O3-O2 mixed crystal type layered oxide lithium cobalt oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention provides an O3-O2 mixed crystal type layered oxide lithium cobalt oxide positive electrode material as well as a preparation method and application thereof. The positive electrode material is obtained by carrying out Li-Na ion replacement on an O3-P2 mixed crystal type lithium cobalt oxide sodium precursor with a high (Na + Li) / Co atomic ratio, washing and drying, the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor is composed of O3 type lithium cobalt oxide and P2 type sodium cobalt oxide, and the atomic ratio of (Na + Li) / Co is 0.9-1.1. Compared with O3-O2 mixed crystal form lithium cobalt oxide converted from near-pure-phase O2 type lithium cobalt oxide, the material synthesis method provided by the invention has the advantages that most of O3 crystal form parts come from O3-P2 mixed crystal form sodium lithium cobalt oxide, and the material is subjected to high-temperature sintering, so that the crystal structure is more complete, the structure is more stable, and the material has better cycle performance.

Description

Technical Field

[0001] The invention relates to an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material and a preparation method and application thereof, belonging to the technical field of lithium ion batteries. Background Art

[0002] Lithium-ion battery is a secondary battery with the characteristic of repeated charge and discharge. The mainstream lithium-ion battery positive electrode materials on the market can be divided into lithium cobalt oxide (LCO), ternary (NCM), NCA, lithium-rich manganese-based positive electrode materials, lithium iron phosphate, and spinel structure lithium manganese oxide or nickel manganese oxide. Among them, lithium cobalt oxide occupies an indispensable position in the fields of mobile phones, notebooks, tablets, drones, electronic cigarettes, etc. due to its higher compaction density and high discharge equalization pressure. Lithium cobalt oxide has a variety of structures, among which O3 type lithium cobalt oxide occupies a dominant position in the market. The "O3" nomenclature comes from Delmas's layered material classification concept. "O" represents Li-O octahedron or Co-O octahedron, and "3" represents Li-O-Co alternately stacked in the crystal unit cell, with a minimum repetition period of 3. Because O3 type lithium cobalt oxide has a stable layered structure, this structure enables it to maintain good stability during the charge and discharge process. At the same time, it also has a high compaction density, which enables the battery to store more energy in a limited space, thereby improving the energy density of the battery and enabling the battery to store more energy in a limited space. However, since Goodenough first discovered O3-type LCO in 1980, the gram capacity of lithium cobalt oxide has been continuously improved with the increase of the upper limit cut-off voltage. At present, the gram capacity has reached 192 mAh / g when charged to 4.53-4.55 V. If the charge cut-off voltage is further increased and the Li / Co atomic ratio is <30%, O3-type LCO will face the collapse of the layered structure caused by excessive delithiation (O3-H 1 / 3 Phase transition and O1 phase transition), which leads to irreversible cycle capacity loss. Faced with the continuous growth of market demand for thinner and higher energy density lithium-ion batteries, O3-type LCO has reached a bottleneck.

[0003] In 1982, Delmas first obtained O2-type LCO by Li-Na replacement of P2-type sodium cobalt oxide (NCO). In 2002, Delmas revealed O2-type Li x The structural evolution of CoO2 (0.16~x~1) during charge and discharge is O2-T2-O6-O2-O2'. In 2024, Yu Xiqian's team at the Chinese Academy of Sciences used P2-type Na 0.7CoO2(NCO) was used to synthesize O2-type LCO, and the electrochemical performance and mechanism of O2-type LCO superior to O3-type LCO were revealed for the first time [1]. Studies have shown that the structure of O2-type lithium cobalt oxide is superior to that of O3-type LCO for the following reasons: (1) O2-type LCO has a lower Li+ diffusion barrier, which makes the diffusion of Li ions more convenient and the Li+ concentration in the particles more uniform during the lithium insertion and removal process; (2) At the same time, during the lithium removal process of O2-type LCO, the elastic modulus along the c-axis of the particles is more continuous, and the elastic modulus along the a-axis hardly changes, resulting in lower internal stress of the particles caused by lithium insertion and removal, and the particles are less likely to crack and pulverize after cycling [1]. However, O2-type LCO is a metastable structure. When the replacement and drying temperature is higher than 400°C, it is very easy to transform into O3-type LCO, thereby losing the structural stability advantage of O2-type LCO. At temperatures below 400°C, it is completely insufficient to convert non-site-occupying Li+ into site-occupying Li+, resulting in an excessively high content of free lithium carbonate in the material, which causes serious deterioration of the circulation, storage gas production and electrochemical system under high voltage applications.

