms or phrases used in this article have the following meanings:

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In this article, atomic percentage (at%) is the percentage of the number of atoms of a certain element relative to the total number of atoms in the system, based on the total number of atoms in the system. It is a unit for measuring the relative concentration of an element.

[0045] Lithium-rich layered cathode material (Li 1+x M 1-x The high energy density of O2 (where M is a transition metal) stems from the triple synergistic effect of "lithium-ion storage, charge compensation, and voltage plateau" driven by the "lithium-rich structure": First, the "lithium-rich" characteristic allows the material to store more lithium ions per unit mass that can participate in insertion and extraction, significantly increasing the initial lithium-ion supply compared to traditional layered cathodes (such as LiCoO2 and NCM), laying the foundation for high capacity; Second, it breaks through the limitation of traditional materials relying solely on the single redox reaction of transition metals, amplifying the specific capacity through the "synergistic mechanism of transition metal redox reaction and lattice oxygen redox reaction"—transition metal ions (such as Ni...). 2+ →Ni 4+ Co 3+ →Co 4+ The fundamental capacity is contributed through valence state changes, while the O in the lattice... 2- It can be reversibly oxidized to a lower oxidation state oxygen substance (such as O2) under high voltage. 2- The additional capacity release makes the specific capacity of the material far exceed that of traditional materials; third, the activation process of active materials (transition metals, lattice oxygen) under high voltage further raises the voltage plateau, and the energy density is the product of the specific capacity and the voltage plateau. Finally, through the chain effect of "multiple lithium ion supply → dual redox energy replenishment → high voltage efficiency enhancement", a breakthrough in high energy density is achieved.

[0046] However, these materials still have some drawbacks in practical applications: The initial coulombic efficiency (FCE) is low. During the first charge and discharge cycle, irreversible oxygen loss easily occurs on the material surface. Simultaneously, severe side reactions occur at the interface between the electrolyte and the cathode material (such as electrolyte decomposition and the reaction of dissolved transition metal ions with electrolyte components to form inert products). This results in a large number of lithium ions being unable to reversibly intercalate and deintercalate during the first charge cycle, leading to an initial coulombic efficiency typically below 80%, significantly reducing the battery's energy output utilization. Cyclic stability is poor, and voltage decay is severe. During long-term charge and discharge cycles, the layered crystal structure is prone to irreversible phase transitions—with repeated lithium ion intercalation and deintercalation, transition metal ions (such as Ni...) in the material... 2 + Mn 4+ Oxygen ions migrate and occupy lithium-ion vacancies, causing the layered structure to transform into a spinel or rock salt phase. This is accompanied by continuous oxygen loss, further damaging the crystal structure's integrity. This structural degradation directly leads to continuous voltage decay in the battery, and the capacity retention rate after 100 cycles is typically below 80%, failing to meet the long cycle life requirements of power batteries. Insufficient thermal safety limits its application in power batteries. The low lattice oxygen binding energy makes it prone to detachment at high temperatures, reacting with the electrolyte in a redox reaction, releasing flammable and explosive substances, and causing thermal runaway, posing serious safety hazards to battery use, especially making it difficult to meet the safety requirements of power batteries in high-temperature environments. These defects limit the application of lithium-rich layered cathode materials.

[0047] To address the aforementioned problems, this invention provides a cathode material, its preparation method, an electrochemical device, and an electronic device, by in-situ constructing a B on the surface of a lithium-rich layered cathode material. 3+ / Zr 4+ Dications and F - Ion synergistic gradient and Na + The multidimensional protective layer enriched on the surface systematically solves the electrochemical and thermal stability problems of lithium-rich materials from three dimensions: chemical bond stability, physical structure support, and interface passivation.

[0048] This invention provides a cathode material comprising a core and a protective layer, wherein the core is a lithium-rich layered oxide with the chemical formula Li. 1+x M 1-xO2, where 0 < x ≤ 0.2, and M is selected from one or more of Ni, Co, and Mn. For example, x can be 0.05, 0.1, 0.15, or 0.2, etc.; M can be any one of the transition metal elements listed above, such as Ni, Mn, or Co; M can also be any combination of two or more of the transition metal elements listed above, such as M being Ni and Mn, or Ni and Co, or Mn and Co, or Ni, Co, and Mn. A protective layer covers the surface of the core. The main structure of the protective layer and the crystal structure of the core are integrally and continuously distributed, meaning there is no obvious interface break or abrupt change in crystal structure between the protective layer and the core, achieving seamless connection at the atomic scale. The protective layer is doped with the cation B. 3+ and Zr 4+ Anion F - and alkali metal Na + In other words, the core is undoped Li. 1+x M 1-x O2, the protective layer is doped Li 1+x M 1-x O2, doped with ions including B 3+ Zr 4+ F - And Na + .

