Carbon-europium-codoped lithium tungstate-coated ternary positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery electrode materials, and particularly discloses a carbon-europium co-doped lithium tungstate coated ternary positive electrode material as well as a preparation method and application thereof. The composite material prepared by uniformly coating the surface of the ternary positive electrode material with nano carbon-europium co-doped lithium tungstate has excellent electrochemical performance, higher reversible capacity, lower internal resistance, more stable interface and more excellent cycle performance, the chemical general formula of the nano carbon-europium co-doped lithium tungstate is LixWy-mEumOz / C, x is equal to 2-6, y is equal to 1-2, z is equal to 4-9, and m is equal to 0.01-0.05. The invention also provides a preparation method of the ternary positive electrode composite material, and the preparation method has the advantages of controllable production conditions, abundant raw material sources, low energy consumption, simple preparation process and the like, and is favorable for realizing industrial production. The method is suitable for the field of preparation of lithium batteries and positive electrode materials thereof.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery electrode materials, and relates to a ternary cathode material coated with carbon and europium co-doped lithium tungstate, a preparation method thereof, and an application thereof. Background Art

[0002] Ternary cathode materials (such as lithium nickel cobalt manganese oxide NCM, lithium nickel cobalt aluminate NCA) are widely used in lithium-ion batteries due to their high energy density, good charge and discharge performance, relatively high voltage platform, and strong designability. However, ternary cathode materials generally have deficiencies such as poor safety, limited cycle life, and the interfacial impedance needs to be further reduced. Forming a coating layer on the surface of the ternary cathode material can not only improve the interfacial contact between the ternary cathode material and the electrolyte, reduce the interfacial impedance, and improve the charge and discharge performance of the battery, but also regulate the charge distribution on the surface of the ternary cathode material, reduce the problem of excessive local current density, thereby improving the cycle stability and safety of the battery.

[0003] In the prior art, a solid-liquid mixing method is usually used to form a coating layer on the surface of the cathode material. However, after drying by the solid-liquid mixing method, agglomeration problems are likely to occur, and it is difficult to obtain a cathode material with a uniform coating, which affects its structural stability and cycle performance, and there is a large uncertainty in obtaining a pure phase of the target coating material. In addition, in the prior art, lithium cobaltate, lithium manganate, lithium nickelate, lithium tungstate, or lithium iron phosphate is used as the coating layer, and during the battery cycle, there are still problems such as the cycle performance needs to be further improved and the resistance is too high. Summary of the Invention

[0004] Aiming at the deficiencies of the ternary cathode composite material with a coating layer in the prior art, such as the uneven distribution of the coating layer on the surface of the cathode material and low electrochemical performance, the present invention provides a ternary cathode material coated with carbon and europium co-doped lithium tungstate, a preparation method thereof, and an application thereof. The battery prepared from the ternary cathode composite material coated with carbon-doped europium lithium tungstate has advantages such as high reversible capacity, low internal resistance, stable interface, and excellent electrochemical performance.

[0005] To achieve the above object of the invention, the embodiments of the present invention adopt the following technical solutions: In the first aspect, the present invention provides a ternary cathode material coated with carbon and europium co-doped lithium tungstate, and the chemical general formula of the carbon and europium co-doped lithium tungstate is Li x W y-m Eu m O z / C, where x = 2 - 6, y = 1 - 2, z = 4 - 9, and m = 0.01 - 0.05.

[0006] The ternary cathode composite material provided by the present invention is prepared by uniformly coating lithium tungstate co-doped with carbon and europium on the surface of the ternary cathode material. After coating, the ternary cathode material has higher reversible capacity, lower internal resistance, more stable interface and more excellent cycle performance, thus having better electrochemical performance. Among them, the reversible capacity is 203 mAh / g to 209 mAh / g, and the DCR is 249 to 265 mΩ. After preparing the ternary cathode material coated with the nano-lithium tungstate into a lithium-ion battery, the overall electrochemical performance of the lithium-ion battery can be significantly improved.

[0007] Further, the lithium tungstate co-doped with carbon and europium is spherical-like particles, with a primary particle size ≤ 500 nm, and the secondary particle size range is: more than 90% of the total volume of the particles have a particle size less than 0.953 μm and greater than 0.517 μm, and the specific surface area ≥ 5.2 m 2 / g.

[0008] The morphology of the nano-lithium tungstate co-doped with carbon and europium coated in the ternary cathode composite material provided by the present invention is spherical-like particles, with a primary particle size ≤ 500 nm, and the secondary particle size range is that more than 90% of the total volume of the particles have a particle size less than 1.123 μm and greater than 0.4 μm. The particle size is uniform, which is conducive to achieving uniform and good coating. The nano-lithium tungstate co-doped with carbon and europium can inhibit the side reactions on the surface of the cathode material and reduce the thickness of the electrolyte film on the surface of the cathode material. After coating it on the ternary cathode material, it not only reduces the battery internal resistance of the ternary cathode material and endows the ternary cathode material with higher reversible capacity, but also can act as a sintering aid for the ternary cathode material, making the particle size distribution of the ternary cathode material more uniform, the particle denseness higher, promoting grain boundary fusion, having higher structural stability, and thus significantly improving the electrochemical performance of the ternary cathode material.

[0009] Further, the ternary cathode material includes at least one of NCM622, NCM111, NCM523 or NCM811.

