Near-pure-phase O2 type lithium cobalt oxide positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a near-pure-phase O2 type lithium cobalt oxide positive electrode material and a preparation method and application thereof.According to the method, a P2 type near-pure-phase NCO precursor material with the high Na / Co specific content is adopted for successfully synthesizing a near-pure-phase O2 type LCO material through Li-Na ion replacement, the Li / Co atomic ratio ranges from 0.9 to 1.2, the content of free Li2CO3 of the material is smaller than or equal to 0.5 wt.%, the content of Li < + > occupied by the structure is high, and the material can be applied to the field of lithium ion battery cathode materials. And an X-ray diffraction pattern has no miscellaneous peaks except the O2-type structure. Therefore, by selecting reasonable doping modification and primary sintering conditions, a near-pure-phase P2 type NCO precursor material with a high Na / Co ratio synthesized in an air atmosphere is provided, and a high-proportion structure of the P2 type precursor material occupies Na, good Na < + > diffusion dynamics performance and a stable structure are utilized, so that the high-purity NCO precursor material is obtained. And the near-pure-phase O2 type lithium cobalt oxide positive electrode material with high Li / Co ratio, low free Li2CO3 content, low Na < + > residue and stable structure is synthesized through Li-Na ion replacement.

Description

Technical Field

[0001] The invention relates to a nearly pure phase O2 type 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 characteristics 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 voltage. Lithium cobalt oxide has a variety of structures, among which O 3 Type lithium cobalt oxide occupies a leading position in the market. 3 The nomenclature is derived from Delmas’s concept of layered material classification. “O” represents Li-O octahedron or Co-O octahedron, and “3” represents that Li-O-Co is stacked alternately in the crystal unit cell, with a minimum repetition period of 3. Since Goodenough first discovered O 3 Since the introduction of LCO, the gram capacity of lithium cobalt oxide has been continuously improved with the increase of the upper limit cut-off voltage. At present, when charged to 4.53-4.55V, the gram capacity has reached 192mAh / g. If the charge cut-off voltage is further increased and the Li / Co atomic ratio is <30%, O 3 Type LCO will face the collapse of layered structure caused by excessive lithium removal (O 3 -H 1 / 3 Phase change and O 1 Phase change), which leads to irreversible cycle capacity loss. Faced with the continuous growth of market demand for thinner and higher energy density lithium-ion batteries, O 3 In 1982, Delmas first passed P 2 O was obtained by Li-Na replacement of NCO 2 In 2002, Delmas revealed O 2 Type x CoO 2 (0.16~x~1) O in the process of charge and discharge 2 -T 2 -O 6 -O 2 -O 2 ' structural evolution process. In 2024, Yu Xiqian's team at the Chinese Academy of Sciences passed P 2 Type Na 0.7 CoO 2 (NCO)Synthesis of O 2type LCO, and revealed for the first time that O 2 Type LCO is better than O 3 The electrochemical performance and mechanism of LCO[1]. 2 The structure of lithium cobalt oxide is better than that of O 3 Type LCO, the reasons are: (1) O 2 (1) O2-type LCO has a lower Li+ diffusion barrier, which makes Li ion diffusion more convenient and the Li+ concentration in the particles more uniform during lithium insertion and extraction. (2) At the same time, during the lithium extraction process of O2-type LCO, the elastic modulus along the c-axis of the particles is more continuous, while the elastic modulus along the a-axis hardly changes, resulting in lower internal stress of the particles caused by lithium insertion and extraction, and the particles are less likely to crack and pulverize after cycling [1].

[0003] So far, all the O reported in public data 2 The layered LCO structures are based on Figure 6 ShownNa x CoO 2 Phase diagram [2] Na / Co atomic ratio < 0.83 P 2 However, P with low Na / Co atomic ratio 2 Synthesis of O from NCO 2 Type LCO will have the following problems:

[0004] (1) Conventional P 2 Type Na x CoO 2 (x<0.83), the average valence state of Co is > +3.17, exceeding +3, and near-pure phase P can only be achieved under pure oxygen conditions or when the oxygen partial pressure exceeds that of normal air. 2 structure, and the synthetic P 2 The oxygen vacancies in the structural material increase, the synthesis cost is high, and the synthesis difficulty is great. 2 The structural stability is poor, the reaction kinetics is poor during the synthesis process, and it is easy to produce uneven Na / Co and impurities caused by poor atmosphere conditions; poor reaction kinetics will aggravate the volatilization of Na during the synthesis process, resulting in P 2 If the temperature is too low during the synthesis of the structure, the material structure will be unstable, and if the temperature is too high, Na will volatilize seriously, which is not conducive to large-scale industrial production.

[0005] (2) During the Li-Na replacement process, the charge balance of the material requires that one Li+ replaces one Na+. 2 The insufficient total amount in the structure and the excessive oxygen vacancies in the material will lead to the O 2The total amount of occupying Li+ (Li+ located in the Li layer of the layered structure) in the structural material is insufficient. Even if the Li / Co atomic ratio after Li-Na substitution is higher than the Na / Co atomic ratio before substitution, the excess Li+ exists in a non-occupying form, resulting in a decrease in the specific capacity of the material.