[0049] Specifically, B 3+ and Zr 4+ They mainly exist in the layered lattice of the protective layer in the form of substitutional dopant. Because their ionic radii are similar to those of lithium ions (Li... + ) or transition metal ions (such as Ni) 2+ Mn 4+ Similar to Li, they will replace some of it. + or transition metals (M 3+ / M 4+ The position of ) . Among them, B 3+ Exhibiting high electronegativity and strong covalent bonding, it tends to form robust BO covalent bonds with oxygen, with bond energies far exceeding those of transition metal-oxygen bonds (such as Ni-O, Mn-O). A key failure mode in lithium-rich layered oxide materials during cycling is the loss of lattice oxygen and the irreversible phase transition from the layered structure to the spinel / rock salt phase. 3+ The introduction of [a specific element] effectively suppressed the release of lattice oxygen by enhancing the covalent nature of the MO bonds, thereby stabilizing the main layered structure and slowing down voltage decay and structural degradation. However, if the B [a specific element] inside the crystal structure... 3+ Excessive content will affect Li + Transmission, therefore, in the protective layer of this application, B 3+The doping concentration increases gradually from the inside to the outside (from near the core to far from the core) along the thickness direction of the protective layer. This improves interface stability without affecting the Li + Transmission. Zr 4+ Zr is an electrochemically inert ion with a large ionic radius. 4+ When occupying some lithium sites or transition metal sites, its stable chemical properties and large volume can effectively support the layered structure framework and suppress lithium / nickel mixing, especially maintaining structural stability in the deep delithiation state. This physical barrier effectively mitigates lattice stress and microcracks caused by repeated lithium-ion insertion / extraction, thereby improving the material's cycle life. In the protective layer of this application, Zr 4+ Along the thickness direction of the protective layer, the doping concentration increases from the inside to the outside. 4+ A smaller internal concentration reduces the impact on lithium-ion insertion / extraction capacity, while a gradually increasing external concentration improves structural stability. Zr 4+ The skeletal support can strengthen B 3+ A stable oxygen environment helps both slow down voltage decay and structural degradation, while also effectively resisting lattice stress caused by repeated ion insertion / extraction, reducing the generation and propagation of microcracks, and laying a structural foundation for improving the material's cycle life.

[0050] F - It mainly replaces part of the O in the crystal lattice 2- F - Compared to O, its electronegativity 2- Furthermore, it reacts with transition metal ions to form chemically stable metal fluorides (such as NiF2 and MnF2). This dense fluoride layer effectively passivates the surface activity of the positive electrode, inhibits the oxidative decomposition of the electrolyte and the dissolution of transition metal ions, thereby constructing a more stable positive electrode-electrolyte interface (CEI). In addition, F... - Within the crystal lattice, this induces electron clouds in surrounding metal cations (M), enhancing the strength of the MO bond, which is similar to B. 3+ The inhibition of lattice oxygen release forms a dual guarantee of bond energy and oxygen stability, jointly suppressing the irreversible phase transformation from layered phase to spinel / rock salt phase and reducing side reactions. In the protective layer of this application, F - The doping concentration increases from the inside to the outside along the thickness direction of the protective layer.

[0051] B 3+ Zr 4+ and F - The gradient distribution resolves the fundamental contradiction between surface stability and bulk electrochemical activity. The high-concentration region, concentrated at the interface, ensures excellent interfacial and thermal stability; while the low-concentration region smoothly transitions to the core, guaranteeing the Li... +This facilitates the rapid transport channels and high capacity utilization of the material matrix. On the other hand, it also reduces interfacial impedance and lattice stress: the core-shell interface with abrupt compositional changes generates significant physical stress due to lattice parameter mismatch, simultaneously forming a barrier that hinders Li... + The energy barrier for traversing the lattice. The smooth concentration gradient structure means that the lattice parameters and chemical potential also change gradually, forming a buffer transition zone. This greatly alleviates the mechanical stress during cycling, avoids coating peeling and particle cracking, and provides a buffer for Li. + It provides a smooth, low-impedance migration path, thereby significantly improving cycle life and rate performance.

[0052] Na + It is a relatively large alkali metal ion, which mainly exists in the surface enrichment form of the protective layer, and its form may be sodium oxide or fluoride. + Enriching the surface of the protective layer can effectively capture HF generated by trace amounts of water in the electrolyte, reducing the dissolution of metal ions from the cathode material and improving the long-term stability and safety of the material. Furthermore, the surface-enriched Na... + It can also change the surface energy and charge distribution of the interface, which helps to form a Li + A thin and stable CEI layer provides better conduction and reduces interface impedance, thereby improving rate performance and first coulomb efficiency.

[0053] The gradient coefficient of dopant ions refers to the average rate of change of dopant ion concentration with depth over the entire thickness of the protective layer. 3+ Zr 4+ and F - The gradient coefficient of ion doping has a significant impact on the performance of cathode materials. A gradient coefficient that is too small indicates a very gentle gradient, resulting in a small concentration difference between the dopant elements inside and outside the protective layer. If the concentrations of dopant elements inside and outside the protective layer are both low, the protective function and structural support of the outermost layer will be greatly reduced, making it difficult to form a high concentration of active material in the most critical surface areas, thus failing to effectively suppress electrolyte oxidation and transition metal dissolution. Conversely, if the concentrations of dopant elements inside and outside the protective layer are both high, the bulk electrochemical activity of the inner layer cannot be guaranteed, and excessively high concentrations of dopant elements in the inner layer can clog the Li. + The rapid transmission channel affects the high capacity utilization of the main material.

[0054] An excessively large gradient coefficient indicates a drastic change in the chemical composition and lattice parameters of the material over a very short distance. This creates an abrupt interface between the core and the protective layer, generating enormous lattice mismatch stress. This stress becomes a structural weakness, leading to particle cracking and coating peeling during electrochemical cycling, accelerating material failure. Simultaneously, the steep chemical potential gradient forms a high energy barrier at this interface, hindering lithium-ion transport. This significantly increases interfacial impedance, reducing the material's initial coulombic efficiency and rate performance.

[0055] In one embodiment, B 3+ The doping gradient coefficient is 0.1~0.5 at% µm. -1 That is, for every 1 μm of advance towards the core along the thickness direction of the protective layer, B 3+ The doping concentration is reduced by 0.1~0.5 at%. For example, B 3+ The doping gradient coefficient can be 0.1 at% µm. -1 0.3 at% µm -1 Or 0.5 at% µm -1 wait.

