O2 phase lithium cobalt oxide cathode material, preparation method thereof, cathode sheet and lithium ion battery

Abstract

To solve the problem of low cycle life of the battery caused by the radial cracks of the existing O2 phase LCO in the preparation process due to ion exchange stress, the application provides an O2 phase lithium cobalt oxide positive electrode material and a preparation method thereof, a positive electrode sheet and a lithium ion battery, wherein the O2 phase lithium cobalt oxide positive electrode material comprises a core and a coating layer, the core is an O2 phase Li y CoO2, wherein y is 0.990-1.01; the coating layer covers the outer surface of the core, and the coating layer fills and covers the radial cracks; the coating layer comprises at least one alternating structure layer, the alternating structure layer comprises an Al2O3 layer and a TiO2 layer, the coating layer filled in the radial cracks, the side close to the center of the core is the Al2O3 layer, and the side of the coating layer away from the core is the TiO2 layer. The O2 phase lithium cobalt oxide positive electrode material provided in the application forms an "anchoring + sealing" composite structure, effectively alleviates the corrosion of the electrolyte in the process of charging and discharging, reduces the transition metal dissolution, and improves the cycle life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to an O2 phase lithium cobalt oxide cathode material and its preparation method, cathode sheet and lithium-ion battery. Background Technology

[0002] With the increasing demand for higher energy density lithium-ion batteries from mobile electronic devices, electric vehicles, and energy storage systems, traditional cathode materials such as O3-phase LiCoO2 (O3-LCO) are no longer sufficient to meet future development requirements due to limitations in their theoretical capacity and voltage platform. The theoretical capacity of O3-LCO is approximately 270 mAh / g, but in practical applications, it is limited by structural stability and electrolyte compatibility, typically operating within a voltage range of 3.0-4.3V, thus limiting the potential for further energy density improvements.

[0003] O2-phase LiCoO2 (O2-LCO), due to its unique layered structure, can theoretically provide a capacity of up to approximately 220-250 mAh / g, and its rock salt phase transition in a deeply delithiated state allows it to operate stably at voltages of 4.5V or even higher. Current high-voltage O2-phase lithium cobalt oxide (LCO) cathode materials face the following problems: Existing methods for preparing O2-phase LiCoO2 involve first preparing sodium cobalt oxide, then using an ion exchange method to exchange sodium for lithium. This process leads to radial cracks due to ion exchange stress, which, during battery charging and discharging, causes electrolyte infiltration, triggering irreversible phase transitions and transition metal dissolution, resulting in low cycle life at 4.5V or even higher voltages. Summary of the Invention

[0004] To address the problem of low battery cycle life caused by radial cracks due to ion exchange stress during the preparation of existing O2-phase LCO, this invention provides an O2-phase lithium cobalt oxide cathode material, its preparation method, cathode sheet, and lithium-ion battery.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides an O2-phase lithium cobalt oxide cathode material, comprising a core and a coating layer, wherein the core is an O2-phase Li₂ oxide with radial cracks. y CoO2, where y is 0.990~1.01; The coating layer covers the outer surface of the core, and the coating layer fills and covers radial cracks on the surface of the core; The coating layer includes at least one alternating structure layer, which includes an Al2O3 layer and a TiO2 layer, filling the radial crack in the coating layer. The side of the coating layer closer to the core center is the Al2O3 layer, and the side of the coating layer away from the core is the TiO2 layer.

[0006] Preferably, the total thickness of the coating layer is δ, where δ = δ1 + δ2, and 3 nm ≤ δ ≤ 5 nm. Wherein, δ2 is the thickness of the coating layer in the radial crack, in nm; δ1 is the thickness of the coating layer on the outer surface of the core, in nm.

[0007] Preferably, the vertical height difference between the outer surface of the coating layer and the bottom of the radial crack is H. H satisfies equation 1. H = d + 2δ1, Equation 1, and 3nm ≤ δ1 ≤ 5nm, 100nm ≤ d ≤ 300nm; Where d is the depth of the radial crack, in nm.

[0008] Preferably, the radial crack has a length ≤1μm and a width of 50~100nm.

[0009] Preferably, the diffusion depth of the elements in the coating layer into the core is ≤2nm.

[0010] Preferably, in each of the alternating structural layers, the thickness of the Al2O3 layer accounts for 60% to 80% of the total thickness of the alternating structural layer, and the thickness of the TiO2 layer accounts for 20% to 40% of the total thickness of the alternating structural layer. Preferably, the ratio of the thickness of each Al2O3 layer to the thickness of each TiO2 layer is (2 to 3):1.

[0011] Secondly, this application provides a method for preparing the O2 phase lithium cobalt oxide cathode material described above, comprising the following steps: Obtain P2 phase Na x CoO2, x is 0.7~0.8; The P2 phase Na x CoO2 is uniformly mixed with a dopant source and sintered to obtain a precursor containing a first dopant element; the first dopant element includes Al, Mg, and Ti; in the precursor, the molar percentage of the first dopant element is 0.5~1.8 mol% The precursor and Li-containing + The molten salts were mixed evenly to obtain a first mixed solution, and the first mixed solution was subjected to an ion exchange reaction to obtain the O2 phase Li. y CoO2, where y is 0.990~1.01; the O2 phase Li y The residual sodium content in CoO2 is ≤1500ppm; To the O2 phase Li y Al2O3 and TiO2 layers are sequentially deposited on CoO2 to form an alternating structure of Al2O3 and TiO2 layers, wherein the O2 phase Li yThe radial cracks of CoO2 and the surface deposition of a coating layer with at least one alternating structural layer are used to obtain the O2 phase lithium cobalt oxide cathode material.

[0012] Preferably, the molar ratio of Li in the Li-containing molten salt to Co in the precursor is 0.990~1.01; The O2 phase Li y The CoO2 particles have a plate-like structure with a thickness of 7.3~7.7 μm, an internal porosity of 5~8%, and lattice parameters a=2.82±0.02Å and c=14.6±0.1Å. The ion exchange reaction temperature is 260-300℃, and the ion exchange reaction time t satisfies Equation 2. Formula 2; Where R is the radius of the precursor, in μm. Deff = 1.0 × 10 -11 cm 2 / s; C Na,0 The initial concentration of sodium ions in the precursor at t=0, in at% (at%). C Na,t The concentration at of sodium ions remaining in the precursor at time t when the ion exchange reaction proceeds to time t is given.

[0013] Thirdly, this application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising the aforementioned O2 phase lithium cobalt oxide positive electrode material, or the O2 phase lithium cobalt oxide positive electrode material prepared by the aforementioned method for preparing the O2 phase lithium cobalt oxide positive electrode material.

[0014] Preferably, the cathode material further includes O3 phase LiCoO2, wherein the O3 phase LiCoO2 comprises first particles with a D50 particle size of 16~20μm and second particles with a D50 particle size of 4~7μm, and the first particles account for 78~82% of the mass of the O3 phase LiCoO2; The D50 particle size of the O2 phase lithium cobalt oxide cathode material is 4.0~9.0μm; In the cathode material, the mass percentage of the O2 phase lithium cobalt oxide cathode material is 5-20%.

[0015] Preferably, the positive electrode sheet includes a positive current collector and a positive active coating disposed on at least one side of the surface of the positive current collector, wherein the thickness T of the positive active coating on one side satisfies Equation 3. T≥2.5×(D1+D2), Where D1 is the D50 particle size of the first particle, in μm; D2 is the D50 particle size of the O2 phase lithium cobalt oxide cathode material, in μm; and T is in μm.

[0016] Fourthly, this application provides a lithium-ion battery, including the positive electrode sheet described above.

[0017] The O2-phase lithium cobalt oxide cathode material provided in this application has the following effects: 1) The alternating structural layers include an Al2O3 layer and a TiO2 layer. The Al2O3 layer is a rigid layer, and the TiO2 layer is a flexible layer. The Al2O3 layer fills the radial crack near the core center and preferentially penetrates into the bottom of the crack to fill the uneven structure. The coating layer on the side away from the core is the TiO2 layer. The outermost TiO2 layer forms a continuous sealing film, making the bonding between the coating layer and the substrate tighter, forming an "anchoring + sealing" composite structure. This structure is achieved through the synergistic effect of rigidity and flexibility: the Al2O3 layer anchors the bottom of the crack to inhibit its propagation, and the TiO2 layer adapts to the volume changes during charging and discharging, maintaining the integrity of the seal. Thus, it effectively alleviates the erosion of the electrolyte during charging and discharging, reduces the dissolution of transition metals, and improves the cycle life of the battery. 2) The Al2O3 layer filled at the bottom of the radial crack and the O2-phase Li y CoO2 forms Co-O-Al bonds, and Ti-O bonds form on the outermost part of the core. The interfacial bonding force is a double chemical bond of Co-O-Al bonds (inner layer) and Ti-O bonds (outer layer). The alternating structural layers cover the inside of the crack, forming an alternating Al / Ti distribution, which completely covers the crack surface, achieves high coverage, reduces the infiltration of electrolyte into the radial crack, and greatly reduces the risk of particle breakage. Attached Figure Description

[0018] Figure 1 This is the SEM image of the O2 phase lithium cobalt oxide cathode material of Example 1 of the present invention; Figure 2 This is a cross-sectional SEM image of the O2 phase lithium cobalt oxide cathode material of Example 1 of the present invention; Figure 3 This is a diagram of the surface coating structure of the O2 phase lithium cobalt oxide cathode material in Example 1 of the present invention; Figure 4 This is the XRD pattern of the O2 phase lithium cobalt oxide cathode material of Example 1 of the present invention; Figure 5 This is a charge-discharge curve of the O2 phase lithium cobalt oxide cathode material of Example 1 of the present invention. Detailed Implementation

[0019] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] An embodiment of the present invention provides an O2-phase lithium cobalt oxide cathode material, comprising a core and a coating layer, wherein the core is an O2-phase Li with radial cracks. y CoO2, where y is 0.990~1.01; the coating layer covers the outer surface of the core, and the coating layer fills and covers the radial cracks on the surface of the core; The coating layer includes at least one alternating structure layer, which includes an Al2O3 layer and a TiO2 layer, filling the radial crack in the coating layer. The side of the coating layer closer to the core center is the Al2O3 layer, and the side of the coating layer away from the core is the TiO2 layer.

[0021] The O2-phase lithium cobalt oxide cathode material provided in this application has the following effects: 1) The alternating structural layers include an Al2O3 layer and a TiO2 layer. The Al2O3 layer is a rigid layer, and the TiO2 layer is a flexible layer. The Al2O3 layer fills the radial crack near the core center and preferentially penetrates into the bottom of the crack to fill the uneven structure. The coating layer on the side away from the core is the TiO2 layer. The outermost TiO2 layer forms a continuous sealing film, making the bonding between the coating layer and the substrate tighter, forming an "anchoring + sealing" composite structure. This structure is achieved through the synergistic effect of rigidity and flexibility: the Al2O3 layer anchors the bottom of the crack to inhibit its propagation, and the TiO2 layer adapts to the volume changes during charging and discharging, maintaining the integrity of the seal. Thus, it effectively alleviates the erosion of the electrolyte during charging and discharging, reduces the dissolution of transition metals, and improves the cycle life of the battery. 2) The Al2O3 layer filled at the bottom of the radial crack and the O2-phase Li y CoO2 forms Co-O-Al bonds, and Ti-O bonds form on the outermost part of the core. The interfacial bonding force is a double chemical bond of Co-O-Al bonds (inner layer) and Ti-O bonds (outer layer). The alternating structural layers cover the inside of the crack, forming an alternating Al / Ti distribution, which completely covers the crack surface, achieves high coverage, reduces the infiltration of electrolyte into the radial crack, and greatly reduces the risk of particle breakage.