[0006] (3)O 2 The LCO structure is a metastable structure. When the replacement and drying temperature is higher than 400℃, it is very easy to transform into O 3 Type structure LCO, thus losing O 2 The structural stability advantage of type LCO is that 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. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention proposes a near-pure phase O2 type lithium cobalt oxide positive electrode material and a preparation method and application thereof. The method uses a P2 type near-pure phase NCO precursor material with a high Na / Co ratio to successfully synthesize a near-pure phase O2 type LCO material through Li-Na ion replacement. The Li / Co atomic ratio is between 0.9 and 1.2, and the free Li 2 CO 3 The content is ≤0.5wt.%, the structure has a high content of Li+, the X-ray diffraction spectrum has no impurity peaks other than the O2 structure, and the structure is stable.

[0008] The technical solution of the present invention is a near-pure phase O2-type lithium cobalt oxide positive electrode material, which is a near-pure phase P with a high Na / Co atomic ratio. 2 The sodium cobalt oxide precursor is obtained by Li-Na ion replacement, washing and drying; the near-pure phase P 2 The Na / Co atomic ratio in the sodium cobaltate precursor is 0.9 to 1.1.

[0009] Furthermore, the expression of the near-pure phase O2-type lithium cobalt oxide 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;

[0010] The M' represents the amount of Li 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;

[0011] In the above expressions, 0.4≤x≤1.2, 0≤a≤0.2, 0≤b≤0.1, 0.8≤c≤1, 0≤d≤0.4, 1.9≤z≤2.2, 0.9≤x+a+b≤1.2, 0.9≤c+d≤1.2.

[0012] Furthermore, in the X-ray diffraction pattern of the near-pure phase O2-type lithium cobalt oxide positive electrode material, O 2 The proportion of the total area of ​​the diffraction peaks with the structural characteristics of the type to the total area of ​​all diffraction peaks is ≥90%, preferably 100%.

[0013] Furthermore, the sodium carbonate content of the nearly pure phase O2-type lithium cobalt oxide positive electrode material measured by aqueous solution titration method is ≤0.5wt.%.

[0014] Furthermore, the Li / Co atomic ratio in the near-pure phase O2-type lithium cobalt oxide positive electrode material is 0.9 to 1.2.

[0015] At the same time, the present invention also provides a method for preparing a nearly pure phase O2 type lithium cobalt oxide positive electrode material, comprising an existing liquid phase ion replacement synthesis method, a nearly pure phase P 2 The sodium cobalt oxide precursor is put into a water or alcohol suspension containing a saturated Li+ compound to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.0-1.2. After stirring at 70-120°C for 0.5-24h, solid-liquid separation and drying at a temperature below 300°C are performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material.

[0016] The preparation method of the above-mentioned nearly pure phase O2 type lithium cobalt oxide positive electrode material can also adopt the existing molten salt ion replacement synthesis method, that is, nearly pure phase P 2 The sodium cobalt oxide precursor and the Li+ compound are mixed evenly according to the Li / Co atomic ratio of 1.0 to 1.2, sintered at 200 to 400 ° C for 2 to 24 hours, washed with water to remove impurities and dried at a temperature below 300 ° C to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material.

[0017] In the above method, the sodium carbonate content in the P2 type sodium cobaltate precursor is ≤15wt.%.

[0018] In the above method, the near pure phase P in the new suspension system 2The weight proportion of the sodium cobalt oxide precursor is ≥20%.

[0019] In the above method, the nearly pure phase P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0020] Step 1, uniformly mixing a Co-containing compound, a modifying element M'-containing compound and an A-containing compound in an aqueous or alcoholic system 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 one or all of Na or Li compounds, and the Na / (Li+Na) atomic ratio is between 0.8 and 1.0;

[0021] Step 2: Dry the mixed system, and then sinter the dried product at 650-950°C for 12-24h to obtain a nearly pure phase P 2 Type sodium cobaltate precursor.

[0022] In the above method, the nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The proportion of the total area of ​​the characteristic diffraction peaks of the sodium cobalt oxide precursor crystal structure to the total area of ​​all diffraction peaks is ≥90%, preferably 100%.

[0023] In the above method, the solid-liquid ratio of the mixed system is ≥20%.

[0024] In the above method, the P 2 The sodium carbonate content of the sodium cobaltate precursor measured by aqueous solution titration method is ≤15wt.%.

[0025] In the above method, the Na atoms and Co atoms in the drying product are in full contact, and the maximum distance between them is nanometer level.

[0026] In the above method, the Co-containing compound and the M'-containing compound are one or more of oxides, hydroxides, oxyhydroxides, nitrates, and chlorides, and the Co-containing compound may contain M'.

[0027] In the above method, the drying method of the mixed system is flash evaporation or spray drying, and the inlet air temperature is 180-700°C.

[0028] 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 a near-pure phase O obtained by the above preparation method. 2 Type lithium cobalt oxide positive electrode material.

[0029] Due to the adoption of the above technical solution, the advantages of the present invention are: the present invention successfully synthesizes a near-pure phase P with a high Na / Co atomic ratio by optimizing the formulation and sintering conditions. 2 NCO precursor, Na / Co ratio between 0.9 and 1.1, X-ray diffraction pattern with P6 3 / mmc space group P 2 Type crystal structure, without impurity peaks, free Na 2 CO 3 The content is ≤15wt.%. Furthermore, the present invention uses a P2-type near-pure NCO precursor material with a high Na / Co ratio to successfully synthesize a near-pure O2-type LCO material by Li-Na ion replacement, with a Li / Co atomic ratio between 0.9 and 1.2, and the free Li 2 CO 3 The content is ≤0.5wt.%, the structural occupies a high content of Li+, the X-ray diffraction spectrum has no impurity peaks other than the O2 type structure, and the structure is stable. Therefore, the near-pure phase O2 type LCO material of the present invention solves the structural stability problem in high voltage applications, has very high high voltage cycle stability, and can achieve higher energy density and lower production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The XRD diffraction pattern of the nearly pure phase P2-type sodium cobalt oxide precursor synthesized in Example 1;