[0056] Zr 4+ The doping gradient coefficient is 0.05~0.3 at% µm. -1 That is, for every 1 μm of Zr advancing towards the core along the thickness direction of the protective layer, 4+ The doping concentration decreased by 0.05~0.3 at%. For example, Zr 4+ The doping gradient coefficient can be 0.05 at% µm -1 0.1 at% µm -1 0.2at% µm -1 Or 0.3 at% µm -1 wait.

[0057] F - The doping gradient coefficient is 0.2~1 at% µm -1 That is, for every 1 μm of advance towards the core along the thickness direction of the protective layer, F - The doping concentration is reduced by 0.2~1 at%. For example, F - The doping gradient coefficient can be 0.2 at% µm. -1 0.5at% µm -1 0.8t% µm -1 or 1 at% µm -1 wait.

[0058] The above B 3+ Zr 4+ and F -The gradient coefficients can be obtained through in-depth analysis using focused ion beam time-of-flight secondary mass spectrometry (FIB-TOF-SIMS), and the specific process is as follows:

[0059] Sample preparation: Using FIB, cut a flat analytical area (e.g., 5 µm × 5 µm) on the secondary spherical particle (e.g., a particle with a diameter of 10 µm), ensuring that the analytical starting point is located on the outermost surface of the particle.

[0060] Depth profiling: TOF-SIMS was used for depth profiling. Sputtered ion beams (such as Cs) + The analytical ion beam (such as Bi) bombards the analytical region vertically at a constant rate, peeling off the material layer by layer. Simultaneously, an analytical ion beam (such as Bi) is used. + Secondary ions are excited, and the TOF analyzer detects their mass-to-charge ratio based on the difference in ion flight time, thereby obtaining the elemental composition information at each depth point.

[0061] Data calibration: The signal intensity of secondary ions was converted to atomic percentage (at%) using standard samples, and sputtering time was converted to depth (µm). This yielded a raw data plot of concentration (at%) vs. depth (µm).

[0062] Gradient coefficient calculation: On the concentration vs. depth curve, identify the region representing the gradient protective layer (e.g., from a depth of 0.1 µm to 4.9 µm, avoiding the outermost Na). + The enriched layer and the boundary between the innermost layer and the kernel.

[0063] A linear regression was performed on the data points within this region. The slope of the fitted line is the gradient coefficient of the doped ions, expressed in at% µm. -1 .

[0064] Besides the doping gradient coefficient of dopants having a significant impact on the performance improvement of cathode materials, the doping concentration also affects the improvement of cathode materials. Because B 3+ Zr 4+ and F - The protective layer exhibits a gradient decrease from the outside to the inside along its thickness direction. Therefore, the doping concentration of the outermost layer and the doping gradient coefficient determine the total amount of doped ions. If the doping concentration of the outermost layer is too low, the total doping amount is insufficient to form an effective protective layer, thus failing to improve performance. If the doping concentration of the outermost layer is too high, it will occupy too many lithium ion or transition metal sites, blocking the lithium ion transport channels, thereby significantly reducing the capacity and rate performance of the material.

[0065] In one embodiment, B 3+The outermost layer of the protective layer has an atomic percentage of 0.5~3 at%, where the outermost layer refers to the region extending 0~0.1 μm from the outside to the inside along the thickness direction of the protective layer. For example, B 3+ The atomic percentage of the outermost layer of the protective layer can be 0.5at%, 1at%, 2at%, or 3at%, etc.

[0066] Zr 4+ The atomic percentage of the outermost layer of the protective layer is 0.2~2 at%, for example, Zr 4+ The atomic percentage of the outermost layer of the protective layer can be 0.2at%, 0.8at%, 1.5at%, or 2at%, etc.

[0067] F - The outermost layer of the protective layer has an atomic percentage of 2-10 at%, for example, F - The atomic percentage of the outermost layer of the protective layer can be 2at%, 5at%, 8at%, or 10%, etc.

[0068] In one embodiment, Na + The atomic percentage of the outermost layer of the protective layer is not less than 0.8 at%, and further, Na + The atomic percentage of the outermost layer of the protective layer is 0.8~5 at%, specifically 0.8at%, 1at%, 3at%, 5at%, etc. Na + Doping the outermost layer can enhance Li + While lithium ions can be transported, excessively high doping concentrations can lead to the formation of a thick, non-conductive sodium salt layer (such as NaF), which hinders lithium ion shuttle movement, increases the overall interfacial impedance, and reduces the material's electrochemical performance. + Within the above range, doping ensures sufficient HF removal and interface optimization capabilities while avoiding the impedance increase problem caused by excessively high concentrations.

[0069] In one embodiment, the thickness of the protective layer is 1~5 μm, that is, the thickness of the lithium-rich layered oxide with doped ions coating the core is 1~5 μm, for example, it can be 1 μm, 3 μm, or 5 μm, etc. Further, Na... + The doping depth in the protective layer extends from the outer surface of the protective layer inward in the range of 0~50nm.

[0070] In one embodiment, the particle size distribution D50 of the cathode material is 5~15 µm, for example, it can be 5 μm, 10 μm or 15 μm, etc., to meet the requirements for the use of particle size distribution composite cathode materials. In this invention, D50 refers to the particle size corresponding to a sample when the cumulative volumetric particle size distribution percentage reaches 50%, which can be measured by a laser particle size analyzer.

[0071] Please see Figure 1 The present invention also provides a method for preparing a positive electrode material, the method comprising the following steps:

[0072] S1. Prepare a salt solution containing transition metal elements according to the chemical formula of the cathode material, add cation source and anion source to the salt solution, adjust the pH value and temperature to carry out co-precipitation, and obtain the doped precursor.

