Aluminum-tantalum modified high-nickel ternary positive electrode material, preparation method and application thereof

Abstract

The application discloses an aluminum-tantalum modified high-nickel ternary positive electrode material and a preparation method and application thereof. The application starts from solution phase synthesis control, first constructs a nano coating containing aluminum-tantalum metal on the surface of the high-nickel ternary positive electrode material, and then further carries out high-temperature heat treatment to promote chemical reaction between the positive electrode material and the surface coating, so that a surface structure with good stability and high charge transport capacity is obtained, thereby significantly improving the stability of the positive electrode material and obtaining the positive electrode material with high specific capacity and good cycle stability. Meanwhile, the method provided by the application can fully meet the needs of scale production on the premise of ensuring that no additional damage is caused to the high-nickel ternary positive electrode material, has the advantages of low cost, high reliability and the like, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of materials, and relates to an aluminum-tantalum metal modified high-stability high-nickel ternary positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] The continuous upgrading of portable electronic devices and new energy vehicles puts forward higher and higher requirements on the performance of lithium ion batteries. High-energy lithium ion batteries with high energy density, long cycle life, good safety and low cost have become one of the goals pursued by researchers in the development and pursuit.

[0003] The positive electrode material, as one of the core components of the lithium ion battery, plays a key role in the comprehensive performance of the battery. Among them, the high-nickel ternary layered transition metal oxide (LiNi x Co y M 1-x-y O2, M = Mn or Al, x > 0.6) has become the focus of research due to its high energy and power density. In this system, with the increase of Ni content, its capacity increases, but it is also accompanied by more serious surface side reactions, poorer structural stability and greater safety risks. Based on this, the regulation of the surface interface of the positive electrode material, the development of high-nickel ternary positive electrode material with good cycle performance and high safety performance has become one of the research hotspots in the field of lithium ion battery positive electrode materials.

[0004] At present, the modification of high-nickel ternary materials mainly adopts methods such as bulk doping, surface coating, construction of radial distribution microstructure, full concentration gradient design to control the surface interface structure and regulate the bulk lattice. However, these methods still have limitations in improving the electrochemical performance of high-nickel materials, the reasons mainly lie in: ① The conventional coating method usually introduces an oxide inert layer with low lithium ion conductivity, which is not conducive to the interface charge transfer, and also wastes part of the reversible capacity; ② The conventional coating method is only based on simple blending, evaporation or hydrolysis in solid or liquid phase, and lacks the means of kinetic control to construct a nano-precision uniform coating layer on the particle surface, and the uncoated area will expose more reaction sites, resulting in poor protection effect; ③ High-nickel materials are very sensitive to moisture and air, and the general aqueous coating method will exacerbate the corrosion, dissolution and surface residual lithium / bulk lithium of active materials, and the side reactions of water and carbon dioxide in the solution, air and carbon dioxide, which will destroy the crystal structure and cause capacity loss; ④ Lack of effective methods to simultaneously stabilize the electrode / electrolyte interface and the bulk lattice, which cannot accurately control the surface interface structure. SUMMARY

[0005] The application aims to provide an aluminum-tantalum metal modified high-stability high-nickel ternary positive electrode material, a preparation method and application thereof, so as to improve the stability and safety of the existing high-nickel ternary positive electrode material. The method provided by the application can not only realize uniform and controllable coating of aluminum and tantalum metals on the surface of the high-nickel ternary, but also can fully meet the needs of large-scale production under the premise of ensuring that the high-nickel ternary positive electrode material is not damaged additionally, and has the advantages of low cost, high reliability and the like.

[0006] To achieve the above-mentioned purpose, the application provides the following technical solutions.

[0007] In a first aspect, the application provides a positive electrode composite material, comprising the following components: a high-nickel ternary positive electrode material and a coating layer on the surface of the high-nickel ternary positive electrode material.

[0008] The structural formula of the high-nickel ternary positive electrode material is LiNi x Co y Mn 1-x-y O2.