[0031] Figure 2 The XRD diffraction pattern of the nearly pure phase O2-type lithium cobalt oxide synthesized in Example 1;

[0032] Figure 3 The XRD diffraction pattern of the non-pure phase P2 type sodium cobalt oxide precursor synthesized in Comparative Example 2;

[0033] Figure 4 The XRD diffraction pattern of the non-pure phase O2 type lithium cobalt oxide synthesized in Comparative Example 2;

[0034] Figure 5 a is a SEM scanning electron micrograph of the nearly pure phase P2 type sodium cobalt oxide precursor synthesized in Example 1;

[0035] Figure 5 b is a SEM scanning electron microscope image of the nearly pure phase small particle O2 type lithium cobalt oxide synthesized in Example 1;

[0036] Figure 5 c is a SEM scanning electron micrograph of the nearly pure phase P2 type sodium cobalt oxide precursor synthesized in Example 10;

[0037] Figure 5d is the SEM scanning electron microscope image of the nearly pure phase large particle O2 type lithium cobalt oxide synthesized in Example 10.

[0038] Figure 6 is Na in the prior art x CoO 2 Phase diagram. DETAILED DESCRIPTION

[0039] 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.

[0040] 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.

[0041] The present application proposes a near-pure phase O2-type lithium cobalt oxide positive electrode material, which is a near-pure phase P with a high Na / Co atomic ratio. 2 The sodium cobalt oxide precursor is obtained by Li-Na ion replacement, washing and drying; the near-pure phase P 2 The Na / Co atomic ratio in the sodium cobaltate precursor is 0.9 to 1.1.

[0042] According to some embodiments of the present application, the expression of the above-mentioned near-pure phase O2-type lithium cobalt oxide 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;

[0043] The M' represents the amount of Li 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;

[0044] In the above expressions, 0.4≤x≤1.2, 0≤a≤0.2, 0≤b≤0.1, 0.8≤c≤1, 0≤d≤0.4, 1.9≤z≤2.2, 0.9≤x+a+b≤1.2, 0.9≤c+d≤1.2.

[0045] According to some embodiments of the present application, in the X-ray diffraction pattern of the above-mentioned near-pure phase O2-type lithium cobalt oxide positive electrode material, O 2 The proportion of the total area of ​​the diffraction peaks with the structural characteristics of the type to the total area of ​​all diffraction peaks is ≥ 90%, preferably 100%.

[0046] According to some embodiments of the present application, the Li / Co atomic ratio in the above-mentioned near-pure phase O2-type lithium cobalt oxide positive electrode material is 0.9 to 1.2.

[0047] At the same time, the present invention provides a method for preparing a nearly pure phase O2 type lithium cobalt oxide positive electrode material, including an existing liquid phase ion replacement synthesis method, a nearly pure phase P 2 The sodium cobalt oxide precursor is put into a water or alcohol suspension containing a saturated Li+ compound to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.0-1.2. After stirring or sand milling at 70-120°C for 0.5-24h, solid-liquid separation and drying at a temperature below 300°C are performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material.

[0048] The preparation method of the above-mentioned nearly pure phase O2 type lithium cobalt oxide positive electrode material can also adopt the existing molten salt ion replacement synthesis method, that is, nearly pure phase P 2 The sodium cobalt oxide precursor and the Li+ compound are mixed evenly according to the Li / Co atomic ratio of 1.0 to 1.2, sintered at 200 to 400 ° C for 2 to 24 hours, washed with water to remove impurities and dried at a temperature below 300 ° C to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material.

[0049] In the above method, the sodium carbonate content of the P2 type sodium cobaltate precursor measured by aqueous solution titration method is ≤15wt.%.

[0050] In the above method, the near pure phase P in the new suspension system 2 The weight proportion of the sodium cobalt oxide precursor is ≥20%.

[0051] In the above method, the nearly pure phase P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0052] Step 1, uniformly mixing a Co-containing compound, a modifying element M'-containing compound and an A-containing compound in an aqueous or alcoholic system 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 one or all of Na or Li compounds, and the Na / (Li+Na) atomic ratio is between 0.8 and 1.0;

[0053] Step 2: Dry the mixed system, and then sinter the dried product at 650-950°C for 12-24h to obtain a nearly pure phase P 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The proportion of the total area of ​​the characteristic diffraction peaks of the sodium cobalt oxide precursor crystal structure to the total area of ​​all diffraction peaks is ≥90%, preferably 100%.

[0054] According to some embodiments of the present application, the solid-liquid ratio of the mixed system is ≥20%.

[0055] According to some embodiments of the present application, the Na atoms and the Co atoms in the drying product are in full contact, and the maximum distance between them is at the nanometer level.

[0056] According to some embodiments of the present application, the Co-containing compound and the M'-containing compound are one or more of oxides, hydroxides, oxyhydroxides, nitrates, and chlorides, and the Co-containing compound may include M'.

[0057] According to some embodiments of the present application, the drying method of the mixed system is flash evaporation or spray drying, and the inlet air temperature is 180-700°C.

[0058] 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 a near-pure phase O2-type lithium cobalt oxide positive electrode material obtained by the above-mentioned preparation method. The lithium ion battery can be used in the fields of digital products, power tools, electronic cigarettes or drones.

