Trace O3-phase lithium cobalt oxide coated O2-phase lithium cobalt oxide positive electrode material as well as preparation and application thereof

Abstract

The invention relates to a trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide positive electrode material as well as preparation and application thereof. The chemical formula of the lithium cobalt oxide positive electrode material is Li Na Co < 1-c > M < c > O < 2 >. N < LiCo < 1-c > M < c > O < 2 >, wherein 0 < = a < = 0.8, 0 < = b < = 0.1, 0 < = c < = 0.1, N is a molar ratio of an O3 phase to an O2 phase, and 0 < N < = 0.05; m comprises at least one of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd or Ti; wherein the lithium cobalt oxide positive electrode material has XRD diffraction characteristic peaks at the same time when 2 [theta] A1 is equal to 18.3 to 18.8 degrees, 2 [theta] A2 is equal to 37.9 to 38.4 degrees, 2 [theta] A3 is equal to 46.7 to 47.3 degrees and 2 [theta] B1 is equal to 18.9 to 19.3 degrees. The surface lithiation of the limited lithium source is combined with the topological phase change, and a trace O3 phase micro-configuration structure is constructed on the surface of the O2 phase lithium cobalt oxide positive electrode material in situ, so that the lithium cobalt oxide positive electrode material keeps high specific capacity, and meanwhile, the structural stability is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of cathode materials technology for new energy batteries, and in particular to a trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material, its preparation and application. Background Technology

[0002] Lithium cobalt oxide (LiCoO2) has a high compaction density (≈4.2 g / cm³). -3 With its high volumetric energy density and mature manufacturing process, lithium cobalt oxide remains an irreplaceable cathode material in the 3C consumer electronics field. However, the actual reversible capacity of existing O3-phase lithium cobalt oxide is only approximately 150 mAh / g. -1 (4.2V vs. Li) + / Li), corresponding to approximately 0.55 mol of Li. + De-intercalation, far below the theoretical capacity of 274 mAh g -1 While further increasing the charging cutoff voltage (≥4.5V) can release more capacity, under high voltage conditions, the O2p orbitals of lattice oxygen participate in the oxidation reaction, inducing an irreversible phase transition from the O3 phase to the O1 phase in the layered structure, leading to abrupt changes in cell volume and grain cracking. Additionally, highly reactive Co... 4+ Side reactions with the electrolyte can lead to cobalt dissolution, significantly increasing the risk of thermal runaway.

[0003] In recent years, O2-phase LiCoO2 (ABBA oxygen stacking) has been observed to maintain its layered framework at 4.6V and achieve a reversible capacity of up to 220 mAh g⁻¹ due to its unique lithium layer slip mechanism. -1 The above. However, the O2 phase is metastable and has the following main problems: (1) poor interface stability: under high voltage, the covalentity of Co–O bonds is enhanced, the energy barrier for surface oxygen vacancy migration is reduced, resulting in lattice oxygen loss, etc.; (2) high surface residual alkali: Li2CO3 / LiOH is easily left on the particle surface, and the reaction with electrolytes will aggravate battery gas production; (3) complicated synthesis process: high temperature solid phase and ion exchange or topological lithiation are required, which is complicated and costly. At present, the improvement of O2 phase lithium cobalt oxide mainly includes optimizing the preparation process to obtain pure phase O2 lithium cobalt oxide, or combining O2 phase lithium cobalt oxide and O3 phase lithium cobalt oxide to improve structural stability, etc. However, the existing technical methods are still difficult to fully utilize the high specific capacity and other characteristics of O2 phase lithium cobalt oxide while ensuring its stability.

[0004] In summary, existing O2 phase lithium cobalt oxide cathode materials still suffer from defects such as interface stability and limited specific capacity improvement, making it difficult to meet the industry's demand for high specific capacity and high safety batteries. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a trace O3-phase lithium cobalt oxide coated O2-phase lithium cobalt oxide cathode material, its preparation, and its application. This invention utilizes surface lithiation combined with topological phase transitions from a limited lithium source to induce an in-situ trace O3-phase lithium cobalt oxide coating structure on the surface of the O2-phase lithium cobalt oxide cathode material, thereby significantly improving the structural stability of the lithium cobalt oxide cathode material while maintaining high specific capacity. To achieve the above objectives, in a first aspect, the present invention provides a trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material, wherein the chemical formula of the lithium cobalt oxide cathode material is: Li a Na b Co 1-c M c O2·NLiCo 1-c M c O2; where 0≤a≤0.8, 0≤b≤0.1, 0≤c≤0.1, N is the molar ratio of O3 phase to O2 phase, 0<N≤0.05; M includes at least one of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd or Ti; Among them, the lithium cobalt oxide cathode material is at 2θ A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 =18.9-19.3° and XRD diffraction characteristic peaks are present.

[0006] Preferably, the lithium cobalt oxide cathode material is at 2θ B1 The absolute value of the peak intensity I of the diffraction characteristic peak at the location B1 With N, k×I B1 =11335N-33; where k is a correction coefficient, 0.9≤k≤1.1.

[0007] Preferably, in the lithium cobalt oxide cathode material, the trace O3 phase lithium cobalt oxide coating layer is generated in situ through induction. The thickness i of the trace O3 phase lithium cobalt oxide coating layer satisfies 50nm≤i≤500nm.

[0008] Preferably, the lithium cobalt oxide cathode material is a micron-sized primary particle with a median particle size D50 of 4-12 μm; more preferably 6-9 μm; and / or, The specific surface area of ​​the lithium cobalt oxide cathode material is 0.2-0.8 m². 2 / g; preferably 0.3-0.6 m 2 / g; and / or, The compaction density of the lithium cobalt oxide cathode material is 2-6 g / cm³.3 Preferably 3-5 g / cm³ 3 ; and / or, The residual alkali content on the surface of the lithium cobalt oxide cathode material is 0.05-0.5 wt%; preferably 0.1-0.3 wt%; and / or, The free sodium content in the lithium cobalt oxide cathode material is 0.01-0.2 wt%; preferably 0.05-0.1 wt%.

[0009] In a second aspect, embodiments of the present invention provide a method for preparing the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material described in the first aspect above, the preparation method comprising: After mixing the cobalt source, sodium source and M source, the mixture is subjected to a first high-temperature calcination at above 700°C to obtain the P2 phase sodium cobalt oxide intermediate. According to the set Li / Co molar ratio, the P2 phase sodium cobalt oxide intermediate is mixed with the first lithium compound and then subjected to a second high-temperature calcination at above 700°C, so that the surface of the P2 phase sodium cobalt oxide intermediate undergoes an in-situ reaction under limited lithium source conditions to generate trace amounts of O3 phase lithium cobalt oxide, thereby obtaining a P2 phase sodium cobalt oxide intermediate with trace amounts of O3 phase lithium cobalt oxide on the surface. According to the set Li / Na molar ratio, the P2 phase sodium cobalt oxide intermediate coated with trace O3 phase lithium cobalt oxide on the surface is mixed with the second lithium compound to construct an ion exchange reaction environment rich in lithium ions, and a mixture is obtained. The mixture was subjected to low-temperature calcination at below 300°C, causing the bulk phase of the P2 phase sodium cobalt oxide intermediate to undergo Na+ oxidative stress under the influence of lithium-ion chemical potential. + / Li + Ion exchange completes the topological phase transition from the P2 phase to the O2 phase. At the same time, the trace O3 phase lithium cobalt oxide retains its original structure and does not undergo a topological transformation, resulting in the trace O3 phase lithium cobalt oxide coated with the O2 phase lithium cobalt oxide cathode material.

[0010] Preferably, after the low-temperature calcination treatment, the method further includes: The product after the low-temperature calcination treatment is washed and dried to obtain the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material.