[0009] Among them:

[0010] 0.6≤x<1, and x is exemplarily 0.6, 0.7, 0.8 or 0.91.

[0011] 0<y≤0.2, and y is exemplarily 0.06, 0.1 or 0.2.

[0012] x+y<1.

[0013] The coating layer is a nanometer coating layer containing aluminum and tantalum metals.

[0014] The high-nickel ternary positive electrode material is LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.91 Co 0.06 Mn 0.03 O2.

[0015] The high-nickel ternary positive electrode material is a single crystal material or a polycrystal material.

[0016] In the positive electrode composite material, the mass fraction of aluminum is 0.03-2%, preferably (0.3-0.9):1, and exemplarily 0.05%, 0.1%, 0.5%, 0.8%, 1.0% or 2.0%.

[0017] The mass fraction of tantalum element in the positive electrode composite is 0.05-1.8%, preferably (0.5-1.5):1, and exemplarily 0.08%, 0.1%, 0.5%, 0.8%, 1.0%, 1.5%.

[0018] The thickness of the coating layer is 0.5-30nm, preferably 1-10nm, and exemplarily 1nm, 3nm, 5nm, 7nm, 9nm.

[0019] In a second aspect, the present application further provides a preparation method of the positive electrode composite, comprising the following steps:

[0020] (1) dissolving a soluble organic aluminum salt, a soluble organic tantalum salt and a complexing agent in a non-aqueous solvent to obtain a solution A;

[0021] (2) taking another non-aqueous solvent, adding a high-nickel ternary positive electrode material and an alkali solution into the non-aqueous solvent to obtain a suspension B;

[0022] (3) pouring the solution A into the suspension B, stirring, centrifuging, washing, drying to obtain an aluminum-tantalum modified surface material;

[0023] (4) calcining the aluminum-tantalum modified surface material to obtain a high-nickel ternary positive electrode material modified by surface aluminum-tantalum species, i.e. the positive electrode composite.

[0024] In step (1), the soluble organic aluminum salt is one or more of aluminum alcoholate, aluminum acetylacetonate and aluminum ethoxide; for example, selected from aluminum alcoholate; and exemplarily, selected from aluminum isopropoxide.

[0025] In the solution A, the concentration of the soluble organic aluminum salt is 1×10 -6 -10mol / L, preferably 1×10 -4 -1mol / L, and exemplarily 1×10 -4 mol / L, 1×10 -3 mol / L, 0.01mol / L, 0.1mol / L or 1mol / L.

[0026] In step (1), the soluble organic tantalum salt is one or more of tantalum alcoholate, tantalum acetylacetonate and tantalum ethoxide; for example, selected from tantalum alcoholate; and exemplarily, selected from tantalum ethoxide.

[0027] In the solution A, the concentration of the soluble organic tantalum salt is 1×10 -6 -10mol / L, preferably 1×10 -4 -1mol / L, and exemplarily 1×10 -4 mol / L, 1×10 -30.01 mol / L, 0.1 mol / L, 1 mol / L.

[0028] In step (1), the complexing agent is at least one of alkanoic acid, dilute acid, acetylenic acid, alkylamine, dilute amine and acetylenic amine; for example, it can be at least one selected from the group consisting of hexadecanethiol, n-pentanoic acid, n-octylamine, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, linoleic acid, eicosanoic acid, dodecylamine, tetradecylamine, hexadecylamine, and the like.

[0029] In the solution A, the concentration of the complexing agent is 3×10 -6 -30 mol / L, further preferably 3×10 -4 -3 mol / L, and exemplarily 3×10 -4 mol / L, 3×10 -3 mol / L, 0.03 mol / L, 0.3 mol / L, 3 mol / L.