[0004] Based on the above, it can be seen that O3-type lithium cobalt oxide and O2-type lithium cobalt oxide have their own advantages and disadvantages. Therefore, it is necessary to study an O3-O2 mixed crystal lithium cobalt oxide so that it can simultaneously play the advantages of O3-type and O2-type lithium cobalt oxide. In the prior art, O3-O2 mixed crystal lithium cobalt oxide is obtained by Li-Na replacement of pure phase P2-type sodium cobalt oxide precursor, and controlling the drying temperature after water washing to obtain O3-O2 mixed crystal lithium cobalt oxide with different proportions. However, O3-type lithium cobalt oxide is converted from the metastable O2-type lithium cobalt oxide structure by low-temperature sintering below 500°C. There are a large number of defects in the crystal structure. Although part of the O2-type structure can be converted to the O3-type structure to provide a higher voltage platform and higher capacity, the newly converted O3-type structure itself has poor stability and will decay rapidly in high-voltage applications, resulting in a reduction in battery life. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention proposes an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material and a preparation method and application thereof. The method can form a stable partial O3 type lithium cobalt oxide structure while forming a P2 type sodium cobalt oxide. The O2 type lithium cobalt oxide structure in the finished product is completely or mostly transformed from the precursor P2 type structure, which is more conducive to reducing structural attenuation in high voltage applications and has better cycle performance.

[0006] The technical solution of the present invention is: an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, which is obtained by replacing an O3-P2 mixed crystal lithium sodium cobalt oxide precursor with a high (Na+Li) / Co atomic ratio with Li-Na ions and then washing and drying; the O3-P2 mixed crystal lithium sodium cobalt oxide precursor is composed of O3 type lithium cobalt oxide and P2 type sodium cobalt oxide, wherein the (Na+Li) / Co atomic ratio is 0.9 to 1.1.

[0007] The expression of the above positive electrode material is: Li x (Li a Na b Co c M' d ) z , wherein M' is a modifying element selected from one or more of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu, and Fe;

[0008] In the above expression, M' represents the amount located in the Li layer or the transition metal layer; x represents the amount of Li located in the Li layer, a represents the amount of Li located in the transition metal layer, b represents the amount of Na located in the Li layer or the transition metal layer, c represents the amount of Co in the transition metal layer, and d represents the amount of the modifying element located in the transition metal layer or the Li layer;

[0009] In the above expressions, 0.4≤x≤1.2, 0≤a≤0.2, 0≤b≤0.1, 0.8≤c≤1, 0≤d≤0.1, 1.9≤z≤2.2, 0.9≤x+a+b≤1.2, 0.9≤c+d≤1.2.

[0010] In the X-ray diffraction spectrum of the above positive electrode material, the total area of ​​the diffraction peaks with structural characteristics of O3-type lithium cobalt oxide and O2-type lithium cobalt oxide accounts for ≥90% of the total area of ​​all diffraction peaks.

[0011] The lithium carbonate content of the above positive electrode material measured by aqueous solution titration method is ≤0.5wt.%.

[0012] The Li / Co atomic ratio in the above positive electrode material is 0.9 to 1.2.

[0013] At the same time, the present invention also provides a preparation method of an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, comprising an existing liquid phase ion replacement synthesis method, wherein an O3-P2 mixed crystal lithium sodium cobalt oxide precursor is put into an aqueous suspension containing a saturated Li+ compound to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 0.9 to 1.2. After stirring at a temperature of 90 to 180°C for 0.5 to 18h under closed conditions, the mixture is solid-liquid separated and dried at a temperature below 300°C to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material.

[0014] In the above preparation method, in the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, the crystal plane diffraction peak height of O2 type lithium cobalt oxide is H2, and the crystal plane diffraction peak height of O3 type lithium cobalt oxide is H3, then H2 / (H2+H3) is 0.3~1.0.

[0015] In the above preparation method, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0016] Step 1, uniformly mixing a Co-containing compound, a modifying element M'-containing compound and an A-containing compound in water to obtain a mixed system, wherein M' is a modifying element selected from one or more of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu and Fe; A is a mixed compound of a Na source and a Li source; the Na / (Li+Na) atomic ratio in the mixed system is 0.4-0.95, and the (Li+Na) / Co atomic ratio is 1.0-1.10;

[0017] Step 2: Dry the mixed system at 250-280° C. by spray drying, and then sinter the dried product at 700-750° C. for 12-36 hours to obtain an O3-P2 mixed crystal sodium lithium cobalt oxide precursor.

[0018] In the above preparation method, the X-ray diffraction spectrum of the O3-P2 mixed crystal sodium cobaltate precursor includes characteristic diffraction spectra of P2-type sodium cobaltate of P63 / mmc space group and O3-type lithium cobaltate of R-3m space group, and the total area of ​​the characteristic diffraction peaks of the P2-type sodium cobaltate and O3-type lithium cobaltate structures accounts for ≥95% of the total area of ​​all diffraction peaks.

[0019] In the above preparation method, the total content of sodium carbonate and lithium carbonate measured by aqueous solution titration method of the O3-P2 mixed crystal sodium lithium cobaltate precursor is ≤15wt.%.

[0020] Another object of the present invention is to provide a lithium-ion battery, comprising a positive electrode active material, wherein the positive electrode active material comprises one or more O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode materials obtained by the above preparation method.