[0011] Preferably, the molar ratio of the cobalt source, sodium source, and M source used to prepare the P2 phase sodium cobaltate intermediate satisfies: 0.5 ≤ n(Na) / n(Co) ≤ 1.0, preferably 0.6 ≤ n(Na) / n(Co) ≤ 0.9; n(M) / n(Co) = 0.003-0.06; wherein M includes at least one of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd, or Ti; The set Li / Co molar ratio n(Li) / n(Co) satisfies: 0 < n(Li) / n(Co) ≤ 0.05; preferably 0.01 ≤ n(Li) / n(Co) ≤ 0.04; wherein the first lithium compound includes one or more of lithium hydroxide, lithium carbonate, lithium chloride, lithium iodide, lithium fluoride, lithium bromide or lithium phosphate; preferably lithium carbonate; The set Li / Na molar ratio n(Li) / n(Na) satisfies: n(Li) / n(Na)≥1.5; preferably n(Li) / n(Na)≥2; wherein the second lithium compound includes one or more of lithium nitrate, lithium hydroxide, lithium chloride, lithium bromide, lithium iodide, lithium hypochlorite or lithium perchlorate; preferably lithium nitrate.

[0012] Preferably, the temperature of the first high-temperature calcination is 700-1000℃, more preferably 800-900℃, and the sintering time is 6-15h, more preferably 8-12h; preferably, the first high-temperature calcination is carried out in an oxygen atmosphere with an oxygen concentration ≥90%. The second high-temperature calcination is carried out at a temperature of 700-1000℃, preferably 800-900℃, and the sintering time is 1-10 hours, preferably 2-8 hours; preferably, the second high-temperature calcination is carried out in an oxygen atmosphere with an oxygen concentration ≥90%. The temperature of the low-temperature calcination treatment is T≥240℃, preferably T≥260℃, and the time of the low-temperature calcination treatment is t≥2h, preferably t≥4h.

[0013] Thirdly, embodiments of the present invention provide an energy storage device, including any one of a lithium battery, a battery cell, or a battery pack; The energy storage device includes the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material described in the first aspect above, or the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material prepared by the preparation method described in the second aspect above.

[0014] The trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material provided in this embodiment of the invention a Na b Co 1-c M c O2·NLiCo1-c M c Compared to existing O2 phase lithium cobalt oxide materials, O2 suppresses the irreversible phase transition of O2 phase lithium cobalt oxide under high voltage, as well as problems such as lattice oxygen evolution and Co dissolution, by coating the surface with trace amounts of O3 phase lithium cobalt oxide. It also improves ion transport performance, enhances interface stability, and exhibits high specific capacity and high cycle stability.

[0015] Specifically, this invention forms an O3 phase microstructure in situ on the surface of an O2 phase lithium cobalt oxide substrate, enabling the epitaxial growth of a trace O3 phase lithium cobalt oxide coating layer on the surface of O2-type lithium cobalt oxide particles, thereby effectively suppressing the phase transition process from the O2 phase to the O1 phase. The trace O3 phase lithium cobalt oxide coating layer forms a coherent interface with the O2 phase substrate, exerting an interfacial pinning effect on lithium layer slippage, which can significantly reduce the lattice shear stress generated during high-voltage charging and discharging.

[0016] Meanwhile, the surface of the O3 phase coating layer is rich in oxygen vacancy structures, which can buffer and constrain the redox activity of lattice oxygen at the interface. That is, it can inhibit the migration of lattice oxygen redox activity to the surface, thereby reducing the tendency of lattice oxygen to migrate to the surface and undergo irreversible precipitation. In addition, since the O3 phase coating layer and the O2 phase matrix both belong to the lithium cobalt oxide system, their lattice matching degree is high, which can effectively avoid the ion transport obstacles introduced by heterogeneous coating materials (such as Al2O3 or other fast ion conductors), making lithium ion transport more continuous and smooth.

[0017] Furthermore, the introduction of a trace O3 phase lithium cobalt oxide coating can reduce the side reactions between alkaline impurities such as residual lithium carbonate on the surface of O2 phase lithium cobalt oxide and HF in the electrolyte, and inhibit the formation of lithium fluoride deposition, thereby further improving the stability of the electrode / electrolyte interface.

[0018] The lithium-ion battery obtained by coating the O2 phase lithium cobalt oxide cathode material with trace O3 phase lithium cobalt oxide according to the present invention has a specific capacity of ≥254mAh / g at 0.1C, ≥249mAh / g at 0.5C, and ≥247mAh / g at 1.0C; the capacity retention rate after 50 cycles at 1.0C is ≥93%, exhibiting excellent high specific capacity and high cycle stability. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation method of trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material of the present invention; Figure 3 This is a scanning electron microscope (SEM) image of the lithium cobalt oxide cathode material prepared in Example 1 of the present invention; Figure 4The X-ray diffraction (XRD) spectra of the lithium cobalt oxide cathode materials prepared in Examples 2 and 3 and Comparative Example 1 of this invention are shown below. Figure 5 The initial charge-discharge curves of the coin cells assembled in Embodiment 2 and Comparative Example 1 of the present invention at 0.1C are shown. Figure 6 The specific capacity of the coin cells assembled in Embodiment 2 and Comparative Example 1 of the present invention after 50 cycles at 1.0C; Figure 7 The capacity retention rate of the coin cells assembled in Example 2 and Comparative Example 1 of this invention after 50 cycles at 1.0C. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] This invention provides a trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material. The chemical formula is: Li a Na b Co 1-c M c O2·NLiCo 1-c M c O2; Li a Na b Co 1-c M c O2 is the chemical structural formula of the O2 phase lithium cobalt oxide matrix, LiCo 1-c M c O2 is the structural formula of the O3 phase lithium cobalt oxide coating layer. Wherein, 0≤a≤0.8, 0≤b≤0.1, 0≤c≤0.1, N is the molar ratio of O3 phase to O2 phase, 0<N≤0.05; M includes at least one of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd or Ti.

[0022] Lithium cobalt oxide cathode material at 2θ A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°. Among them, 2θ A1 2θ A2 2θ A3 The peaks are typical characteristic of the O2 phase lithium cobalt oxide structure, 2θ B1These are typical characteristic peaks of the O3 phase lithium cobalt oxide structure. The lithium cobalt oxide cathode material of the present invention exhibits XRD diffraction characteristic peaks at the above positions, indicating that the main structure of the material is O2-configured lithium cobalt oxide with a P63mc structure, while also containing trace amounts of O3-configured lithium cobalt oxide.

[0023] O2-phase lithium cobalt oxide possesses a unique lithium layer slip mechanism, maintaining its layered framework even above 4.6V, thus preserving higher capacity. The trace O3-phase lithium cobalt oxide coating layer forms a coherent interface with the O2-phase matrix, exerting an interfacial pinning effect on lithium layer slip. In other words, the O3-phase coating layer and the O2-phase matrix are latticeally continuous at the atomic scale. When the lithium layer inside the O2 phase tends to slip relative to the matrix under high voltage, the surface O3 phase, due to its structural stability, acts as a boundary constraint on this slip, thereby suppressing overall lithium layer dislocation, reducing lattice shear stress, inhibiting the diffusion of lattice oxygen oxidation-reduction to the surface, and reducing capacity decay during cycling.

[0024] Furthermore, lithium cobalt oxide cathode materials at 2θ B1 The absolute value of the peak intensity I of the diffraction characteristic peak at the location B1 With N, k×I B1 =11335N-33; where k is a correction coefficient, 0.9≤k≤1.1. The more O3 phases, the higher the 2θ. B1 The stronger the peak intensity of the diffraction characteristic peaks, the better. This invention achieves surface lithiation using a limited lithium source by limiting the molar ratio N of the O3 phase to the O2 phase to the range of 0 < N ≤ 0.05, effectively forming a trace O3-type lithium cobalt oxide coating layer with a moderate thickness i on the surface of the cathode material. The O3-phase lithium cobalt oxide coating layer and the O2-phase lithium cobalt oxide matrix can work synergistically to ensure the normal operation of the high specific capacity of the lithium cobalt oxide cathode material, while significantly improving the cycle performance of the cathode material; that is, while improving the cycle performance of the cathode material, it hardly affects the capacity performance.

