Positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a positive electrode material, a preparation method thereof and a lithium ion battery. The positive electrode material sequentially comprises an inner core, a middle layer and a passivation layer from inside to outside, the component of the inner core is Li < y > < 1 > Ni < 1 > Co < 1 > Mn < c > < 1 > Me < 1 M is a doping element and comprises at least one of Al, Mg, Zr, Sr, Y, Mo and W; the component of the middle layer is Li < y > < 2 > Ni < 2 > Co < 2 > Mn < c > < 2 > Ne2 < O2 >; n is a first coating element and comprises at least one of Al, Zr, Sr and F; the component of the passivation layer is QF [alpha] S [beta] O [gamma]; q is a second coating element and comprises at least one of Al, Ti, W, Sn and P. The positive electrode material provided by the invention is composed of an inner core, a middle layer and a passivation layer, and a doping element M is added into the inner core to serve as column ions in a layered structure, so that the internal structure of the positive electrode material is stabilized; a middle layer containing a Mn / Co spinel structure is constructed, so that produced gas release is inhibited; by introducing the passivation layer containing fluorine and sulfur, it is guaranteed that fluorine can inhibit corrosion of electrolyte, and sulfur can stabilize and replace lattice oxygen.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a cathode material and its preparation method, and a lithium-ion battery. Background Technology

[0002] Layered oxides (LLOs) have been developed as a primary cathode material for lithium-ion batteries due to their significant advantages in high energy density, high voltage, and well-developed synthesis processes. However, achieving higher energy density in LLOs requires removing more lithium ions during high-voltage charging, which leads to structural instability and poor battery cycle performance. To effectively address the inherent trade-off between high energy density and cycleability in LLOs, several strategies have been employed to stabilize the bulk structure, including doping, single-crystal synthesis, and microstructure engineering. Preventing surface O2 release is challenging for these strategies. Surface coatings and surface structure modification have been explored to mitigate surface instability; for example, layers with spinel-like structures prepared by oleic acid-assisted impregnation, gas-solid reaction treatment, gradient doping, or phase composition adjustment have been introduced onto the surface of LLO particles. However, some shortcomings remain in existing technologies. CN113921786A discloses a high-voltage cathode material and its preparation method based on surface ion exchange reaction to achieve structural reconstruction. The principle involves utilizing the ion exchange reaction between metal ions (A) and the oxide cathode surface to achieve structural reconstruction of the cathode material's surface, forming a stable heterostructure. However, the heterostructure is mainly derived from the transformation of surface layered structures, and its thickness and uniformity cannot be guaranteed; furthermore, the lack of a passivation coating layer prevents effective suppression of electrolyte corrosion.

[0003] CN116190593A discloses a mixed-phase structure in which layered and non-layered phases are arranged alternately. During high-voltage charging, the lattice oxygen migration and oxygen evolution processes in the layered phase structure are suppressed by the adjacent non-layered phase. However, an excessive amount of non-layered phase will affect lithium-ion transport, resulting in a decrease in capacity and rate performance.

[0004] CN115332511A discloses a lithium-rich manganese-based cathode material with sulfur implantation-induced spinel and oxygen vacancies, which is obtained by sintering the cathode material with sulfur in an inert atmosphere. However, the oxygen vacancies and spinel structures generated by this material are too simple and are not passivated to protect them from corrosion by the electrode solution.

[0005] CN114094080A uses acid etching to etch unstable heterogeneous structures on the material surface, which helps to eliminate the sharp edges of the single crystal surface and make the overall crystal structure smoother. The etched element ions can be further recombine and rearranged during heat treatment to form a stable composite oxide coating layer. However, the etching degree of acid etching is difficult to control, which can easily cause over-etching and result in a large number of structural failures, affecting the material's performance.

[0006] CN106910882B achieves spinel phase formation through a single lithium-deficient sintering process, promoting the fusion and growth of primary grains to obtain composite phase primary grains or pure phase primary grains with large micron-sized grains. Lithium is then added to these primary grains, and after calcination at high temperature, a large single-crystal layered cathode material for lithium-ion batteries is obtained. However, obtaining a large single-crystal layered cathode material through a secondary sintering process increases costs, and the lithium ions added during the secondary sintering are difficult to integrate into the large grains obtained after the first lithium-deficient sintering, resulting in a lower lithium-ion content and thus a lower capacity.

[0007] The two main reasons for the instability of layered cathode structures in lithium-ion batteries are anisotropic lattice strain within the cathode particle bulk and surface structure degradation. When lithium ions are removed from the lithium layer, the Coulomb repulsion between oxygen ions causes the lattice to expand along the c-axis. Deep delithiation activates the oxidation of lattice oxygen, leading to c-space collapse and O2 formation. During long-term cycling, repeated expansion and contraction of the c-space can cause cracks and irreversible phase transitions in the bulk, while O2 released from the particle surface promotes surface structure degradation. Furthermore, side reactions between the particle surface and the electrolyte exacerbate the collapse of the surface structure.

[0008] Therefore, how to design a new type of cathode material to improve the gas generation performance of cathode materials under high voltage conditions is an urgent problem to be solved. Summary of the Invention

[0009] The present invention aims to provide a cathode material and its preparation method, and a lithium-ion battery, thereby solving the problems of structural instability, surface degradation and electrolyte corrosion that exist when layered oxides are used as cathode materials for lithium-ion batteries during high-voltage charging.

[0010] To address the above problems, the present invention provides a positive electrode material, which comprises, from the inside out, a core, an intermediate layer, and a passivation layer. The components of the kernel are shown in equation (Ⅰ): Li y1 Ni a1 Co b1 Mn c1 M e1 O2 formula (Ⅰ); The values ​​of y1, a1, b1, c1, and e1 are as follows: 1.0≤y1≤1.1, 0.5≤a1<1, 0≤b1≤0.3, 0<c1≤0.4, and 0.001<e1<0.1; M is a doping element, including at least one of Al, Mg, Zr, Sr, Y, Mo, and W. The composition of the intermediate layer is shown in formula (II): Liy2 Ni a2 Co b2 Mn c2 N e2 O2 formula (II); The ranges of values ​​for y2, a2, b2, c2, and e2 are as follows: 0 < y2 < 1.0, 0 < a2 < 0.5, 0 < b2 < 0.8, 0 < c2 < 0.8, and 0 < e2 < 0.1. N is the first coating element, including at least one of Al, Zr, Sr, and F; The composition of the passivation layer is shown in formula (Ⅲ): QF α S β O γ Formula (Ⅲ); The values ​​of α, β, and γ are as follows: 0 < α < 0.1, 0.02 < β < 0.1, 1.8 < γ < 2.0, and 1.94 < α + β + γ < 2.0; Q is the second coating element, which includes at least one of Al, Ti, W, Sn, and P.