[0030] In step (1), the non-aqueous solvent is anhydrous organic solvent, for example, selected from anhydrous alcohol solvent and / or anhydrous ketone solvent; preferably, the non-aqueous solvent is at least one selected from the group consisting of methanol, anhydrous ethanol, isopropanol, n-propanol, ethylene glycol, propylene glycol, n-butanol and acetone; more preferably, the non-aqueous solvent is anhydrous ethanol. Further, the purity of the non-aqueous solvent is chromatographic purity level, and the water content is ≤0.1wt%.

[0031] In step (2), the high-nickel ternary positive electrode material has a structural formula of LiNi x Co y Mn 1-x-y O2; wherein: 0.6≤x<1, exemplarily, x=0.6, 0.7, 0.8, 0.91; 0 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.91 Co 0.06 Mn 0.03 O2.

[0032] The high-nickel ternary positive electrode material is a single crystal material or a polycrystalline material.

[0033] In the suspension B, the concentration of the high-nickel ternary positive electrode material is 0.001-1000 g / L; for example, the concentration is 0.05-50 g / L, 1-10 g / L; and exemplarily, the concentration is 2 g / L, 5 g / L, 8 g / L.

[0034] In step (2), the mass ratio of aluminum ions in the soluble organic aluminum salt, tantalum ions in the soluble organic tantalum salt and the high-nickel ternary positive electrode material is (0.03-2):(0.05-1.8):1; preferably (0.3-0.9):(0.5-1.5):1; and exemplarily, the mass ratio is 0.5:0.8:1.

[0035] The base is one of ammonia, sodium hydroxide or potassium hydroxide. The pH of the base solution preferably ranges from 8 to 10.

[0036] In step (3), the volume ratio of the solution A to the suspension B is 1:(1-300), preferably 1:(5-150).

[0037] The stirring condition is that the temperature is -10-80℃, preferably 20-30℃, exemplarily 25℃, and the time is 0.1-48h, preferably 0.5-3h, exemplarily 0.5h, 1h, 3h.

[0038] In step (4), the calcination condition is that the temperature is 300-1000℃, preferably 500-800℃, further preferably 550-650℃, exemplarily 500℃, 600℃, 700℃, 800℃, and the time is 0.5-24h, preferably 1-5h, exemplarily 1h, 1h, 3h, 5h.

[0039] The heating rate of the calcination is 1-10℃ / min, exemplarily 1℃ / min, 5℃ / min, 10℃ / min.

[0040] In a third aspect, the application further provides a lithium ion battery, comprising a positive electrode and a negative electrode; the material used in the positive electrode is the above-mentioned positive electrode composite material.

[0041] The positive electrode further comprises a conductive agent and a binder; the conductive agent can be a commonly used conductive agent such as Super-P; and the binder can be a commonly used binder such as polyvinylidene fluoride (PVDF).

[0042] In the positive electrode, the mass ratio of the positive electrode material, the conductive agent and the binder is (3-65):1:1, exemplarily 8:1:1.

[0043] The application has the following beneficial effects:

[0044] 1. Based on the reaction environment provided by the non-aqueous solvent, the application can effectively avoid the damage of environmental water to the high-nickel ternary positive electrode material while introducing aluminum-tantalum metal coating species on the surface of the positive electrode material.

[0045] 2、The application starts from the selection and control of coating species, is based on a low-cost and high-efficiency surface treatment process, further combines a high-temperature heat treatment process in the later period, regulates and controls the chemical reaction of the surface coating species and the high-nickel positive electrode on the surface, obtains the positive electrode material with structural stability which is modified by aluminum-tantalum metal, realizes the regulation and optimization of the physical and chemical properties of the high-nickel positive electrode surface, thereby obtaining a high-stable positive electrode / electrolyte interface, and further showing better electrochemical stability in the battery test process.

[0046] 3、The preparation method provided by the application has the advantages of simple process, low cost, environmental friendliness and large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The X-ray diffraction (XRD) spectrum of the aluminum-tantalum metal modified high-nickel single crystal positive electrode material in Example 1.