[0021] Due to the adoption of the above technical solution, the advantages of the present invention are:

[0022] 1. Since O2-type LCO has a lower discharge average voltage, it can exert a higher gram capacity than O3-type LCO at the same voltage, and the comprehensive energy density can be higher than that of O3-type LCO. The O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material of the present invention has an additional characteristic O3-type discharge platform near 3.9V on the basis of O2-type LCO, and the discharge average voltage and gram capacity are further improved compared with the pure phase O2-type LCO. Since the ratio of O3-type lithium cobalt oxide to O2-type lithium cobalt oxide has a significant effect on the material capacity, the higher the O2 phase ratio, the higher the discharge average voltage. Taking into account the gram capacity and discharge average voltage, the present invention controls the ratio of O3-type lithium cobalt oxide to O2-type lithium cobalt oxide within a reasonable range in the mixed crystal LCO, such as Figure 5 As shown, the H2 / (H2+H3) ratio is preferably between 40% and 80%, which can make the material have the highest energy density.

[0023] 2. Compared with the O3-O2 mixed crystal lithium cobalt oxide converted from nearly pure phase O2 lithium cobalt oxide, the material synthesis method provided by the present invention has a more complete crystal structure and a more stable structure, and has better cycle performance because most of the O3 crystal part comes from the O3-P2 mixed crystal lithium sodium cobalt oxide, which has undergone high-temperature sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The XRD diffraction pattern of the O3-P2 mixed crystal sodium lithium cobalt oxide precursor synthesized in Example 7;

[0025] Figure 2 This is a SEM scanning electron microscope image of the O3-P2 mixed crystal sodium lithium cobalt oxide precursor synthesized in Example 7;

[0026] Figure 3 The XRD diffraction pattern of the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material synthesized in Example 7;

[0027] Figure 4 This is a SEM scanning electron microscope image of the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material synthesized in Example 7;

[0028] Figure 5 Schematic diagram of the change of material gram capacity with H2 / (H2+H3) in the examples and comparative examples;

[0029] Figure 6 Schematic diagram of the change of discharge average voltage of materials in the embodiment and comparative example with H2 / (H2+H3). DETAILED DESCRIPTION

[0030] In order to better understand the technical solutions of the embodiments of the present application, they are further described below in conjunction with some preferred embodiments of the present application.

[0031] In this specification, amounts, ratios and other numerical values ​​are sometimes presented herein in a range format. It should be understood that such a range format is used for convenience and brevity, and should be flexibly understood to include not only the values ​​explicitly specified as range limits, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0032] The present application proposes an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, which is obtained by replacing an O3-P2 mixed crystal lithium sodium cobalt oxide precursor with a high (Na+Li) / Co atomic ratio by Li-Na ions and then washing and drying; the O3-P2 mixed crystal lithium sodium cobalt oxide precursor is composed of O3 type lithium cobalt oxide and P2 type sodium cobalt oxide, wherein the (Na+Li) / Co atomic ratio is 0.9 to 1.1.

[0033] According to some embodiments of the present application, the expression of the positive electrode material is: Li x (Li a Na b Co c M' d ) z , wherein M' is a modifying element selected from one or more of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu, and Fe;

[0034] In the above expression, M' represents the amount located in the Li layer or the transition metal layer; x represents the amount of Li located in the Li layer, a represents the amount of Li located in the transition metal layer, b represents the amount of Na located in the Li layer or the transition metal layer, c represents the amount of Co in the transition metal layer, and d represents the amount of the modifying element located in the transition metal layer or the Li layer;

[0035] In the above expressions, 0.4≤x≤1.2, 0≤a≤0.2, 0≤b≤0.1, 0.8≤c≤1, 0≤d≤0.1, 1.9≤z≤2.2, 0.9≤x+a+b≤1.2, 0.9≤c+d≤1.2.

[0036] According to some embodiments of the present application, in the X-ray diffraction pattern of the above-mentioned positive electrode material, the total area of ​​the diffraction peaks with structural characteristics of O3-type lithium cobalt oxide and O2-type lithium cobalt oxide accounts for ≥90% of the total area of ​​all diffraction peaks.

[0037] According to some embodiments of the present application, the lithium carbonate content of the above-mentioned positive electrode material measured by aqueous solution titration method is ≤0.5wt.%.

[0038] According to some embodiments of the present application, the Li / Co atomic ratio in the above-mentioned positive electrode material is 0.9 to 1.2.

[0039] At the same time, the present invention also provides a preparation method of an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, comprising an existing liquid phase ion replacement synthesis method, wherein an O3-P2 mixed crystal lithium sodium cobalt oxide precursor is put into an aqueous suspension containing a saturated Li+ compound to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 0.9 to 1.2. After stirring at a temperature of 90 to 180°C for 0.5 to 18h under closed conditions, the mixture is solid-liquid separated and dried at a temperature below 300°C to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material.

[0040] According to some embodiments of the present application, in the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, the crystal plane diffraction peak height of the O2 type lithium cobalt oxide is H2, and the crystal plane diffraction peak height of the O3 type lithium cobalt oxide is H3, then H2 / (H2+H3) is 0.3~1.0.

[0041] According to some embodiments of the present application, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0042] Step 1, uniformly mixing a Co-containing compound, a modifying element M'-containing compound and an A-containing compound in water to obtain a mixed system, wherein M' is a modifying element selected from one or more of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu and Fe; A is a mixed compound of a Na source and a Li source; the Na / (Li+Na) atomic ratio in the mixed system is 0.4-0.95, and the (Li+Na) / Co atomic ratio is 1.0-1.10;

[0043] Step 2: Dry the mixed system at 250-280° C. by spray drying, and then sinter the dried product at 700-750° C. for 12-36 hours to obtain an O3-P2 mixed crystal sodium lithium cobalt oxide precursor.