[0011] The cathode material provided by this invention consists of a core, an intermediate layer, and a passivation layer. The core is doped with element M to act as a pillar ion in the layered structure, thereby stabilizing the internal structure of the cathode material. An intermediate layer containing an Mn / Co spinel structure is constructed on the surface of the core to suppress gas generation. A passivation layer containing fluorine and sulfur is introduced on the outermost surface of the cathode material to ensure that fluorine inhibits electrolyte corrosion, and that sulfur stabilizes and replaces lattice oxygen, with sulfur-oxygen vacancies absorbing lattice oxygen. The synergistic effect between the layered structures of the cathode material effectively improves the gas generation performance of the material under high voltage.

[0012] The dopant element M in the core can act as a pillar ion in the layered structure of the cathode material, thereby stabilizing the internal structure of the cathode material, improving the cycle stability under high voltage and reducing the internal resistance; at the same time, compared with the TM-O bond, the Al-O bond has a higher bond energy, which can generate oxygen fixation, reduce the precipitation of internal lattice oxygen and the release of oxygen.

[0013] The intermediate layer is a Mn / Co spinel structure layer formed on the surface of the core, thus hindering oxygen release. Electrons are concentrated in the oxygen regions at the spinel phase interface, forming an electron-rich layer. This not only lowers the lattice oxygen O-2p non-bonding energy band but also allows for the formation of highly reactive O. n- Ions are affected by the Coulomb repulsion at the interface, making it more difficult for lattice oxygen in the bulk core to be oxidized to O2. Even if the internal lattice oxygen is oxidized to O2 under high voltage, it will be encapsulated and blocked by the spinel-like structure on the core surface, thus preventing further escape from the material.

[0014] A passivation layer is applied to the outermost surface of the positive electrode material, introducing a fluorine-containing compound with a composition similar to the electrolyte to inhibit electrolyte corrosion. During calcination, sulfur and oxygen react as S... σ O δ The sulfur vacancies in the oxide cathode are replaced by sulfur, while the sulfur vacancies in the coating are occupied by oxygen. Sulfur anions in the crystal lattice cannot be released from the lattice, and the presence of both oxygen and sulfur vacancies allows for the capture of O2 released during discharge. n- This reduces irreversible oxygen release and stabilizes the structure.

[0015] In any of the above technical solutions, the proportion of Al in the core is not less than 0.1 mol%; and / or the proportion of Ni in the intermediate layer is not less than 0.1 mol%. 2+ The ratio of the number of Ni ions in the intermediate layer to the number of Ni ions in the core is higher than that in the core. 2+ The ratio of the number of Ni ions to the number of Ni ions in the core; and / or the Ni ions in the intermediate layer. 2+ The ratio of the number of ions to the number of Ni ions in the intermediate layer is not less than 30%.

[0016] The core contains a dopant element M, which includes at least one of Al, Mg, Zr, Sr, Y, Mo, and W. Al accounts for at least 0.1 mol% of the core. Doping the core with aluminum can improve the electrochemical performance of the cathode material, such as increasing the battery's energy density, cycle life, or safety performance. The core has a similar composition to the intermediate layer, but the proportions differ. Ni... 3+ with Ni 4+ This can easily lead to electrolyte oxidation and decomposition, as well as lattice oxygen loss, while Ni 2+ More chemically stable, with a high proportion of Ni 2+ The intermediate layer facilitates the transformation from layered to spinel structure and maintains the integrity of the intermediate layer structure, providing stable Li + The transport channels improve gas generation and cycling performance, and also promote ion transport, thereby improving the battery's charge / discharge efficiency and response speed; the Ni in the intermediate layer 2+ The ratio of the number of Ni ions in the intermediate layer to the number of Ni ions in the core is higher than that in the core. 2 + The ratio of the number of ions to the number of Ni ions in the core makes the core and the intermediate Ni layer... 2+ The gradient design reduces interfacial stress during cycling, which can suppress particle cracking.

[0017] In any of the above technical solutions, the intermediate layer is a spinel-like structure extending 10nm-100nm outward from the surface of the core; and / or the thickness of the passivation layer is 1nm-10nm.

[0018] The intermediate layer is a 10nm-100nm thick extended fast-ion conductor on the outer surface of the core, containing a spinel structure. This spinel structure is formed by sintering Mn or Co elements. The Mn / Co oxygen-suppressing spinel structure in the intermediate layer improves structural stability and hinders oxygen evolution. The appropriate thickness range of the intermediate layer ensures that oxygen release is suppressed without excessively increasing the overall mass and volume of the battery. The passivation layer is located on the outermost layer of the positive electrode material, with a thickness ranging from 1nm to 10nm. The passivation layer consists of electrolyte passivation and SO2 exchange material, specifically fluorine-sulfur oxides. An excessively thick passivation layer increases the internal impedance of the battery, while an excessively thin layer may lead to rapid performance degradation. An appropriate passivation layer thickness effectively blocks electrolyte erosion and chemical instability while maintaining good electron and ion transport.

[0019] In any of the above technical solutions, the passivation layer contains oxygen vacancies, the content of which accounts for 0.2 mol%-2 mol% of the cathode material; and / or the content of F element accounts for 0.02 mol%-0.5 mol% of the cathode material; and / or the content of S element accounts for 0.02 mol%-0.5 mol% of the cathode material.

[0020] The presence of oxygen vacancies provides more pathways for electrons and ions to pass through, thereby increasing the material's conductivity and ion transport performance. Proper control of oxygen vacancies and F and S elements allows the passivation layer to maintain stability while suppressing undesirable chemical reactions. This helps reduce performance degradation during long-term battery use, thus extending battery life. The fluorine-sulfur passivation layer, located on the outermost layer of the positive electrode material, inhibits electrolyte corrosion. Sulfur can stabilize and replace lattice oxygen, and sulfur-oxygen vacancies can absorb lattice oxygen, thereby suppressing oxygen release.

[0021] In any of the above technical solutions, the morphology of the cathode material is a single crystal structure; and / or the size of the single crystal of the cathode material ranges from 2.0 μm to 4.5 μm.

[0022] Choosing a single-crystal structure for the cathode material offers several advantages. The single-crystal structure results in lower structural damage during battery cycling, reducing capacity decay and extending overall battery life while improving cycle performance. Larger single-crystal sizes reduce the contact area with the electrode liquid, minimizing interfacial side reactions and leading to better capacity retention, lower internal resistance growth, and reduced gas generation. Targeting a specific range of single-crystal sizes helps optimize lithium-ion transport efficiency and battery internal resistance, particularly in fast-charge / discharge applications where controlled crystal size improves response speed and efficiency. Precise control of the single-crystal structure and size reduces the risk of thermal runaway and physical damage caused by rapid charging and discharging, ensuring battery reliability and safety under high-load conditions.

[0023] This invention also provides a method for preparing a cathode material, which is used to prepare the cathode material as described above. The preparation method includes: a first sintering: mixing a precursor, a lithium source, and a dopant, and performing a first sintering to obtain a first sintered product; a second sintering: mixing the first sintered product and a first coating agent, and performing a second sintering to obtain a second sintered product; and a third sintering: mixing the second sintered product and a second coating agent, and performing a third sintering to obtain the cathode material; wherein the dopant includes a doping element, the first coating agent includes at least one of Co, Mn, and a first coating element, and the second coating agent includes at least one of F, S, and a second coating element.