[0073] S2. The doped precursor is mixed with a lithium source and then subjected to gradient diffusion sintering to obtain an intermediate with cation and anion gradient doping.

[0074] S3. Introduce a sodium source into the intermediate to form sodium enrichment on the surface of the intermediate, thereby obtaining the cathode material.

[0075] Specifically, the chemical formula of the cathode material in step S1 is Li 1+x M 1-x O2, where 0 < x ≤ 0.2, and M is selected from one or more of Ni, Co, and Mn. For example, x can be 0.05, 0.1, 0.15, or 0.2, etc.; M can be selected from any one or more of the transition metal elements listed above. For example, the chemical formula of the cathode material is Li. 1.2 Ni 0.6 Mn 0.2 O2, Li 1.2 Ni 0.8 O2, Li 1.2 Mn 0.8 O2 or Li 1.2 Ni 0.6 Co 0.1 Mn 0.1 O2, etc.

[0076] Step S1, the precursor co-precipitation step, involves selecting a compound containing the corresponding transition metal element and its amount based on the chemical formula and stoichiometry of the cathode material to be prepared, and preparing a salt solution containing the transition metal element. This transition metal element is selected from one or more of Ni, Co, and Mn elements according to its chemical formula. The salt solution can be any one of a sulfate solution, nitrate solution, acetate solution, or chloride solution. Specifically, a sulfate, nitrate, acetate, or chloride containing the transition metal element is dissolved in deionized water to obtain the salt solution containing the transition metal element. Furthermore, using a sulfate solution containing the transition metal element is preferable due to its low cost, good solubility, and low impurity content.

[0077] Next, a doped ion source, such as a boron source, a zirconium source, or a fluorine source, is added to the salt solution containing a transition metal, and the mixture is stirred until the doped ion source is completely dissolved to obtain a mixture. The boron source includes one or more of boric acid (H3BO3), ammonium borate ((NH4)3O3), sodium borate (Na3BO3), and other soluble borates. For example, the boron source can be boric acid, or amine borate, or a combination of boric acid and sodium borate. The zirconium source includes one or more of zirconium sulfate (Zr(SO4)2) and zirconium tetrachloride (ZrCl4), for example, zirconium sulfate, or zirconium tetrachloride, or a combination of zirconium sulfate and zirconium tetrachloride, etc. The fluorine source includes one or more of ammonium fluoride (NH4F) and hydrogen fluoride (HF), for example, ammonium fluoride, or hydrogen fluoride, or a combination of amine fluoride and hydrogen fluoride, etc. It should be noted that the amount of doped ion source added is determined based on the doping concentration of the doping element in the protective layer of the cathode material.

[0078] Then, the pH and temperature of the mixture are adjusted to allow the transition metal and dopant ions to co-precipitate and obtain the doped precursor. The pH and temperature can be selected based on the type of salt solution. For example, when using a sulfate solution, the pH of the mixture is 9.5–11, such as 9.5, 10, or 11, etc. If the pH is too low, Ni / Co / Mn precipitation will be incomplete; if the pH is too high, the precipitation rate will be too fast, leading to uneven particle morphology or agglomeration. The temperature is controlled at 40–60°C, such as 40°C, 50°C, or 60°C, etc. A coprecipitation temperature of 40–60°C provides a moderate reaction rate, which is beneficial for forming spherical precursors with good crystallinity and uniform particle size.

[0079] Step S2, the gradient diffusion step, involves thoroughly mixing the doped precursor obtained in step S1 with a lithium source. The lithium source includes, but is not limited to, lithium carbonate (Li₂CO₃) and lithium hydroxide (LiOH). The amount of lithium source added is adjusted according to the stoichiometry of the cathode material's chemical formula. The mixing method can be conventional in the art, such as using a mixer. After the mixture is homogeneous, it undergoes two sintering processes.

[0080] The first sintering is performed at 650-750°C for 2-6 hours to form a doped ion-rich interface layer in the mixture. This sintering, conducted at a relatively low temperature and for a short time, allows for the initial reaction between the lithium salt and the doped precursor, with limited diffusion of B, Zr, and F ions only near the particle surface, forming a thin and enriched interface layer. For example, the sintering temperature can be 650°C, 700°C, or 750°C, and the sintering time can be 2 hours, 4 hours, or 6 hours, etc. Too low a temperature or too short a time can lead to insufficient diffusion; too high a temperature or too long a time may result in excessive element diffusion, affecting subsequent gradient formation.

[0081] The second sintering, conducted at 780–850°C for 10–20 hours, drives the diffusion of dopant ions in the interface layer to form a smooth dopant concentration gradient. This sintering utilizes a higher temperature and longer time, leveraging the differences in ion diffusion kinetics at high temperatures to drive the diffusion of B, Zr, and F elements inward, creating a smooth concentration gradient. Specifically, after the first sintering, the heating rate is controlled at 2°C / min to reach the second sintering temperature. An excessively rapid heating rate can lead to temperature differences between the inside and outside of the material, potentially causing uneven stress or non-uniform diffusion; an excessively slow rate will prolong the preparation cycle. For example, the sintering temperature for the second sintering can be 780°C, 810°C, or 850°C, and the sintering time can be 10 hours, 15 hours, or 20 hours. The sintering temperature controls the diffusion rate, thereby affecting the degree of diffusion and the smoothness of the gradient.