[0048] Figure 2 The scanning electron microscope (SEM) picture of the aluminum-tantalum metal modified high-nickel single crystal positive electrode material in Example 1.

[0049] Figure 3 The transmission electron microscope (TEM) picture of the aluminum-tantalum metal modified high-nickel single crystal positive electrode material in Example 1.

[0050] Figure 4 The high-resolution electron microscope (HRTEM) picture of the aluminum-tantalum metal modified high-nickel single crystal positive electrode material in Example 1.

[0051] Figure 5 The X-ray energy spectrum analysis (EDS) picture of the aluminum-tantalum metal modified high-nickel single crystal positive electrode material in Example 1.

[0052] Figure 6 The charge-discharge curve graph of the high-nickel ternary single crystal positive electrode material in Example 1 and the comparative example at 0.1C rate.

[0053] Figure 7 The cycle graph of the high-nickel ternary single crystal positive electrode material in Example 1 and the comparative example at 1C rate. DETAILED DESCRIPTION

[0054] The application will be further described below in combination with specific embodiments, but the application is not limited to the following embodiments.

[0055] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0056] The reagents, materials, instruments and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0057] Example 1

[0058] (I) Preparation of the positive electrode material

[0059] At 25℃, 20.4 mg of aluminum isopropoxide and 37.5 μL of ethanol tantalum were dissolved in 1 ml of anhydrous ethanol, 30 μL of tetradecylamine was added, and a clear transparent solution A was obtained by stirring uniformly; 1.95 g of single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B; solution A was poured into suspension B, and stirring reaction was carried out at 25℃ for 1 h, and the positive electrode material powder was obtained after centrifugation, washing and drying; the powder was calcined in a tube furnace under an oxygen atmosphere at a temperature rising rate of 5℃ / min to 600℃ for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal modified positive electrode material was obtained by grinding with a mortar.

[0060] In the positive electrode material obtained in the example, the mass fraction of aluminum element was 0.5%, and the mass fraction of tantalum element was 0.8%.

[0061] (II) Structural and morphological characterization

[0062] The crystal structure of the positive electrode material prepared in the example was analyzed by powder X-ray diffractometer (D8 Advance, Bruke), and the results are shown in Figure 1 From the figure, it can be seen that the positive electrode material prepared in the example conforms to the diffraction peak of the layered ternary material, and there is no other impurity peak, indicating that the material has high purity.

[0063] Further, the morphology of the positive electrode material prepared in the example was characterized by scanning electron microscope (SEM-4800), and the results are shown in Figure 2 From the figure, it can be seen that after surface modification, the material maintains the morphology of the single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM) positive electrode material.

[0064] The morphology of the aluminum-tantalum metal coated high-nickel ternary single-crystal positive electrode material before calcination was characterized by transmission electron microscope (TEM-2100F), and the results are shown in Figure 3 From the figure, it can be seen that the thickness of the aluminum-tantalum metal coating layer is about 5 nm.

[0065] Figure 4 The high-resolution electron microscope (HRTEM) picture of the aluminum-tantalum metal modified high-nickel single-crystal positive electrode material in Example 1 is shown in Figure 4 It can be seen from the figure that the coating layer formed on the surface of the positive electrode material is in an amorphous state, and does not affect the typical crystal structure of the positive electrode material.

[0066] Figure 5 The X-ray energy spectrum analysis (EDS) diagram of the high-nickel ternary single-crystal cathode material coated with aluminum-tantalum metal before calcination shows that there is a uniform and continuous aluminum-tantalum metal coating layer on the surface of the high-nickel ternary single-crystal cathode material.