[0022] In some embodiments, the total thickness of the coating layer is δ, where δ = δ1 + δ2, and 3 nm ≤ δ ≤ 5 nm. Wherein, δ2 is the thickness of the coating layer in the radial crack, in nm; δ1 is the thickness of the coating layer on the outer surface of the core, in nm.

[0023] Specifically, since the coating layer partially fills the radial cracks, it includes a thickness δ2 filling the radial cracks and a thickness δ1 covering the outer surface of the core. The total thickness of the coating layer is limited to δ, with 3nm ≤ δ ≤ 5nm. This ensures complete coverage of the radial cracks, achieving high coverage and maintaining the sealing integrity of the cracks. Simultaneously, the O2 phase lithium cobalt oxide cathode material exhibits low impedance. If the total thickness of the coating layer is less than 3nm, the coating layer is too thin and cannot completely cover the radial cracks, resulting in sealing failure. If δ > 5nm, the total thickness of the coating layer is too high, significantly increasing the overall impedance of the O2 phase lithium cobalt oxide cathode material, thus increasing battery impedance and affecting battery performance.

[0024] The total thickness δ of the coating layer can be 3nm, 3.2nm, 3.5nm, 3.7nm, 3.8nm, 4.0nm, 4.2nm, 4.3nm, 4.5nm, 4.8nm, 5.0nm, etc.

[0025] The thicknesses δ, δ1, and δ2 of the coating layer can be determined by cross-sectioning the O2 phase lithium cobalt oxide cathode material and measuring the coating layer thickness using a transmission electron microscope (TEM). For example, take 10 particles of O2 phase lithium cobalt oxide cathode material and take their average values.

[0026] In some embodiments, the vertical height difference between the outer surface of the coating layer and the bottom of the radial crack is H. H satisfies equation 1. H = d + 2δ1, Equation 1, and 3nm ≤ δ1 ≤ 5nm, 100nm ≤ d ≤ 300nm; Where d is the depth of the radial crack, in nm.

[0027] The crack depth d can be obtained through 3D reconstruction using FIB-SEM and measured along the longest crack path.

[0028] Specifically, the vertical height difference between the outer surface of the coating layer and the bottom of the radial crack is H, where H is in nm. H is calculated using Equation 1, satisfying H = d + 2δ1, Equation 1, and the conditions 3nm ≤ δ1 ≤ 5nm and 100nm ≤ d ≤ 300nm. This ensures that the radial crack is completely sealed, preventing the radial crack from spreading inward during cycling and inducing particle breakage and pulverization. If d > 300nm, stress concentration occurs, increasing the risk of particle breakage. When δ1 < 3nm, the coating layer fails to seal the radial crack. If the crack depth is too small, it cannot effectively provide a lithium-ion diffusion channel, and may instead hinder ion transport due to the failure to form a continuous channel, affecting rate performance, etc.; at the same time, problems such as high residual sodium content or structural instability may also occur.

[0029] d can be 100nm, 120nm, 140nm, 150nm, 200nm, 230nm, 260nm, 280nm, 300nm, etc.

[0030] In some embodiments, the radial crack has a length ≤1μm and a width of 50~100nm.

[0031] Specifically, the O2 phase Li provided in this application y CoO2, space group P63mc, has a radial crack structure inside the matrix. The length of the radial crack is ≤1μm and the width is in the range of 50~100nm. The crack can provide ion diffusion channels and improve the rate performance of the cathode material. The coating layer is embedded in the radial crack and completely covers the crack surface. The alternating structural layers can seal the crack, thereby effectively mitigating the erosion of the electrolyte during charging and discharging and greatly reducing the risk of particle breakage.

[0032] If the radial crack is longer than 1 μm, the excessive crack length increases the risk of particle breakage during the rolling process.

[0033] If the crack width is >100nm, the mechanical strength of the particles decreases, making it easier for electrolyte to penetrate; while if the crack width is <50nm, lithium ion diffusion is hindered.

[0034] In some embodiments, the diffusion depth of the elements in the coating layer into the core is ≤2nm.

[0035] Specifically, by limiting the deposition temperature of the Al2O3 and TiO2 layers to ≤200℃, the diffusion depth of elements in the coating layer into the core is ≤2nm. A low-temperature ALD process at ≤200℃ is used to confine the TiO2 layer as the outermost coating layer, and the element diffusion depth at its interface with the core is controlled to ≤2nm, thereby physically isolating the TiO2 layer from the core. 4+ Co 3+ Direct contact with Co at high temperatures is fundamentally avoided. 3+ The disproportionation reaction occurs, and the oxygen vacancies and mixed valence states of TiO2 are utilized to endow it with new functions such as enhancing interfacial ion / electron conduction and catalyzing the formation of a stable CEI film; this solves the problem that Ti doping in the core enhances electron conduction but induces Co. 3+ The problem of disproportionation reaction.

[0036] In some embodiments, in each of the alternating structural layers, the thickness of the Al2O3 layer accounts for 60% to 80% of the total thickness of the alternating structural layer, and the thickness of the TiO2 layer accounts for 20% to 40% of the total thickness of the alternating structural layer.

[0037] Specifically, the thickness of the Al2O3 layer in each alternating structural layer is limited to 60-80%, with its main function being mechanical reinforcement. Its amorphous structure is beneficial for filling grain boundaries and inhibiting crack propagation. The thickness of the TiO2 layer in each alternating structural layer is limited to 25-40%, with its main function being to promote ion conduction. Oxygen vacancies provide Li⁺ jumping sites. This ratio range can form an interpenetrating network structure of continuous Al2O3 layer (mechanical support) + TiO2 penetration channels (ion conduction), forming a stable protective layer while improving the lithium-ion diffusion rate and improving the cycle performance of the battery.

[0038] The thickness percentage of the Al2O3 layer in each alternating structural layer can be 60%, 62%, 63%, 65%, 66%, 68%, 70%, 72%, 73%, 75%, 78%, 80%, or any two of the above.

[0039] The thickness percentage of the TiO2 layer in each alternating structural layer can be 20%, 22%, 24%, 25%, 27%, 29%, 30%, 32%, 34%, 36%, 38%, 40%, or any two of the above.

[0040] When the Al2O3 layer thickness in each alternating structural layer is less than 60%, the excessive TiO2 leads to a loose layered structure, resulting in severe crack propagation during cycling. When the Al2O3 layer thickness in each alternating structural layer is greater than 75%, the low ionic conductivity of Al2O3 blocks ion channels, leading to a decrease in the overall Li⁺ diffusion coefficient and severe capacity decay at high-rate charge and discharge rates. When the TiO2 layer thickness in each alternating structural layer is less than 25%, insufficient mechanical strength leads to an increased electrode breakage rate during rolling, reduced electrode compaction, and a decreased fracture strain in electrode flexibility tests. When the TiO2 layer thickness in each alternating structural layer is greater than 40%, it catalyzes electrolyte decomposition at high temperatures, resulting in increased gas production during battery storage.

[0041] In some preferred embodiments, the ratio of the thickness of the Al2O3 layer to the thickness of the TiO2 layer in each of the alternating structural layers is (2~3):1.

[0042] Specifically, in each of the alternating structural layers, the ratio of the thickness of the Al2O3 layer to the thickness of the TiO2 layer is controlled to be in the range of (2~3):1, which can control the balance between ion transport and mechanical strength at the interface of the O2 phase lithium cobalt oxide cathode material.

[0043] On the one hand, the outer layer of TiO2 is beneficial to improving the interfacial lithium-ion conductivity (the (001) crystal plane of anatase TiO2 has intrinsic oxygen vacancies (VO), forming Li + Jump Channel, Ti 4+ +VO→Ti3+ +□Li + The □ represents the lithium site, with a migration barrier of only 0.3 eV, far lower than the 0.8 eV of Al2O3. On the other hand, TiO2 has better compatibility with electrolytes containing LiPO2F2 (mainly due to band structure matching; the work function of TiO2 (around 4.2 eV) and the HOMO level of the electrolyte (1.2 V vs. Li) are similar). + The Li₂ / Li₂ form a 0.6 eV positive electric field, which can effectively drive the Li₂ / Li₂. + Directed migration (enhancing ion mobility) synergistically forms a stable LiF-rich CEI film. Regarding the thickness ratio of the two coating layers, an excessively high Al2O3 content leads to a surge in interfacial impedance; while a TiO2 content >40% results in decreased structural stability.

[0044] When an Al2O3 layer is used as the outer layer, the lack of catalytic sites leads to disordered growth of the passivation film, thickening of the CEI film, and increased ion diffusion resistance.

[0045] The innermost layer is an Al2O3 layer, primarily due to the high crystal plane compatibility and low mismatch between the Al2O3(001) and LiCoO2(003) layers, which facilitates the formation of a coherent interface and achieves a smooth transition. Furthermore, the Co-O-Al bonds formed at the interface exhibit high stability compared to Ti. 4+ Easily induces Co 3+ Disproportionation reaction occurs (2Co) 3+ → Co 2+ +Co 4+ This can lead to the segregation of interface elements and affect the stability of the overlay layer.

[0046] In some preferred embodiments, the alternating structural layers consist of alternating Al2O3 layers and TiO2 layers.

[0047] Secondly, this application provides a method for preparing the O2 phase lithium cobalt oxide cathode material described above, comprising the following steps: Obtain P2 phase Na x CoO2, x is 0.7~0.8; The P2 phase Na x CoO2 is uniformly mixed with a dopant source and sintered to obtain a precursor containing a first dopant element; the first dopant element includes Al, Mg, and Ti; in the precursor, the molar percentage of the first dopant element is 0.5~1.8 mol% The precursor and Li-containing + The molten salts were mixed evenly to obtain a first mixed solution, and the first mixed solution was subjected to an ion exchange reaction to obtain the O2 phase Li. y CoO2, where y is 0.990~1.01; the O2 phase Li yThe residual sodium content in CoO2 is ≤1500ppm; To the O2 phase Li y Al2O3 and TiO2 layers are sequentially deposited on CoO2 to form an alternating structure of Al2O3 and TiO2 layers, wherein the O2 phase Li y Radial cracks in CoO2 and surface deposition of a coating layer containing at least one alternating structural layer are used to obtain the O2 phase lithium cobalt oxide cathode material.

[0048] The method for preparing O2-phase lithium cobalt oxide cathode material provided in this application first obtains P2-phase Na... x CoO2, x is 0.7~0.8, then for P2 phase Na x CoO2 is doped to obtain a precursor containing doped elements, and then an ion exchange reaction is carried out to prepare O2-phase Li containing doped elements. y CoO2, finally in the O2 phase Li y The radial cracks and surface deposition of CoO2 include alternating layers of Al2O3 and TiO2, thus forming a structure in the O2 phase Li y A coating layer is formed on the CoO2 surface, and an Al2O3 layer is deposited on the side of the radial crack near the core center. The outermost layer of the coating layer is a TiO2 layer. The resulting O2-phase lithium cobalt oxide cathode material effectively mitigates electrolyte erosion, reduces transition metal dissolution, and improves battery cycle life during charge and discharge. The preparation method provided in this application is simple, requires low temperature, and reduces costs.