[0025] This invention obtains a trace O3 phase lithium cobalt oxide coating layer in situ induced on the surface of O2 phase lithium cobalt oxide. In situ induction means that this invention does not require the additional introduction of the O3 phase; rather, a trace amount of O3 phase lithium cobalt oxide is generated on the surface of the O2 phase lithium cobalt oxide during its synthesis process without disrupting the main O2 phase structure. The thickness i of the trace O3 phase lithium cobalt oxide coating layer satisfies: 50nm ≤ i ≤ 500nm, and can be any value within the above range, such as 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, 500nm, but is not limited to these values.

[0026] The lithium cobalt oxide cathode material has a near-single-crystal morphology composed of primary particles, with a median particle size D50 of 4-12 μm, preferably 6-9 μm; it can be any value within the above range, such as 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, but is not limited to these. The median particle size is obtained by laser particle size analyzer.

[0027] The specific surface area of ​​lithium cobalt oxide cathode materials is 0.2-0.8 m². 2 / g; preferably 0.3-0.6 m 2 / g; can be any value within the above range, such as 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7 m 2 g, 0.8 m 2 / g, but not limited to this. Specific surface area is obtained by a specific surface area analyzer.

[0028] The compaction density of lithium cobalt oxide cathode material is 2-6 g / cm³. 3 Preferably 3-5 g / cm³ 3 It can be any value within the above range, such as 2g / cm³. 3 3g / cm 3 4g / cm 3 5g / cm 3 6g / cm 3 However, it is not limited to this. The compaction density is obtained by testing with a fully automated compaction density analyzer using the gas displacement method.

[0029] The residual alkali content on the surface of the lithium cobalt oxide cathode material is 0.05-0.5 wt%; preferably 0.1-0.3 wt%; it can be any value within the above range, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, but is not limited thereto. The residual alkali is determined by potentiometric titration.

[0030] In the lithium cobalt oxide cathode material, the free sodium content is 0.01-0.2 wt%; preferably 0.05-0.1 wt%; it can be any value within the above range, such as 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.2%, but is not limited thereto. The free sodium content is determined by potentiometric titration.

[0031] The trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material provided in this embodiment of the invention a Na b Co 1-c M c O2·NLiCo 1-c M cCompared to existing O2 phase lithium cobalt oxide materials, O2 suppresses the irreversible phase transition of O2 phase lithium cobalt oxide under high voltage, as well as problems such as lattice oxygen evolution and Co dissolution, by coating the surface with trace amounts of O3 phase lithium cobalt oxide. It also improves ion transport performance, enhances interface stability, and exhibits high specific capacity and high cycle stability.

[0032] Specifically, this invention forms an O3 phase microstructure in situ on the surface of an O2 phase lithium cobalt oxide substrate, enabling the epitaxial growth of a trace O3 phase lithium cobalt oxide coating layer on the surface of O2-type lithium cobalt oxide particles, thereby effectively suppressing the phase transition process from the O2 phase to the O1 phase. The trace O3 phase lithium cobalt oxide coating layer forms a coherent interface with the O2 phase substrate, exerting an interfacial pinning effect on lithium layer slippage, which can significantly reduce the lattice shear stress generated during high-voltage charging and discharging.

[0033] Meanwhile, the surface of the O3 phase coating layer is rich in oxygen vacancy structures, which can buffer and constrain the redox activity of lattice oxygen at the interface. That is, it can inhibit the migration of lattice oxygen redox activity to the surface, thereby reducing the tendency of lattice oxygen to migrate to the surface and undergo irreversible precipitation. In addition, since the O3 phase coating layer and the O2 phase matrix both belong to the lithium cobalt oxide system, their lattice matching degree is high, which can effectively avoid the ion transport obstacles introduced by heterogeneous coating materials (such as Al2O3 or other fast ion conductors), making lithium ion transport more continuous and smooth.

[0034] Furthermore, the introduction of a trace O3 phase lithium cobalt oxide coating can reduce the side reactions between alkaline impurities such as residual lithium carbonate on the surface of O2 phase lithium cobalt oxide and HF in the electrolyte, and inhibit the formation of lithium fluoride deposition, thereby further improving the stability of the electrode / electrolyte interface.

[0035] The trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material of the present invention can be prepared by the following preparation method.

[0036] In the preparation embodiments of this invention, unless specific experimental steps or conditions are specified, the procedures or conditions described in conventional experimental procedures in the literature of this art can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0037] The specific preparation method and steps are as follows: Figure 1 As shown, it includes: Step 110: After mixing the cobalt source, sodium source and M source, the mixture is subjected to a first high-temperature calcination at a temperature above 700°C to obtain the P2 phase sodium cobalt oxide intermediate.

[0038] The cobalt source includes any one or more of cobalt oxides, cobalt hydroxides, and cobalt salts; for example, it includes one or more selected from Co3O4, CoCO3, and Co(OH)2. Alternatively, it can be a doped cobalt source, such as any one or more of M-doped cobalt oxides, cobalt hydroxides, and cobalt salts. M includes one or more of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd, or Ti, but is not limited thereto.

[0039] The sodium source can be any one or more of sodium oxides, sodium hydroxides, and sodium salts, such as one or more selected from Na2O, NaOH, Na2CO3, NaHCO3, and NaCl, but is not limited thereto.

[0040] In the lithium cobalt oxide cathode material of the present invention, M can be derived from a doping element in the precursor (such as a cobalt source), that is, introduced during the preparation of the precursor, or the M source can be introduced during the synthesis of the cathode material. The M source includes, but is not limited to, at least one of the oxides, hydroxides, fluorides, inorganic salts, and organic salts containing Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd, or Ti.

[0041] The molar ratio of cobalt source to sodium source satisfies: 0.5 ≤ n(Na) / n(Co) ≤ 1.0, preferably 0.6 ≤ n(Na) / n(Co) ≤ 0.9; it can be any value within the above range, including but not limited to 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, but is not limited thereto. When the initial feed range of sodium cobaltate material is large, the pure phase sodium cobaltate material is ultimately formed with a fixed stoichiometric ratio (e.g., x = 0.67, 0.83). By limiting the molar ratio of sodium and cobalt in the precursor, it can be ensured that the P2 phase pure phase sodium cobaltate is fully generated after the first high-temperature calcination.

[0042] The molar amount M satisfies n(M) / n(Co) = 0.003-0.06, and can be any value within the above range, including but not limited to 0.003, 0.005, 0.008, 0.01, 0.015, 0.02, 0.025, 0.03, 0.04, 0.05, and 0.06.

[0043] When each precursor of lithium cobalt oxide cathode material meets the range of the above-mentioned parameters, the precursor has high reactivity. When used to prepare lithium cobalt oxide cathode material, it has excellent ion diffusion performance, which can ensure the synthesis of cathode material with high purity.

[0044] The temperature of the first high-temperature calcination is 700-1000℃, preferably 800-900℃, but can be any value within the above range, such as 700℃, 800℃, 900℃, or 1000℃, but is not limited to these values. The sintering time is 6-15 hours, preferably 8-12 hours; it can be any value within the above range, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours, but is not limited to these values. Preferably, the first high-temperature calcination is carried out in an oxygen atmosphere with an oxygen concentration ≥90%.

[0045] The present invention performs high-temperature calcination under the above conditions, which enables the obtained material particles to be uniform in size and round, providing favorable conditions for subsequent ion exchange.