[0024] This invention provides a method for preparing cathode materials, comprising three sintering steps using a precursor, a lithium source, a dopant, and two different coating agents. The first sintering forms the basic cathode structure; the second sintering enhances the material's microstructure and improves its electrochemical performance; and the third sintering further optimizes the material's performance, improving its stability and lifespan. Through three sintering steps and the use of two different coating agents, the integrity of the material's microstructure and its stress resistance are enhanced, contributing to improved battery stability and reduced capacity decay during long-term use.

[0025] In any of the above technical solutions, the molar ratio of precursor, lithium source and dopant is 1:(1.02-1.10):(0.001-0.01); and / or the molar ratio of first sintered product and first coating agent is 1:(0.02-0.06); and / or the molar ratio of second sintered product and second coating agent is 1:(0.001-0.01).

[0026] Choosing appropriate ratios of precursor, lithium source, and dopant, with a slight excess of lithium source to ensure sufficient reaction and avoid capacity loss due to insufficient lithium, and using doping elements such as aluminum and magnesium to significantly improve the electrochemical performance and structural stability of the material, is crucial. After the first sintering, the product is mixed with a first coating agent. The first coating agent, in a small proportion, forms a thin coating layer, optimizing the material's interfacial properties and improving electrochemical stability while effectively preventing oxygen release. After the second sintering, the product is mixed with a second coating agent, in an even smaller proportion, further enhancing the chemical stability of the material surface, reducing side reactions, and improving battery life.

[0027] In any of the above technical solutions, the first sintering is carried out in an air or oxygen atmosphere; and / or the second sintering is carried out in an air atmosphere; and / or the third sintering is carried out in an air atmosphere.

[0028] The sintering steps in the material preparation process are specified to be carried out under a specific atmosphere. Specifically, the first sintering can be performed in an air or oxygen atmosphere, while the second and third sintering are both performed in an air atmosphere. In the initial stage of preparing battery cathode materials, the first sintering is carried out in an oxygen-containing environment, which helps to ensure that the metal elements in the material are fully oxidized to form a stable metal oxide structure. The choice of air or pure oxygen environment can be adjusted according to the specific precursor composition and expected physicochemical properties. The subsequent sintering steps of the second and third sintering are carried out in air, mainly to further improve the crystal structure of the material and enhance its structural stability and electrochemical performance. Repeated sintering processes help to eliminate defects that may be left by the first sintering, such as lattice irregularities and porosity.

[0029] In any of the above technical solutions, the sintering temperature for the first sintering is 850℃-980℃; and / or the sintering time for the first sintering is 8h-15h; and / or the sintering temperature for the second sintering is 700℃-800℃; and / or the sintering time for the second sintering is 6h-12h; and / or the sintering temperature for the third sintering is 350℃-550℃; and / or the sintering time for the third sintering is 6h-12h.

[0030] The high-temperature sintering in the first sintering stage helps the material initially form the desired crystal structure and promotes the reaction and bonding of the original material, providing a solid foundation for subsequent sintering steps. The lower sintering temperature in the second sintering stage is suitable for further refining the crystal structure and optimizing the material's microstructure, while reducing excessively rapid crystal growth and structural damage caused by high temperatures. The third sintering stage uses even lower temperatures and is mainly used to improve the surface properties and stability of the material, especially suitable for forming a protective layer on the material surface or for final physicochemical property adjustments.

[0031] The present invention also provides a lithium-ion battery comprising the positive electrode material as described above. The lithium-ion battery has the same beneficial effects as the positive electrode material, and therefore will not be described further here.

[0032] By adopting the technical solution of the present invention, the following technical effects can be achieved: (1) The core is doped with elements to act as pillar ions in the layered structure, thereby stabilizing the internal structure of the cathode material and reducing the precipitation of lattice oxygen by higher bond energy. (2) By constructing an intermediate layer containing a Mn / Co spinel structure on the surface of the core, gas production and release can be suppressed; (3) By introducing a passivation layer containing fluorine and sulfur on the outermost surface of the positive electrode material, it is ensured that fluorine can inhibit the corrosion of the electrolyte, sulfur can stabilize and replace lattice oxygen, and sulfur-oxygen vacancies can absorb lattice oxygen. (4) The cathode material consists of a core, an intermediate layer and a passivation layer. The synergistic effect between the layered structures of the cathode material can effectively improve the gas generation performance of the material under high voltage. Attached Figure Description

[0033] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 Line graphs showing the volume growth rate of different samples under 70°C storage conditions, provided for embodiments of the present invention. Figure 2 Valence state analysis diagrams of Ni element in Example 1 and Comparative Example 2 provided for embodiments of the present invention; Figure 3 The surface structure and elemental distribution diagram of the cathode material provided in Embodiment 1 of the present invention; Figure 4 The elemental distribution diagram of the cross-section of the positive electrode material provided in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the oxygen absorption mechanism of sulfide coating provided in an embodiment of the present invention. Detailed Implementation

[0034] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] An embodiment of the present invention provides a positive electrode material, which comprises, from the inside out, a core, an intermediate layer and a passivation layer; The components of the kernel are shown in equation (Ⅰ): Li y1 Ni a1 Co b1 Mn c1 M e1 O2 formula (Ⅰ); The values ​​of y1, a1, b1, c1, and e1 are as follows: 1.0≤y1≤1.1, 0.5≤a1<1, 0≤b1≤0.3, 0<c1≤0.4, and 0.001<e1<0.1; M is a doping element, including at least one of Al, Mg, Zr, Sr, Y, Mo, and W. The composition of the intermediate layer is shown in formula (II): Li y2 Ni a2 Co b2 Mn c2 N e2 O2 formula (II); The ranges of values ​​for y2, a2, b2, c2, and e2 are as follows: 0 < y2 < 1.0, 0 < a2 < 0.5, 0 < b2 < 0.8, 0 < c2 < 0.8, and 0 < e2 < 0.1. N is the first coating element, including at least one of Al, Zr, Sr, and F; The composition of the passivation layer is shown in formula (Ⅲ): QF α S β O γ Formula (Ⅲ); The values ​​of α, β, and γ are as follows: 0 < α < 0.1, 0.02 < β < 0.1, 1.8 < γ < 2.0, and 1.94 < α + β + γ < 2.0; Q is the second coating element, which includes at least one of Al, Ti, W, Sn, and P.

[0036] The cathode material provided by this invention consists of a core, an intermediate layer, and a passivation layer. The core is doped with element M to act as a pillar ion in the layered structure, thereby stabilizing the internal structure of the cathode material. An intermediate layer containing an Mn / Co spinel structure is constructed on the surface of the core to suppress gas generation. A passivation layer containing fluorine and sulfur is introduced on the outermost surface of the cathode material to ensure that fluorine inhibits electrolyte corrosion, and that sulfur stabilizes and replaces lattice oxygen, with sulfur-oxygen vacancies absorbing lattice oxygen. The synergistic effect between the layered structures of the cathode material effectively improves the gas generation performance of the material under high voltage.