[0044] According to some embodiments of the present application, the X-ray diffraction pattern of the O3-P2 mixed crystal sodium cobaltate precursor includes characteristic diffraction spectra of P2-type sodium cobaltate of P63 / mmc space group and O3-type lithium cobaltate of R-3m space group, and the total area of ​​the characteristic diffraction peaks of the P2-type sodium cobaltate and O3-type lithium cobaltate structures accounts for ≥95% of the total area of ​​all diffraction peaks.

[0045] According to some embodiments of the present application, the total content of sodium carbonate and lithium carbonate in the O3-P2 mixed crystal sodium lithium cobaltate precursor measured by aqueous solution titration method is ≤15wt.%.

[0046] Another object of the present invention is to provide a lithium-ion battery, comprising a positive electrode active material, wherein the positive electrode active material comprises one or more O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode materials obtained by the above preparation method.

[0047] The equipment and analysis methods used in the following examples of this application are as follows:

[0048] 1. Determination of residual sodium carbonate by aqueous solution method

[0049] Determination method of residual sodium carbonate by aqueous solution method: accurately weigh 15g±0.5g(m) sample, put the sample into a 250mL conical flask, put in a magnet, add 100mL(L1) deionized water; put it on a magnetic stirrer, turn on the stirrer to stir for 30min, and use a clean filtration device to filter; transfer 1mL(L2) filtrate into a 100mL titration cup, add deionized water to 40mL, use 0.05mol / L hydrochloric acid, and use a fully automatic potentiometric titrator (METTLER TOLEDO T5) to measure the initial volume V0, titrate the first equivalence point V1, and titrate the second equivalence point V2.

[0050] Calculation of residual sodium carbonate:

[0051]

[0052] c---concentration of standard hydrochloric acid titration solution; m---mass of sample; M1---relative atomic mass of sodium; M2---relative molecular mass of sodium carbonate; M3---relative molecular mass of sodium hydroxide; V0---initial volume; V1---the first titration equivalence point; V2---the second titration equivalence point; L1---total volume of residual sodium carbonate solution; L2---volume of the removed residual sodium carbonate solution. Note: The sodium carbonate content obtained in this application is based on the titration of carbonate. Strictly speaking, the free sodium in the samples of certain embodiments of this application may contain a small amount of free lithium, which is not strictly distinguished in this application.

[0053] 2. Determination of residual lithium carbonate by aqueous solution method

[0054] Determination method of residual lithium carbonate by aqueous solution method: accurately weigh 30g±0.5g(m) sample, put the sample into a 250mL conical flask, put in a magnet, add 100mL(L1) deionized water; put it on a magnetic stirrer, turn on the stirrer to stir for 30min, and filter it with a clean funnel; transfer 50mL(L2) filtrate into a 100mL titration cup, use 0.05mol / L hydrochloric acid, and use a fully automatic potentiometric titrator (METTLER TOLEDO T5) to measure the initial volume V0, titrate the first equivalence point V1, and titrate the second equivalence point V2.

[0055] Calculation of residual lithium carbonate:

[0056]

[0057] c---concentration of standard hydrochloric acid titration solution; m---mass of sample; M1---relative atomic mass of lithium; M2---relative molecular mass of lithium carbonate; M3---relative molecular mass of lithium hydroxide; V0---initial volume; V1---first titration equivalence point; V2---second titration equivalence point; L1---total volume of residual lithium carbonate solution; L2---volume of residual lithium carbonate solution removed. Note: The lithium carbonate or sodium carbonate content obtained in this application is based on the titration of carbonate. Strictly speaking, the lithium carbonate results of samples in some embodiments of this application may contain free sodium, and the sodium carbonate results may also contain part of lithium carbonate. This patent does not make a strict distinction.