[0082] Step S3, the surface modification step, involves cooling the surface to 450-600°C under an inert atmosphere, such as nitrogen, after the second sintering. Sodium source vapor is then introduced and maintained for 30 minutes to enrich the surface with sodium. In this step, the sodium source includes sodium fluoride (NaF), sodium carbonate (Na₂CO₃), etc., and the temperature can be 450°C, 500°C, or 600°C. At this temperature, some of the sodium source will sublimate or decompose, generating sodium-containing vapor, while simultaneously ensuring the stability of the main crystal structure. The amount of sodium source used can be determined based on the surface Na content of the final product. + The target concentration is determined.

[0083] After step S3, secondary spherical particles with a particle size D50 of 5~15µm are selected by sieving as positive electrode materials.

[0084] 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.

[0085] In one embodiment, the electrochemical device is 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.

[0086] 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.

[0087] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive current collector is, for example, aluminum foil or carbon-coated aluminum foil, and 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 a positive active material, a positive conductive agent, and a positive binder, wherein the positive active material is the positive material described above in this invention. 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, polyhexafluoropropylene, etc. Exemplarily, 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. The ratio of the positive electrode active material, conductive agent, and binder can be set according to conventional settings in the art.

[0088] The preparation process of the positive electrode sheet is as follows: First, the positive active material, positive conductive agent and positive binder are mixed and stirred evenly in a solvent such as N-methylpyrrolidone (NMP) according to a certain ratio to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive current collector. After drying, rolling, cutting and other processes, the positive electrode sheet is obtained.

[0089] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative current collector is, for example, selected from copper foil or carbon-coated copper foil, and has two surfaces disposed 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.

[0090] For example, the negative electrode active material includes, but is not limited to, artificial graphite, natural graphite, silicon carbide materials, etc. The negative electrode conductive agent is selected from one or more of acetylene black, conductive carbon black (Super P), carbon fiber (VGCF), carbon nanotubes (CNT), Ketjen black, and graphene; for example, it can 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 vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, and styrene-butadiene rubber, or a combination of several in any proportion; for example, it can be vinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, or styrene-butadiene rubber, etc. The thickener is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0091] 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 a certain 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.

[0092] A separator is placed between the positive and negative electrodes to separate them, preventing short circuits inside the battery. It also allows lithium ions to move between the positive and negative electrodes, facilitating the charging and discharging process. The separator can be made of porous materials such as polyethylene (PE), polypropylene (PP), glass fiber, or composite membranes.

[0093] 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 may be selected from one or more of the following: fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC).

[0094] Non-aqueous electrolytes may also include functional additives, such as fluoroethylene carbonate (FEC), propylene-1,3-sulfonyl lactone (PST), tetravinylsilane (TVSI), vinylene carbonate (VC), ethylene sulfate (DTD), etc., which can be added according to the actual needs of production.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] This application also provides an electronic device that includes the aforementioned 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.

[0099] 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.

[0100] 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.

[0101] Example 1

[0102] This embodiment provides a cathode material comprising a core and a protective layer, wherein the core has the chemical formula Li. 1.2 Ni 0.6 Mn0.2 O2, the main structure of the protective layer is Li 1.2 Ni 0.6 Mn 0.2 O2, and the protective layer is doped with B 3+ Zr 4+ F - and Na + Among them, B 3+ Zr 4+ and F - Along the thickness direction of the protective layer, the doping concentration increases from near the core to far away from the core. Na + The doping concentration and concentration gradient of each element on the outermost layer of the protective layer are shown in Table 1.

[0103] The preparation method of the cathode material in this embodiment includes the following steps:

[0104] (1) Precursor coprecipitation: 0.2 mol L of Ni and Mn (molar ratio 0.6:0.2) was added to a sulfate solution. -1 H3BO3, 0.05 mol L -1 Zr(SO4)2 and 0.15 mol L -1 After all the dopant source is dissolved, the pH of the mixture is adjusted to 10, and co-precipitation is carried out at 50°C to obtain the B / Zr / F pre-doped precursor.

[0105] (2) Gradient diffusion sintering: The doped precursor is mixed with Li2CO3 (molar ratio of Li to transition metals (Ni and Mn) = 1.5:1) and sintered twice:

[0106] The first sintering was carried out at 700℃ for 4 hours. This step allowed the lithium salt to react initially and form a B / Zr / F-rich interfacial layer.

[0107] The second sintering was performed at 820℃ for 20 hours. This step utilizes the differences in ion diffusion kinetics at high temperatures to drive the migration of B, Zr, and F elements towards the core, forming a smooth concentration gradient. The heating rate was controlled at 2℃ / min. -1 .

[0108] (3) Surface modification: When cooled to 500℃, steam generated from heated NaF powder is introduced under N2 atmosphere for 30 minutes to complete the surface Na modification. + Enrichment, wherein 0.5g NaF is added for every 100g of sintered powder.

[0109] (4) Screening for secondary spherical particles with D50=10 µm.

[0110]

Examples 2-4

[0111] The difference between each embodiment and Embodiment 1 is that the doping concentration of each doping element in the outermost layer remains unchanged in each embodiment. The thickness of the protective layer and the gradient coefficient of each doping element are adjusted by adjusting the sintering parameters. For specific parameters, please refer to Table 1 and Table 2.

[0112]

Examples 5-8

[0113] The difference between each embodiment and Embodiment 2 is that the outermost layer B of the protective layer 3+ Changes in doping concentration, B 3+ The gradient coefficients change accordingly, while the others remain unchanged; see Tables 1 and 2 for details.

[0114]

Examples 9-12

[0115] The difference between each embodiment and Embodiment 2 is that the outermost layer of the protective layer, Zr 4+ Changes in doping concentration, Zr 4+ The gradient coefficients change accordingly, while the others remain unchanged; see Tables 1 and 2 for details.