[0046] Step 120: According to the set Li / Co molar ratio, the P2 phase sodium cobalt oxide intermediate is mixed with the first lithium compound and then subjected to a second high-temperature calcination at above 700°C. This causes the surface of the P2 phase sodium cobalt oxide intermediate to undergo an in-situ reaction under limited lithium source conditions, generating trace amounts of O3 phase lithium cobalt oxide, thereby obtaining a P2 phase sodium cobalt oxide intermediate with trace amounts of O3 phase lithium cobalt oxide on its surface.

[0047] Specifically, the Li / Co molar ratio satisfies: 0 < n(Li) / n(Co) ≤ 0.05, preferably 0.01 ≤ n(Li) / n(Co) ≤ 0.4; it can be any value within the above range, such as 0.01, 0.02, 0.03, 0.04, 0.05, but is not limited to this.

[0048] The first lithium compound is selected from one or more of lithium hydroxide, lithium carbonate, lithium chloride, lithium iodide, lithium fluoride, lithium bromide, and lithium phosphate, preferably lithium carbonate. The first lithium compound provides a lithium source for the formation of trace O3 phase lithium cobalt oxide. When the amount of the first lithium compound added meets the above-mentioned range, a trace O3 phase lithium cobalt oxide coating layer of appropriate thickness can be induced in situ.

[0049] The second high-temperature calcination temperature is 700-1000℃, preferably 800-900℃, but can be any value within the above range, such as 700℃, 800℃, 900℃, or 1000℃, but is not limited to these values. The sintering time is 1-10 hours, preferably 2-8 hours, but can be any value within the above range, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, but is not limited to these values. Furthermore, the calcination is carried out in an oxygen atmosphere with an oxygen concentration ≥90%.

[0050] Under the aforementioned conditions, the present invention performs a secondary high-temperature calcination treatment, enabling the rapid and stable formation of an O3-type lithium cobalt oxide coating layer on the surface of the Na intermediate. Due to the limitation of the Li / Co molar ratio, and constrained by both kinetic diffusion and thermodynamic stability, lithium preferentially distributes on the surface of the P2-phase sodium cobalt oxide intermediate, inducing an in-situ reaction of the surface P2-phase sodium cobalt oxide to generate trace amounts of O3-phase lithium cobalt oxide.

[0051] Specifically, during the second high-temperature calcination process, by strictly controlling the amount of the first lithium compound added, the Li / Co molar ratio was kept significantly lower than the stoichiometric ratio required for the formation of bulk lithium cobalt oxide. This resulted in the lithium introduction process being simultaneously constrained by limited lithium supply, limited diffusion kinetics, and the thermodynamic stability of the intermediate structure. Specifically, under the condition of a low Li / Co molar ratio, the total amount of lithium available for reaction in the system was only sufficient for localized reactions on the surface of the P2-phase sodium cobalt oxide intermediate particles, making it difficult to support deep diffusion of lithium into the bulk phase and overall lithiation. Simultaneously, the P2-phase sodium cobalt oxide intermediate has a dense layered structure, requiring lithium ions to overcome interlayer barriers and be accompanied by Na+ diffusion from the surface into the bulk phase. + The migration and expulsion of lithium cobalt oxide (LCO) is significantly slower than the in-situ surface reaction process. Under high-temperature, oxygen-rich atmospheres, lithium preferentially undergoes local structural rearrangement with the CoO2 layer on the intermediate surface, generating a more thermodynamically stable O3-type LCO configuration in situ without initiating a bulk topological phase transition. Simultaneously, due to the high structural stability of the bulk P2-phase sodium cobalt oxide within this temperature range, and because bulk lithiation requires interlayer slip and stacking reconstruction, it does not possess a thermodynamic advantage under low lithium chemical potential conditions. Therefore, lithium is preferentially consumed on the particle surface during the reaction, forming only a trace O3-phase LCO coating layer on the surface, while the intermediate bulk phase retains the P2-type LCO structure. Through this mechanism, the present invention achieves the in-situ generation of trace O3-type LCO on the surface of the P2-type LCO intermediate without the need for additional coating processes, providing a stable surface microstructure basis for subsequent topological phase transitions and ion exchange processes.

[0052] Step 130: According to the set Li / Na molar ratio, the P2 phase sodium cobalt oxide intermediate coated with trace amounts of O3 phase lithium cobalt oxide is mixed with the second lithium compound to construct an ion exchange reaction environment rich in lithium ions, and a mixture is obtained.

[0053] Specifically, the Li / Na molar ratio is n(Li) / n(Na) ≥ 1.5, preferably n(Li) / n(Na) ≥ 2, and can be any value within the above range, such as 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., but is not limited to these. There is no upper limit to the Li / Na molar ratio in this step; its purpose is to ensure the smooth progress of subsequent ion exchange. The Li / Na molar ratio in this step directly affects the driving force and extent of the subsequent ion exchange reaction. A higher Li / Na molar ratio can increase the chemical potential of lithium ions in the system, thereby promoting the Na+ exchange. + Migration to the molten salt phase and acceleration of Na in the solid phase + / Li + The exchange process allows ion exchange to be completed at relatively low temperatures or in short processing times.

[0054] The second lithium compound may be selected from one or more of lithium nitrate, lithium hydroxide, lithium chloride, lithium bromide, lithium iodide, lithium hypochlorite, and lithium perchlorate, with lithium nitrate being preferred.

[0055] Step 140: The mixture is subjected to low-temperature calcination treatment below 300°C, so that the bulk phase of the P2 phase sodium cobalt oxide intermediate undergoes Na2 oxidation under the driving force of lithium-ion chemical potential. + / Li + Ion exchange completes the topological phase transition from the P2 phase to the O2 phase. At the same time, the trace O3 phase lithium cobalt oxide retains its original structure and does not undergo a topological transformation, resulting in a trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material.

[0056] Specifically, the temperature of the low-temperature calcination treatment is T ≥ 240℃, preferably T ≥ 260℃, but can be any value within the above range, such as 240℃, 250℃, 260℃, 270℃, 280℃, but is not limited to this. The time of the low-temperature calcination treatment is t ≥ 2h, preferably t ≥ 4h, such as 2h, 3h, 4h, 5h, 6h, but is not limited to this.

[0057] During low-temperature ion exchange, trace amounts of O3-phase lithium cobalt oxide maintain their original configuration without participating in topological transformations due to their high structural stability in a lithium-ion molten salt environment. Simultaneously, the bulk phase of the P2-phase sodium cobalt oxide intermediate undergoes Na+ transformation driven by the lithium-ion chemical potential. + / Li + Exchange, Na + / Li +Ion exchange occurs in the bulk phase via interlayer diffusion and defect / interface channels, achieving a topological phase transition from a P2 to an O2 configuration. Simultaneously, since the outer O3 phase lithium cobalt oxide is present in trace amounts, it does not constitute a barrier layer for ion exchange and does not hinder the ion exchange process in the bulk phase. Furthermore, the O3 phase lithium cobalt oxide is structurally locked on its surface and does not participate in the topological transition. Therefore, the low-temperature sintering process in this step allows the P2 phase in the bulk phase to complete its own topological phase transition under the premise that the O3 phase lithium cobalt oxide is structurally locked, ultimately obtaining a composite structure in which trace O3 phase lithium cobalt oxide coats O2 phase lithium cobalt oxide.

[0058] Preferably, after the low-temperature calcination treatment, the product after the low-temperature calcination treatment can be washed and dried to obtain the final trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material.

[0059] Specifically, the washing cycle is ≥3 times, preferably 5 times; drying can be done using vacuum drying at a temperature of 60-150℃, preferably 80-130℃.