[0067] (Three) Assembly of the battery

[0068] The 200 mg cathode material prepared above, 25 mg of the binder polyvinylidene fluoride (PVDF), and 25 mg of the conductive agent Super-P were mixed, and about 200 μL of N-methylpyrrolidone (NMP) was added to prepare a slurry. The slurry was uniformly coated on an aluminum foil with the aluminum foil as the current collector, and the coating thickness was 2 μm. The coated aluminum foil was dried at 80 °C for 12 h in a vacuum to obtain a cathode film. A lithium metal sheet was used as the anode, a polypropylene microporous film (Celgard 2400) was used as the separator, and 1 mol / L LiPF6 (EC:DMC:DEC = 1:4:2) was used as the electrolyte to assemble a coin battery in an argon-protected glove box.

[0069] (Four) Performance test

[0070] The assembled battery was subjected to constant current charge-discharge test on a blue charge-discharge tester, and the charge-discharge rate was 0.1C (1C = 200 mA / g), and the charge-discharge interval was 3.0-4.3 V. The first cycle charge-discharge curve is shown in FIG. 1. As can be seen from the figure, the discharge specific capacity of the NCM cathode material can reach 197 mAh / g. The capacity retention rate after 100 cycles at a 1C rate in the charge-discharge interval of 3.0-4.3 V is 96% (as shown in FIG. 2), which indicates that the cathode material has good cycle stability. Figure 6 Figure 7

[0071] Example 2

[0072] (One) Preparation of the cathode material

[0073] At 25 °C, 10.2 mg of aluminum isopropoxide and 18.8 μL of tantalum ethoxide were dissolved in 1 ml of anhydrous ethanol, 30 μL of tetradecylamine was added, and the mixture was stirred uniformly to obtain a clear and transparent solution A. 1.95 g of single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, and 100 μL of ammonia water was added to obtain a suspension B. Solution A was poured into suspension B, and the mixture was stirred at 25 °C for 1 h. After centrifugation, washing, and drying, a cathode material powder was obtained. The powder was calcined in a tube furnace under an oxygen atmosphere at a temperature rising rate of 5 °C / min to 600 °C for 3 h, and then naturally cooled to room temperature. The powder was ground with a mortar to obtain an aluminum-tantalum metal modified cathode material. ​​

[0074] (II) Structure and morphology characterization (specific steps same as Example 1).

[0075] (III) Assembly of the battery (specific steps same as Example 1).

[0076] (IV) Performance test (specific steps same as Example 1).

[0077] Example 3

[0078] (I) Preparation of the positive electrode material

[0079] At 25°C, 40.8 mg of aluminum isopropoxide and 75 μL of ethanol tantalum were dissolved in 1 ml of anhydrous ethanol, 30 μL of myristylamine was added, and a clear transparent solution A was obtained by stirring uniformly; 1.95 g of single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added, and a suspension B was obtained; solution A was poured into suspension B, and stirring reaction was carried out at 25°C for 1 h; the positive electrode material powder was obtained by centrifugation, washing, and drying; the powder was calcined in a tube furnace under an oxygen atmosphere at a temperature increasing rate of 5°C / min to 600°C for 3 h, and the aluminum tantalum metal modified positive electrode material was obtained by natural cooling to room temperature and grinding with a mortar.

[0080] (II) Structure and morphology characterization (specific steps same as Example 1).

[0081] (III) Assembly of the battery (specific steps same as Example 1).

[0082] (IV) Performance test (specific steps same as Example 1).

[0083] Comparative Example 1

[0084] (I) Preparation of the positive electrode material

[0085] At 25°C, 40.8 mg of aluminum isopropoxide and 75 μL of ethanol tantalum were dissolved in 1 ml of anhydrous ethanol, 30 μL of myristylamine was added, and a clear transparent solution A was obtained by stirring uniformly; 1.95 g of single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added, and a suspension B was obtained; solution A was poured into suspension B, and stirring reaction was carried out at 25°C for 1 h; the positive electrode material powder was obtained by centrifugation, washing, and drying; the powder was calcined in a tube furnace under an oxygen atmosphere at a temperature increasing rate of 5°C / min to 600°C for 3 h, and the aluminum tantalum metal modified positive electrode material was obtained by natural cooling to room temperature and grinding with a mortar.