[0049] In some embodiments, in the precursor, the concentration of the first dopant element is distributed in a radial gradient, and the doping concentration of Al is 0.5~1.2 at%, with more than 80% of Al occupying Co sites; The Mg doping concentration is 0.3~0.8 at%, and more than 60% of the Mg occupies the O sites; The Ti doping concentration is 0.1~0.5 at%, with more than 60% of the Ti occupying O vacancies and the remainder occupying Co sites; The doping source includes a first nitrate and tetraethyl titanate, wherein the first nitrate includes aluminum nitrate and magnesium nitrate.

[0050] Specifically, in the precursor, the concentration of the first dopant element gradually increases radially from the inner layer to the outer layer, with the highest concentration in the outer layer and very low concentration in the inner layer; the dopant element Al accumulates inside the radial cracks and forms Al-O-Al bonds with the Al2O3 layer, enhancing the interfacial bonding between the coating layer and the core; Ti 4+ Doping-induced oxygen vacancies can improve the ionic conductivity of the TiO2 coating layer and reduce the EIS impedance.

[0051] The Al doping concentration is 0.5~1.2 at%, with over 80% of the Al occupying Co sites. 3+ High bond energy (512 kJ / mol) stabilizes the O-Co framework, improving the reversibility of sodium removal and thus suppressing lattice oxygen release. The Mg doping concentration is 0.3–0.8 at%, with over 60% of Mg occupying O sites. 2+ Increase interlayer spacing and reduce Na + The diffusion barrier can be reduced by Mg doping, which widens the sodium ion transport channel and increases the ion exchange rate. + A diffusion barrier of 0.15 eV increases the lithium-ion exchange rate. The Ti doping concentration is 0.1~0.5 at%, with over 60% of the Ti occupying O vacancies and the remainder occupying Co sites. 4+ / Ti 3+ Mixed valence states create electron hopping channels, enhancing electronic conductivity and improving the rate performance of the O2 phase LCO in the battery; in addition, Ti 4+ Doping-induced oxygen vacancies also help to improve the ionic conductivity of the TiO2 coating layer.

[0052] Through Al 3+ Its radial concentration gradient distribution from the inside out makes Al 3+ Al is mainly enriched in the particle surface region, fully utilizing its role in stabilizing the surface oxygen framework and inhibiting oxygen release and transition metal dissolution; while in the core lithium-ion diffusion channel region inside the particle, Al... 3+ The low concentration minimizes its impact on Li. + Migration hindrance. Synergistic effect with the coating layer: The Al-doped layer on the surface and the subsequently deposited Al2O3 coating layer can form Co-O-Al bonds, further enhancing the interfacial bonding force without affecting bulk ion migration.

[0053] Specifically, the doping concentration of Al can be 0.5at%, 0.7at%, 0.8at%, 1.0at%, 1.1at%, 1.2at%, etc. The doping concentration of Mg can be 0.3at%, 0.4at%, 0.5at%, 0.7at%, 0.8at%, etc. The doping concentration of Ti can be 0.1at%, 0.2at%, 0.3at%, 0.4at%, 0.5at%, etc.

[0054] The doping sources include nitrate methyl ether and tetraethyl titanate, where nitrate methyl ether comprises aluminum nitrate and magnesium nitrate. The selection of nitrate methyl ether and tetraethyl titanate as doping sources offers the following advantages: 1) Good chemical compatibility: Magnesium nitrate / aluminum nitrate decomposes at high temperature to generate MgO / Al2O3, which matches the CoO2 lattice (lattice mismatch <3%). Tetraethyl titanate hydrolyzes to generate TiO2, filling O vacancies. 2) Sulfate: Introduces sulfur impurities (SO4 detected by XPS).2- Residues (leading to electrolyte decomposition); Chlorides: releasing Cl at high temperatures. - Corrosion equipment. Selecting from the above categories eliminates other metal sources.

[0055] Calculate the occupation energy (ΔE) of the dopant element using DFT: ΔEMg-Co sites = -2.7 eV, ΔEAl-Na sites = -1.9 eV; ΔEMg-Co sites = -2.7 eV, ΔEAl-Na sites = -1.9 eV: Mg 2+ Priority occupation of Co 3+ Position (ionic radius matching), Al 3+ Occupy Na + Vacancies are created, forming a stable gradient doping structure.

[0056] Limited to the precursor, the molar percentage of the first dopant element is 0.5~1.8 mol%, which can effectively suppress oxygen vacancy generation and reduce particle cracking. If it is below 0.5 mol%, it cannot effectively suppress oxygen vacancy generation (DFT calculation shows that the oxygen vacancy formation energy is only increased by 0.3 eV); if it is above 1.8 mol%, exceeding this value will cause lattice distortion (XRD refinement shows that the c-axis shrinkage of the cell parameter is >1%), which will cause particle cracking.

[0057] In some embodiments, in the precursor, the gradient concentration distribution of each dopant element in the first dopant element satisfies: C(r) = 2.0 * [1 - (r / R)] 1.5 ]); Where r is the distance from the center of the precursor particle to the measurement point, in μm; 1.5 is an index; R is the radius of the precursor particle, in μm; C(r) represents the total concentration (at%) of the doped element at a distance r from the center of the sphere.

[0058] Specifically, 1.5 is an index that controls the “shape” or “steepness” of the change in the concentration of dopants.

[0059] (r / R) represents the "relative position". When r=0 (at the center), r / R=0; when r=R (on the surface), r / R=1.

[0060] The physical meaning of this formula is that it proves that the doping concentration (C) of the first doped element gradually increases from the particle center (r=0) to the surface (r=R).

[0061] In some embodiments, P2 phase Na is obtained x CoO2, with x being 0.7~0.8, includes the following steps: Cobalt nitrate and sodium nitrate solutions were mixed at a Na / Co molar ratio of 0.70-0.80, and a precipitant was added to carry out a co-precipitation reaction. After the precipitation reaction was completed, the mixture was spray-dried, and then sintered under an oxygen atmosphere to obtain the P2 phase Na. x CoO2, x is 0.7~0.8; The spray drying inlet temperature is 180~200℃, and the outlet temperature is 80-100℃; The precipitant includes at least one of NaOH and NH4HCO3; The pH value of the coprecipitation reaction system is 10.5-11.5.

[0062] Specifically, P2 phase Na was prepared using a co-precipitation reaction and spray drying method. x CoO2, x is 0.7~0.8. A precipitant is added to a cobalt nitrate and sodium nitrate solution, and the pH of the coprecipitation reaction system is limited to the range of 10.5-11.5. This allows the cobalt nitrate and sodium nitrate in the solution to react with the precipitant, ensuring complete precipitation of cobalt ions and obtaining P2 phase Na. x CoO2, x is a product of 0.7~0.8. If the pH value is less than 10.5, some cobalt ions will not precipitate completely, affecting the Na / Co molar ratio, and x will not be in the 0.7~0.8 range; if the pH value is greater than 11.5, although complete precipitation of cobalt can be guaranteed, excess OH- will result in... - This leads to the adsorption of a large amount of Na on the precursor surface. + This disrupts the crystal structure of sodium cobaltate.

[0063] P2 phase Na obtained after spray drying x CoO2, wall thickness ≤1μm, void ratio 15-20%.

[0064] In some embodiments, during the sintering step after spray drying in an oxygen atmosphere, the sintering temperature is 850~900℃ and the sintering time is 10~14h.

[0065] In some embodiments, the concentration of NaOH is 2 mol / L and the concentration of NH4HCO3 is 1 mol / L.

[0066] In some embodiments, the reaction temperature of the coprecipitation reaction is 70~90℃, and the reaction time of the coprecipitation reaction is 10~14h.

[0067] In some embodiments, the P2 phase Na x The process of uniformly mixing CoO2 with a dopant source and sintering it to obtain a precursor containing doped elements includes the following steps: mixing the P2 phase Na... xCoO2 is mixed with a dopant source and pulverized. The pulverized mixture is then subjected to a first sintering and a second sintering. After the second sintering, the precursor is obtained. The precursor has a D50 particle size of 4.0-9.0 μm and a specific surface area of ​​1.0-1.8 m². 2 / g, the intensity of the impurity phase peak in the XRD pattern is <3%, the half-width of the (002) crystal plane is ≤0.15°, and the surface roughness Ra is ≥1.0μm; the first sintering temperature is 700~800℃ and the first sintering time is 4~8h; the second sintering temperature is 850~900℃ and the second sintering time is 10~14h.

[0068] Specifically, the P2 phase Na x CoO2 is mixed with a dopant source and then pulverized. The pulverization method can be grinding, shearing, extrusion, impact, etc.

[0069] After being crushed, the material undergoes a first sintering process at a temperature lower than that of the second sintering process.

[0070] Both the first and second sintering were carried out in an oxygen atmosphere.

[0071] The formation of gradient doping is achieved through a two-step sintering process of low-temperature pre-sintering (i.e., the first sintering) + high-temperature diffusion (i.e., the second sintering). First, the dopant element is initially attached to the particle surface at a lower temperature, and then it is promoted to diffuse into the interior at a higher temperature, forming a gradient distribution with decreasing concentration from the surface to the interior.

[0072] When the temperatures and times for the first and second sinterings are within the aforementioned ranges, the first doping element can be incorporated into the P2 phase sodium cobaltate, improving crystallinity and structural order, reducing defect density, promoting particle densification, and increasing product purity, resulting in D50 particles with a diameter of 4.0-9.0 μm and a specific surface area of ​​1.0-1.8 m². 2 / g, precursor with impurity phase peak intensity <3% in XRD pattern, (002) crystal plane half peak width ≤0.15°, and surface roughness Ra≥1.0μm.

[0073] In some embodiments, the molar ratio of Li in the Li-containing molten salt to Co in the precursor is 0.990 to 1.01.

[0074] Specifically, limiting the molar ratio of Li in the Li-containing molten salt to Co in the precursor to the range of 0.990 to 1.01 is beneficial for preparing O2-phase Li. y CoO2, where y is 0.990~1.01.

[0075] In some embodiments, the Li-containing molten salt comprises a LiNO3-LiCl eutectic mixture.

[0076] Specifically, the molten salt containing Li is selected from the above types, which can undergo ion exchange reactions with the precursor without producing other impurities, thus improving the preparation efficiency.

[0077] In some embodiments, in the LiNO3-LiCl eutectic mixture, the molar ratio of LiNO3 to LiCl is (6~8):(4~2).

[0078] In some embodiments, the lithium-ion activity coefficient in the molten salt is >0.85.

[0079] Specifically, a precursor is first prepared, and then the precursor is subjected to an ion exchange reaction with a molten salt containing lithium ions. The activity coefficient of lithium ions in the molten salt is controlled to be >0.85, thereby achieving a sodium ion replacement rate of ≥96.5%.

[0080] In some embodiments, the O2 phase Li y The CoO2 particles have a plate-like structure with a thickness of 7.3~7.7 μm, an internal porosity of 5~8%, and lattice parameters a=2.82±0.02Å and c=14.6±0.1Å.

[0081] Specifically, the internal void ratio can be obtained using the BET method. The lattice parameters a and c can be obtained using XRD.