[0037] Specifically, the dopant element M in the core acts as a pillar ion in the layered structure of the cathode material, thereby stabilizing the internal structure of the cathode material, improving cycle stability at high voltage, and reducing internal resistance. Simultaneously, compared to the TM-O bond, the Al-O bond has a higher bond energy, enabling oxygen fixation and reducing the precipitation of lattice oxygen and the release of oxygen. Furthermore, the higher bond energy of the Zr-O bond in the dopant element further fixes lattice oxygen, reducing lattice oxygen precipitation and exhibiting better gas generation performance.

[0038] The intermediate layer is a Mn / Co spinel structure layer formed on the surface of the core, thus hindering oxygen release. Electrons are concentrated in the oxygen regions at the spinel phase interface, forming an electron-rich layer. This not only lowers the lattice oxygen O-2p non-bonding energy band but also allows for the formation of highly reactive O. n- Ions are affected by Coulomb repulsion at the interface, making it more difficult for lattice oxygen in the bulk core to be oxidized to O2. Even if internal lattice oxygen is oxidized to O2 under high voltage, it is encapsulated and hindered by the spinel-like structure on the core surface, thus preventing further escape from the material. Furthermore, the large amount of confined O2 within the material hinders the contraction of the internal layered structure, suppressing anisotropic lattice displacement and strain accumulation, thereby stabilizing the internal structure during long cycling. The spinel structure layer improves surface dynamics and also enhances the diffusion rate of lithium ions in the cathode material. Compared to conventional single-pack Co processes, this embodiment limits the intermediate layer to contain a certain amount of MnO2, with high-valence Mn... 4+ Beneficial for improving Ni 2+ This process generates spinel, leading to a proper transformation of the spinel structure and improving gas production and circulation performance.

[0039] A passivation layer is applied to the outermost surface of the positive electrode material, introducing a fluorine-containing compound with a composition similar to the electrolyte to inhibit electrolyte corrosion. During calcination, sulfur and oxygen react as S... σ O δ The sulfur vacancies in the oxide cathode are replaced by sulfur, while the sulfur vacancies in the coating are occupied by oxygen. Sulfur anions in the crystal lattice cannot be released from the lattice, and the presence of both oxygen and sulfur vacancies allows for the capture of O2 released during discharge. n- The value of n is 0≤n<2, which reduces irreversible oxygen release and stabilizes the structure.

[0040] like Figure 5 The diagram shows the oxygen absorption mechanism of sulfide coating. S, O, and SO4 were detected on the surface of the cathode material. 2- The signal indicates that S and O have mutually substituted for each other. After charging, the sample shows a weakened S signal in the XPS S-2p spectrum. 2- The signal is accompanied by SO4 2- The signal increase indicates that S in the coating2- It reacts with oxidized lattice oxygen to produce SO4. 2- This reduces oxygen evolution. After discharge, Li ions and oxygen are reinserted, arranging into an ordered layered structure. Vacancies formed by oxygen evolution at the deep surface are further replaced by sulfur, thus deepening sulfur substitution after discharge. Due to the reintercalation of oxygen, most of the S in the coating... 6+ Reduced to S 2− .

[0041] In some embodiments of this application, the proportion of Al in the core is not less than 0.1 mol%; and / or the proportion of Ni in the intermediate layer is not less than 0.1 mol%. 2+ The ratio of the number of Ni ions in the intermediate layer to the number of Ni ions in the core is higher than that in the core. 2+ The ratio of the number of Ni ions to the number of Ni ions in the core; and / or the Ni ions in the intermediate layer. 2+ The ratio of the number of ions to the number of Ni ions in the intermediate layer is not less than 30%.

[0042] The core contains a dopant element M, which includes at least one of Al, Mg, Zr, Sr, Y, Mo, and W. Al accounts for at least 0.1 mol% of the core. Doping the core with Al can improve the electrochemical performance of the cathode material, such as increasing the battery's energy density, cycle life, or safety performance. The core has a similar composition to the intermediate layer, but the proportions differ, with a higher proportion of Ni. 2+ The intermediate layer facilitates the transformation from layered to spinel structure, improves gas generation and cycle performance, and also promotes ion transport, thereby improving the battery's charge / discharge efficiency and response speed. 2+ Choosing the right ratio can improve battery capacity and cycle life.

[0043] The intermediate layer comprises a first coating element N, which includes at least one of Al, Zr, Sr, and F. Ni ions include Ni. 2+ and Ni 3+ In cathode materials, Ni ions are mostly Ni 3+ In this embodiment, Co is introduced into the intermediate layer. 3+ Mn 4+ These high-valence ions, and in order to maintain electroneutrality, the cathode material will have Ni diffused from the core into the intermediate layer. 3+ Price reduction for Ni 2+ This leads to the expression of Ni 2+ The ratio of Ni ions to Ni ions in the intermediate layer is higher than that of Ni. 2+ The ratio of the number of Ni ions to the number of Ni ions in the core. It should be noted that the number of Ni ions represents the Ni content in the cathode material. 2+ and Ni 3+The sum of the number of ions. Preferably, the proportion of Al element in the core is not less than 0.2 mol%, and Ni in the intermediate layer 2+ The ratio of the number of Ni ions to the number of Ni ions is not less than 35%.

[0044] In some embodiments of this application, the intermediate layer is a spinel-like mixed-phase structure extending 10nm-100nm outward from the surface of the core; and / or the passivation layer has a thickness of 1nm-10nm.

[0045] The intermediate layer is a 10nm-100nm thick extended fast ion conductor extending from the outer surface of the core, containing a spinel structure. The spinel structure is formed by sintering Mn or Co elements. The Mn / Co oxygen-suppressing spinel structure in the intermediate layer improves structural stability and hinders oxygen evolution. The appropriate thickness range of the intermediate layer ensures that oxygen release is suppressed without excessively increasing the overall mass and volume of the battery. The passivation layer is located on the outermost layer of the positive electrode material, with a thickness ranging from 1nm to 10nm. The passivation layer consists of electrolyte passivation and SO2 exchange material, specifically a fluorine-sulfur oxide compound. An excessively thick passivation layer increases the internal impedance of the battery, while an excessively thin layer may lead to rapid performance degradation. An appropriate passivation layer thickness effectively blocks electrolyte erosion and chemical instability while maintaining good electron and ion transport. Preferably, the intermediate layer is a layered structure extending 20nm-80nm outward from the surface of the core, and the passivation layer has a thickness of 3nm-8nm.

[0046] In some embodiments of this application, the passivation layer contains oxygen vacancies, the content of which accounts for 0.2 mol%-2 mol% of the cathode material; and / or the content of F element accounts for 0.02 mol%-0.5 mol% of the cathode material; and / or the content of S element accounts for 0.02 mol%-0.5 mol% of the cathode material.