[0059] It is particularly noted that the definition of "nearly pure phase" in the present application is: the ratio of the sum of the characteristic diffraction peak areas of the target structure in the X-ray diffraction spectrum to the sum of all diffraction peak areas is ≥ 90%.

[0060] In this patent, it is used to calculate P 2 The XRD standard PDF card number of the peak area ratio of sodium cobaltate is: 00-030-1182, and the chemical formula is Na 0.71 Co 0.96 O 2 ; used to calculate O 2 The XRD standard PDF card number of the peak area ratio of lithium cobalt oxide is: 00-036-1004, and the chemical formula is LiCoO 2 .

[0061] The equipment and analysis methods used in the following examples of this application are as follows:

[0062] 1. Determination of residual sodium carbonate by aqueous solution method

[0063] Determination method of residual sodium carbonate in aqueous solution: accurately weigh 15g ± 0.5g (m) sample, put the sample into a 250mL conical flask, put in a magnetic particle, add 100mL (L 1 ) deionized water; put it on a magnetic stirrer, turn on the stirrer and stir for 30 minutes, use a clean suction filter to filter; remove 1mL (L 2 ) The filtrate was placed in a 100 mL titration cup, deionized water was added to 40 mL, and 0.05 mol / L hydrochloric acid was used to measure the initial volume V using a fully automatic potentiometric titrator (METTLER TOLEDO T5). 0 , titrate the first equivalence point V 1 , titrate the second equivalence point V 2 .

[0064] Calculation of residual sodium carbonate:

[0065]

[0066] c---concentration of standard hydrochloric acid titration solution; m---mass of sample; M 1 ---Relative atomic mass of sodium; M 2 ---Relative molecular mass of sodium carbonate; M 3 ---Relative molecular mass of sodium hydroxide; V 0 --- Initial volume; V 1 --- is the first titration equivalence point; V 2 --- is the second titration equivalence point; L 1 ---Total volume of residual sodium carbonate solution; L 2 --- Remove the volume of the residual sodium carbonate solution. Note: The sodium carbonate content obtained in this application is based on the titration of carbonate ions. Strictly speaking, the free sodium in the samples of some embodiments of this application may contain a small amount of free lithium, which is not strictly distinguished in this application.

[0067] 2. Determination of residual lithium carbonate by aqueous solution method

[0068] Determination method of residual lithium carbonate in aqueous solution: accurately weigh 30g ± 0.5g (m) sample, put the sample into a 250mL conical flask, put in a magnetic bar, add 100mL (L 1 ) deionized water; put it on a magnetic stirrer, turn on the stirrer and stir for 30 minutes, filter it using a clean funnel; remove 50mL (L 2 ) The filtrate was placed in a 100 mL titration cup and 0.05 mol / L hydrochloric acid was used to measure the initial volume V using a fully automatic potentiometric titrator (METTLER TOLEDO T5). 0, titrate the first equivalence point V 1 , titrate the second equivalence point V 2 .

[0069] Calculation of residual lithium carbonate:

[0070]

[0071] c---concentration of standard hydrochloric acid titration solution; m---mass of sample; M 1 ---Relative atomic mass of lithium; M 2 ---Relative molecular mass of lithium carbonate; M 3 ---Relative molecular mass of lithium hydroxide; V 0 --- Initial volume; V 1 --- is the first titration equivalence point; V 2 --- is the second titration equivalence point; L 1 ---Total volume of residual lithium carbonate solution; L 2 --- Remove the volume of the residual lithium carbonate solution. Note: The lithium carbonate content obtained in this application is based on the titration of carbonate ions. Strictly speaking, the free lithium in the samples of some embodiments of this application may contain a small amount of free sodium, which is not strictly distinguished in this patent.

[0072] 3. XRD test method

[0073] 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 a series of analysis operations such as background calibration, peak finding, secondary or higher peak fitting, and spectrum matching, the obtained X-ray diffraction spectrum is subjected to a peak list, and the area data of each diffraction peak is obtained from the peak list. The obtained area data are processed and the area percentage data is obtained.

[0074] 4. Test method of lithium-cobalt atomic ratio

[0075] 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.

[0076] Lithium-cobalt ratio results settlement:

[0077]

[0078] Li%---ICP test shows the content of Li; Co%---ICP test shows the content of Co;

[0079] M Li ---Relative atomic mass of Li; M Co ---Relative atomic mass of Co

[0080] 5. Test method of sodium-cobalt atomic ratio

[0081] 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.

[0082] Sodium-cobalt ratio result settlement:

[0083]

[0084] Na%---ICP test shows the content of Na; Co%---ICP test shows the content of Co;

[0085] M Na ---Relative atomic mass of Na; M Co ---Relative atomic mass of Co

[0086] 6. Power-off test method

[0087] 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.

[0088] Charging capacity = charging current * charging time

[0089] Discharge capacity = discharge current * discharge time

[0090] First charge gram capacity = first charge capacity / active material mass

[0091] First discharge capacity in grams = first discharge capacity / mass of active material

[0092] First efficiency = first discharge capacity / first charge capacity

[0093] The nearly pure phase O2-type lithium cobalt oxide positive electrode material and preparation method proposed in the present application are described below through specific embodiments. The reagents or instruments not described in the present application text are all contents that can be routinely confirmed by ordinary technicians in this field.