[0116]

Examples 13-16

[0117] The difference between each embodiment and Embodiment 2 is that the outermost layer F of the protective layer - Changes in doping concentration, F - The gradient coefficients change accordingly, while the others remain unchanged; see Tables 1 and 2 for details.

[0118]

Examples 17-20

[0119] The difference between each embodiment and Embodiment 2 is that the Na in the protective layer + The doping concentration of the sample changes, while the rest remain unchanged; see Tables 1 and 2 for details.

[0120] Example 21

[0121] The difference between this embodiment and Embodiment 2 is that the core material is Li. 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, the parameters for the second sintering are: sintering at 810℃ for 16h.

[0122] Example 22

[0123] The difference between this embodiment and Embodiment 2 is that the core material is Li. 1.2 Mn 0.6 Ni 0.2 O2.

[0124] Comparative Example 1

[0125] The cathode material in this comparative example is Li. 1.2 Ni 0.6 Mn 0.2 O2, without protective coating treatment.

[0126] Comparative Example 2

[0127] The difference between this comparative example and Example 2 is that all doping elements are uniformly doped, and the amount of each dopant source added remains unchanged during preparation.

[0128] Comparative Example 3

[0129] The difference between this comparative example and Example 2 is that the protective layer contains only B. 3+ During doping, the amount of boron source added remains unchanged during preparation.

[0130] Comparative Example 4

[0131] The difference between this comparative example and Example 2 is that only B is present in the protective layer. 3+ and Zr 4+ During doping, the amounts of boron and zirconium sources remain unchanged during preparation.

[0132] Comparative Example 5

[0133] The difference between this comparative example and Example 2 is that the protective layer contains only F. - During doping, the amount of fluorine source added remains unchanged during preparation.

[0134] Comparative Example 6

[0135] The difference between this comparative example and Example 2 is that the protective layer contains only Na. + During doping, the amount of sodium source added remains unchanged during preparation.

[0136] Comparative Example 7

[0137] The difference between this comparative example and Example 2 is that: B 3+ Replace with Al 3+ Zr 4+ Replace with Ti 4+ F - Replace with Cl - Na + Replace with K + During preparation, the amount of corresponding elements added is the same.

[0138] Comparative Example 8

[0139] The difference between this comparative example and Example 21 is that the positive electrode material is Li. 1.2 Ni 0.13 Co 0.13Mn 0.54 O2, without a protective coating.

[0140] Comparative Example 9

[0141] The difference between this comparative example and Example 22 is that the positive electrode material is Li. 1.2 Mn 0.6 Ni 0.2 O2, without a protective coating.

[0142] Table 1: Parameters of Examples 1-22 and Comparative Examples 1-9

[0143]

[0144] Table 2: Amount of dopant source added in each embodiment

[0145]

[0146] To verify the performance of the cathode material of this application, the cathode materials of each embodiment and comparative example were assembled in a battery. The specific composition of the battery is as follows:

[0147] (1) Preparation of positive electrode sheet

[0148] The above-mentioned positive electrode material, binder polyvinylidene fluoride, and conductive agent carbon black (Super P) are mixed in a mass ratio of 97:1:2. N-methylpyrrolidone (NMP) is added and the mixture is stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on aluminum foil, dried at room temperature, and then transferred to an oven for drying. The positive electrode sheet is then obtained through cold pressing, slitting and other processes.

[0149] (2) Negative electrode: lithium metal sheet.

[0150] (3) Separator: PP / PE / PP three-layer composite porous membrane, manufacturer and model Celgard® 2325.

[0151] (4) Electrolyte preparation

[0152] In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 and additive fluoroethylene carbonate (FEC) were dissolved in the organic solvent and mixed evenly to obtain an electrolyte. The lithium salt concentration was 1 mol / L, and the amount of FEC added accounted for 0.5% of the total mass of the electrolyte.

[0153] (5) Battery assembly

[0154] Using a lithium metal sheet as the counter electrode and the aforementioned positive electrode sheet as the positive electrode, a coin cell (CR 2025 type) is assembled, with a nominal capacity of 6mAh.

[0155] Then, performance tests were conducted on each button cell, and the test results are shown in Table 3. The test methods are as follows:

[0156] (1) First Coulomb efficiency test

[0157] The assembled button batteries are left to stand in a constant temperature chamber at 25°C for 2-4 hours, and then subjected to the first charge and discharge test using a battery testing system (Blue Battery).

[0158] Charging process: Charge from open circuit voltage to 4.8 V with a constant current of 0.1C, and record the charging capacity.

[0159] Discharge process: Discharge to 2.0 V with the same constant current and record the discharge capacity.

[0160] Calculation formula: Initial coulombic efficiency FCE = (Initial discharge capacity / Initial charge capacity) × 100%.

[0161] (2) Loop testing process:

[0162] Test method: After activating the newly made battery (activation process: let the newly made battery rest for 1 hour, then charge it to 3.5V with a constant current of 0.3mA, and then let it rest for 1 hour), perform multiple charge and discharge cycles.

[0163] Charge and discharge regime: Constant current-constant voltage (CC-CV) charging and constant current (CC) discharging are adopted.

[0164] Charging: Charge to 4.6 V with a constant current of 0.5 C (3mA), then switch to constant voltage charging until the current drops to 0.05 C.

[0165] Discharge: Discharge to 2.0 V with a constant current of 0.5C.

[0166] Number of loops: 200.