[0047] The presence of oxygen vacancies provides more pathways for electrons and ions to pass through, thereby increasing the material's conductivity and ion transport performance. Proper control of oxygen vacancies and the amounts of F and S elements allows the passivation layer to maintain stability while suppressing undesirable chemical reactions. This helps reduce performance degradation during long-term battery use, thus extending battery life. The fluorine-sulfur passivation layer, located on the outermost layer of the positive electrode material, inhibits electrolyte corrosion. Sulfur can stabilize and replace lattice oxygen, and sulfur-oxygen vacancies can absorb lattice oxygen, thereby suppressing oxygen release. Preferably, the oxygen vacancy content accounts for 0.33 mol%-1.8 mol% of the positive electrode material, and the F and S elements each account for 0.025 mol%-0.45 mol% of the passivation layer.

[0048] In some embodiments of this application, the morphology of the cathode material is a single crystal structure; and / or the size of the single crystal of the cathode material ranges from 2.0 μm to 4.5 μm.

[0049] Choosing a single-crystal structure for the cathode material is advantageous because it exhibits lower structural damage during battery cycling, helping to reduce capacity decay and thus extending the overall battery life and improving its cycle performance. Larger single-crystal sizes reduce the contact area with the electrode liquid, thereby minimizing interfacial side reactions, resulting in excellent capacity retention, lower internal resistance growth, and preventing gas generation. Targeting a specific range of single-crystal sizes helps optimize lithium-ion transport efficiency and battery internal resistance, especially in fast-charge / discharge applications, where this control improves charge / discharge response speed and efficiency. Precise control of the single-crystal structure and size reduces the risk of thermal runaway and physical damage caused by rapid charge / discharge, ensuring battery reliability and safety under high-load conditions. Preferably, the cathode material has a particle size range of 2.2 μm to 4 μm.

[0050] Embodiments of the present invention also provide a method for preparing a cathode material, which is used to prepare the cathode material as described above. The preparation method includes: a first sintering: mixing a precursor, a lithium source, and a dopant, and performing a first sintering to obtain a first sintered product; a second sintering: mixing the first sintered product and a first coating agent, and performing a second sintering to obtain a second sintered product; and a third sintering: mixing the second sintered product and a second coating agent, and performing a third sintering to obtain the cathode material; wherein the dopant includes a doping element, the first coating agent includes at least one of Co, Mn, and a first coating element, and the second coating agent includes at least one of F, S, and a second coating element.

[0051] This invention provides a method for preparing cathode materials, comprising three sintering steps using a precursor, a lithium source, a dopant, and two different coating agents. The first sintering forms the basic cathode structure; the second sintering enhances the material's microstructure and improves its electrochemical performance; and the third sintering further optimizes the material's performance, improving its stability and lifespan. Through three sintering steps and the use of two different coating agents, the integrity of the material's microstructure and its stress resistance are enhanced, contributing to improved battery stability and reduced capacity decay during long-term use.

[0052] It should be noted that the first coating agent includes at least one of Co, Mn, and the first coating element. Further, the first coating agent includes at least one of Co and Mn. The intermediate layer can employ a conventional single-coat Co process. High-temperature coating with a cobalt-containing compound enables micro-doping of the material surface, improving material stability and ionic conductivity. The cobalt-containing compound, after high-temperature calcination, reacts with residual alkali on the surface, effectively reducing the content of Li₂CO₃ and LiOH, generating fast ion conductors such as lithium cobalt oxide, activating residual lithium on the surface to increase material capacity, replacing the complex water washing step, thereby reducing production costs, eliminating the damage to the material structure caused by water washing, improving the structural stability and cycle performance of the material, and reducing surface internal resistance. Simultaneously, Co… 3+ It itself generates Co3O4 particles with a spinel phase, stabilizing the material structure and reducing internal resistance, but it does not improve the performance of Ni. 2+ The proportion of Mn has a relatively small impact, and the reduction is not significant. 4+ The addition of Ni can further improve 2+ The increased proportion of [certain elements] leads to an increase in the spinel structure, which can stabilize the structure and reduce gas production, but will reduce the material capacity.

[0053] The second coating agent includes at least one of the elements F, S, and the second coating element. For example, the passivation layer comprises at least one of Al2O3, WO3, TiO2, Al2S3, Tl2S, SnS2, AlF3, NH4F, AlPO4, and NH4H2PO4, and contains the elements F, S, O, and the second coating element.

[0054] Furthermore, the oxygen content in the secondary sintering atmosphere should not be higher than that of air; a reducing atmosphere is preferred for sintering, which is beneficial for improving Ni... 2+ This process generates spinel, leading to a suitable spinel structure transformation. The oxygen content in the tertiary sintering atmosphere should not exceed that of air; a vacuum atmosphere is preferred for sintering to promote the formation of S. σ O δ Gas generation is conducive to the formation of a special fluorine-sulfur-oxygen coating structure.

[0055] In addition, a second crushing process is required after the first sintering. Specifically, after the first sintered product is cooled to room temperature, airflow crushing is performed. A second crushing process is also required after the second sintering. This second crushing process improves the dispersibility of the cathode material particles, thereby enhancing the coating effect.

[0056] In some embodiments of this application, the molar ratio of precursor, lithium source and dopant is 1:(1.02-1.10):(0.001-0.01); and / or the molar ratio of first sintered product and first coating agent is 1:(0.02-0.06); and / or the molar ratio of second sintered product and second coating agent is 1:(0.001-0.01).

[0057] Choosing appropriate ratios of precursor, lithium source, and dopant, with a slight excess of lithium source to ensure sufficient reaction and avoid capacity loss due to insufficient lithium, and using doping elements such as aluminum and magnesium to significantly improve the electrochemical performance and structural stability of the material, is crucial. After the first sintering, the product is mixed with a first coating agent. The first coating agent, in a small proportion, forms a thin coating layer, optimizing the material's interfacial properties and improving electrochemical stability while effectively preventing oxygen release. After the second sintering, the product is mixed with a second coating agent, in an even smaller proportion, further enhancing the chemical stability of the material surface, reducing side reactions, and improving battery life.

[0058] In some embodiments of this application, the first sintering is carried out in an air or oxygen atmosphere; and / or the second sintering is carried out in an air atmosphere; and / or the third sintering is carried out in an air atmosphere.

[0059] This embodiment specifies that the sintering steps in the material preparation process are carried out under a specific atmosphere. Specifically, the first sintering can be performed in an air or oxygen atmosphere, while the second and third sinterings are both performed in an air atmosphere. In the initial stage of preparing the battery cathode material, the first sintering is carried out in an oxygen-containing environment, which helps to ensure that the metal elements in the material are fully oxidized to form a stable metal oxide structure. The choice of air or pure oxygen environment can be adjusted according to the specific precursor composition and expected physicochemical properties. The subsequent sintering steps of the second and third sinterings are carried out in air, mainly to further improve the crystal structure of the material and enhance its structural stability and electrochemical performance. Repeated sintering processes help to eliminate defects that may be left by the first sintering, such as lattice irregularities and porosity. Preferably, the oxygen content in the oxygen atmosphere is above 80%.