[0086] (II) Structure and morphology characterization (specific steps same as Example 1).

[0087] (Three) Assembly of the battery (the specific steps are the same as in Example 1).

[0088] (Four) Performance test (the specific steps are the same as in Example 1).

[0089] Comparative Example 2

[0090] (One) Preparation of the positive electrode material

[0091] At 25°C, 37.5 μL of tantalum ethoxide was dissolved in 1 ml of anhydrous ethanol, 30 μL of tetradecylamine was added, and a clear transparent solution A was obtained by stirring uniformly; 1.95 g of single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B; solution A was poured into suspension B, and stirred at 25°C for 1 h, and the positive electrode material powder was obtained by centrifugation, washing and drying; the powder was calcined in a tube furnace under an oxygen atmosphere at a temperature increasing rate of 5°C / min to 600°C for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal modified positive electrode material was obtained by grinding with a mortar.

[0092] (Two) Structure and morphology characterization (the specific steps are the same as in Example 1).

[0093] (Three) Assembly of the battery (the specific steps are the same as in Example 1).

[0094] (Four) Performance test (the specific steps are the same as in Example 1).

[0095] Comparative Example 3

[0096] (One) Preparation of the positive electrode material

[0097] At 25°C, 30 μL of tetradecylamine was added to 1 ml of anhydrous ethanol, and a clear transparent solution A was obtained by stirring uniformly; 1.95 g of single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B; solution A was poured into suspension B, and stirred at 25°C for 1 h, and the positive electrode material powder was obtained by centrifugation, washing and drying; the powder was calcined in a tube furnace under an oxygen atmosphere at a temperature increasing rate of 5°C / min to 600°C for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal modified positive electrode material was obtained by grinding with a mortar.

[0098] (Two) Structure and morphology characterization (the specific steps are the same as in Example 1).

[0099] (Three) Assembly of the battery (the specific steps are the same as in Example 1).

[0100] (IV) Performance test (specific steps are the same as in Example 1).

[0101] Comparative Example 4

[0102] (I) Preparation of the positive electrode material

[0103] At 25°C, 20.4 mg of aluminum isopropoxide and 37.5 μL of tantalum ethoxide were dissolved in 1 ml of anhydrous ethanol, 30 μL of myristylamine was added, and a clear transparent solution A was obtained by stirring uniformly. 1.95 g of single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B. Solution A was poured into suspension B, and the reaction was stirred at 25°C for 1 h. After centrifugation, washing, and drying, a positive electrode material powder was obtained. The powder was calcined in a tube furnace under an oxygen atmosphere at a temperature rising rate of 5°C / min to 500°C for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal-modified positive electrode material was obtained by grinding with a mortar. 0.8 Co 0.1 Mn 0.1 O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B. Solution A was poured into suspension B, and the reaction was stirred at 25°C for 1 h. After centrifugation, washing, and drying, a positive electrode material powder was obtained. The powder was calcined in a tube furnace under an oxygen atmosphere at a temperature rising rate of 5°C / min to 500°C for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal-modified positive electrode material was obtained by grinding with a mortar.

[0104] (II) Structure and morphology characterization (specific steps are the same as in Example 1).

[0105] (III) Assembly of the battery (specific steps are the same as in Example 1).

[0106] (IV) Performance test (specific steps are the same as in Example 1).