[0094] The specific embodiments are as follows

[0095] Example 1

[0096] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0097] Step 1: Co(OH) 2 ,MgO,Na 2 CO 3 and LiOH(H 2 O) uniformly stirring in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 53%, the Na / (Li+Na) atomic ratio is 0.95, and the (Li+Na) / Co atomic ratio is 1.04;

[0098] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 750°C in an air atmosphere for 24 hours to obtain a nearly pure phase P. 2The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group crystal structure; see Figure 1 , the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The SEM scanning electron microscope image of the sodium cobalt oxide precursor is as follows Figure 5 Its characterization data are shown in Table 1.

[0099] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 500g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95°C for 18h, solid-liquid separation and drying at 280°C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material; see Figure 2 In the X-ray diffraction pattern of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 99% of the total area of ​​all diffraction peaks. 2 SEM scanning electron microscope image of lithium cobalt oxide positive electrode material Figure 5 b, and its characterization data are shown in Table 1.

[0100] Example 2

[0101] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0102] Step 1: Co(OH) 2 , K 2 CO 3 and NaOH is uniformly stirred in a water system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 48%, the atomic ratio of Na / (Li+Na) is 1.00, and the atomic ratio of (Li+Na) / Co is 0.90;

[0103] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 850°C in an air atmosphere for 12 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 1.

[0104] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95 °C for 4 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 96% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 1.

[0105] Example 3

[0106] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0107] Step 1: CoCO 3 , MgO and NaOH are mixed by sand grinding in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 41%, the atomic ratio of Na / (Li+Na) is 1.00, and the atomic ratio of (Li+Na) / Co is 0.94;

[0108] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 750°C in an air atmosphere for 24 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 1.

[0109] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 120°C for 0.5h, solid-liquid separation and drying at 200°C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with structural characteristics accounts for ≥99% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 1.

[0110] Example 4

[0111] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0112] Step 1: Co 3 O 4 , Ca(OH) 2 and mixing NaOH in water by sand milling to obtain a mixed system, wherein the mixed system has a solid-liquid ratio of 36%, a Na / (Li+Na) atomic ratio of 1.00, and a (Li+Na) / Co atomic ratio of 0.96;

[0113] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 850°C in an air atmosphere for 12 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 1.

[0114] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 100g of water to obtain a suspension, and then 100g of the above P 2The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 70 °C for 4 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 93% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 1.

[0115] Table 1 Characterization data of the compounds obtained in Examples 1 to 4

[0116]

[0117] Example 5

[0118] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0119] Step 1: Co(OH) 2 , SrO and NaOH are uniformly stirred in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 48%, the atomic ratio of Na / (Li+Na) is 1.00, and the atomic ratio of (Li+Na) / Co is 0.98;

[0120] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 850°C in an air atmosphere for 12 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 2.

[0121] In this embodiment, a molten salt ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 100g of the above P 2 type sodium cobalt oxide precursor, 66.7 g of LiNO 3 and 9.09 g of LiCl were mixed evenly, wherein the Li / Co atomic ratio was 1.20, and then sintered at 400 °C for 2 h, washed with water to remove impurities, and dried at 200 °C to obtain a nearly pure phase O 2Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 96% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 2.

[0122] Example 6

[0123] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0124] Step 1: Co(OH) 2 , Y 2 O 3 , NaOH and LiOH (H 2 O) uniformly stirring in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 48%, the Na / (Li+Na) atomic ratio is 0.95, and the (Li+Na) / Co atomic ratio is 1.00;

[0125] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 700°C in an air atmosphere for 24 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 91% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 2.

[0126] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95 °C for 4 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 2.

[0127] Example 7

[0128] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0129] Step 1: Co(OH) 2 ,La 2 O 3 , NaOH and LiOH (H 2 O) uniformly stirring in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 48%, the Na / (Li+Na) atomic ratio is 0.95, and the (Li+Na) / Co atomic ratio is 1.02;

[0130] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 750°C in an air atmosphere for 18 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the characteristic diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 94% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 2.

[0131] In this embodiment, a molten salt ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 100g of the above P 2 type sodium cobalt oxide precursor, 42.7 g of LiNO 3 and 23 g of LiOH (H 2 O) were mixed evenly, wherein the atomic ratio of Li / Co was 1.20, and then sintered at 200°C for 24h, washed with water to remove impurities, and dried at 200°C to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 97% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 2.

[0132] Example 8

[0133] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0134] Step 1: Co(OH) 2 、CeO2 、Na 2 CO 3 and LiOH(H 2 O) uniformly stirring in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 53%, the Na / (Li+Na) atomic ratio is 0.90, and the (Li+Na) / Co atomic ratio is 1.04;

[0135] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 800°C in an air atmosphere for 24 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 2.

[0136] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95 °C for 4 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 94% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 2.

[0137] Table 2 Characterization data of the compounds obtained in Examples 5 to 6

[0138]

[0139] Example 9

[0140] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0141] Step 1: Co(OH) 2 、ZnO、Na 2 CO3 and LiOH(H 2 O) uniformly stirring in an aqueous system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 53%, the Na / (Li+Na) atomic ratio is 0.80, and the (Li+Na) / Co atomic ratio is 1.06;

[0142] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 850°C in an air atmosphere for 16 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 3.

[0143] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 500g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95°C for 18h, solid-liquid separation and drying at 200°C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 96% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 3.

[0144] Example 10

[0145] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0146] Step 1: Co(OH) 2 , CuO and Na 2 CO 3 The mixed system was uniformly stirred in a water system, wherein the solid-liquid ratio of the mixed system was 53%, the atomic ratio of Na / (Li+Na) was 1.00, and the atomic ratio of (Li+Na) / Co was 1.08;

[0147] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 950°C in an air atmosphere for 12 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The SEM scanning electron microscope image of the sodium cobalt oxide precursor is as follows Figure 5 c, and its characterization data are shown in Table 3.