[0167] Capacity retention calculation: Capacity retention = (Discharge capacity at 200th cycle / Initial discharge capacity) × 100%

[0168] (3) Voltage attenuation test:

[0169] Test method: During the cyclic test, record the average discharge voltage for each cycle.

[0170] Average discharge voltage: The average discharge voltage is calculated by integrating the discharge curve for each cycle.

[0171] Voltage decay percentage = ((Average discharge voltage of the first cycle - Average discharge voltage of the 200th cycle) / Average discharge voltage of the first cycle) × 100%;

[0172] Based on the voltage decay value of the prior art sample (Comparative Example 1), the voltage decay value reduction of each group of batteries is calculated: for example, "the voltage decay is reduced by 50% after 200 cycles", that is, the voltage decay value of the sample of the present invention is half that of the prior art sample (Comparative Example 1).

[0173] (5) Differential Scanning Calorimetry (DSC) analysis and testing:

[0174] Sample preparation: The cathode material particles were removed from the battery (which had undergone 200 cycles of testing) inside a glove box (in an ultra-dry argon atmosphere).

[0175] Mixing: The extracted positive electrode material is mixed with the electrolyte at a mass ratio of 1:1 and sealed in a specially designed pressure-resistant DSC crucible.

[0176] Test: Place the crucible in the DSC instrument and heat it from room temperature to above 300 °C at a constant heating rate of 5 °C / min under an inert atmosphere.

[0177] Analysis results: Record the onset temperature, peak temperature, and total heat release of the DSC exothermic peak. A higher onset temperature, a higher peak temperature, and a smaller total heat release indicate better thermal stability of the material.

[0178] Table 3: Test results of Examples 1-22 and Comparative Examples 1-9

[0179]

[0180] As can be seen from Tables 1 and 3, compared with Comparative Example 1, Examples 1-4 formed a protective layer with multi-ion gradient doping, and the initial coulombic efficiency, cycle performance and thermal stability of the battery were significantly improved, and the voltage decay was improved.

[0181] Furthermore, in Examples 1-4, the concentration of doped ions in the outermost layer of the protective layer remains constant. The thickness of the protective layer and B can be controlled by adjusting the second sintering temperature. 3+ Zr 4+ and F -The gradient coefficient is such that higher temperatures and longer diffusion times result in faster and farther ion diffusion, leading to a gentler gradient and a thicker protective layer. Conversely, slower and closer ion diffusion results in a steeper gradient and a thinner protective layer. Test results show that the protective layer thickness is 1~5μm. 3+ The doping gradient coefficient is 0.1~0.5 at% µm. -1 Zr 4+ The doping gradient coefficient is 0.05~0.3 at% µm. -1 and F - The doping gradient coefficient is 0.2~1 at% µm -1 At that time, the improvement effect on the cathode material was better.

[0182] Examples 2, 5-8, with other conditions remaining unchanged, the outermost layer B of the protective layer 3+ The doping concentration changes, B 3+ The gradient coefficient changes accordingly. Studies have found that the higher the doping concentration of the outermost layer, the higher the starting point of the gradient curve, and under the same diffusion conditions, the final gradient is steeper. In Example 7, the high doping concentration of the outermost layer resulted in a larger gradient coefficient, indicating that the chemical composition and lattice parameters of the material changed significantly within a very short distance. This creates an abrupt interface between the core and shell, generating significant lattice mismatch stress, leading to particle cracking, coating peeling, and accelerated material failure during cycling. Furthermore, it increases interfacial impedance, resulting in a decrease in the material's initial coulombic efficiency and cycle capacity retention. In Example 8, the low doping concentration of the outermost layer and insufficient total doping amount resulted in a relatively poor improvement effect.

[0183] Examples 2, 9-12, with other conditions remaining unchanged, the outermost layer of the protective layer Zr 4+ The change in doping concentration of Zr 4+ The gradient coefficient changes accordingly; studies have found that the higher the doping concentration of the outermost layer, the higher the starting point of the gradient curve, and under the same diffusion conditions, the final gradient is steeper. In Example 11, the high doping concentration of the outermost layer resulted in a larger gradient coefficient, indicating that the chemical composition and lattice parameters of the material changed significantly within a very short distance. This creates an abrupt interface between the core and shell, generating significant lattice mismatch stress, leading to particle cracking, coating peeling, and accelerated material failure during cycling. Furthermore, it increases interfacial impedance, resulting in a decrease in the material's initial coulombic efficiency and cycle capacity retention. In Example 12, the low doping concentration of the outermost layer and the smaller total doping amount resulted in a relatively poor improvement effect.

[0184] Examples 2 and 13-16 remain unchanged, except for the outermost layer F of the protective layer. -As the concentration changes, the gradient coefficient also changes. Studies have found that the higher the doping concentration of the outermost layer, the higher the starting point of the gradient curve, and under the same diffusion conditions, the resulting gradient is steeper. In Example 15, the outermost layer doping concentration was low, resulting in a small total doping amount and no significant improvement effect. In Example 16, the outermost layer doping concentration was high, resulting in a larger gradient coefficient, indicating a significant change in the material's chemical composition and lattice parameters within a very short distance. This creates an abrupt interface between the core and shell, generating significant lattice mismatch stress, leading to particle cracking, coating peeling, and accelerated material failure during cycling. Furthermore, it increases interfacial impedance, causing a decrease in the material's initial coulombic efficiency and cycle capacity retention.