[0060] This invention employs a preparation process of "surface lithiation via a limited lithium source + topological phase transition" to construct a trace O3 phase lithium cobalt oxide coating layer in situ on the surface of an O2 phase lithium cobalt oxide cathode material. By introducing an appropriate amount of a first lithium compound and inducing a surface lithiation reaction through high-temperature calcination, a trace O3 phase lithium cobalt oxide structure is formed on the surface of a P2 phase sodium cobalt oxide intermediate. Subsequently, a low-temperature ion exchange treatment is performed on this surface-lithiated intermediate to transform the main structure into an O2 configuration lithium cobalt oxide, thereby obtaining a cathode material with trace O3 phase lithium cobalt oxide coating an O2 phase lithium cobalt oxide layer. Its structure is as follows: Figure 2 As shown.

[0061] In the cathode material obtained by the above process, a coherent interface is formed between the O3 phase coating layer and the O2 phase bulk. This interface effectively alleviates lattice shear stress through the lithium layer slip mechanism, inhibits the migration of lattice oxygen redox activity to the material surface, and reduces capacity decay caused by structural instability during cycling. Simultaneously, the introduction of trace amounts of O3 phase stabilizes the surface microstructure of the O2 phase lithium cobalt oxide, thereby significantly improving the structural stability and cycling performance of the material under high voltage conditions while maintaining high specific capacity.

[0062] The trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material proposed in this invention can be used as the positive electrode active material in positive electrode sheets and in energy storage devices. Energy storage devices can include any of the following: lithium batteries, battery cells, or battery packs.

[0063] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0064] The following examples illustrate the preparation process and characteristics of the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material of the present invention. Where specific experimental steps or conditions are not specified in the examples, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products.

[0065] Example 1 The chemical formula of the lithium cobalt oxide cathode material provided in this embodiment is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2·0.01LiCo 0.971 Al 0.029 O2, prepared as follows: Step 1) Mix cobalt oxide, sodium carbonate, and aluminum oxide uniformly in a molar ratio of n(Co):n(Na):n(Al) = 0.986:0.7:0.014 to obtain a mixture; Step 2) The mixture is subjected to a first high-temperature calcination, with the heating rate controlled at 5℃ / min. Under an oxygen atmosphere, it is calcined at 900℃ for 10h to obtain the P2 phase sodium cobalt oxide intermediate. Step 3) Weigh lithium carbonate according to n(Li) / n(Co)=0.01, and mix it evenly with the P2 phase sodium cobalt oxide intermediate obtained in Step 2) to obtain a mixture; Step 4) The mixture is subjected to a second high-temperature calcination, with the heating rate controlled at 5℃ / min. Under an oxygen atmosphere, it is calcined at 900℃ for 4h to obtain a P2 phase sodium cobalt oxide intermediate with trace amounts of O3 phase lithium cobalt oxide on the surface. Step 5) Weigh lithium nitrate according to n(Li) / n(Na)=2 and mix it uniformly with the P2 phase sodium cobalt oxide intermediate with trace O3 phase lithium cobalt oxide surface obtained in Step 4); Step 6) The mixed material is calcined at 260℃ for 4 hours to remove Na. + / Li + Ion exchange yields the ion-exchange products. Step 7) The ion-exchange product is washed five times and dried to obtain trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material. It is denoted as LCO-1.

[0066] Figure 3 This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 1 of the present invention. Figure 3 As shown, a small number of tiny particles are uniformly distributed on the surface of the lithium cobalt oxide cathode material, forming a microstructure that is tracely coated on the substrate surface.

[0067] XRD tests show that the lithium cobalt oxide cathode material of Example 1 exhibits high performance at 2θ. A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°, and at 2θ B1 absolute value of peak intensity I of diffraction characteristic peak at location B1 The following relationship exists between k and N: B1 =11335N-33, where k is 0.91.

[0068] Example 2 The chemical formula of the lithium cobalt oxide cathode material provided in this embodiment is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2·0.02LiCo 0.971 Al 0.029 O2, the preparation process is as follows: Steps 1)-2) are the same as in Example 1; Step 3) Weigh lithium carbonate according to n(Li) / n(Co)=0.02, and mix it evenly with the P2 phase sodium cobalt oxide intermediate obtained in Step 2) to obtain a mixture; Steps 4)-7) are the same as in Example 1.

[0069] like Figure 4 As shown, XRD tests indicate that the lithium cobalt oxide cathode material (denoted as LCO-2) of Example 2 exhibits good performance at 2θ. A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°, and at 2θ B1 absolute value of peak intensity I of diffraction characteristic peak at location B1 The following relationship exists between k and N: B1 =11335N-33, where k is 1.05.

[0070] Example 3 The chemical formula of the lithium cobalt oxide cathode material provided in this embodiment is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2·0.04LiCo 0.971 Al 0.029 O2, prepared as follows: Steps 1)-2) are the same as in Example 1; Step 3) Weigh out lithium carbonate according to n(Li) / n(Co)=0.04, and mix it evenly with the P2 phase sodium cobalt oxide intermediate obtained in Step 2) to obtain a mixture; Steps 4)-7) are the same as in Example 1; like Figure 4 As shown, XRD tests indicate that the lithium cobalt oxide cathode material (denoted as LCO-3) of Example 3 exhibits good performance at 2θ. A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°, and at 2θ B1 absolute value of peak intensity I of diffraction characteristic peak at location B1 The following relationship exists between k and N: B1 =11335N-33, where k is 0.94.

[0071] Example 4 The chemical formula of the lithium cobalt oxide cathode material provided in this embodiment is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2·0.05LiCo 0.971 Al 0.029 O2, prepared as follows: Steps 1)-2) are the same as in Example 1; Step 3) Weigh out lithium carbonate according to n(Li) / n(Co)=0.05, and mix it evenly with the P2 phase sodium cobalt oxide intermediate obtained in Step 2) to obtain a mixture; Steps 4)-7) are the same as in Example 1; XRD tests show that the lithium cobalt oxide cathode material (denoted as LCO-4) of Example 4 exhibits high XRD performance at 2θ. A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°, and at 2θ B1absolute value of peak intensity I of diffraction characteristic peak at location B1 The following relationship exists between k and N: B1 =16350N-163, where k is 1.03.

[0072] Example 5 The chemical formula of the lithium cobalt oxide cathode material provided in this embodiment is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2·0.02LiCo 0.971 Al 0.029 O2, prepared as follows: Steps 1)-2) are the same as in Example 1; Step 3) Weigh lithium hydroxide according to n(Li) / n(Co)=0.02, and mix it evenly with the P2 phase sodium cobalt oxide intermediate obtained in Step 2) to obtain a mixture; Steps 4)-7) are the same as in Example 1; XRD tests show that the lithium cobalt oxide cathode material of Example 5 (denoted as LCO-5) exhibits high XRD performance at 2θ. A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°, and at 2θ B1 absolute value of peak intensity I of diffraction characteristic peak at location B1 It satisfies the following relationship with N: k×I B1 =11335N-33, where k is 1.03.

[0073] Example 6 The chemical formula of the lithium cobalt oxide cathode material provided in this embodiment is: Li 0.69 Na 0.01 Co 0.971 Mg 0.029 O2·0.02LiCo 0.971 Mg 0.029 O2, prepared as follows: Step 1) Mix cobalt oxide, sodium carbonate, and magnesium oxide uniformly in a molar ratio of n(Co):n(Na):n(Mg) = 0.986:0.7:0.014 to obtain a mixture; Steps 2)-7) are the same as in Example 1; XRD tests show that the lithium cobalt oxide cathode material (denoted as LCO-6) of Example 6 exhibits high XRD performance at 2θ. A1 =18.3-18.8°, 2θ A2=37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°, and at 2θ B1 absolute value of peak intensity I of diffraction characteristic peak at location B1 The following relationship exists between k and N: B1 =11335N-33, where k is 1.02.