[0058] 3. XRD test method

[0059] XRD test method: using X'Pert PRO MPD PANalytical powder diffraction analyzer, light tube - Cu target, wavelength Be window; incident light path - Soller slit 0.04rad, divergence slit 1 / 2°, shading plate 10mm, anti-scattering slit 1°; diffraction light path - anti-scattering slit 8.0mm, Soller slit 0.04rad, large Ni filter; scanning range 10°-80°, scanning step 0.013°, dwell time 30.6s per step, voltage 40kV, current 40mA, analysis software High-Score Plus. Powder sample preparation: Put the powder into the groove of the slide with a clean sampling spoon (for large particle samples, grind into powder <50um), put one side of the scraper (>20mm) against the surface of the slide, and slightly lift the other end (angle <10°), use the edge of the scraper to scrape the surface of the powder sample flat, rotate the slide 90°, scrape it flat again, scrape it repeatedly in both directions several times, until the sample surface has no texture, remove the excess powder around the slide, and put it into the powder X-ray diffraction analyzer. Sample analysis: Use the analysis software High-Score Plus to open the tested sample file; first determine the background, select peak search for peak confirmation, repeat fitting, record Williamson-Hall plot to calculate the grain size, select the corresponding phase for physical matching and unit cell refinement, and record the unit cell parameters. Test principle: The Bragg equation reflects the relationship between the diffraction line direction and the crystal structure. Diffraction must satisfy the Bragg formula: 2dsinθ=nλ (d: crystal plane spacing; θ: Bragg angle; λ: wavelength of X-rays; n: reflection order). When X-rays irradiate the sample, the scattered X-rays of each atom in the crystal interfere and produce strong X-ray diffraction lines in a specific direction. When X-rays irradiate the sample from different angles, diffraction will occur on different crystal planes, and the detector will receive the number of diffracted photons reflected from the crystal plane, thereby obtaining a spectrum of the relationship between angle and intensity. After the obtained X-ray diffraction spectrum is subjected to a series of analysis operations such as background calibration, peak search, peak type fitting of more than two times, and matching spectrum recognized by the academic community, the area data of each diffraction peak is obtained from the peak list, and the obtained area data is processed to obtain the area ratio data. In order to analyze the influence of the O2 type structure ratio on the material gram capacity and discharge average pressure in this embodiment, it is defined as follows: the height of the O2 type (002) crystal plane characteristic diffraction peak is H2, the height of the O3 type (003) crystal plane characteristic diffraction peak is H3, and the O2 type structure ratio = H2 / (H2+H3).

[0060] 4. Test method of lithium-cobalt atomic ratio

[0061] ICP test method: using ICP-OES iCAP 6300 inductively coupled plasma atomic emission spectrometer, detector detection unit> 290000, detector cooling system Camera temperature <-35℃, optical system light chamber temperature: 38℃±0.1℃, optical system wavelength range 166nm~847nm, plasma observation method vertical observation, plasma observation height 14mm, RF power 1150W, frequency 27.12MHz, injection system auxiliary gas flow 0.5L / min, injection system nebulizer gas flow 0.6L / min, pump speed 50rpm. Micro-volume test: accurately weigh 0.2000g-0.2100g of sample into a 50mL quartz beaker, add 10ml 1:1 aqua regia, cover with a watch glass, dissolve completely on a heating furnace, transfer to a 50mL volumetric flask, dilute to volume, shake well, test on the machine, and record data; Major volume measurement: transfer 1ml of the above shaken solution to a 100mL volumetric flask, dilute to 100mL, shake well, test on the machine, and record data.

[0062] Lithium-cobalt ratio results settlement:

[0063]

[0064] Li%---ICP test shows the content of Li; Co%---ICP test shows the content of Co;

[0065] M Li ---Relative atomic mass of Li; M Co ---Relative atomic mass of Co

[0066] 5. Test method of sodium-cobalt atomic ratio

[0067] ICP test method: using ICP-OES iCAP 6300 inductively coupled plasma atomic emission spectrometer, detector detection unit> 290000, detector cooling system Camera temperature <-35℃, optical system light chamber temperature: 38℃±0.1℃, optical system wavelength range 166nm~847nm, plasma observation method vertical observation, plasma observation height 14mm, RF power 1150W, frequency 27.12MHz, injection system auxiliary gas flow 0.5L / min, injection system nebulizer gas flow 0.6L / min, pump speed 50rpm. Micro-test: Accurately weigh 0.2000g-0.2100g of sample into a 50mL quartz beaker, add 9mL concentrated hydrochloric acid + 3mL concentrated nitric acid, shake well, cover with a watch glass, dissolve completely on a heating furnace, transfer to a 100mL volumetric flask, dilute to 100mL, shake well, test on a computer, and record data; Major measurement: Transfer 1ml of the above shaken solution to a 100mL volumetric flask, dilute to 100mL, shake well, test on a computer, and record data.

[0068] Sodium-cobalt ratio result settlement:

[0069]

[0070] Na%---ICP test shows the content of Na; Co%---ICP test shows the content of Co;

[0071] M Na ---Relative atomic mass of Na; M Co ---Relative atomic mass of Co

[0072] 6. Power-off test method

[0073] 4.6V-3.0V buckle 0.1C gram capacity determination method: The gram capacity test method refers to GB / T37201-2018 "Nickel Cobalt Manganese Oxide Lithium Electrochemical Performance Test First Discharge Specific Capacity and First Charge and Discharge Efficiency Test Method", which is measured by NEWARE high-performance battery testing system CT-4008-5V50mA-164. Weigh 159g of NMP solution in a container, place it on a mixer, adjust the speed to 800r / min, weigh 6g of PVDF powder, and slowly add it to the NMP solution. After the addition is completed, adjust the speed to 2000r / min, stir for 10min, until there are no PVDF particles in the solution, adjust the speed to 800r / min, add 6g of SP powder, and then adjust the speed to 2000r / min, and stir for 30min. After stirring, transfer the container to the ARE-310 stirrer and stir for 16min. After stirring, the slurry is called conductive glue. Weigh 5.7000g of conductive glue and 3.6000g of positive electrode material into a 5D stirring container, cover the container lid, place the container in a Nissin ARE-310 mixer and stir at 850rpm for 1min, then stir at 2000rpm for 15min. After stirring, take out the stirring container, open the sealing cover, and apply the slurry on a 14μm aluminum foil with a 150μm salary coater. After coating, place it in an oven and dry it at 100℃ for 2hrs. After drying, cut off the excess collectors on both sides of the pole piece that are not coated, and cold press the pole piece to make the compaction density reach (3.3~3.5)g / cm 3. Place the compacted membrane on the punching platform of the punching machine, with the uncoated side of the aluminum foil facing up, swing the rocker of the punching machine to move the punching machine mold downward to make a small disc of φ14mm, select 4 small discs of similar weight as a group of pole pieces, and bake them in a vacuum oven at 105℃ and -0.085Mpa for 1h. After the small discs are vacuum-baked, transfer them to the glove box and assemble them into a battery in the following order: negative electrode shell-nickel foam-lithium sheet-electrolyte-diaphragm-electrolyte-small disc-positive electrode shell-seal. Then place the battery in a (25±0.5)℃ constant temperature box, connect the CT-4008-5V50mA-164 detection system, and test the battery's charge and discharge performance at 0.1C under 4.6V-3.0V conditions.