[0060] In some embodiments of this application, the sintering temperature for the first sintering is 850℃-980℃; and / or the sintering time for the first sintering is 8h-15h; and / or the sintering temperature for the second sintering is 700℃-800℃; and / or the sintering time for the second sintering is 6h-12h; and / or the sintering temperature for the third sintering is 350℃-550℃; and / or the sintering time for the third sintering is 6h-12h.

[0061] The high-temperature sintering in the first sintering stage helps the material initially form the desired crystal structure and promotes the reaction and bonding of the original material, providing a solid foundation for subsequent sintering steps. The lower sintering temperature in the second sintering stage is suitable for further refining the crystal structure and optimizing the material's microstructure, while reducing excessively rapid crystal growth and structural damage caused by high temperatures. The third sintering stage uses even lower temperatures and is mainly used to improve the surface properties and stability of the material, especially suitable for forming a protective layer on the material surface or for final physicochemical property adjustments.

[0062] Multi-step sintering processes allow for gradual optimization of material properties, ensuring higher performance consistency and reliability in the final product. By controlling the temperature and time of different sintering stages, the microstructure and chemical composition of the material can be more precisely controlled, achieving optimal physical and chemical properties. Staged sintering reduces material defects caused by excessively high temperatures or prolonged times, such as improper grain boundary growth or phase separation. The final low-temperature sintering stage helps achieve fine surface tuning, improving contact performance and corrosion resistance. Preferably, the sintering temperature for one sintering is 880℃-950℃, and the sintering time is 9h-12h; the sintering temperature for one sintering is 720℃-780℃, and the sintering time is 7h-10h; the sintering temperature for one sintering is 400℃-500℃, and the sintering time is 7h-10h.

[0063] Embodiments of the present invention also provide a lithium-ion battery comprising the positive electrode material as described above. The lithium-ion battery has the same beneficial effects as the positive electrode material, and therefore will not be described further here.

[0064] Example 1 This embodiment provides a method for preparing a cathode material, including the following steps: S1. First sintering. NCM650530 precursor, Li2CO3 and Al2O3 were mixed in a molar ratio of 1:1.025:0.001 and then sintered at 950℃ for 12h in air atmosphere to control the single crystal size at 2.6μm.

[0065] S2. Primary crushing. Cool to room temperature, then perform airflow crushing, controlling D50 to 3.5±0.5μm, to obtain the first sintered product.

[0066] S3. Secondary sintering. The first sintering product is mixed with Co3O4 and LiOH·H2O in a molar ratio of 1:0.01:0.03, and then sintered at 750℃ for 10h in air atmosphere.

[0067] S4. Secondary crushing. Cool to room temperature, then perform airflow crushing, controlling D50 to 3.5±0.5μm, to obtain the second sintered product.

[0068] S5. Third sintering. The second sintering product is mixed with Al2O3, AlF3 and Al2S3 in a molar ratio of 1:0.005:0.001:0.001, and then sintered at 550℃ for 8 hours in air atmosphere to obtain the cathode material.

[0069] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn 0.299 Al 0.002 O2; the intermediate layer is composed of Li 0.711 Ni 0.175 Co 0.729 Mn 0.095 Al 0.001 O2; the passivation layer is composed of AlF. 0.03 S 0.03 O 1.93 In the core composition, Al accounts for 0.2 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 37%. The intermediate layer is a spinel-like structure extending 45 nm outward from the surface of the core; the passivation layer is 3 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 3.6 μm.

[0070] The spinel-like structure and passivation layer thickness can be obtained by TEM testing, the elemental composition at different locations can be obtained by cross-sectional line scan analysis using EDS technology, and the oxygen vacancies can be obtained by O XPS peak area analysis.

[0071] like Figure 3 The diagram shows the surface structure and elemental distribution of the cathode material in Example 1. The material surface is uniformly coated with F and S elements; the cross-section shows that the material has a layered core, a spinel-like intermediate layer, and an amorphous passivation layer. I is the electron diffraction pattern of the spinel-like structure, with a lattice spacing of 0.294 nm; II is the electron diffraction pattern of the layered structure, with a lattice spacing of 0.48 nm.

[0072] like Figure 4 As shown, this is an elemental distribution diagram of the cross-section of the cathode material in Example 1. By performing main elemental tests on the material, it can be seen that the cross-section of the material exhibits a Co coating layer.

[0073] Example 2 This embodiment provides a method for preparing a cathode material. The specific steps are the same as in Example 1, except that in S1, NCM900505 precursor, LiOH·H2O, Al2O3, and ZrO2 are mixed in a molar ratio of 1:1.07:0.008:0.002, and then sintered at 860°C for 10 hours in air to control the single crystal size at 2.8 μm. In S3, the first sintered product is mixed with Co3O4, LiOH·H2O, and Al2O3 in a molar ratio of 1:0.003:0.03:0.001, and then sintered at 720°C for 8 hours in air.

[0074] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.07 Ni 0.885 Co 0.049 Mn 0.049 Al 0.015 Zr 0.002 O2; the intermediate layer is composed of Li 0.57 Ni 0.493 Co 0.471 Mn 0.023 Al 0.013 O2; the passivation layer is composed of AlF. 0.03 S 0.03 O 1.93 In the core composition, Al accounts for 0.3 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 27%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 40%. The intermediate layer is a spinel-like structure extending 53 nm outward from the surface of the core; the passivation layer is 3 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 3.8 μm.

[0075] Example 3 This embodiment provides a method for preparing a cathode material. The specific steps are described in Example 1, except that in step S1, Ni... 0.52 Co 0.20 Mn 0.28 (OH)2 precursor, Li2CO3 and Al2O3 were mixed in a molar ratio of 1:1.02:0.002 and sintered at 970℃ for 12h in air atmosphere to control the single crystal size at 3.8μm.

[0076] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.04Ni 0.516 Co 0.20 Mn 0.28 Al 0.004 O2; the intermediate layer is composed of Li 0.723 Ni 0.152 Co 0.756 Mn 0.091 Al 0.001 O2; the passivation layer is composed of AlF. 0.03 S 0.03 O 1.88 In the core composition, Al accounts for 0.8 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 18%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 32%. The intermediate layer is a spinel-like structure extending 47 nm outward from the surface of the core; the passivation layer is 3 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 4.0 μm.

[0077] Example 4 This embodiment provides a method for preparing a cathode material. The specific steps are described in Example 1. The difference is that in S3, the first sintering product is mixed with Co3O4, MnO2 and LiOH·H2O in a molar ratio of 1:0.001:0.008:0.008, and then sintered at 780°C for 12 hours in an air atmosphere.

[0078] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn 0.299 Al 0.002 O2; the intermediate layer is composed of Li 0.743 Ni 0.188 Co 0.166 Mn 0.645 Al 0.001 O2; the passivation layer is composed of AlF. 0.03 S 0.03 O 1.93 In the core composition, Al accounts for 0.2 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 40%. The intermediate layer is a spinel-like structure extending 73 nm outward from the surface of the core; the passivation layer is 3 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 3.6 μm.