[0107] Comparative Example 5

[0108] (I) Preparation of the positive electrode material

[0109] At 25°C, 20.4 mg of aluminum isopropoxide and 37.5 μL of tantalum ethoxide were dissolved in 1 ml of anhydrous ethanol, 30 μL of myristylamine was added, and a clear transparent solution A was obtained by stirring uniformly. 1.95 g of single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B. Solution A was poured into suspension B, and the reaction was stirred at 25°C for 1 h. After centrifugation, washing, and drying, a positive electrode material powder was obtained. The powder was calcined in a tube furnace under an oxygen atmosphere at a temperature rising rate of 5°C / min to 500°C for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal-modified positive electrode material was obtained by grinding with a mortar. 0.8 Co 0.1 Mn 0.1 O2 (NCM) was accurately weighed and dispersed in 9 ml of anhydrous ethanol, 100 μL of ammonia water was added to obtain a suspension B. Solution A was poured into suspension B, and the reaction was stirred at 25°C for 1 h. After centrifugation, washing, and drying, a positive electrode material powder was obtained. The powder was calcined in a tube furnace under an oxygen atmosphere at a temperature rising rate of 5°C / min to 500°C for 3 h, and after natural cooling to room temperature, the aluminum-tantalum metal-modified positive electrode material was obtained by grinding with a mortar.

[0110] (II) Structure and morphology characterization (specific steps are the same as in Example 1).

[0111] (III) Assembly of the battery (specific steps are the same as in Example 1).

[0112] (iv) Performance test (the specific steps are the same as in Example 1).

[0113] Effect verification

[0114] The performance test results of the batteries of Examples 1-3 and Comparative Examples 1-5 are shown in Table 1 below.

[0115] Table 1 Performance indicators of the batteries prepared from the materials of Examples and Comparative Examples

[0116] Initial discharge specific capacity (mAh / g) 100 cycle capacity retention (%) Example 1 195.6 96.5 Example 2 195.2 95.6 Example 3 194.5 96.0 Comparative Example 1 194.5 95.2 Comparative Example 2 193.8 94.7 Comparative Example 3 193.7 86.8 Comparative Example 4 193.9 94.8 Comparative Example 5 194.2 93.7

[0117] As can be seen from the comparison of Examples 1-3, the coating amount of the aluminum-tantalum species has an influence on the first-cycle specific discharge capacity and the cycle stability of the positive electrode material. When the coating amount of the aluminum-tantalum species is too low, as shown in Example 2, a sufficient stable layer cannot be formed on the surface of the ternary positive electrode material, and thus the surface of the positive electrode material cannot be comprehensively protected. However, when the coating amount of the aluminum-tantalum species is too high, as shown in Example 3, other unstable impurities are formed on the surface of the positive electrode, and thus the first-cycle specific discharge capacity of the positive electrode material is reduced, and the cycle stability is poor. Therefore, the mass ratio of aluminum to the positive electrode material in the present application is preferably in the range of (0.3-0.9): 1, and the mass ratio of tantalum to the positive electrode material is preferably in the range of (0.5-1.5): 1.

[0118] As can be seen from the comparison of Example 1 and Comparative Examples 4-5, the calcination temperature has an influence on the first-cycle specific discharge capacity and the cycle stability of the positive electrode material. When the calcination temperature is too low, as shown in Comparative Example 4, the solid-phase reaction between the aluminum-tantalum coating layer and the surface of the positive electrode material is incomplete, and thus the cycle performance of the positive electrode material is improved to a limited extent. However, when the calcination temperature is too high, as shown in Comparative Example 5, the crystal structure of the positive electrode material itself is destroyed, and harmful impurities are generated, and thus the first-cycle specific discharge capacity of the positive electrode material is reduced. Therefore, the preferred range of the calcination temperature in the present application is 550-650°C.

[0119] As can be seen from the comparison of Examples 1-3 and Comparative Examples 1-3, the cycle stability of the positive electrode material obtained in Examples 1-3 is higher than that of Comparative Examples 1-3, and the specific discharge capacity is not reduced, which indicates that the surface of the positive electrode material can be modified by the aluminum-tantalum metal to improve the cycle stability of the positive electrode material, and the appropriate addition amount will not sacrifice the specific discharge capacity. In particular, Example 1 has a significant improvement in the cycle performance and the specific discharge capacity.

[0120] Although the present application has been described in detail by the general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application are within the scope of the present application.