[0082] In some embodiments, the ion exchange reaction temperature is 260-300℃, and the ion exchange reaction time t satisfies Equation 2. Formula 2; Where R is the radius of the precursor, in μm. Deff = 1.0 × 10 -11 cm 2 / s; C Na,0 The initial concentration of sodium ions in the precursor at t=0, in at% (at%). C Na,t The concentration at of sodium ions remaining in the precursor at time t when the ion exchange reaction proceeds to time t is given.

[0083] Specifically, the ion exchange reaction time t is calculated using Equation 2, where R is the radius of the precursor in μm. For example, if the radius of the precursor particles is 3.75 μm, for C... Na,t The value can be set to a fixed value, based on the O2 phase Li y Given a residual sodium content of ≤1500ppm in CoO2, a C0 is set. Na,t Substituting the value of into Equation 2, and based on Equation 2, we can obtain the value of t.

[0084] In some embodiments, the O2 phase Li y Al2O3 and TiO2 layers are deposited sequentially on CoO2, with the deposition temperature ≤200℃.

[0085] Specifically, during high-temperature LCO coating, coating elements (such as Al) diffuse into the LCO matrix, forming harmful gradient doping. This application limits the deposition temperature to ≤200℃. This low deposition temperature avoids the possibility of coating elements diffusing into the matrix due to high-temperature coating (interfacial diffusion depth ≤2nm), effectively solving the problem of gradient doping caused by the diffusion of coating material into the bulk phase during high-temperature coating processes (>600℃), which damages the intrinsic structure of the O2 phase and reduces interfacial adhesion.

[0086] The dual control of deposition temperature and an outer TiO2 layer ensures that the element diffusion depth at the interface with the substrate is ≤2nm, thereby physically isolating Ti. 4+ Co 3+ Direct contact with Co at high temperatures is fundamentally avoided. 3+ The disproportionation reaction occurs, and the oxygen vacancies and mixed valence state characteristics of TiO2 are utilized to endow it with new functions such as improving interfacial ion / electron conduction and catalyzing the formation of a stable CEI film.

[0087] The method for preparing O2-phase lithium cobalt oxide cathode material provided in this application first obtains a precursor with a radial concentration gradient of doped elements from the inside to the outside, and then, at a deposition temperature ≤200℃, atomic layer deposition is used to deposit the O2-phase Li... y Radial cracks in CoO2 and surface deposition of a coating layer containing at least one alternating structural layer yield the O2-phase lithium cobalt oxide cathode material. The low deposition temperature avoids high-temperature thermal diffusion from the precursor surface, preventing the coating material from diffusing into the bulk phase, thus improving the structural stability and interfacial adhesion of the O2-phase lithium cobalt oxide cathode material. This effectively solves the problem of gradient doping caused by the diffusion of the coating material into the bulk phase during high-temperature coating processes (>600℃), which disrupts the intrinsic structure of the O2 phase and reduces interfacial adhesion. The preparation method provided in this application is simple, uses low temperatures, and reduces costs. The resulting O2-phase lithium cobalt oxide cathode material effectively mitigates electrolyte erosion during charge and discharge, reduces transition metal dissolution, and improves battery cycle life.

[0088] In specific embodiments, the deposition temperature can be 50, 80, 100, 110, 120, 130, 150, 160, 180, 200 or any range between the two.

[0089] In some preferred embodiments, the deposition temperature is 80~120°C.

[0090] The low deposition temperature effectively avoids high-temperature thermal diffusion from the precursor surface, preventing the coating material from diffusing into the bulk phase, further improving the structural stability of the O2 phase lithium cobalt oxide cathode material and enhancing interfacial adhesion. The even lower deposition temperature results in a shallower diffusion depth of elements into the matrix interface, effectively preventing the diffusion of Co at high temperatures. 3+ The occurrence of disproportionation reaction effectively enhances interfacial ion / electron conduction, which is beneficial for the catalytic formation of a stable CEI membrane.

[0091] It is understandable that the O2 phase Li y Al2O3 and TiO2 layers were deposited sequentially on CoO2 using ALD atomic deposition methods.

[0092] A "cycle" refers to a set of pulse-purge steps required to complete a single-layer deposition of an oxide (such as an Al2O3 layer or a TiO2 layer). An Al2O3 layer cycle includes a TMA pulse → N2 purge → H2O pulse → N2 purge. "Every 5 cycles" means that thickness monitoring is performed after every 5 such single-oxide deposition cycles. The termination condition for the aforementioned ALD atomic deposition is confirmed by in-situ ellipsometry thickness measurement every 5 cycles; a fluctuation of <0.02 nm / layer is considered a steady-state deposition.

[0093] Thirdly, this application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode material, the positive electrode material comprising the aforementioned O2 phase lithium cobalt oxide positive electrode material, or the O2 phase lithium cobalt oxide positive electrode material prepared by the aforementioned method for preparing the O2 phase lithium cobalt oxide positive electrode material.

[0094] The cathode sheet provided in this application contains O2 phase lithium cobalt oxide cathode material. The Al2O3 layer preferentially penetrates into the bottom of the crack to fill the uneven structure. The side of the coating layer away from the core is a TiO2 layer. The outermost TiO2 layer forms a continuous sealing film, which makes the coating layer and the substrate more tightly bonded, forming an "anchoring + sealing" composite structure. This reduces the infiltration of electrolyte into the radial crack, greatly reduces the risk of particle breakage, improves the structural stability of the cathode sheet, and improves the cycle performance and safety performance of the battery.

[0095] In some embodiments, the cathode material further includes O3 phase LiCoO2, wherein the O3 phase LiCoO2 comprises first particles with a D50 particle size of 16~20μm and second particles with a D50 particle size of 4~7μm, and the first particles account for 78~82% of the mass of the O3 phase LiCoO2; The D50 particle size of the O2 phase lithium cobalt oxide cathode material is 4.0~9.0μm; In the cathode material, the mass percentage of the O2 phase lithium cobalt oxide cathode material is 5-20%.

[0096] Specifically, if the D50 particle size of the O2 phase lithium cobalt oxide cathode material is <4.0 μm, agglomeration is aggravated; if it is >9.0 μm, filling failure occurs; in the cathode material, if the mass percentage of the O2 phase lithium cobalt oxide cathode material is >20%, cycle degradation is accelerated.

[0097] The D50 particle size of the O2 phase lithium cobalt oxide cathode material is in the range of 4.0 ~ 9.0 μm. In the cathode material, the mass ratio of the O2 phase lithium cobalt oxide cathode material is in the range of 5-20%. During the preparation of cathode slurry, it can be evenly dispersed and effectively fill the gaps between the O3 phase LiCoO2, ensuring the stability of the system compaction density and improving the cycle life and safety performance of the battery.

[0098] The positive electrode includes O3-phase LiCoO2, which comprises first particles with a D50 particle size of 16-20 μm and second particles with a D50 particle size of 4-7 μm. In the O3-phase LiCoO2, the first particles account for 78-82% of the mass. The small particles of the O2 phase fill the gaps between the large particles of the O3 phase, ensuring the stability of the system's compaction density or a certain degree of improvement, while also steadily improving the discharge specific capacity and energy density of the material system. In addition, the O2-phase lithium cobalt oxide positive electrode material can provide crystal structure support during the charging and discharging process, suppressing the H1-H3 phase transition in the O3-phase LiCoO2, thereby improving the structural stability of the system and further enhancing the cycle life and safety performance of the battery.

[0099] In some preferred embodiments, the D50 particle size of the second particle is (1.5~1.8):1 for the D50 particle size of the O2 phase lithium cobalt oxide cathode material.

[0100] The optimal void filling rate is achieved when the particle size ratio is 1.5-1.8. SEM-EDS verification shows that when the void ratio is <5%, the small particles of the O2 phase effectively fill the gaps between the large particles of the O3 phase, improving the structural stability of the system and further enhancing the cycle life and safety performance of the battery.

[0101] In some embodiments, the tap density of the cathode material is ≥3.8 g / cm³. 3 Compacted density ≥ 4.1 g / cm³ 3 .

[0102] Specifically, the tap density of the cathode material is ≥3.8 g / cm³. 3 Compacted density ≥ 4.1 g / cm³ 3 It is a mixed material containing O2 phase lithium cobalt oxide cathode material and O3 phase LiCoO2; it is used to prepare cathode sheets, and the resulting battery has high cathode sheet structural stability, longer cycle life, and better safety.

[0103] In some embodiments, the O3 phase LiCoO2 contains a second doping element, which includes Al and Mg; the molar percentage of the second doping element in the O3 phase LiCoO2 is 0.1-0.5 mol%. The surface of the O3 phase LiCoO2 is provided with a ZrO2 coating layer, the thickness of which is 2~3 nm.

[0104] Specifically, the surface of the O3 phase LiCoO2 is coated with a ZrO2 layer. The ZrO2 coating layer on the surface of the O3 phase LiCoO2 can be prepared by the sol-gel method.

[0105] The O3 phase LiCoO2 contains Al and Mg as second doping elements, which inhibit lattice expansion / collapse, reduce cobalt ion dissolution, reduce side reactions, and improve cycle performance. The surface is coated with a ZrO2 coating layer, which inhibits electrolyte oxidation and decomposition, improves lithium ion transport rate, and improves battery cycle performance. The battery's first discharge specific capacity is ≥185mAh / g (0.1C, 3.0-4.55V).

[0106] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active coating disposed on at least one surface of the positive current collector, wherein the thickness T of the positive active coating on one side satisfies Equation 3. T≥2.5×(D1+D2), where D1 is the D50 particle size of the first particle in μm; D2 is the D50 particle size of the O2 phase lithium cobalt oxide cathode material in μm; and T is in μm.

[0107] Specifically, the thickness T of the positive electrode active coating on one side is limited to satisfy Equation 3 to ensure a dual continuous ion / electron pathway, reduce DC impedance, and limit ion transport when the thickness is insufficient; the maximum thickness can be adjusted through conventional coating processes to meet battery design requirements.

[0108] The uniformity of particle distribution in the positive electrode can be characterized by the area ratio of the O2 phase in the SEM image of the electrode. When the coefficient of variation (CV) is ≤5%, it indicates a highly uniform distribution. CV (coefficient of variation) is the ratio of the standard deviation to the mean of the area ratio of the O2 phase in the SEM image of different regions of the electrode, that is, CV (coefficient of variation) = standard deviation / mean. The smaller the CV value, the more uniform the distribution.

[0109] In some embodiments, the areal density of the positive electrode is 145-200 mg / cm³. 2 .

[0110] Fourthly, this application provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps: uniformly mixing the positive electrode material, positive electrode conductive agent, positive electrode binder and solvent to obtain a positive electrode slurry, coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and drying to obtain the positive electrode sheet.

[0111] The mass ratio of the positive electrode material, positive electrode conductive agent, and positive electrode binder is (94~98):(1~3):(1~3).

[0112] Solvents include NMP.

[0113] Positive electrode conductive agents include SP, CNT, etc., and positive electrode binders include PVDF. Positive electrode conductive agents and positive electrode binders are commonly used in this field and are not limited here.

[0114] The positive electrode sheet is rolled, and the porosity of the rolled positive electrode sheet is 15-25%.