[0074] Comparative Example 1 The chemical formula of the lithium cobalt oxide cathode material in this comparative example is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2, prepared as follows: Step 1) Mix cobalt oxide, sodium carbonate, and aluminum oxide uniformly in a molar ratio of n(Co):n(Na):n(Al) = 0.986:0.7:0.014 to obtain a mixture; Step 2) The mixture is subjected to a first high-temperature calcination, with the heating rate controlled at 5℃ / min. Under an oxygen atmosphere, it is calcined at 900℃ for 10h to obtain the P2 phase sodium cobalt oxide intermediate. Step 3) Weigh lithium nitrate according to n(Li) / n(Na)=2 and mix it evenly with the P2 phase sodium cobaltate intermediate obtained in Step 4); Step 4) The mixed material is calcined at 260℃ for 4 hours to remove Na. + / Li + Ion exchange yields the ion-exchange products. Step 5) The ion-exchange product is washed five times and dried to obtain the O2 phase lithium cobalt oxide cathode material, denoted as LCO-D1.

[0075] like Figure 4 As shown, XRD tests indicate that the lithium cobalt oxide cathode material of Comparative Example 1 (denoted as LCO-D1) exhibits performance at 2θ A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 XRD diffraction characteristic peaks exist at 46.7-47.3°, but at 2θ... B1 No characteristic XRD diffraction peaks were found in the range of 18.9-19.3°.

[0076] Comparative Example 2 The chemical formula of the lithium cobalt oxide cathode material in this comparative example is: Li 0.69 Na 0.01 Co 0.971 Al 0.029 O2·0.06LiCo 0.971Al 0.029 O2, prepared as follows: Steps 1)-2) are the same as in Example 1; Step 3) Weigh out lithium carbonate according to n(Li) / n(Co)=0.06, and mix it evenly with the P2 phase sodium cobalt oxide intermediate obtained in Step 2) to obtain a mixture; Steps 4)-7) are the same as in Example 1; XRD tests show that the lithium cobalt oxide cathode material of Comparative Example 2 (denoted as LCO-D2) exhibits a 2θ... A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 XRD diffraction characteristic peaks exist simultaneously at 18.9-19.3°. However, at 2θ... B1 absolute value of peak intensity I of diffraction characteristic peak at location B1 N does not satisfy k×I B1 =11335N-33.

[0077] I. Physicochemical properties of the materials in the above embodiments and comparative examples were analyzed and tested. The test items and methods are as follows: Particle size determination: The particle size was measured using a Hitachi S-4800 scanning electron microscope from Japan, with a test voltage of 1kV-5kV and a magnification of 1k-30k.

[0078] Median particle size test: The Malvern Mastersizer 3000 laser particle size analyzer was used. A certain amount of sodium pyrophosphate dispersant was added to the sample, and the shading was increased to 10% to 20%. The sample was sonicated for 3 minutes before the test was started. The average of three tests was taken as the median particle size measurement value.

[0079] Specific surface area test: The specific surface area was tested using a Tristar II 3020 specific surface area tester from MicromerAlcs, USA. The degassing temperature was set to 300℃ and the degassing time to 120min.

[0080] Residual alkali and free sodium were tested by potentiometric titration. All reagents used were of analytical grade and water conforming to Grade I standards as specified in GB / T 6682. The mixture was stirred at 800 rpm for 5 min, and then titrated with 0.1 mol / L hydrochloric acid standard solution. Before titration, the pH electrode of the potentiometric titrator was calibrated using a three-point pH standard buffer solution with a slope in the range of 0.95–1.05.

[0081] Determination of the compacted density: It was measured using a compacted density meter of model MCP-PD51 from Mitsubishi Chemical Corporation, Japan. Weigh 1 ± 0.01 g of the sample and select a pressure of 3 T for testing.

[0082] XRD test: It was tested using an X-ray powder diffractometer of model XRD-6000 from Shimadzu, Japan. Set the voltage to 40 kV, the current to 40 mA, the step size to 0.005°, the height limit slit to 10 mm, the divergence slit to 1 / 2°, the anti-scattering slit to 8 mm, the receiving slit to open, set the test scanning 2θ angle to 10° - 80°, continuously scan in 1D mode, and the scanning speed is 1.2° / min.

[0083] Test for the content of elements: It was measured using an ICP-OES spectrometer of model 5800 from Agilent, USA. The argon partial pressure gauge is controlled at 80 psi - 100 psi, the liquid argon booster valve compresses and controls the pressure above 200 psi, nitrogen is 60 psi - 100 psi, and compressed air is 80 psi - 100 psi; when making the standard curve, three-point calibration needs to be done according to the concentration of the sample, and the coefficient of the standard curve is above 0.9999.

[0084] Table 1 summarizes the test results of the material physical and chemical indexes of Examples 1 - 6 and Comparative Examples 1 - 2: From the test data in Table 1, taking the O2-phase lithium cobaltate as 100 mol%, the lithium cobaltate cathode materials of Examples 1 - 6 of the present invention are respectively coated with 1 - 5 mol% of O3-phase lithium cobaltate materials on the O2-phase matrix. Each example corresponds to the diffraction characteristic peaks of XRD existing simultaneously at 2θ A1 = 18.3 - 18.8°, 2θ A2 = 37.9 - 38.4°, 2θ A3 = 46.7 - 47.3° and 2θ B1 = 18.9 - 19.3°, which proves the simultaneous existence of O2-phase and O3-phase. The absolute value of the peak intensity I B1 of the diffraction characteristic peak at 2θ of each example and N can both satisfy the relationship: k × I B1 = 11335N - 33. B1

[0085] In Comparative Example 1, no trace of O3-phase lithium cobaltate was coated, and the prepared cathode material only had the characteristic diffraction peaks of O2-phase lithium cobaltate, and no characteristic diffraction peaks of O3-phase lithium cobaltate appeared, indicating that it does not contain O3-phase in the lithium cobaltate cathode material. In Comparative Example 2, the ratio n(Li) / n(Co) corresponding to the addition amount of the first lithium compound was as high as 0.06, and finally 6 mol% of O3-phase lithium cobaltate material was coated on the O2-phase lithium cobaltate matrix, exceeding the amount of trace coating. The content of O3-phase is relatively large, and at 2θB1 absolute value of peak intensity I of diffraction characteristic peak at location B1 Significantly improved, I B1 The condition k×I is no longer satisfied with N. B1 =11335N-33.

[0086] Furthermore, the lithium cobalt oxide of Comparative Example 1 differs from the embodiments and comparative examples of the present invention in terms of median particle size of secondary particles and residual Li content; the median particle size, specific surface area, tap density, residual Li, and free sodium content of Comparative Example 2 are not significantly different.

[0087] II. Using the materials from the above embodiments and comparative examples, coin half-cells were prepared and their electrochemical performance was tested. The battery assembly and testing process is as follows: The preparation steps of the coin cell half-cell are as follows: The positive electrode materials of the examples and comparative examples are respectively mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 98:1:1, and N-methylpyrrolidone solvent is added to form a uniform slurry. Then the slurry is coated on a 10 μm thick aluminum foil with an areal loading of 14 mg / cm³. 2 After drying, the material is cut into circular positive electrode sheets with a diameter of 12 mm. Using the prepared circular electrode sheets as the positive electrode, lithium metal as the negative electrode, and a polyethylene (PE) membrane coated with alumina on both sides as the separator, an R2032 coin cell is assembled with an electrolyte solution of 1 mol / L LiPF6 dissolved in ethylene carbonate (EC): dimethyl carbonate (DMC) = 1:1, and the electrolyte volume is 70 μL.