[0148] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95 °C for 24 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 91% of the total area of ​​all diffraction peaks. 2 SEM scanning electron microscope image of lithium cobalt oxide positive electrode material Figure 5 Its characterization data are shown in Table 3.

[0149] Embodiment 11

[0150] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0151] Step 1: Co(OH) 2 、Al 2 O 3 and NaOH is uniformly stirred in a water system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 49%, the atomic ratio of Na / (Li+Na) is 1.00, and the atomic ratio of (Li+Na) / Co is 1.10;

[0152] Step 2: Dry the mixed system by flash drying at an inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 700°C in an air atmosphere for 12 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 97% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 3.

[0153] In this embodiment, a molten salt ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 100g of the above P 2 type sodium cobalt oxide precursor, 66.7 g of LiNO 3 and 9.09 g of LiCl were mixed evenly, wherein the Li / Co atomic ratio was 1.15, and then sintered at 280 ° C for 4 h, washed with water to remove impurities and dried at 200 ° C to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 98% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 3.

[0154] Example 12

[0155] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0156] Step 1: Co(OH) 2 、Ni(OH) 2 and uniformly grinding NaOH in a water system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 48%, the atomic ratio of Na / (Li+Na) is 1.00, and the atomic ratio of (Li+Na) / Co is 1.02;

[0157] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 750°C in an air atmosphere for 24 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 100% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 3.

[0158] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95 °C for 4 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 96% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 3.

[0159] Embodiment 13

[0160] Nearly pure P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0161] Step 1: Co(OH) 2 、MnCO 3 and uniformly grinding NaOH in a water system to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 48%, the atomic ratio of Na / (Li+Na) is 1.00, and the atomic ratio of (Li+Na) / Co is 1.02;

[0162] Step 2: Dry the mixed system by spray drying at an air inlet temperature of 250°C to obtain a dried product in which Na atoms and Co atoms are in full contact with each other and the maximum spacing is nanometers. Then, sinter the dried product at 750°C in an air atmosphere for 18 hours to obtain a nearly pure phase P. 2 The nearly pure phase P 2 The X-ray diffraction pattern of the sodium cobalt oxide precursor has P6 3 / mmc space group, the nearly pure phase P 2 The total area of ​​the diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 97% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 3.

[0163] In this embodiment, a liquid phase ion replacement synthesis method is used to prepare a nearly pure phase O2 type lithium cobalt oxide positive electrode material: 40.6g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.10. After stirring at 95 °C for 4 h, solid-liquid separation and drying at 200 °C were performed to obtain a nearly pure phase O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 99% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 3.

[0164] Table 3 Characterization data of the compounds obtained in Examples 9 to 13

[0165]

[0166] Comparative Example 1

[0167] P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0168] Step 1: Use a kneader to mix Co(OH) 2 , NaOH and LiOH (H 2 O) kneading and stirring with water to obtain a mixed system, wherein the solid-liquid ratio of the mixed system is 6.6, the Na / (Li+Na) atomic ratio is 0.70, and the (Li+Na) / Co atomic ratio is 0.75;

[0169] Step 2: Dry the mixed system in an oven at an air inlet temperature of 200°C to obtain a dried product, and then sinter the dried product at 850°C in an air atmosphere for 12 hours to obtain P 2 Type sodium cobalt oxide precursor. 2 The total area of ​​the characteristic diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 92% of the total area of ​​all diffraction peaks, and its XRD diffraction pattern is similar to that of Comparative Example 2. 。 P 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 4.

[0170] In this comparative example, a liquid phase ion replacement synthesis method was used to prepare an O2 type lithium cobalt oxide positive electrode material: 44.3 g of LiOH (H 2 0) was mixed with 200g of water to obtain a suspension, and then 100g of the above P 2The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.20. After stirring at 95°C for 16h, solid-liquid separation and drying at 200°C were performed to obtain O 2 Type lithium cobalt oxide positive electrode material, in the X-ray diffraction spectrum of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the structural characteristics of the type accounts for 61% of the total area of ​​all diffraction peaks, and its XRD diffraction pattern is similar to that of Comparative Example 2. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 4.

[0171] Comparative Example 2

[0172] P 2 The synthesis steps of the sodium cobalt oxide precursor are as follows:

[0173] Step 1: Co 3 O 4 and Na 2 CO 3 After dry ball milling, a mixed system was obtained, in which the atomic ratio of Na / (Li+Na) was 1.00 and the atomic ratio of (Li+Na) / Co was 0.85;

[0174] Step 2: Sinter the mixed system at 850°C in air atmosphere for 12 hours to obtain the impure phase P 2 Type sodium cobalt oxide precursor. Figure 3 , the impure phase P 2 The total area of ​​the characteristic diffraction peaks of the sodium cobalt oxide precursor crystal structure accounts for 89% of the total area of ​​all diffraction peaks. 2 The characterization data of the sodium cobalt oxide precursor are shown in Table 4.