[0074] Charging capacity = charging current * charging time

[0075] Discharge capacity = discharge current * discharge time

[0076] First charge gram capacity = first charge capacity / active material mass

[0077] First discharge capacity in grams = first discharge capacity / mass of active material

[0078] First efficiency = first discharge capacity / first charge capacity

[0079] The following specific examples illustrate the preparation method of the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material proposed in this application. The reagents or instruments not described in the text of this application are all contents that can be routinely confirmed by ordinary technicians in this field.

[0080] The specific embodiments are as follows:

[0081] Example 1

[0082] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0083] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.95, the atomic ratio of (Li+Na) / Co is 1.10, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.04, 0.02 and 0.04 respectively.

[0084] Step 2: Dry the mixed system at 280°C by spray drying, and then sinter the dried product at 750°C in air atmosphere for 36 hours to obtain an O3-P2 mixed crystal type sodium lithium cobalt oxide precursor. The total area of ​​the structural characteristic diffraction peaks of P2 type sodium cobalt oxide and O3 type lithium cobalt oxide in the precursor accounts for 100% of the total area of ​​all diffraction peaks, and its characterization data are shown in Table 1.

[0085] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 40.6g of LiOH (H2O) is mixed with 500g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal sodium lithium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 18h under closed conditions, solid-liquid separation and drying at 280°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 1.

[0086] Example 2

[0087] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0088] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.80, the atomic ratio of (Li+Na) / Co is 1.05, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0089] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 700°C in an air atmosphere for 24 hours to obtain an O3-P2 mixed crystal type sodium lithium cobalt oxide precursor. The total area of ​​the characteristic diffraction peaks of the P2 type sodium cobalt oxide and the O3 type lithium cobalt oxide in the precursor accounts for 100% of the total area of ​​all diffraction peaks. The characterization data is shown in Table 1.

[0090] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 40.6g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at a temperature of 180°C for 0.5h under closed conditions, solid-liquid separation and drying at a temperature of 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction spectrum of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 1.

[0091] Example 3

[0092] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0093] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.80, the atomic ratio of (Li+Na) / Co is 1.05, and the atomic ratios of Mg / Co and Al / Co are 0.04 and 0.02, respectively.

[0094] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 750°C in an air atmosphere for 12 hours to obtain an O3-P2 mixed crystal type sodium lithium cobalt oxide precursor. The total area of ​​the structural characteristic diffraction peaks of P2 type sodium cobalt oxide and O3 type lithium cobalt oxide in the precursor accounts for 100% of the total area of ​​all diffraction peaks, and its characterization data are shown in Table 1.

[0095] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 40.6g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4h under closed conditions, solid-liquid separation and drying at 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 1.

[0096] Example 4

[0097] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0098] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.90, the atomic ratio of (Li+Na) / Co is 1.02, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0099] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 700°C in an air atmosphere for 18 hours to obtain an O3-P2 mixed crystal type sodium lithium cobalt oxide precursor. The total area of ​​the structural characteristic diffraction peaks of P2 type sodium cobalt oxide and O3 type lithium cobalt oxide in the precursor accounts for 100% of the total area of ​​all diffraction peaks, and its characterization data are shown in Table 1.

[0100] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 40.6g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4h under closed conditions, solid-liquid separation and drying at 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 1.

[0101] Example 5

[0102] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0103] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.80, the atomic ratio of (Li+Na) / Co is 1.02, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0104] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 750°C in air atmosphere for 18 hours to obtain an O3-P2 mixed crystal type sodium lithium cobalt oxide precursor. The total area of ​​the structural characteristic diffraction peaks of P2 type sodium cobalt oxide and O3 type lithium cobalt oxide in the precursor accounts for 100% of the total area of ​​all diffraction peaks. The characterization data is shown in Table 1.

[0105] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 32.5g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4h under closed conditions, solid-liquid separation and drying at 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 1.