[0088] The assembled R2032 button cell was tested using a charge / discharge tester, and the steps are as follows: (1) First charge-discharge test at 0.1C at 30℃: The coin cell half-cell was placed in a constant temperature chamber at 30℃. A current density of 20.0 mA / g (0.1C) was set, and the charging cut-off voltage was 4.65V (vs Li + / Li), the discharge cutoff voltage is 3V (vs Li) + / Li), cycle for 1 week.

[0089] (2) First charge-discharge test at 0.5C at 30℃: The button cell half-cell was placed in a constant temperature chamber at 30℃. After one cycle in step (1), the current was reset to 100mA / g (0.5C), and the charging cut-off voltage was 4.65V (vs Li + / Li), the discharge cutoff voltage is 3V (vs Li) + / Li) cycle for 1 week.

[0090] (3) Cyclic performance test at 30℃: The button cell half-cell was placed in a constant temperature chamber at 30℃. After cycling for 1 week according to step (1) and then cycling for 1 week according to step (2), the current was reset to 200mA / g (1.0C), and the charging cut-off voltage was 4.65V (vs Li + / Li), the discharge cutoff voltage is 3V (vs Li) + / Li) Cycle 50 times.

[0091] The initial charge-discharge curves of the coin half-cells assembled in Example 2 and Comparative Example 1 at 0.1C are shown below. Figure 5 As shown, the discharge specific capacity of the button half-cell assembled in Example 2 is significantly higher than that of the battery in Comparative Example 1.

[0092] The coin cell half-cells assembled in Example 2 and Comparative Example 1 exhibited the following capacity after 50 cycles at 1.0C: Figure 6 As shown, the discharge specific capacity of the button cell assembled in Example 2 is significantly higher than that of the button cell in Comparative Example 1.

[0093] The capacity retention of the coin half-cells assembled in Example 2 and Comparative Example 1 after 50 cycles at 1.0C is as follows: Figure 7 As shown, the coin cell containing the lithium cobalt oxide cathode material of Example 2 exhibits a significantly higher capacity retention rate at 1.0C for 50 cycles compared to the coin cell of Comparative Example 1.

[0094] The specific capacity of the first discharge at 0.1C, the first coulombic efficiency, the specific capacity of the discharge at 0.5C, the specific capacity of the discharge at 1.0C, the specific capacity of the 50th discharge at 1.0C, and the capacity retention rate of the 50th discharge at each embodiment and comparative example are summarized in Table 2.

[0095] Table 2 As shown in Table 2, in the O2-phase Al-doped lithium cobalt oxide cathode materials of Examples 1-4, the molar amount of O3-phase lithium cobalt oxide coated on the surface for every 1 mol of lithium cobalt oxide was 0.01 mol, 0.02 mol, 0.04 mol, and 0.05 mol, respectively. The coin cells prepared from these materials exhibited first-cycle discharge specific capacities of 258.7 mAh / g, 257.8 mAh / g, 255.1 mAh / g, and 254.8 mAh / g at 0.1C, respectively. The cathode materials in each embodiment exhibit excellent first-cycle specific capacity, all exceeding 254.0 mAh / g, with first-cycle coulombic efficiencies of 115.9%, 115.4%, 114.6%, and 115.0%, respectively, all exceeding 110%. The first-cycle discharge specific capacities at 0.5C are 254.2 mAh / g, 253.3 mAh / g, 250.2 mAh / g, and 249.7 mAh / g, respectively, all exceeding 249 mAh / g. The first-cycle discharge specific capacities at 1C are 251.6 mAh / g, 250.7 mAh / g, 247.8 mAh / g, and 247.6 mAh / g, respectively, all exceeding 245 mAh / g. The discharge specific capacities after 50 cycles at 1C were 236.8 mAh / g, 236.5 mAh / g, 232.9 mAh / g, and 233.5 mAh / g, respectively, all exceeding 230 mAh / g. The retention rates of the discharge specific capacity after 50 cycles at 1C were 94.1%, 94.3%, 94.0%, and 94.3%, respectively, demonstrating good cycle stability in all embodiments. It can be seen that the Al-doped O2 phase lithium cobalt oxide cathode material of this invention, with an O3 phase lithium cobalt oxide molar percentage coated on its surface within a suitable range, exhibits excellent initial discharge specific capacity and capacity retention after 50 cycles. In summary, the molar percentage of O3 phase lithium cobalt oxide coated on the surface in Examples 1-4 is within the trace range. However, with the increase of O3 phase content, the first-cycle discharge specific capacity at 0.1C, 0.5C, and 1.0C all show a certain decrease, while the 50-cycle discharge capacity retention rate at 1.0C is within the optimal range.

[0096] Comparative Example 1 did not involve coating with trace amounts of O3-phase lithium cobalt oxide; instead, it prepared an O2-phase lithium cobalt oxide cathode material. The first-cycle discharge specific capacity at 0.1C was 258.2 mAh / g, at 0.5C it was 254.8 mAh / g, and at 1C it was 251.3 mAh / g. These first-cycle specific capacities at various rates were not significantly different from those in the embodiments of this invention. However, the discharge specific capacity after 50 cycles at 1C was only 226.2 mAh / g, with a capacity retention of 90.0%. This indicates that while the O2-phase lithium cobalt oxide without O3-phase surface coating has a superior first-cycle discharge specific capacity, its cycle stability is poor. This is mainly because at a high charging cutoff voltage of 4.6V, as charge-discharge cycles progress, the interfacial stability of the O2-phase lithium cobalt oxide deteriorates, lattice oxygen evolution occurs, and battery gas generation intensifies, leading to a more prominent problem with its cycle stability.

[0097] In Comparative Example 2, 6 mol% of O3-phase lithium cobalt oxide material was coated onto an O2-phase lithium cobalt oxide substrate. The first-cycle discharge specific capacity at 0.1C was 248.3 mAh / g, at 0.5C it was 244.3 mAh / g, and at 1C it was 240.8 mAh / g. Compared to the embodiments of this invention, the first-cycle specific capacity at each rate was significantly reduced. The discharge specific capacity after 50 cycles at 1C was also 215.6 mAh / g, with a capacity retention of 89.5%, lower than 90%. This indicates that excessive surface coating of O3-phase lithium cobalt oxide can also lead to a significant decrease in the performance of O2-phase lithium cobalt oxide. This is because when the content of O3-phase lithium cobalt oxide exceeds the trace threshold, the cathode material undergoes an irreversible phase transition from O3 to O1 phase under high voltage, resulting in a deterioration in the performance of the cathode material, with serious problems in both discharge specific capacity and cycle stability. This invention discovers that the O3 phase material on the surface of O2 phase lithium cobalt oxide needs to be controlled within a suitable range in order to ensure that the lithium cobalt oxide cathode material can achieve both high specific capacity and cycle stability.

[0098] Compared to Example 2, in Example 5, the first lithium compound in step 3) is lithium hydroxide, and the molar amount of O3-phase lithium cobalt oxide coated on the surface remains 0.02 mol. The resulting coin cell has a first-cycle discharge specific capacity of 255.8 mAh / g at 0.1C, 250.2 mAh / g at 0.5C, and 247.5 mAh / g at 1C. Compared to Example 2, the first-cycle discharge specific capacity at each rate decreased by 2.0 mAh / g, 3.1 mAh / g, and 3.2 mAh / g, respectively. This indicates that the lithium compound used for surface lithiation affects the specific capacity of the lithium cobalt oxide cathode material to some extent. The cathode material of Example 5 has a discharge specific capacity of 233.8 mAh / g after 50 cycles at 1C, with a capacity retention of 94.5%. Compared to Example 2, the discharge specific capacity of Example 5 after 50 cycles at 1C decreased by 2.7 mAh / g. As shown in Table 1, the residual lithium content on the surface of the cathode materials in Examples 2 and 5 is 0.15% and 0.16%, respectively. This indicates that using lithium hydroxide for surface lithiation to generate trace amounts of O3-phase lithium cobalt oxide coating will lead to an increase in the residual alkali content on the surface, which directly affects the discharge specific capacity of the cathode material. Therefore, the first lithium compound directly affects the residual alkali content on the cathode material surface. Compared to lithium-containing hydroxides (such as lithium hydroxide), when the first lithium compound for surface lithiation is a lithium salt (such as lithium carbonate), the lithium cobalt oxide cathode material exhibits a better discharge specific capacity.