[0115] After the rolled positive electrode sheet was vacuum dried at 120℃ for 12 hours, the surface impedance was 0.2~5Ω·cm. 2 Among them, the surface impedance was measured directly using the dual-probe resistance method to measure the overall resistivity of the diaphragm.

[0116] Fifthly, this application provides a lithium-ion battery, including the positive electrode sheet described above.

[0117] The lithium-ion battery provided in this application includes a positive electrode sheet containing an O2 phase lithium cobalt oxide positive electrode material. An Al2O3 layer preferentially penetrates into the bottom of the crack to fill the uneven structure. The side of the coating layer away from the core is a TiO2 layer, which covers the outermost part of the core. The TiO2 layer covers the outermost part of the core to form a continuous sealing film, making the bonding between the coating layer and the substrate tighter and forming an "anchoring + sealing" composite structure. This structure is achieved through a rigid-flexible synergistic effect: the Al2O3 layer anchors the bottom of the crack to inhibit its propagation, and the TiO2 layer adapts to the volume changes during charging and discharging, maintaining the integrity of the seal. During charging and discharging, it effectively alleviates the erosion of the electrolyte, reduces the dissolution of transition metals, and improves the cycle life of the battery.

[0118] In some embodiments, the battery further includes an electrolyte comprising additives, the additives being ethylene sulfate and lithium difluorophosphate, wherein the ethylene sulfate content is 0.5-1% by mass and the lithium difluorophosphate content is 1-3% by mass.

[0119] Specifically, the mass content of the vinyl sulfate is 0.5-1%, and the mass content of the lithium difluorophosphate is in the range of 1-3%, utilizing the oxygen vacancies (concentration ≥10) on the (001) crystal plane of the outer TiO2 coating layer. 18 cm -3This method catalyzes the decomposition of lithium difluorophosphate (LiPO2F2) in the electrolyte, synergistically using vinyl sulfate (DTD) to capture HF, and generates a LiF-rich self-healing CEI film (LiF content ≥60%) in situ. This film is a self-healing interface film formed by the reaction of an electrolyte additive and a coating layer, which can inhibit the dissolution of transition metals under high voltage. The process is accelerated by a built-in electric field driven by the work function of TiO2 and the HOMO energy level difference (≥0.5 eV) of the electrolyte. Ultimately, this results in a capacity retention rate of 83% after 500 cycles at 4.6V high voltage, and reduces the electrode breakage rate to below 5%, solving the industrial challenge of achieving both high energy density and long lifespan.

[0120] 1.0 wt% LiPO2F2 ensures that oxygen vacancies on the TiO2 surface are fully utilized (per cm²). 2 Requires 1.2 × 10 16 (LiPO2F2 molecules). A LiPO2F2 content below 1% easily leads to incomplete catalysis, decreased CEI film coverage, and reduced LiF content, increasing interfacial impedance. When the LiPO2F2 content exceeds 3wt%, self-decomposition in the bulk electrolyte occurs, inducing gas production. 0.5wt% DTD is the minimum requirement for neutralizing HF in the electrolyte; insufficient DTD leads to residual HF corroding the CEI film. When DTD > 1wt%, excessive DTD reduction consumes active lithium, resulting in decreased initial efficiency, and simultaneously generates a lithium vinyl sulfate deposit layer that blocks Li⁺ migration channels.

[0121] In some preferred embodiments, the mass ratio of lithium difluorophosphate to vinyl sulfate is 2.5:0.8.

[0122] Specifically, when the mass ratio of lithium difluorophosphate to vinyl sulfate is 2.5:0.8, the CEI film growth rate and repair rate are in equilibrium, the thickness fluctuation measured by in-situ AFM is <1 nm / week, and the DTD hydrolysis products (ethylene hydroxysulfate) and Li x Co-deposition of PO₂F₂ enhances film toughness, with a nanoindentation modulus ≥8 GPa.

[0123] In some preferred embodiments, the mass content of lithium difluorophosphate is 1.5-2.5%.

[0124] Further limiting the lithium difluorophosphate content to 1.5~2.5% effectively suppresses the dissolution of transition metals under high voltage, thereby improving battery energy density and cycle life.

[0125] The lithium-ion battery provided in this application pioneers a three-level synergistic technology path of "crack-coating-electrolyte": First, an O2-phase lithium cobalt oxide cathode material with radial cracks is designed, and an Al2O3 and TiO2 composite layer is alternately deposited using a low-temperature ALD process at 200℃ or less to achieve conformal coating within the cracks (coverage ≥95%) and no elemental interpenetration at the interface (diffusion depth ≤2nm); Second, an Al / Mg / Ti gradient doping layer is constructed to form an "Al2O3-Ti-coating-electrolyte" composite layer. 3+ Oxygen framework-Mg 2+ Extended Layer - Ti 4+ / 3+ An electron channel "bulk stable network" is constructed; then, the oxygen vacancies on the (001) crystal plane of the outer TiO2 layer catalyze the decomposition of LiPO2F2 in the electrolyte, and HF is captured by DTD in situ, generating a LiF-rich self-healing CEI film (LiF content ≥60%). This process is accelerated by the built-in electric field driven by the work function of TiO2 and the HOMO energy level difference (≥0.5eV) of the electrolyte. Ultimately, the capacity retention rate reaches 83% after 500 cycles at a high voltage of 4.6V, and the electrode roll breakage rate is reduced to below 5%, solving the industrial problem of the incompatibility between high energy density and long life.

[0126] In some embodiments, the electrolyte further includes an organic solvent, including carbonate solvents.

[0127] Furthermore, carbonate solvents include at least one of fluoroethylene carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, dimethyl carbonate, and diethyl carbonate.

[0128] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, which includes a negative electrode active material, including at least one of silicon-carbon composite material and carbon material.

[0129] It should be noted that the negative electrode sheet in a lithium-ion battery can be prepared using existing technologies.

[0130] An embodiment of this application also provides an electrical device, including the lithium-ion battery described above.

[0131] For example, the aforementioned electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, and energy storage systems. More preferably, lithium-ion batteries are used in the manufacture of batteries for portable electronic devices with an operating voltage ≥4.5V, power batteries for drones, or energy storage batteries for medical devices.

[0132] The present invention will be further illustrated by the following examples.

[0133] Example 1 This embodiment is used to illustrate the O2 phase lithium cobalt oxide cathode material and its preparation method disclosed in this invention, as well as the lithium-ion battery.

[0134] 1. Preparation of O2 phase lithium cobalt oxide cathode material: S1: P2 phase Na 0.72 CoO2 preparation S11: Dissolve Co(NO3)2·6H2O and NaNO3 in deionized water at a Na / Co molar ratio of 0.72, control the pH at 11.0±0.2, and add a precipitant dropwise to carry out a coprecipitation reaction. The coprecipitation reaction temperature is 80℃, and the coprecipitation reaction time is 12h. The precipitant is a mixed solution of 2mol / L NaOH and 1mol / L NH4HCO3.

[0135] S12: Then, set the spray drying equipment parameters to an inlet temperature of 190℃ and an outlet temperature of 90℃, controlling the droplet size D32 = 25μm to obtain an intermediate product. Add the intermediate product to a muffle furnace, and heat the muffle furnace to 875℃ at a rate of 2℃ / min under an oxygen atmosphere, holding for 12 hours to obtain P2 phase Na. 0.72 The CoO2, D50 particle size is 8.5 μm, and its specific surface area is 1.3 m². 2 / g, XRD (002) peak half width 0.12°.

[0136] S2: Precursor Preparation S21: The P2 phase Na obtained in step S12 is... 0.72 CoO2, Mg(NO3)2, Al(NO3)3, and Ti(OC2H5)4 were ground and mixed evenly at a Mg:Al:Ti molar ratio of 2:1:0.3 to obtain a first mixture. The first mixture was added to a muffle furnace and sintered for the first time in an oxygen atmosphere at a temperature of 750℃ for 6 hours. After the first sintering, the temperature was increased to 875℃ at a rate of 2℃ / min for a second sintering for 12 hours. After the second sintering, the mixture was allowed to cool naturally to obtain the precursor.

[0137] In the precursor, the gradient concentration distribution of the first dopant element satisfies: C(r) = 2.0 * [1 - (r / R)] 1.5 ]).

[0138] In the precursor, the Al doping concentration is 1.0 at%, with more than 80% of the Al occupying Co sites; the Mg doping concentration is 0.5%, with more than 60% of the Mg occupying O sites; the Ti doping concentration is 0.3 at%, with more than 60% of the Ti occupying O vacancies, and the remaining Ti occupying Co sites.

[0139] The precursor has a D50 particle size of 8.5 μm and a specific surface area of ​​1.3 m². 2 / g, the intensity of the impurity phase peak in the XRD pattern is 1%, the half-peak width of the (002) crystal plane is 0.12°, and the surface roughness Ra≥1.0μm; S3: Preparation of O2 phase Li y CoO2, y=0.995 S31: The precursor obtained in step S21 and the Li-containing molten salt are mixed evenly at a Li / Co molar ratio of 0.995, and an ion exchange reaction is carried out at 280℃ for 7 hours to obtain the product, a gradient-doped O2 phase Li. y CoO2, y=0.995; ICP testing of the product showed that the residual sodium content of O2-LCO was 1100ppm (ICP-OES), XRD analysis showed lattice parameters a=2.82Å, c=14.6Å, and internal porosity of 6.5% (BET analysis). The Li-containing molten salt consisted of LiNO3 and LiCl in a mass ratio of 7:3.

[0140] The ion exchange reaction time mentioned above was calculated using Equation 2, where R is 4.3 μm and Deff = 1.0 × 10⁻⁶. -11 cm 2 / s;C Na,0 41.86 at%, C Na,t Given 0.15 at%, we calculate t = 7.2 h.

[0141] S4: Preparation of O2-phase lithium cobalt oxide cathode material S41: The O2 phase Li product obtained in step S3 is... y CoO2, y=0.995, was loaded into the ALD reaction chamber and pretreated under vacuum at 200℃ for 1 hour. This process was repeated for 8 cycles in the following manner.

[0142] First in O2 phase Li y Radial crack deposition of Al2O3 layer for CoO2 product: 3 cycles were performed (each cycle consisted of 0.2s TMA pulse → 10s N2 purging → 0.2s H2O pulse → 10s N2 purging (single layer thickness ≈ 0.13nm)). S42: Next, deposit a TiO2 layer on the surface of the Al2O3 layer: perform 2 cycles (each cycle consists of 0.4s TTIP pulse → 15s N2 purge → 0.2s H2O pulse → 15s N2 purge (single layer thickness ≈ 0.06nm)).

[0143] Following steps S41 and S42 above, in the O2 phase Li yRadial cracks and surface formation of CoO2 products consist of alternating Al2O3 and TiO2 layers. The deposition rate was monitored in real time using a quartz crystal microbalance (QCM).

[0144] The process is repeated 8 times according to steps S41 and S42 above, thereby achieving the desired effect in the O2 phase Li. y The radial cracks and surface of the CoO2 product are coated with at least one alternating structural layer, and the coating layer is far from the O2 phase Li. y One side of the CoO2 product is a TiO2 layer, resulting in the product O2 phase lithium cobalt oxide cathode material.

[0145] The total thickness δ of the coating layer is 4.08 nm.