[0106] Table 1 Characterization data of the compounds obtained in Examples 1 to 5

[0107]

[0108] Example 6

[0109] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0110] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.70, the atomic ratio of (Li+Na) / Co is 1.02, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0111] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 700°C in an air atmosphere for 18 hours to obtain an O3-P2 mixed crystal type sodium lithium cobalt oxide precursor. The total area of ​​the characteristic diffraction peaks of the P2 type sodium cobalt oxide and the O3 type lithium cobalt oxide in the precursor accounts for 100% of the total area of ​​all diffraction peaks. The characterization data is shown in Table 2.

[0112] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 28.4g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4h under closed conditions, solid-liquid separation and drying at 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 2.

[0113] Example 7

[0114] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0115] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.60, the atomic ratio of (Li+Na) / Co is 1.02, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0116] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 750°C in air atmosphere for 18 hours to obtain an O3-P2 mixed crystal sodium lithium cobalt oxide precursor, as shown in the SEM scanning electron microscope image. Figure 2 As shown. Figure 1 As shown, the total area of ​​the characteristic diffraction peaks of the P2-type sodium cobaltate and O3-type lithium cobaltate structures in the precursor accounts for 100% of the total area of ​​all diffraction peaks. The characterization data is shown in Table 2.

[0117] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 24.4 g of LiOH (H2O) is evenly mixed with 200 g of water to obtain a suspension, and then 100 g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4 hours under closed conditions, the mixture is dried at 200°C after solid-liquid separation to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, and its SEM scanning electron microscope image is as shown in the figure. Figure 4 As shown. Figure 3As shown in the X-ray diffraction spectrum of the positive electrode material, the total area of ​​the diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure characteristics accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material can be found in Table 2.

[0118] Example 8

[0119] In this embodiment, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0120] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.40, the atomic ratio of (Li+Na) / Co is 1.02, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0121] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 700°C in an air atmosphere for 18 hours to obtain an O3-P2 mixed crystal sodium lithium cobalt oxide precursor. The characterization data of the precursor are shown in Table 2.

[0122] This embodiment adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 16.2g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4h under closed conditions, solid-liquid separation and drying at 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 100% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 2.

[0123] Comparative Example 1

[0124] In order to compare the technical effects of the present application, this comparative example uses conventional O3 type lithium cobalt oxide for comparison, and its preparation method is as follows:

[0125] Co3O4 doped with 1% Al content and with a D50 particle size of 5 um and lithium carbonate were evenly mixed by a ball mill with a Li / Co ratio of 1.02 and sintered at 950°C for 12 hours to synthesize conventional O3 type lithium cobalt oxide. The characterization data are shown in Table 2.

[0126] Comparative Example 2

[0127] In this comparative example, the synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows:

[0128] Step 1: Evenly mix Co(OH)2, MgO, Al2O3, Y2O3, NaOH and LiOH(H2O) in water to obtain a mixed system, wherein the atomic ratio of Na / (Li+Na) in the mixed system is 0.40, the atomic ratio of (Li+Na) / Co is 1.02, and the atomic ratios of Mg / Co, Al / Co and Y / Co are 0.02, 0.02 and 0.01 respectively.

[0129] Step 2: Dry the mixed system at 250°C by spray drying, and then sinter the dried product at 850°C in air atmosphere for 18 hours to obtain an O3-P2 mixed crystal sodium cobalt oxide precursor. The total area of ​​the characteristic diffraction peaks of the P2 type sodium cobalt oxide and the O3 type lithium cobalt oxide in the precursor accounts for 78.4% of the total area of ​​all diffraction peaks. The characterization data is shown in Table 2.

[0130] This comparative example adopts a liquid phase ion replacement synthesis method to prepare an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material: 32.5g of LiOH (H2O) is mixed with 200g of water to obtain a suspension, and then 100g of the above-mentioned O3-P2 mixed crystal lithium sodium cobalt oxide precursor is added to the suspension to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.10. After stirring at 95°C for 4h under closed conditions, solid-liquid separation and drying at 200°C are performed to obtain an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material. In the X-ray diffraction pattern of the positive electrode material, the total area of ​​the characteristic diffraction peaks of the O3 type lithium cobalt oxide and the O2 type lithium cobalt oxide structure accounts for 61% of the total area of ​​all diffraction peaks. The characterization data of the positive electrode material are shown in Table 2.

[0131] Table 2 Characterization data of the compounds obtained in Examples 6 to 8 and Comparative Examples 1 and 2

[0132]

[0133] In the above-mentioned Examples 1 to 6 and Example 8, the XRD diffraction pattern of the O3-P2 mixed crystal lithium sodium cobalt oxide precursor and the XRD diffraction pattern of the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material are similar to those in Example 7. In order to simplify the application documents, they are no longer shown one by one in the drawings of the specification.

[0134] From the characterization data in Table 1 and Table 2, it can be seen that the sintering temperature is crucial to obtain the O3-P2 mixed crystal type lithium sodium cobalt oxide precursor. When the temperature is lower than 700°C, the sodium-containing part tends to form a P3-type crystal structure of the R3m space group; when the temperature is higher than 750°C, the P2-type sodium cobalt oxide will further react with the O3-type lithium cobalt oxide to form a more complex multiphase structure. Precursors formed at too low or too high temperatures cannot be converted into O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode materials after lithium-sodium ion replacement.