Claims

1. A positive electrode composite material, comprising: a high-nickel ternary positive electrode material and a coating layer on the surface of the high-nickel ternary positive electrode material; 0 < y ≤ 0.2; x + y < 1; the coating layer is a nano-coating layer containing aluminum-tantalum metal; and a preparation method of the positive electrode composite material, comprising the following steps: (1) dissolving a soluble organic aluminum salt, a soluble organic tantalum salt and a complexing agent in a non-aqueous solvent to obtain a solution A; (2) adding a high-nickel ternary positive electrode material and an alkali solution into the non-aqueous solvent to obtain a suspension B; (3) pouring the solution A into the suspension B, stirring, centrifuging, washing, drying to obtain an aluminum-tantalum modified surface material; and (4) calcining the aluminum-tantalum modified surface material to obtain a high-nickel ternary positive electrode material modified by aluminum-tantalum surface species, i.e., the positive electrode composite material. The high-nickel ternary positive electrode material has a structural formula of LiNi x Co y Mn 1-x-y O2; wherein: 0.6≤x＜1； The mass fraction of aluminum in the positive electrode composite material is 0.03-2%, and the mass fraction of tantalum is 0.05-1.8%. The thickness of the coating layer is 0.5-30 nm. 4.A preparation method of the positive electrode composite material according to any one of claims 1-3, comprising the following steps: (1) dissolving a soluble organic aluminum salt, a soluble organic tantalum salt and a complexing agent in a non-aqueous solvent to obtain a solution A; (2) adding a high-nickel ternary positive electrode material and an alkali solution into the non-aqueous solvent to obtain a suspension B; (3) pouring the solution A into the suspension B, stirring, centrifuging, washing, drying to obtain an aluminum-tantalum modified surface material; and (4) calcining the aluminum-tantalum modified surface material to obtain a high-nickel ternary positive electrode material modified by aluminum-tantalum surface species, i.e., the positive electrode composite material. In step (1), the soluble organic aluminum salt is one or more of an aluminum alcoholate, an aluminum acetylacetonate and an aluminum ethoxide; the soluble organic tantalum salt is one or more of a tantalum alcoholate, a tantalum acetylacetonate and a tantalum ethoxide; and the complexing agent is at least one of an alkanoic acid, a dilute acid, an alkyne acid, an alkylamine, a dilute amine and an alkyne amine. The non-aqueous solvent is anhydrous alcohol solvent and / or anhydrous ketone solvent. In step (2), the mass ratio of aluminum ions in the soluble organic aluminum salt, tantalum ions in the soluble organic tantalum salt and the high-nickel ternary positive electrode material is (0.03-2):(0.05-1.8):1; and the alkali is one of aqueous ammonia, sodium hydroxide or potassium hydroxide. In step (3), the stirring conditions are: a temperature of -10-80 ℃ and a time of 0.1-48 h.

2. The positive electrode composite according to claim 1, characterized by: The high-nickel ternary positive electrode material is LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.91 Co 0.06 Mn 0.03 O2.

3. The positive electrode composite according to claim 1 or 2, characterized in that: In step (4), the calcination conditions are: a temperature of 300-1000 ℃ and a time of 0.5-24 h; and the calcination rate is 1-10 ℃ / min. 10.A lithium ion battery, comprising a positive electrode and a negative electrode; the material used in the positive electrode is the positive electrode composite material according to any one of claims 1-3. ​ ​ ​ ​ ​ 5. The method of claim 4, wherein: ​ The concentration of the soluble organic aluminum salt in the solution A is 1 x 10 -6 -10 mol / L; ​ The concentration of the soluble organic tantalum salt in the solution A is 1 x 10 -6 -10 mol / L.

6. The production method according to claim 4 or 5, characterized by: ​ The concentration of the complexing agent in the solution A is 3 x 10 -6 - 30 mol / L; ​ 7. The method of any one of claims 4-6, wherein: ​ ​ 8. The method of any one of claims 4-7, wherein: ​ 9. The method of any one of claims 4-8, wherein: ​ ​ ​

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