[0146] The O2-phase lithium cobalt oxide cathode material prepared in step S4 was characterized by SEM. Specific test results are shown in [link to SEM]. Figure 1 It can be seen that the particles are spherical and thick, with the particle size mainly concentrated around 8.5 μm. High-magnification SEM images show that the surface roughness Ra of the particles is ≥1.0 μm, and a distinct uneven structure is visible. Figure 1 (The arrow in the image points to the direction of the image), providing a diffusion channel for molten salt ion exchange; at the same time, nanoparticles are uniformly attached to the particle surface, corresponding to the Al2O3 / TiO2 coating layer of the low-temperature interface zero-diffusion coating technology.

[0147] The O2-phase lithium cobalt oxide cathode material prepared in step S4 was characterized by cross-sectional SEM. Specific test results are shown in [link to SEM]. Figure 2 It can be seen that radial cracks exist inside the particles. Figure 2 (As indicated by the arrow in the image), the radial cracks are 0.8–1.0 μm long and 80–100 nm wide, and are mainly caused by ion exchange stress.

[0148] The O2-phase lithium cobalt oxide cathode material prepared in step S4 was characterized by XRD, and the results are as follows: Figure 3 It can be seen that the interlayer spacing of the characteristic peak (002) at 18.6° is 4.77, which is completely consistent with the O2 phase LiCoO2 standard card (ICDD 00-050-0653). The (103) peak at 2θ≈47.07° is also a key feature that distinguishes the O2 phase lithium cobalt oxide cathode material from the O3 phase LiCoO2 (the O3 phase here is the (104) / (105) overlapping peak). In addition, it can be seen that there are no impurities in the XRD pattern (peak intensity <1%), indicating that a pure phase O2 phase lithium cobalt oxide cathode material has been synthesized, and the ultrathin alternating coating layer does not affect the peak shape and peak position of the XRD diffraction peak.

[0149] The thickness δ1 of the coating layer on the outer surface of the core of the O2 phase lithium cobalt oxide cathode material prepared in step S4 was 3 ~ 5 nm, the depth d of the radial crack was 100 ~ 300 nm, and the vertical height difference between the outer surface of the coating layer and the bottom of the radial crack was H, where H = d + 2δ1 and H was 206 ~ 208 nm.

[0150] The maximum diffusion depth of elements in the O2 phase lithium cobalt oxide cathode material coating layer prepared in step S4 into the core was 2 nm. The thickness of the Al2O3 layer in each alternating structural layer was 0.39 nm, and the total thickness of the Al2O3 layers in the coating layer was 3.12 nm. The thickness of the TiO2 layer in each alternating structural layer was 0.12 nm, and the total thickness of the TiO2 layers in the coating layer was 0.96 nm. The thickness of the Al2O3 layer in each alternating structural layer accounted for 76.5% of the total thickness of that alternating structural layer (0.39 / (0.39+0.12) = 76.5%), and the thickness of the TiO2 layer in each alternating structural layer accounted for 23.5% of the total thickness of that alternating structural layer (0.12 / (0.39+0.12) = 23.5%).

[0151] Testing of O2-phase lithium cobalt oxide cathode materials, elements in the coating layer shift towards the core O2-phase Li y The diffusion depth of the CoO2 product is 1.5 nm, which satisfies the condition that the diffusion depth of elements in the coating layer to the core is ≤2 nm.

[0152] 2. Preparation of positive electrode sheet S51: The O2 phase lithium cobalt oxide cathode material prepared in step 1 is uniformly mixed with the traditional O3 phase LiCoO2 material at a mass ratio of 5%:95% as the cathode active material of the soft-pack battery. The materials are mixed evenly according to the mass ratio of cathode active material:PVDF:SP:CNT=96:2:1:1. Then, the solvent NMP is added and mixed evenly to obtain the cathode slurry. The solid content of the cathode slurry is 65%.

[0153] In the cathode material, the D50 particle size of the O2 phase lithium cobalt oxide cathode material is 8.5 μm; the O3 phase LiCoO2 material includes a first particle with a D50 of 18 μm and a second particle with a D50 of 5 μm, and the mass ratio of the first particle in the O3 phase LiCoO2 material is 80%.

[0154] In the cathode material, the O2 phase lithium cobalt oxide cathode material fills the gaps between the O3 phase LiCoO2 material, and the porosity is verified to be 3% using SEM-EDS. The overall tap density of the cathode material is 4.0 g / cm³. 3 The compacted density is 4.3 g / cm³. 3 S52: The above-mentioned positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil, dried, and a positive electrode active material layer is formed on the surface of the aluminum foil, wherein the surface density of the positive electrode active material layer on one side is 150 mg / cm³. 2 .

[0155] After coating, the electrode is rolled, and the porosity of the rolled electrode is 18%. The thickness T of the positive electrode active material layer on one side after rolling is 52.5 μm; where T satisfies Equation 3, T≥2.5×(D1+D2), where D1 is the D50 particle size of the first particle, in μm; and D2 is the D50 particle size of the O2 phase lithium cobalt oxide positive electrode material, in μm.

[0156] After rolling, the electrode was vacuum dried at 120℃ for 12 hours. The overall resistivity of the film was then directly measured using the dual-probe resistance method. The surface impedance of the electrode was 1.2 Ω·cm. 2 .

[0157] Before rolling after coating, the thickness of the positive electrode sheet is: 3. Preparation of negative electrode sheet S53: Mix the negative electrode active material, conductive agent, CMC and SBR in a mass ratio of 97:1:1:1, then add deionized water and stir evenly to obtain the negative electrode slurry.

[0158] The negative electrode active material is a mixture of SiOx:C = 10:90 by mass, where x is 1, and the specific capacity of the negative electrode active material is 600 mAh / g.

[0159] S54: Coat the negative electrode paste obtained in step S53 onto both sides of the copper foil, with a coating surface density of 60 mg / cm³. 2 The negative electrode sheet is obtained by drying, rolling, and slitting.

[0160] Battery manufacturing The positive electrode, separator, and negative electrode prepared above are wound sequentially into a battery cell. Pay attention to electrode alignment and tension control to prevent separator damage or internal short circuits. Baking is required after winding to set the shape. Place the wound battery cell in a soft-pack aluminum-plastic film housing and slowly and evenly inject the calculated amount of electrolyte. Ensure the electrolyte fully wets the electrodes and separator.

[0161] The electrolyte is 1.2 mol / L LiPF6, the solvent is FEC / EMC with a volume ratio of 3:7, and the additives are 2 wt% LiPO2F2 and 1 wt% DTD.

[0162] Example 2 This embodiment is the same as embodiment 1 in most steps, except that in step S41 the process is adjusted to obtain a total coating thickness δ of 3.0 nm, and the rest is the same as in embodiment 1.

[0163] Example 3 This embodiment is the same as embodiment 1 in most steps, except that in step S41 the process is adjusted to obtain a total coating thickness δ of 4.93 nm, and the rest is the same as in embodiment 1.

[0164] Example 4 This embodiment is the same as embodiment 1 in most steps, except that in step S41 the process is adjusted to obtain a total coating thickness δ of 2.5 nm, and the rest is the same as in embodiment 1.

[0165] Example 5 This embodiment is the same as embodiment 1 in most steps, except that in step S41 the process is adjusted to obtain a total coating thickness δ of 5.3 nm, and the rest is the same as in embodiment 1.

[0166] Example 6 This embodiment is largely the same as Embodiment 1, except that in step S4, the number of atomic layer deposition cycles is adjusted so that the Al2O3 layer accounts for 70% of the total thickness of each alternating structural layer, and the TiO2 layer accounts for 30% of the total thickness of the alternating structural layer. The rest is the same as in Embodiment 1. The Al2O3 layer accounts for 0.39 / (0.39+0.12) = 76.5% of the total thickness of the alternating structural layer, and the TiO2 layer accounts for 30% of the total thickness of each alternating structural layer. Example 7 This embodiment is the same as most of the steps in Embodiment 1. The difference is that in step S4, the number of atomic layer deposition cycles is adjusted so that the thickness of the Al2O3 layer in each alternating structure layer accounts for 80% of the total thickness of the alternating structure layer, and the thickness of the TiO2 layer accounts for 20% of the total thickness of the alternating structure layer. The rest is the same as in Embodiment 1.

[0167] Example 8 This embodiment is the same as most of the steps in Embodiment 1. The difference is that in step S4, the number of atomic layer deposition cycles is adjusted so that the thickness of the Al2O3 layer in each alternating structure layer accounts for 55% of the total thickness of the alternating structure layer, and the thickness of the TiO2 layer accounts for 45% of the total thickness of the alternating structure layer. The rest is the same as in Embodiment 1.

[0168] Example 9 This embodiment is similar to most of the steps in Embodiment 1, except that step S31 is different; an ion exchange reaction is carried out at 330°C to obtain a gradient-doped O2 phase Li product.y CoO2, y=0.995.

[0169] The results of ICP testing on the product showed that the residual sodium content of O2-LCO was 800 ppm (ICP-OES), the XRD test showed that the lattice parameters were a=2.82Å and c=14.6Å, and the internal porosity was 6.5% (obtained by BET test).

[0170] The ion exchange reaction time mentioned above was calculated using Equation 2, where R is 4.3 μm and Deff = 1.0 × 10⁻⁶. -11 cm 2 / s;C Na,0 It is 41.86 at%, C Na,t The value is 0.13 at%, and t is calculated to be 7.4 h. The rest is the same as in Example 1.

[0171] The O2 phase lithium cobalt oxide cathode material obtained in Example 9 has radial cracks with a length of 1.8-2.2 μm and a width of 100-120 nm.

[0172] Example 10 This embodiment is similar to most of the steps in Embodiment 1, except that step S31 is different; an ion exchange reaction is carried out at 300°C to obtain a gradient-doped O2 phase Li product. y CoO2, y=0.995.

[0173] The results of ICP testing on the product showed that the residual sodium content of O2-LCO was 900 ppm (ICP-OES), the XRD test showed that the lattice parameters were a=2.82Å and c=14.6Å, and the internal porosity was 6.5% (obtained by BET test).

[0174] The ion exchange reaction time mentioned above was calculated using Equation 2, where R is 4.3 μm and Deff = 1.0 × 10⁻⁶. -11 cm 2 / s;C Na,0 It is 41.86 at%, C Na,t The value is 0.23 at%, and t is calculated to be 6.7 h. The rest is the same as in Example 1.

[0175] The O2 phase lithium cobalt oxide cathode material obtained in Example 10 has radial cracks with a length of 0.8-1.0 μm and a width of 60-80 nm.

[0176] Example 11 This embodiment is similar to most of the steps in Embodiment 1, except that step S31 is different; an ion exchange reaction is carried out at 230°C to obtain a gradient-doped O2-phase Li product. y CoO2, y=0.995.

[0177] The results of ICP testing on the product showed that the residual sodium content of O2-LCO was 1200 ppm (ICP-OES), the XRD test showed that the lattice parameters were a=2.82Å and c=14.6Å, and the internal porosity was 6.5% (obtained by BET test).

[0178] The ion exchange reaction time mentioned above was calculated using Equation 2, where R is 4.3 μm and Deff = 1.0 × 10⁻⁶. -11 cm 2 / s;C Na,0 It is 41.86 at%, C Na,t The value was 0.15 at%, and t was calculated to be 7.2 h. The rest was the same as in Example 1.

[0179] The O2 phase lithium cobalt oxide cathode material obtained in Example 11 has radial cracks with a length of 0.3-0.5 μm and a width of 30-50 nm.