[0175] In this comparative example, a liquid phase ion replacement synthesis method was used to prepare an O2 type lithium cobalt oxide positive electrode material: 44.3 g of LiOH (H 2 O) and 200g of water were mixed to obtain a suspension, and then 100g of the impure phase P 2 The sodium cobalt oxide precursor was put into the suspension to form a new suspension system. The Li / Co atomic ratio in the new suspension system was 1.20. After stirring at 95 °C for 4 h, solid-liquid separation and drying at 300 °C were performed to obtain O 2 Type lithium cobalt oxide positive electrode material. Figure 4 In the X-ray diffraction pattern of the positive electrode material, O 2 The total area of ​​the diffraction peaks with the characteristic structure accounts for 72% of the total area of ​​all diffraction peaks. 2 The characterization data of the type lithium cobalt oxide positive electrode material are shown in Table 4.

[0176] Table 4 Characterization data of the compounds obtained in Comparative Example 1 and Comparative Example 2

[0177]

[0178] In the above-mentioned Examples 2 to 13, the XRD diffraction patterns of the nearly pure phase P2-type sodium cobalt oxide precursor and the XRD diffraction patterns of the nearly pure phase O2-type lithium cobalt oxide are similar to those in Example 1. In order to simplify the application documents, they are no longer shown one by one in the drawings of the specification.

[0179] According to the characterization data of Examples 1 to 13 and Comparative Examples 1 to 2, the synthesized near-pure phase O 2 The type of lithium cobalt oxide cathode material requires a near-pure phase P with a high Na / Co ratio. 2 Type sodium cobalt oxide precursor, nearly pure phase P 2 The synthesis of sodium cobalt oxide precursor needs to meet the following conditions:

[0180] (1) The radius of Na+ is about 1.5 times that of Li+, and it is difficult for Na+ to diffuse between the Co-O octahedral layers. Therefore, the present invention adopts wet batching to shorten the diffusion distance between Na atoms and Co atoms as much as possible to avoid the formation of impurities and the volatilization of local excess Na during the primary sintering process.

[0181] (2) After wet batching, drying is performed by flash evaporation or spray drying to avoid Na segregation during the drying process. After drying, Na atoms and Co atoms in the product are in full contact, and the maximum spacing is at the nanometer level.

[0182] (3) Compared with the difficulty of Na+ diffusion, Li+ diffusion is easier. The introduction of a small amount of Li+ in the early batching is conducive to the formation of a stable structure to occupy Li under a high-temperature sintering, reducing the amount of Na+ added, which is more difficult to diffuse, and reducing the difficulty of synthesizing high Na / Co ratio P2-type NCO. The Na / (Li+Na) atomic ratio is between 0.8 and 1.0, which is the easiest to form a stable near-pure phase P2-type crystal structure. If the proportion of Li added is too high, it is easy to form O during the sintering process. 3 Type structure, reducing the final O 2 The structural stability of the finished product.

[0183] (4) The Na+ content in the synthesized O2-type LCO structure should be as low as possible (in this application, the expression of the near-pure phase O2-type lithium cobalt oxide positive electrode material is: Li x (Li a Na b Co c M' d ) z, limited to 0≤b≤0.1), preferably 0≤b≤0.05; Na+ content is too high, it will be released during the charging process of O2-type LCO, and the negative electrode graphite structure used in lithium-ion batteries cannot allow Na+ to be smoothly embedded and released, resulting in sodium precipitation and graphite flake shedding at the negative electrode, causing battery safety and cycle problems. This requires that the Na+ in the formed P2-type NCO precursor should be as much as possible, and at the same time, it can be quickly released and replaced by Li+ during the replacement process. Without any doping modification, P2-type NCO cannot meet the requirements. Therefore, the strategy of this application is to introduce a modifying element M' during the P2 wet batching process, which not only ensures that the P2 structure can be stabilized under a high Na / Co ratio, but also can provide good Na+ diffusion kinetics, while stabilizing the O2 layered structure after Li-Na ion replacement, and improving the barrier for the conversion of O2-type LCO to O3-type LCO, so that O2-type LCO can remain stable at the highest possible temperature. The modifying element M' is one or a combination of more than one of Mg, Ca, Sr, Ba, K, Rb, Cs, Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, Mo, Ni, Mn, Cr, Cu, and Fe. According to their functions, they can be divided into the following categories:

[0184] 1. Ni, Mn, Cr, Cu, and Fe are elements with variable valence during the charge and discharge process. Doping them into the Co position is beneficial to reducing the discharge voltage of O2-type LCO, so that it can exert a higher gram capacity within the same voltage range;

[0185] 2. Group II elements such as Mg, Ca, Sr, and Ba can occupy the Na position of P2-type NCO, play a pillaring role, improve the Na+ diffusion kinetics, stabilize the lattice structure of O2-type LCO products, reduce the slip of Co-O octahedral layers, and increase the barrier for the transformation of O2-type LCO to O3-type LCO;

[0186] 3. Group I elements such as K, Rb, and Cs can enter the Na position of P2-type NCO. These ions can expand the interlayer spacing of the Na layer, which is conducive to the replacement of Na+ by Li+ during the replacement process. At the same time, these ions are also very easy to be replaced by Li+ or removed by water washing. There is very little residue in the O2-type LCO material, and the effect on the performance of the finished material is minimal;

[0187] 4. Elements such as Y, La, Ce, Zn, Al, Ti, Zr, W, Nb, and Mo are more likely to occupy the Co position or be enriched on the surface of P2-type NCO. After Li-Na ion replacement, they remain in situ at the Co position of O2-type LCO or are enriched on the surface of the material. The modified elements occupying the Co position can play a pinning role or form a stronger M'-O bond to stabilize the structure of O2-type LCO. The elements enriched on the surface of the material can improve the surface stability of the material, reduce the electrolyte side reactions at the interface under high voltage and the lattice oxygen valence change near the dangling bond, and improve the high-voltage cycle stability of the material.