[0185] Examples 2, 17-20, keep other conditions unchanged, Na + Changes in doping concentration, as detected by the test results, show that when Na... + When the doping concentration is too high, the initial coulombic efficiency, cycle performance, and voltage decay of the battery all decrease. This is because Na... + High doping concentrations can lead to the formation of excessively thick, non-conductive sodium salt layers (such as NaF). This overly thick "insulating" layer hinders lithium-ion shuttle passage, increases the overall interfacial impedance, and reduces the material's electrochemical performance. When Na... + When the doping concentration is too low, it is impossible to completely remove the HF acid generated by trace amounts of water in the electrolyte. HF acid causes metal ions to dissolve, affecting the capacity of the cathode material and resulting in slightly poor electrochemical performance of the battery.

[0186] Examples 21 and 22 respectively replaced the main material, and compared with Comparative Examples 8 and 9, the performance of the battery was significantly improved. This shows that the protective layer formed by the present invention is suitable for various lithium-rich layered oxide materials.

[0187] Comparative Example 2 compared to Example 2: B 3+ Zr 4+ and F - Uniform doping within the protective layer does not significantly improve material performance. This is because excessively high internal doping concentrations can clog the Li₂ layer. + The rapid transport channels affect the high capacity utilization of the main material, thus affecting the electrochemical performance of the battery.

[0188] Comparative Examples 3-6, compared to Example 2, are partially doped with ions. The detection results show that only B... 3+ Zr 4+ F - and Na + The battery performs best when all four types of ions are doped simultaneously.

[0189] Compared to Example 2, Comparative Example 7 used other doped ions with the same valence state as Example 2. The test results showed that compared to the cathode material without protective coating (Comparative Example 1), its initial coulombic efficiency, cycle performance, voltage decay and thermal stability were improved to a certain extent. However, compared to Example 2, the improvement effect was not good.

[0190] The cathode material provided by this invention utilizes B, which is formed in situ on the surface of a lithium-rich layered cathode material. 3+ / Zr 4+ Dications and F - Cooperative gradient and Na + The multidimensional protective layer enriched with surface area enhances material performance from the perspectives of structural stability, interface protection, and ion transport. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0191] 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, include: The core, the chemical formula of which is Li 1+x M 1-x O2, where 0 < x ≤ 0.2, and M is selected from one or more of Ni, Co, and Mn; A protective layer is formed on the surface of the core, and the protective layer is a doped Li. 1+x M 1-x O2; the main structure of the protective layer and the crystal structure of the core are integrated and continuously distributed, and the protective layer is doped with cations, anions and alkali metal ions; The cations and anions are distributed along the thickness direction of the protective layer in an increasing doping concentration gradient from the inside to the outside, and the alkali metal ions are doped on the surface of the protective layer; the cations include B. 3+ and Zr 4+ The anion includes F - The alkali metal ions include Na + .

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies one or more of the following conditions: The B 3+ The doping gradient coefficient is 0.1~0.5 at% µm. -1 The B 3+ The atomic percentage of the outermost layer of the protective layer is 0.5~3 at%, wherein the outermost layer refers to the region of the protective layer that extends from the outside to the inside along the thickness direction of 0~0.1 μm; The Zr 4+ The doping gradient coefficient is 0.05~0.3 at% µm. -1 The Zr 4+ The atomic percentage of the outermost layer of the protective layer is 0.2~2 at%; The F - The doping gradient coefficient is 0.2~1 at% µm -1 The F - The atomic percentage of the outermost layer of the protective layer is 2-10 at% The Na + The atomic percentage of the outermost layer of the protective layer is 0.8~5 at%.

3. The cathode material according to claim 1, characterized in that, The thickness of the protective layer is 1~5μm, and / or, the Na + The doping depth in the protective layer is in the range of 0~50nm extending inward from the outer surface of the protective layer.

4. The cathode material according to claim 1, characterized in that, The particle size distribution D50 of the cathode material is 5~15µm.

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: Precursor co-precipitation: Prepare a salt solution containing transition metal elements according to the chemical formula of the cathode material, add a cation source and an anion source to the salt solution, adjust the pH value and temperature to carry out co-precipitation, and obtain the doped precursor; Gradient diffusion sintering: The doped precursor is mixed with a lithium source and then subjected to gradient diffusion sintering to obtain an intermediate doped with cations and anions. Surface modification: A sodium source is introduced into the intermediate to form sodium enrichment on the surface of the intermediate, thereby obtaining the cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that, The gradient diffusion sintering includes: The first sintering is carried out at a temperature of 650~750℃ for 2~6 hours to form an interface layer rich in doped ions; The second sintering is carried out at a temperature of 780~850℃ for 10~20 hours to drive the diffusion of dopant ions in the interface layer to form a smooth dopant concentration gradient.

7. The method for preparing the cathode material according to claim 5, characterized in that, The surface modification includes: introducing sodium source vapor into the intermediate at a temperature of 450~600°C under an inert atmosphere and maintaining it for 30 minutes; and / or, The precursor co-precipitation occurs at a pH of 9.5-11 and a temperature of 40-60℃.

8. The method for preparing the cathode material according to claim 5, characterized in that, Includes one or more of the following items A through E: A. The transition metal element is selected from one or more of Ni, Co, and Mn, and the salt solution containing the transition metal element includes any one of sulfate solution, nitrate solution, acetate solution, and chloride solution; B. The lithium source includes one or more of lithium carbonate and lithium hydroxide; C. The cation source includes a boron source and a zirconium source, wherein the boron source includes one or more of boric acid, ammonium borate, and sodium borate, and the zirconium source includes one or more of zirconium sulfate and zirconium tetrachloride. D. The anion source includes a fluorine source, which includes one or more of ammonium fluoride and hydrogen fluoride. E. The sodium source includes one or more of sodium fluoride and sodium carbonate.

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.

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