[0079] Example 5 This embodiment provides a method for preparing a cathode material. The specific steps are the same as in Example 1. The difference is that in S3, the first sintering product is mixed with Co3O4 and AlOOH in an atomic molar ratio of 1:0.01:0.002.

[0080] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn 0.299 Al 0.002 O2; the intermediate layer is composed of Li 0.011 Ni 0.175 Co 0.729 Mn 0.095 Al 0.003 O2; the passivation layer is composed of AlF. 0.03 S 0.03 O 1.94 In the core composition, Al accounts for 0.2 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 37%. The intermediate layer is a spinel-like structure extending 88 nm outward from the surface of the core; the passivation layer is 3 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 3.6 μm.

[0081] Example 6 This embodiment provides a method for preparing a cathode material. The specific steps are the same as in Example 1. The difference is that in S5, the second sintering product is mixed with Al2O3, NH4F and SnS2 in a molar ratio of 1:0.005:0.005:0.003.

[0082] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn0.299 Al 0.002 O2; the intermediate layer is composed of Li 0.710 Ni 0.174 Co 0.728 Mn 0.095 Al 0.001 O2; the passivation layer is composed of Al. 0.72 Sn 0.28 F 0.09 S 0.08 O 1.68 In the core composition, Al accounts for 0.2 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 37%. The intermediate layer is a spinel-like structure extending 58 nm outward from the surface of the core; the passivation layer is 8 nm thick. The passivation layer contains 1.8 mol% oxygen vacancies, 0.40 mol% F, and 0.43 mol% S in the cathode material. The single crystal size of the cathode material is 3.7 μm.

[0083] Example 7 This embodiment provides a method for preparing a cathode material. The specific steps are the same as in Example 1. The difference is that in S5, the second sintering product is mixed with AlPO4, AlF3 and Al2S3 in a molar ratio of 1:0.006:0.001:0.001.

[0084] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn 0.299 Al 0.002 O2; the intermediate layer is composed of Li 0.811 Ni 0.175 Co 0.729 Mn 0.095 Al 0.001 O2; the passivation layer is composed of AlPF. 0.03 S 0.03 O 1.88 In the core composition, Al accounts for 0.2 mol%. Ni in the core... 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 37%. The intermediate layer is a spinel-like structure extending 45 nm outward from the surface of the core; the passivation layer is 6 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 3.7 μm.

[0085] Comparative Example 1 This comparative example provides a method for preparing a cathode material. The specific steps are described in Example 1. The difference is that NCM650530 precursor and Li2CO3 are mixed in a molar ratio of 1:1.025 and then sintered at 940°C for 12 hours in an air atmosphere to control the single crystal size at 1.8 μm.

[0086] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.65 Co 0.05 Mn 0.30 O2; the intermediate layer is composed of Li 0.811 Ni 0.175 Co 0.730 Mn 0.095 O2; the passivation layer is composed of AlF. 0.03 S 0.03 O 1.93 In the core composition, Al accounts for 0 mol%. The core contains Ni. 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 37%. The intermediate layer is a spinel-like structure extending 45 nm outward from the surface of the core; the passivation layer is 3 nm thick. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 1.9 μm.

[0087] Comparative Example 2 This comparative example provides a method for preparing a cathode material. The specific steps are described in Example 1, except that steps S3 and S4 are omitted.

[0088] The cathode material consists of a core and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn 0.29 9Al 0.002 O2; the passivation layer is composed of AlF. 0.03 S0.03 O 1.92 In the core composition, Al accounts for 0.2 mol%. The passivation layer thickness is 3 nm. The passivation layer contains 0.4 mol% oxygen vacancies, 0.23 mol% F, and 0.18 mol% S in the cathode material. The single crystal size of the cathode material is 2.6 μm.

[0089] Comparative Example 3 This comparative example provides a method for preparing a cathode material. The specific steps are described in Example 1. The difference is that in S5, the second sintering product and Al2O3 are mixed in a molar ratio of 1:0.001.

[0090] The cathode material consists of a core, an intermediate layer, and a passivation layer from the inside out; the core is composed of Li. 1.05 Ni 0.649 Co 0.05 Mn 0.299 Al 0.002 O2; the intermediate layer is composed of Li 0.811 Ni 0.175 Co 0.729 Mn 0.095 Al 0.001 O2; the passivation layer is composed of Al2O3. In the core composition, Al accounts for 0.2 mol%. The core contains Ni. 2+ The ratio of the number of Ni ions in the core to the number of Ni ions in the intermediate layer is 20%. 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is 37%. The intermediate layer is a spinel-like structure extending 45 nm outward from the surface of the core; the passivation layer is 1 nm thick. The single crystal size of the cathode material is 3.5 μm.

[0091] The cathode materials of the examples and comparative examples were fabricated into batteries, and the volume growth rate of different samples under full charge at 70°C was tested at voltages of 4.4V-3.0V.

[0092] The expansion volume is calculated using the water displacement method. Batteries with varying degrees of expansion are placed in a water tank, and their weight after water displacement is measured using an electronic density meter. The volume is then converted to the desired expansion amount. During the recharging process, the electrode tabs must be properly protected.

[0093] Specific steps: S10. Prepare batteries from the positive electrode materials of the examples and comparative examples, fully charge them in a voltage window of 4.4V-3.0V, then protect the fully charged battery tabs and slowly place them into a 70°C water tank. After waiting for 30 seconds, measure the weight of the water discharged from the water tank and divide it by the dielectric density to obtain the initial volume V0 of the battery.

[0094] S20. After drying the battery, place it in an insulated box and store it at a high temperature of 70°C for 7 days.

[0095] S30. After the battery has been stored at high temperature, protect the battery tabs and slowly place it into a 70°C water tank. After 30 seconds, measure the weight of the water drained from the tank and divide it by the dielectric density to obtain the battery volume V7. The volume growth rate after 7 days can be calculated by (V7-V0) / V0×100%.

[0096] S40. After drying the battery, fully charge it at 4.35V and store it in an insulated box at 70℃ for 7 days.

[0097] S50. Repeating steps S30 and S40, the volume growth rate under different numbers of days of high-temperature storage can be obtained.

[0098] The volume growth rate of different samples under 70℃ storage conditions is shown in Table 1. The line graph obtained from the data in Table 1 is shown in [reference needed]. Figure 1 .

[0099] Table 1. Volume growth rate of different samples under storage conditions at 70℃ A comparison between Example 2 and Example 1 shows that by adjusting the precursor composition and doping coating scheme, good gas generation performance can still be achieved. The addition of ZrO2 dopant, with its higher Zr-O bond energy, further fixes lattice oxygen and reduces lattice oxygen precipitation.