[0180] Example 12 This embodiment is the same as embodiment 1 in most steps, except that in step S41, the O2 phase Li product prepared in step S3 is... y CoO2, y=0.995, was loaded into the ALD reaction chamber and pretreated under vacuum at 180°C for 1 hour, otherwise the process was the same as in Example 1. The O2 phase lithium cobalt oxide cathode material was tested, and the elements in the coating layer shifted towards the core O2 phase Li. y The diffusion depth of CoO2 products is 1.0-1.5 nm.

[0181] Example 13 This embodiment is the same as embodiment 1 in most steps, except that in step S41, the O2 phase Li product prepared in step S3 is... y CoO2, y=0.995, was loaded into the ALD reaction chamber and pretreated under vacuum at 220°C for 1 hour, otherwise the same as in Example 1. The O2 phase lithium cobalt oxide cathode material was tested, and the elements in the coating layer shifted towards the core O2 phase Li. y The diffusion depth of CoO2 products is 3.0-4.0 nm.

[0182] Example 14 This embodiment is largely the same as Example 1, except that in the cathode preparation step, the mass percentage of the first particle in the O3 phase LiCoO2 material is 70%, while the rest is the same as in Example 1. In the cathode material, the O2 phase lithium cobalt oxide cathode material fills the gaps between the O3 phase LiCoO2 material, and the porosity is verified to be 8% using SEM-EDS.

[0183] Example 15 This embodiment is the same as Example 1 in most steps, except that in the battery preparation step, the electrolyte used contains 1% lithium difluorophosphate and 0.5% DTD (ethylene sulfate). The rest is the same as in Example 1.

[0184] Example 16 This embodiment is the same as embodiment 1 in most steps, except that in the battery preparation step, the electrolyte used contains 0.5% lithium difluorophosphate by mass. The rest is the same as in embodiment 1.

[0185] Example 17 This embodiment is the same as embodiment 1 in most steps, except that in the battery preparation step, the electrolyte used contains 3.5% lithium difluorophosphate by mass. The rest is the same as in embodiment 1.

[0186] Example 18 This embodiment is the same as embodiment 1 in most steps, except that in the battery preparation step, the DTD content in the electrolyte is 0.2% by mass. The rest is the same as in embodiment 1.

[0187] Example 19 This embodiment is the same as embodiment 1 in most steps, except that in the battery preparation step, the DTD content in the electrolyte is 1.2% by mass. The rest is the same as in embodiment 1.

[0188] Example 20 This embodiment is the same as most of the steps in Embodiment 1, except that in the step of preparing the positive electrode sheet, the thickness T of the positive electrode active material layer on one side after rolling is 40 μm; T does not satisfy Equation 3, T≥2.5×(D1+D2).

[0189] Example 21 This embodiment is largely the same as Embodiment 1, except that in the positive electrode preparation step, the O2 phase lithium cobalt oxide positive electrode material and the traditional O3 phase LiCoO2 material are uniformly mixed at a mass ratio of 20%:80% as the positive electrode active material for the pouch battery. The rest is the same as in Embodiment 1.

[0190] Example 22 This embodiment is largely the same as Embodiment 1, except that in the positive electrode preparation step, the O2 phase lithium cobalt oxide positive electrode material and the traditional O3 phase LiCoO2 material are uniformly mixed at a mass ratio of 22%:78% as the positive electrode active material for the pouch battery. The rest is the same as in Embodiment 1.

[0191] Example 23 This embodiment is largely the same as Example 1, except that after the ion exchange reaction in step S3, the obtained O2-phase LiyCoO2 product is subjected to high-temperature heat treatment, annealing at 500°C for 2 hours, resulting in a certain degree of particle fusion and growth. The D50 particle size of the obtained O2-phase lithium cobalt oxide cathode material is greater than 9 μm. Laser particle size analyzer test results show that the D50 particle size of the obtained O2-phase lithium cobalt oxide cathode material is 22 μm. The rest is the same as in Example 1.

[0192] Example 24 This embodiment is the same as most of the steps in Embodiment 1, except that in step S21, the first mixture does not contain Ti(OC2H5)4, the Mg:Al molar ratio is 2:1, and the rest is the same as in Embodiment 1.

[0193] Example 25 This embodiment is the same as most of the steps in Embodiment 1, except that in step S21, the first mixture does not contain Mg(NO3)2, the Al:Ti molar ratio is 1:0.3, and the rest is the same as in Embodiment 1.

[0194] Comparative Example 1 This comparative example is similar to Example 1 in most steps, except that in step S21, the first mixture does not contain Mg(NO3)2, Ti(OC2H5)4, or P2 phase Na. 0.72 The molar ratio of CoO2 to Al(NO3)3 was 1:0.015; the mixture was ball-milled in ethanol for 2 hours (replacing the dry mixing method used in Example 1 for gradient doping) to ensure uniform elemental distribution. The first mixture was then placed in a muffle furnace and rapidly heated (10°C / min) to 800°C and held for 6 hours. After cooling, a homogeneous doped body was obtained.

[0195] Step S4 differs from step S4, where the ALD coating process involves depositing only an Al2O3 layer at 250°C (40 cycles) with a pulse duration of 0.2 s, i.e., in the O2 phase Li y The radial cracks and surface of CoO2 with y=0.995 are coated with an Al2O3 layer, without an alternating structure layer composed of Al2O3 and TiO2 layers.

[0196] Comparative Example 2 In this comparative example, step S4 was omitted from the preparation of the cathode material; the O2-phase Li obtained in step S3 was used directly. y CoO2, y=0.995 material is mixed with O3 phase LiCoO2 material as the positive electrode material, and the rest is the same as in Example 1.

[0197] Comparative Example 3 This comparative example is the same as Example 1 in most steps, except that in step S4, the O2 phase Li is first introduced into the O2 phase in the same manner as in Example 1. y A TiO2 layer is deposited within the radial crack of the CoO2 product, followed by an Al2O3 layer, forming a structural layer composed of TiO2 and Al2O3 layers, resulting in product O2-phase lithium cobalt oxide cathode material 1. In O2-phase lithium cobalt oxide cathode material 1, the innermost layer of its coating is TiO2, and the outermost layer is Al2O3. The rest is the same as in Example 1. "Innermost" refers to the bottom side of the radial crack. "Outermost" refers to the coating layer furthest from the O2-phase Li. y One side of the CoO2 product.

[0198] Comparative Example 4 This comparative example is largely the same as Example 1, except that in step S4, the final TiO2 layer deposition is not performed, resulting in product O2 phase lithium cobalt oxide cathode material 2. Specifically, in the coating layer of O2 phase lithium cobalt oxide cathode material 2, both the innermost and outermost layers are Al2O3 layers. The rest is the same as in Example 1. "Innermost" refers to the side at the bottom of the radial crack. "Outermost" refers to the coating layer furthest from the O2 phase Li. y One side of the CoO2 product.

[0199] Performance testing I. The following performance tests were performed on the cathode materials and batteries obtained in the above embodiments and comparative examples: 1. Using the O2-phase lithium cobalt oxide cathode material prepared in Example 1 as the cathode, a coin cell was assembled with lithium foil and a separator. The discharge specific capacity was tested at 0.1C and 3.0-4.6V, showing a specific capacity of 224 mAh / g, an initial coulombic efficiency of 96.1%, and a discharge voltage plateau of 3.96V. The charge-discharge curves of the O2-phase lithium cobalt oxide cathode material are shown below. Figure 5 The XRD pattern of the O2 phase lithium cobalt oxide cathode material is shown below. Figure 4 .

[0200] 2. The soft-pack battery prepared in Example 1 was subjected to charge-discharge tests in a voltage range of 3.0-4.55V. The discharge specific capacity at 0.2C rate was 187.17mAh / g, the coulombic efficiency of the first charge-discharge was 91.2%, and the capacity retention rate was 86.17% after 300 cycles at 45℃@1C.

[0201] 3. Loop testing method: High-temperature cycling performance: The batteries prepared in the examples and comparative examples were charged at 45°C with the following steps: ① charged at a constant current of 1C to 4.55V, with a cutoff current of 0.05C; ② discharged at a constant current of 1C to 3.0V. These steps were repeated for 300 cycles. The discharge capacity and battery thickness of the first cycle and the discharge capacity and battery thickness of the 300th cycle were recorded. The cycle capacity retention rate and thickness expansion rate were calculated. Three batteries were tested for each example.

[0202] Cyclic life test The batteries prepared in the examples and comparative examples were charged to 4.55V at 25°C using a constant current of 1C, and then discharged to 3.0V using a constant current of 1C. The cycle was repeated until the cycle capacity retention rate was less than 80%, and the number of cycles was recorded.

[0203] 4. Energy density test: The battery was charged to 4.55 V at a constant current of 0.7C, with a cutoff current of 0.05C, and then discharged to 3.0 V at a rate of 0.2C. The discharge capacity and voltage plateau data were recorded. The mass energy density of the battery was obtained using the formula: mass energy density = discharge capacity * voltage plateau / cell mass.

[0204] The test results are shown in Table 1.

[0205] Table 1 Continued from Table 1-1 As shown in Table 1, comparing Examples 1-3 and Examples 4-5, the total thickness δ of the coating layer in Example 4 is less than 3 nm, resulting in low high-temperature cycle capacity retention, high thickness expansion rate, and low cycle life. In Example 5, the total thickness δ of the coating layer is greater than 5 nm, resulting in low high-temperature cycle capacity retention, high thickness expansion rate, and low cycle life. It is speculated that if the coating layer thickness is too low, the sealing of radial cracks will fail. If the coating layer thickness is too high, the battery impedance will increase, affecting battery performance. This indicates that if the total thickness δ of the coating layer satisfies 3 nm ≤ δ ≤ 5 nm, it can completely cover the radial cracks, achieve high coverage, maintain the sealing integrity of the radial cracks, and at the same time, the low impedance of the O2 phase lithium cobalt oxide cathode material improves the high-temperature cycle performance and cycle life of the battery. Comparing Examples 1 and 6 with Examples 7 and 8, in Example 7, the thickness of the Al2O3 layer is greater than 60-80%, and the thickness of the TiO2 layer is less than 20-40%. In Example 8, the thickness of the Al2O3 layer is less than 60-80%, and the thickness of the TiO2 layer is greater than 20-40%. The battery exhibits poor high-temperature cycling performance and low cycle life. This indicates that in each of the alternating structural layers, the thickness of the Al2O3 layer accounts for 60%-80% of the total thickness of the alternating structural layer, and the thickness of the TiO2 layer accounts for 20%-40% of the total thickness of the alternating structural layer. This is beneficial for forming an interpenetrating network structure of continuous Al2O3 phase (mechanical support) + TiO2 penetration channels (ion conduction), forming a stable protective layer while improving the lithium-ion diffusion rate and improving the battery's cycle performance. Comparing Examples 1 and 10 with Examples 9 and 11, the ion exchange temperature in Example 9 was in the range of 260-300℃. This excessively high temperature resulted in excessive ion exchange stress, leading to cracks with a length greater than 1 μm and a width greater than 100 nm. In Example 11, the ion exchange temperature was less than 260-300℃, which was too low, resulting in incomplete ion exchange (residual sodium content reached its upper limit), and the cracks were too shallow and narrow, with a width less than 50 nm, potentially affecting the lithium-ion diffusion channel. This indicates that an ion exchange reaction temperature within the range of 260-300℃ is beneficial for obtaining O2-phase lithium cobalt oxide cathode materials with radial crack lengths ≤1 μm and widths of 50-100 nm, thus improving battery performance.