[0135] like Figure 6 As shown in the figure, the average discharge voltage of the material decreases linearly with the increase of the O2 type ratio. The main reason is that with the increase of the O2 type ratio, the proportion of the 3.9V discharge platform of the O3 type characteristic gradually decreases, resulting in a decrease in the discharge average voltage. Figure 5 As shown, the discharge capacity of the material increases first and then decreases with the increase of the O2-type ratio. The pure O2-type LCO has a lower lithium ion diffusion barrier. In the same voltage range, the discharge capacity is significantly higher than that of the O3-type LCO. When the O2-O3-type structure of the material coexists, the characteristics of the O3-type and O2-type will be simultaneously shown in the charge and discharge curve. Compared with the pure O2-type structural material, the capacity improvement mainly comes from the characteristic discharge platform of the O3-type near 3.9V. Therefore, since the ratio of O3-type lithium cobalt oxide and O2-type lithium cobalt oxide has a significant impact on the material capacity, the higher the O2 phase ratio, the higher the discharge average voltage. Taking the capacity and discharge average voltage into consideration, the mixed crystal LCO in this application controls the ratio of O3-type lithium cobalt oxide and O2-type lithium cobalt oxide within a reasonable range, so that it has the highest energy density.

Claims

1. An O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, characterized in that: The positive electrode material is obtained by washing and drying an O3-P2 mixed crystal sodium cobaltate precursor with a high (Na+Li) / Co atomic ratio after Li-Na ion replacement; the O3-P2 mixed crystal sodium cobaltate precursor is composed of O3 type lithium cobaltate and P2 type sodium cobaltate, wherein the (Na+Li) / Co atomic ratio is 0.9-1.

1.

2. The O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 1, characterized in that: Its expression is: Li x (Li a Na b Co c M' d ) z , wherein M' is a modifying element selected from one or more of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu, and Fe; In the above expressions, 0.4≤x≤1.2, 0≤a≤0.2, 0≤b≤0.1, 0.8≤c≤1, 0≤d≤0.1, 1.9≤z≤2.2, 0.9≤x+a+b≤1.2, 0.9≤c+d≤1.

2.

3. The O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 1, characterized in that: In the X-ray diffraction spectrum of the positive electrode material, the total area of ​​the diffraction peaks with structural characteristics of O3-type lithium cobalt oxide and O2-type lithium cobalt oxide accounts for ≥90% of the total area of ​​all diffraction peaks.

4. The O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The lithium carbonate content of the positive electrode material measured by aqueous solution titration method is less than or equal to 0.5 wt.%.

5. The O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The Li / Co atomic ratio in the positive electrode material is 0.9 to 1.

2.

6. A method for preparing an O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, comprising an existing liquid phase ion replacement synthesis method, characterized in that: An O3-P2 mixed crystal lithium sodium cobaltate precursor is put into an aqueous suspension containing a saturated Li+ compound to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 0.9-1.

2. After stirring at a temperature of 90-180°C for 0.5-18h under closed conditions, the mixture is separated from the solid and liquid and dried at a temperature below 300°C to obtain an O3-O2 mixed crystal layered oxide lithium cobaltate positive electrode material.

7. The method for preparing the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 6, characterized in that: In the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material, the crystal plane diffraction peak height of O2 type lithium cobalt oxide is H2, and the crystal plane diffraction peak height of O3 type lithium cobalt oxide is H3, then H2 / (H2+H3) is 0.3 to 1.

0.

8. The method for preparing the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 6, characterized in that: The synthesis steps of the O3-P2 mixed crystal type sodium lithium cobalt oxide precursor are as follows: Step 1, uniformly mixing a Co-containing compound, a modifying element M'-containing compound and an A-containing compound in water to obtain a mixed system, wherein M' is a modifying element selected from one or more of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu and Fe; A is a mixed compound of a Na source and a Li source; the Na / (Li+Na) atomic ratio in the mixed system is 0.4-0.95, and the (Li+Na) / Co atomic ratio is 1.0-1.10; Step 2: Dry the mixed system at 250-280° C. by spray drying, and then sinter the dried product at 700-750° C. for 12-36 hours to obtain an O3-P2 mixed crystal sodium lithium cobalt oxide precursor.

9. The method for preparing the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 7, characterized in that: The X-ray diffraction spectrum of the O3-P2 mixed crystal sodium cobaltate precursor includes characteristic diffraction spectra of P2 type sodium cobaltate of P63 / mmc space group and O3 type lithium cobaltate of R-3m space group, and the total area of ​​the characteristic diffraction peaks of the P2 type sodium cobaltate and O3 type lithium cobaltate structures accounts for ≥95% of the total area of ​​all diffraction peaks.

10. The method for preparing the O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode material according to claim 8, characterized in that: The total content of sodium carbonate and lithium carbonate in the O3-P2 mixed crystal sodium lithium cobaltate precursor measured by aqueous solution titration method is ≤15wt.%.

11. A lithium ion battery comprising a positive electrode active material, characterized in that: The positive electrode active material comprises one or more O3-O2 mixed crystal layered oxide lithium cobalt oxide positive electrode materials obtained by the preparation method according to any one of claims 6 to 10.

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