[0188] (5) Under the conditions of high Li and Na addition and doping modification as above, P 2 The sintering condition of the type crystal structure is to sinter at a temperature of 650-950℃ for 12-24h. This temperature range allows the material to form a nearly pure phase P2 NCO structure. If the sintering temperature is too low or the time is too short, the P2 structure will be incomplete, the material will have many internal defects, and the proportion of non-occupied Na will be high. If the sintering temperature is too high or the time is too long, the a and c lattice constants will shrink excessively, affecting the diffusion of Na+, or in the case of poor local element uniformity, a lower energy and more stable impurity phase will be preferentially formed, thereby destroying the performance of the final O2 LCO.

[0189] In summary, the present application creatively provides a near-pure phase P2-type NCO precursor material with a high Na / Co ratio in an air atmosphere by selecting reasonable doping modification and primary sintering conditions, and synthesizes a high Li / Co ratio and low free Li by Li-Na ion replacement, by virtue of the high proportion of structural site-occupying Na in the P2-type precursor material, good Na+ diffusion kinetics and stable structure. 2 CO 3 Nearly pure phase O2-type LCO material with low Na+ content, low residual Na+ and stable structure.

[0190] The references involved in this application are as follows:

[0191] [1]On the Much-Improved High-Voltage Cycling Performance of LiCoO2 byPhase Alteration from O3 to O2 Structure,Small Sci.2024,2400162.

[0192] [2]The interplay between thermodynamics and kinetics in the solid-state synthesis of layered oxides,Nature Materials,2020,19(10):10.1038 / s41563-020-0688-6.

Claims

1. A nearly pure phase O2 type lithium cobalt oxide positive electrode material, characterized in that: The positive electrode material is obtained by washing and drying a nearly pure phase P2 type sodium cobaltate precursor with a high Na / Co atomic ratio after Li-Na ion replacement; the Na / Co atomic ratio in the nearly pure phase P2 type sodium cobaltate precursor is 0.9-1.

1.

2. The near-pure phase O2-type 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≤0.4, 1.9≤z≤2.2, 0.9≤x+a+b≤1.2, 0.9≤c+d≤1.

2.

3. The near-pure phase O2-type 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 the O2 structure characteristics accounts for ≥90% of the total area of ​​all diffraction peaks, preferably 100%.

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

5. The near-pure phase O2-type 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 a near-pure phase O2-type lithium cobalt oxide positive electrode material, comprising an existing liquid phase ion replacement synthesis method, characterized in that: A nearly pure phase P2 type sodium cobalt oxide precursor is put into an aqueous or alcoholic suspension containing a saturated Li+ compound to form a new suspension system, and the Li / Co atomic ratio in the new suspension system is 1.0-1.

2. After stirring at 70-120°C for 0.5-24h, the mixture is subjected to solid-liquid separation and dried at a temperature below 300°C to obtain a nearly pure phase O2 type lithium cobalt oxide positive electrode material.

7. The method for preparing a near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 6 comprises an existing molten salt ion replacement synthesis method, characterized in that: A nearly pure phase P2 type sodium cobalt oxide precursor is uniformly mixed with a Li-containing compound in a Li / Co atomic ratio of 1.0 to 1.2, sintered at a temperature of 200 to 400°C for 2 to 24 hours, washed with water to remove impurities and dried at a temperature below 300°C to obtain a nearly pure phase O2 type lithium cobalt oxide positive electrode material.

8. The method for preparing the near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 6, characterized in that: The weight proportion of the nearly pure phase P2 type sodium cobalt oxide precursor in the new suspension system is ≥20%.

9. The method for preparing a near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 6 or 7, characterized in that: The synthesis steps of the nearly pure phase P2 type sodium 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 an aqueous or alcoholic system 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 one or all of Na or Li compounds, and the Na / (Li+Na) atomic ratio is between 0.8 and 1.0; Step 2: Dry the mixed system, and then sinter the dried product at a temperature of 650-950° C. for 12-24 hours to obtain a nearly pure phase P2 type sodium cobalt oxide precursor.

10. The method for preparing the near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 9, characterized in that: The X-ray diffraction spectrum of the nearly pure phase P2 type sodium cobaltate precursor has a crystal structure of the P63 / mmc space group, and the total area of ​​the characteristic diffraction peaks of the crystal structure of the nearly pure phase P2 type sodium cobaltate precursor accounts for ≥90% of the total area of ​​all diffraction peaks, preferably 100%.

11. The method for preparing the near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 9, characterized in that: The solid-liquid ratio of the mixed system is ≥20%.

12. The method for preparing the near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 9, characterized in that: The sodium carbonate content of the P2 type sodium cobaltate precursor measured by aqueous solution titration method is ≤15wt.%.

13. The method for preparing a near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 9, characterized in that: The Co-containing compound and the M'-containing compound are one or more of oxides, hydroxides, oxyhydroxides, nitrates, and chlorides, and the Co-containing compound may contain M'.

14. The method for preparing a near-pure phase O2-type lithium cobalt oxide positive electrode material according to claim 9, characterized in that: The drying method of the mixed system is flash evaporation or spray drying, and the inlet air temperature is 180-700°C.

15. A lithium ion battery comprising a positive electrode active material, characterized in that: The positive electrode active material comprises one or more near-pure phase O2-type lithium cobalt oxide positive electrode materials obtained by the preparation method described in any one of claims 6 to 14.

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