[0206] Comparing Examples 1, 12, and 13, the deposition temperature in Example 13 was greater than 200°C, and the elements in the coating layer shifted towards the core O2 phase Li. y The diffusion depth of CoO2 products is greater than 2nm, and the battery Ti... 4+ Co 3+ Interdiffusion can occur, potentially inducing disproportionation reactions, leading to decreased interfacial stability and accelerated cycle capacity decay. This indicates that at deposition temperatures ≤200℃, elements in the coating layer migrate to the core O2 phase Li. y The diffusion depth of CoO2 products is ≤2nm, thus physically isolating Ti.4+ Co 3+ Direct contact with Co at high temperatures is fundamentally avoided. 3+ The disproportionation reaction occurs, and the oxygen vacancies and mixed valence state characteristics of TiO2 are utilized to endow it with new functions such as improving interfacial ion / electron conduction and catalyzing the formation of a stable CEI film, thereby improving the battery cycle performance. Comparing Example 1 and Example 14, the mass ratio of the first particle in the O3 phase LiCoO2 material in Example 14 is less than 78-82%, and the insufficient proportion of large particles leads to poor particle gradation. Too many small particles cannot effectively fill the gaps between large particles, resulting in increased electrode porosity and decreased compaction density, which in turn affects the battery cycle performance. This indicates that the mass ratio of the first particle in the O3 phase LiCoO2 material is in the range of 78-82%, and the small particles of the O2 phase fill the gaps between the large particles of the O3 phase, improving the battery cycle performance. Comparing Examples 1 and 15 with Examples 16 and 17, and Examples 1 with Examples 18 and 19, it is shown that the mass content of ethylene sulfate is 0.5-1%, and the mass content of lithium difluorophosphate is in the range of 1-3%. The oxygen vacancies (concentration ≥10) on the (001) crystal plane of the outer TiO2 coating layer are utilized. 18 cm -3 It catalyzes the decomposition of lithium difluorophosphate (LiPO2F2) in the electrolyte, and synergistically captures HF with ethylene sulfate (DTD), generating a LiF-rich self-healing CEI film (LiF content ≥60%) in situ. This can inhibit the dissolution of transition metals under high voltage, improve the cycle performance of the battery, and reduce gas production.

[0207] Comparing Examples 1 and 20, the thickness T of the single-sided positive electrode active material layer after rolling does not satisfy Equation 3, T≥2.5×(D1+D2). The coating thickness is insufficient, resulting in an overly thin active material layer. This restricts ion transport paths, significantly increases DC impedance (DCIR), reduces battery cycle capacity retention, and decreases cycle life. This indicates that the thickness T of the single-sided positive electrode active coating must satisfy Equation 3 to ensure a continuous ion / electron pathway, reduce DC impedance, and improve battery cycle performance. Comparing Examples 1, 21, and 22, it is shown that an O2 phase content in the range of 5~20% is beneficial for uniform dispersion and effectively fills the gaps between the O3 phase LiCoO2, improving battery cycle life. Comparing Examples 1 and 23, the added O2-phase lithium cobalt oxide cathode material with a D50 particle size greater than 4.0~9.0 μm resulted in a decrease in battery energy density, a reduction in high-temperature cycle capacity retention, an increase in expansion rate, and a decrease in cycle life. This indicates that the D50 particle size of the O2-phase lithium cobalt oxide cathode material within the range of 4.0~9.0 μm effectively fills the gaps between the O3-phase LiCoO2, improving the battery's cycle life and cycle performance. Comparing Examples 1 and 24-25, the obtained O2-phase lithium cobalt oxide cathode material did not simultaneously contain Al, Mg, and Ti, resulting in a slightly lower battery cycle life and slightly lower energy density. This indicates that the O2-phase lithium cobalt oxide cathode material simultaneously contains Al, Mg, and Ti doping elements, and the Al2O3 layer filling the bottom of the radial cracks interacts with the O2-phase Li... y CoO2 forms Co-O-Al bonds, and Ti-O bonds form on the outermost part of the core. The interfacial bonding force is a double chemical bond of Co-O-Al bonds (inner layer) and Ti-O bonds (outer layer). The alternating structural layers cover the inside of the crack, forming an alternating Al / Ti distribution, which completely covers the crack surface, achieves high coverage, reduces electrolyte immersion into radial cracks, greatly reduces the risk of particle breakage, and improves battery cycle performance.

[0208] Comparing Example 1 with Comparative Examples 1-4, in Comparative Example 1, the O2 phase Li y Radial cracks with CoO2 and y=0.995 were coated with an Al2O3 layer, as shown in Comparative Example 2, where the O2 phase Li... yCoO2 does not contain alternating layers composed of Al2O3 and TiO2 layers. In Comparative Example 3, the innermost layer of its coating is TiO2, and the outermost layer is Al2O3. Although Comparative Example 4 contains a titanium dioxide layer, the innermost and outermost layers of the coating of the O2 phase lithium cobalt oxide cathode material 2 are both Al2O3. The batteries in Comparative Examples 1-4 all have low high-temperature cycle capacity retention, high high-temperature cycle thickness expansion, and low room-temperature cycle life, indicating that the Al2O3 layer is filled in the outermost layer of the coating. On the side of the crack closer to the core center, the Al2O3 layer preferentially penetrates into the bottom of the crack to fill the uneven structure. On the side of the coating layer away from the core, there is a TiO2 layer. The outermost TiO2 layer forms a continuous sealing film, making the bonding between the coating layer and the substrate tighter, forming an "anchoring + sealing" composite structure. The Al2O3 layer anchors the bottom of the crack to inhibit its propagation, while the TiO2 layer adapts to the volume changes during charging and discharging, maintaining the integrity of the seal. Thus, it effectively alleviates the erosion of the electrolyte during charging and discharging, reduces the dissolution of transition metals, and improves the cycle life of the battery.

[0209] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this application generally indicates that the preceding and following related objects have an "and" relationship. The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An O2-phase lithium cobalt oxide cathode material, characterized in that, It includes a core and a coating layer, wherein the core is an O2 phase Li with radial cracks. y CoO2, where y is 0.990~1.01; The coating layer covers the outer surface of the core, and the coating layer fills and covers radial cracks on the surface of the core; The coating layer includes at least one alternating structure layer, which includes an Al2O3 layer and a TiO2 layer, filling the coating layer of the radial crack. The side of the coating layer closer to the core center is the Al2O3 layer, and the side of the coating layer away from the core is the TiO2 layer. The core contains a first doping element, which includes Al, Mg and Ti, and the concentration of the first doping element gradually increases radially from the inner layer to the outer layer. The total thickness of the coating layer is δ, where δ = δ1 + δ2, 3nm ≤ δ ≤ 5nm, and 3nm ≤ δ1 ≤ 5nm. Wherein, δ2 is the thickness of the coating layer in the radial crack, in nm; δ1 is the thickness of the coating layer on the outer surface of the core, in nm; The radial crack has a length ≤1μm and a width of 50~100nm; In each of the alternating structural layers, the thickness of the Al2O3 layer accounts for 60% to 80% of the total thickness of the alternating structural layer, and the thickness of the TiO2 layer accounts for 20% to 40% of the total thickness of the alternating structural layer.

2. The O2-phase lithium cobalt oxide cathode material according to claim 1, characterized in that, The vertical height difference between the outer surface of the coating layer and the bottom of the radial crack is H. H satisfies equation 1. H = d + 2δ1, Equation 1, and 100nm ≤ d ≤ 300nm; Where d is the depth of the radial crack, in nm.

3. The O2-phase lithium cobalt oxide cathode material according to claim 1, characterized in that, The diffusion depth of the elements in the coating layer into the core is ≤2nm.

4. The O2-phase lithium cobalt oxide cathode material according to claim 1, characterized in that, In each of the alternating structural layers, the ratio of the thickness of the Al2O3 layer to the thickness of the TiO2 layer is (2~3):

1.

5. A method for preparing the O2 phase lithium cobalt oxide cathode material according to any one of claims 1-4, characterized in that, Includes the following steps: Obtain P2 phase Na x CoO2, x is 0.7~0.8; The P2 phase Na x CoO2 is uniformly mixed with a dopant source and sintered to obtain a precursor containing a first dopant element; the first dopant element includes Al, Mg, and Ti; in the precursor, the molar percentage of the first dopant element is 0.5~1.8 mol% The precursor and Li-containing + The molten salts were mixed evenly to obtain a first mixed solution, and the first mixed solution was subjected to an ion exchange reaction to obtain the O2 phase Li. y CoO2, where y is 0.990~1.01; the O2 phase Li y The residual sodium content in CoO2 is ≤1500ppm; To the O2 phase Li y Al2O3 and TiO2 layers are sequentially deposited on CoO2 to form an alternating structure of Al2O3 and TiO2 layers, wherein the O2 phase Li y The radial cracks of CoO2 and the surface deposition of a coating layer with at least one alternating structural layer are used to obtain the O2 phase lithium cobalt oxide cathode material.

6. The method for preparing the O2 phase lithium cobalt oxide cathode material according to claim 5, characterized in that, The molar ratio of Li to Co in the precursor in the Li-containing molten salt is 0.990~1.01; The O2 phase Li y The CoO2 particles have a plate-like structure with a thickness of 7.3~7.7 μm, an internal porosity of 5~8%, and lattice parameters a=2.82±0.02Å and c=14.6±0.1Å. The ion exchange reaction temperature is 260-300℃, and the ion exchange reaction time t satisfies Equation 2. Formula 2; Where R is the radius of the precursor, in μm. Deff=1.0×10 -11 cm 2 / s; C Na,0 The initial concentration of sodium ions in the precursor at t=0, in at% (at%). C Na,t The concentration at of sodium ions remaining in the precursor at time t when the ion exchange reaction proceeds to time t is given.

7. A positive electrode plate, characterized in that, The positive electrode sheet includes the O2 phase lithium cobalt oxide positive electrode material according to any one of claims 1-4, or the O2 phase lithium cobalt oxide positive electrode material prepared by the preparation method of the O2 phase lithium cobalt oxide positive electrode material according to any one of claims 5 or 6.

8. The positive electrode sheet according to claim 7, characterized in that, The cathode material also includes O3 phase LiCoO2, which comprises first particles with a D50 particle size of 16~20μm and second particles with a D50 particle size of 4~7μm. In the O3 phase LiCoO2, the mass percentage of the first particles is 78~82%. The D50 particle size of the O2 phase lithium cobalt oxide cathode material is 4.0 ~ 9.0 μm; In the cathode material, the mass percentage of the O2 phase lithium cobalt oxide cathode material is 5-20%.

9. The positive electrode sheet according to claim 8, characterized in that, The positive electrode sheet includes a positive current collector and a positive active coating disposed on at least one side of the surface of the positive current collector, wherein the thickness T of the positive active coating on one side satisfies Equation 3. T≥2.5×(D1+D2), Where D1 is the D50 particle size of the first particle, in μm; D2 is the D50 particle size of the O2 phase lithium cobalt oxide cathode material, in μm; The unit of T is μm.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 7-9.

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