[0100] A comparison between Example 3 and Example 1 shows that adjusting the precursor and increasing the single crystal size are beneficial for improving gas generation performance. Increasing the single crystal size reduces the sample's specific surface area, thus reducing interfacial side reactions. Simultaneously, high Al doping stabilizes lattice oxygen, further improving gas generation performance.

[0101] A comparison between Example 4 and Example 1 shows that when Co is partially replaced with Mn, the high-valence Mn... 4+ Ni 2+ The increase facilitates the transformation from layered to spinel structure, increases the thickness of the spinel structure, and improves gas production and circulation performance.

[0102] A comparison between Example 5 and Example 1 shows that without additional Li element supplementation, the Co3O4 coating agent will mostly maintain the spinel structure, thereby increasing the spinel thickness of the coating layer; by adding additional Al coating element, micro-doping will occur under high temperature sintering, occupying TM sites, further improving the stability of the spinel structure layer, and exhibiting better gas generation performance.

[0103] A comparison between Example 6 and Example 1 shows that by strengthening the passivation layer of fluorine and sulfur, increasing the proportion of corrosion-resistant elements and the film thickness, the ammonia gas generated by the pyrolysis of NH4F will be beneficial for reducing Ni. 2+ It generates oxygen vacancies, thereby increasing the proportion of spinel phase structure, which can synergistically suppress gas generation in materials.

[0104] A comparison between Example 7 and Example 1 shows that changing the coating agent, increasing the amount of phosphorus (P) and improving the passivation thickness further improves gas production.

[0105] The comparison between Comparative Example 1 and Example 1 shows that the core has no Al element doping, resulting in poor lattice oxygen stability; moreover, the single crystal size is reduced, the specific surface area of ​​the sample is increased, and the interfacial side reactions increase, which is not conducive to improving gas production performance.

[0106] A comparison of Comparative Example 2 and Example 1 shows that the absence of a spinel structure layer does not impede the absorption of lattice oxygen in the bulk phase, thus increasing gas production. Figure 2 The figure shows the valence state analysis diagrams of Ni in Example 1 and Comparative Example 2. After adding the Co coating process in Example 1, the Ni content in the sample... 2+ The increased content indicates that the cathode material surface has more spinel-like structures. (Ni 2p in the figure) 3 / 2 The voltage drops to two peaks at 854.4 eV and 855.9 eV, representing Ni, respectively. 2+ and Ni 3+ Furthermore, the Ni in the intermediate layer of Example 1 2+ The ratio of the number of Ni ions to the number of Ni ions in the intermediate layer is not less than 30%. The surface chemical state of Ni can be analyzed by cross-sectional XPS, and the area ratio of different peaks can be calculated.

[0107] The comparison between Comparative Example 3 and Example 1 shows that without fluorine and sulfur compounds, interfacial side reactions increase, which cannot reduce the precipitation of lattice oxygen under high voltage, resulting in a significant increase in gas production.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that, The positive electrode material comprises, from the inside out, a core, an intermediate layer, and a passivation layer; The components of the kernel are shown in equation (Ⅰ): Li y1 Ni a1 Co b1 Mn c1 M e1 O2 of formula (I); The value ranges of y1, a1, b1, c1, and e1 are as follows: 1.0≤y1≤1.1, 0.5≤a1<1, 0≤b1≤0.3, 0<c1≤0.4, and 0.001<e1<0.

1. M is a doping element, including at least one of Al, Mg, Zr, Sr, Y, Mo, and W; The composition of the intermediate layer is shown in formula (II): Li y2 Ni a2 Co b2 Mn c2 N e2 O₂ of formula (II); The ranges of values ​​for y2, a2, b2, c2, and e2 are as follows: 0 < y2 < 1.0, 0 < a2 < 0.5, 0 < b2 < 0.8, 0 < c2 < 0.8, and 0 < e2 < 0.

1. N is the first coating element, including at least one of Al, Zr, Sr, and F; The composition of the passivation layer is shown in formula (Ⅲ): QF α S β O γ Formula (III); The ranges of α, β, and γ are as follows: 0 < α < 0.1, 0.02 < β < 0.1, 1.8 < γ < 2.0, and 1.94 < α + β + γ < 2.

0. Q is the second coating element, including at least one of Al, Ti, W, Sn, and P.

2. The cathode material according to claim 1, characterized in that, In the composition of the kernel, the proportion of Al element in the kernel is not less than 0.1 mol%; and / or The intermediate layer Ni 2+ The ratio of the number of Ni ions in the intermediate layer to the number of Ni ions in the core is higher than that in the core. 2+ The ratio of the number of ions to the number of Ni ions in the core; and / or The intermediate layer Ni 2+ The ratio of the number of ions to the number of Ni ions in the intermediate layer is not less than 30%.

3. The cathode material according to claim 1, characterized in that, The intermediate layer is a spinel-like structure extending 10nm-100nm outward from the surface of the core; and / or The thickness of the passivation layer is 1nm-10nm.

4. The cathode material according to claim 1, characterized in that, The passivation layer contains oxygen vacancies, and the content of the oxygen vacancies accounts for 0.2 mol%-2 mol% of the positive electrode material; and / or The content of element F is 0.02 mol%-0.5 mol% of the positive electrode material; and / or The sulfur content is 0.02 mol% to 0.5 mol% of the cathode material.

5. The positive electrode material according to claim 1, characterized in that, The cathode material has a single-crystal structure; and / or The single crystal size of the cathode material ranges from 2.0 μm to 4.5 μm.

6. A method for preparing a cathode material, used to prepare the cathode material as described in any one of claims 1-5, characterized in that, The preparation method includes: First sintering: The precursor, lithium source and dopant are mixed and sintered in one step to obtain the first sintered product; Secondary sintering: The first sintering product and the first coating agent are mixed and sintered a second time to obtain the second sintering product; Three-stage sintering: The second sintering product and the second coating agent are mixed and sintered three times to obtain the cathode material; The dopant includes the doping element, the first coating agent includes at least one of Co and Mn and at least one of the first coating element, and the second coating agent includes at least one of F, S and the second coating element.

7. The preparation method according to claim 6, characterized in that, The molar ratio of the precursor, the lithium source, and the dopant is 1:(1.02-1.10):(0.001-0.01); and / or The molar ratio of the first sintered product to the first coating agent is 1:(0.02-0.06); and / or The molar ratio of the second sintered product to the second coating agent is 1:(0.001-0.01).

8. The preparation method according to claim 6, characterized in that, The first sintering is carried out in an air or oxygen atmosphere; and / or The secondary sintering is performed in an air atmosphere; and / or The three sintering processes were carried out in an air atmosphere.

9. The preparation method according to claim 6, characterized in that, The sintering temperature for the first sintering is 850℃-980℃; and / or The sintering time for the first sintering is 8h-15h; and / or The sintering temperature for the secondary sintering is 700℃-800℃; and / or The sintering time for the secondary sintering is 6h-12h; and / or The sintering temperature for the three sintering processes is 350℃-550℃; and / or The sintering time for the three sintering processes is 6-12 hours.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material as described in any one of claims 1-5.

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