[0099] Compared to Example 2, in Example 6, the in-situ doping of the O2 phase lithium cobalt oxide cathode material was Mg, and the molar amount of the O3 phase lithium cobalt oxide coating on the surface remained at 0.02 mol. The resulting coin cell exhibited a first-cycle discharge specific capacity of 255.2 mAh / g at 0.1C, 250.8 mAh / g at 0.5C, and 248.5 mAh / g at 1C. Compared to Example 2, the first-cycle discharge specific capacity at each rate in Example 6 decreased by 2.6 mAh / g, 2.5 mAh / g, and 2.2 mAh / g, respectively. This indicates that different metal doping elements have a certain impact on the specific capacity of the cathode material. The cathode material of Example 6 exhibited a discharge specific capacity of 233.3 mAh / g after 50 cycles at 1C, with a capacity retention rate of 93.9%. In summary, compared to magnesium doping, the lithium cobalt oxide cathode material doped with aluminum exhibits superior discharge specific capacity and cycle stability.

[0100] Overall, the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material of the present invention has excellent discharge specific capacity and high capacity retention rate, which can meet the battery's demand for high energy density.

[0101] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material, characterized in that, The chemical formula of the lithium cobalt oxide cathode material is: Li a Na b Co 1-c M c O2·NLiCo 1-c M c O2; where 0≤a≤0.8, 0≤b≤0.1, 0≤c≤0.1, N is the molar ratio of O3 phase to O2 phase, 0<N≤0.05; M includes at least one of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd or Ti; Among them, the lithium cobalt oxide cathode material is at 2θ A1 =18.3-18.8°, 2θ A2 =37.9-38.4°, 2θ A3 =46.7-47.3° and 2θ B1 =18.9-19.3° and XRD diffraction characteristic peaks are present.

2. The lithium cobalt oxide cathode material according to claim 1, characterized in that, The lithium cobalt oxide cathode material at 2θ B1 The absolute value of the peak intensity I of the diffraction characteristic peak at the location B1 With N, k×I B1 =11335N-33; where k is a correction coefficient, 0.9≤k≤1.

1.

3. The lithium cobalt oxide cathode material according to claim 1, characterized in that, In the lithium cobalt oxide cathode material, the trace O3 phase lithium cobalt oxide coating layer is generated in situ through induction. The thickness i of the trace O3 phase lithium cobalt oxide coating layer satisfies 50nm≤i≤500nm.

4. The lithium cobalt oxide cathode material according to claim 1, characterized in that, The lithium cobalt oxide cathode material is composed of micron-sized primary particles with a median particle size D50 of 4-12 μm; preferably 6-9 μm; and / or, The specific surface area of ​​the lithium cobalt oxide cathode material is 0.2-0.8 m². 2 / g; preferably 0.3-0.6 m 2 / g; and / or, The compaction density of the lithium cobalt oxide cathode material is 2-6 g / cm³. 3 Preferably 3-5 g / cm³ 3 ; and / or, The residual alkali content on the surface of the lithium cobalt oxide cathode material is 0.05-0.5 wt%; preferably 0.1-0.3 wt%; and / or, The free sodium content in the lithium cobalt oxide cathode material is 0.01-0.2 wt%; preferably 0.05-0.1 wt%.

5. A method for preparing a trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material according to any one of claims 1-4, characterized in that, The preparation method includes: After mixing the cobalt source, sodium source and M source, the mixture is subjected to a first high-temperature calcination at above 700°C to obtain the P2 phase sodium cobalt oxide intermediate. According to the set Li / Co molar ratio, the P2 phase sodium cobalt oxide intermediate is mixed with the first lithium compound and then subjected to a second high-temperature calcination at above 700°C, so that the surface of the P2 phase sodium cobalt oxide intermediate undergoes an in-situ reaction under limited lithium source conditions to generate trace amounts of O3 phase lithium cobalt oxide, thereby obtaining a P2 phase sodium cobalt oxide intermediate with trace amounts of O3 phase lithium cobalt oxide on the surface. According to the set Li / Na molar ratio, the P2 phase sodium cobalt oxide intermediate coated with trace O3 phase lithium cobalt oxide on the surface is mixed with the second lithium compound to construct an ion exchange reaction environment rich in lithium ions, and a mixture is obtained. The mixture was subjected to low-temperature calcination at below 300°C, causing the bulk phase of the P2 phase sodium cobalt oxide intermediate to undergo Na+ oxidative stress under the influence of lithium-ion chemical potential. + / Li + Ion exchange completes the topological phase transition from the P2 phase to the O2 phase. At the same time, the trace O3 phase lithium cobalt oxide retains its original structure and does not undergo a topological transformation, resulting in the trace O3 phase lithium cobalt oxide coated with the O2 phase lithium cobalt oxide cathode material.

6. The preparation method according to claim 5, characterized in that, After the low-temperature calcination treatment, the method further includes: The product after the low-temperature calcination treatment is washed and dried to obtain the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the cobalt source, sodium source, and M source used to prepare the P2 phase sodium cobaltate intermediate satisfies: 0.5 ≤ n(Na) / n(Co) ≤ 1.0, preferably 0.6 ≤ n(Na) / n(Co) ≤ 0.9; n(M) / n(Co) = 0.003-0.06; wherein M includes at least one of Ni, Mn, Al, Mg, Co, Cu, Ca, Zn, Zr, B, Nb, Fe, Cr, Y, La, Ce, Cd, or Ti; The set Li / Co molar ratio n(Li) / n(Co) satisfies: 0 < n(Li) / n(Co) ≤ 0.05; preferably 0.01 ≤ n(Li) / n(Co) ≤ 0.04; wherein the first lithium compound includes one or more of lithium hydroxide, lithium carbonate, lithium chloride, lithium iodide, lithium fluoride, lithium bromide or lithium phosphate; preferably lithium carbonate; The set Li / Na molar ratio n(Li) / n(Na) satisfies: n(Li) / n(Na)≥1.5; preferably n(Li) / n(Na)≥2; wherein the second lithium compound includes one or more of lithium nitrate, lithium hydroxide, lithium chloride, lithium bromide, lithium iodide, lithium hypochlorite or lithium perchlorate; preferably lithium nitrate.

8. The preparation method according to claim 5, characterized in that, The first high-temperature calcination is carried out at a temperature of 700-1000℃, preferably 800-900℃, and the sintering time is 6-15 hours, preferably 8-12 hours; preferably, the first high-temperature calcination is carried out in an oxygen atmosphere with an oxygen concentration ≥90%. The second high-temperature calcination is carried out at a temperature of 700-1000℃, preferably 800-900℃, and the sintering time is 1-10h, preferably 2-8h; preferably, the second high-temperature calcination is carried out in an oxygen atmosphere with an oxygen concentration ≥90%.

9. The preparation method according to claim 5, characterized in that, The temperature of the low-temperature calcination treatment is T≥240℃, preferably T≥260℃, and the time of the low-temperature calcination treatment is t≥2h, preferably t≥4h.

10. An energy storage device, characterized in that, The energy storage device includes any one of lithium batteries, cells, or battery packs. The energy storage device includes the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material as described in any one of claims 1-4, or the trace O3 phase lithium cobalt oxide coated O2 phase lithium cobalt oxide cathode material prepared by the preparation method described in any one of claims 5-9.

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