[0010] In the second aspect, the present invention provides a preparation method of the ternary cathode material coated with the above lithium tungstate co-doped with carbon and europium. The preparation method includes the following steps: S1. After preparing a slurry from a lithium source, a tungsten source, a europium source, a templating agent and water, dry it to obtain a mixed powder; S2. In a protective gas atmosphere, heat the mixed powder to 800 °C to 900 °C, keep it warm for 0.5 h to 2 h, then cool it down to 500 °C to 700 °C, keep it warm for 2 h to 10 h, and crush it to obtain a lithium tungstate co-doped with carbon and europium material; S3. Mix the lithium tungstate co-doped with carbon and europium material with the ternary cathode material and perform heat treatment to obtain a ternary cathode material coated with lithium tungstate co-doped with carbon and europium.

[0011] The preparation method of the ternary cathode material coated with carbon-europium co-doped lithium tungstate provided by the present invention has the advantages of controllable production conditions, rich raw material sources, low energy consumption, and simple preparation process. Moreover, the prepared ternary cathode composite material has excellent electrochemical performance, which is conducive to realizing industrial production.

[0012] Further, the lithium source includes any one of lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium nitrate (LiNO3), or lithium acetate (CH3COOLi2).

[0013] Further, the tungsten source includes any one of tungsten trioxide (WO3), tungstic acid (H2WO4), or ammonium tungstate [(NH4)6W7O 24 •6H2O].

[0014] Further, the europium source includes any one of europium oxide (Eu2O3), europium carbonate [Eu2(CO3)3], or europium hydroxide [Eu(OH)3].

[0015] Further, the template agent includes any one of glucose, sucrose, starch, or citric acid.

[0016] The template agent has the following functions in the present invention: On the first hand, the addition of the template agent is beneficial to enhancing the stability of the slurry, reducing the agglomeration of particles, and thus is conducive to the subsequent control of the particle size of lithium tungstate; on the second hand, the template agent can be coated in the ternary cathode material during the sintering process, which can effectively avoid the concentration and growth of lithium tungstate grains, further effectively inhibit the growth size of the carbon-europium co-doped lithium tungstate material during the coating process of the ternary cathode material, and the coated carbon can further enhance the conductivity of the material and improve the electronic conductivity.

[0017] Further, S1 specifically includes: mixing the lithium source with water to form a solution, then adding the tungsten source and the europium source and mixing evenly, reacting for 1 h to 6 h, then adding the template agent to obtain a slurry, and drying to obtain a mixed powder.

[0018] Further, in S1, the solid-liquid mass ratio of the slurry is 0.2:1 to 0.5:1.

[0019] Further, the mass ratio of the template agent in the slurry is 0.02% to 0.05%.

[0020] Under the preferred dosage of the template agent and the solid-liquid ratio of the slurry, it can not only ensure the uniform mixing of the slurry, reduce agglomeration and improve the sanding efficiency, but also ensure that no impurities are introduced to avoid the influence of impurities on the target components. If the solid content of the template agent or the slurry is too large, the slurry will be viscous and not conducive to dispersion, affecting the sanding effect.

[0021] Further, in S1, the drying includes any one of spray drying, microwave drying, or convective drying.

[0022] Further, in S2, the crushing includes crushing by a pneumatic crusher.

[0023] Further, in S3, the temperature of the heat treatment is 650°C to 750°C, and the time is 7h to 10h.

[0024] Preferably, spray drying is selected, wherein the inlet air temperature of the spray drying is 200°C to 300°C, the outlet air temperature is 100°C to 150°C, the bag filter temperature is 50°C to 100°C, and the atomizer frequency is 200Hz to 350Hz.

[0025] In a third aspect, the present invention provides an application of the ternary cathode material coated with carbon-europium co-doped lithium tungstate provided in the first aspect in a lithium-ion battery.

[0026] In a fourth aspect, the present invention further provides a lithium-ion battery, which includes the ternary cathode material coated with carbon-europium co-doped lithium tungstate provided in the first aspect, or the ternary cathode composite material prepared by the preparation method of the ternary cathode material coated with carbon-europium co-doped lithium tungstate provided in the second aspect.

[0027] Compared with conventional lithium-ion batteries, the electrochemical performance of the lithium-ion battery assembled with the ternary cathode material coated with carbon-europium co-doped lithium tungstate is significantly improved, wherein the reversible capacity is 203mAh / g to 209mAh / g, the DCR is 249 to 265mΩ, and the capacity retention rate after 50 cycles is not less than 91%. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is the XRD pattern of carbon-europium co-doped lithium tungstate I in Example 1 of the present invention; Figure 2 It is the SEM image of carbon-europium co-doped lithium tungstate I in Example 1 of the present invention; Figure 3 It is the particle size distribution diagram of carbon-europium co-doped lithium tungstate I in Example 1 of the present invention; Figure 4 It is the SEM image of the ternary cathode composite material I in Example 1 of the present invention; Figure 5SEM image of carbon and europium co-doped lithium tungstate Ⅱ in Embodiment 2 of the present invention; Figure 6 SEM image of carbon and europium co-doped lithium tungstate Ⅲ in Embodiment 3 of the present invention. Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Embodiment 1 This embodiment provides a ternary cathode material coated with carbon and europium co-doped lithium tungstate, which is a composite material prepared by uniformly coating nano carbon and europium co-doped lithium tungstate on the surface of the ternary cathode material; Among them, the chemical general formula of the nano carbon and europium co-doped lithium tungstate is Li2W 0.99 Eu 0.01 O4 / C.

[0032] This embodiment also provides a preparation method of the above-mentioned ternary cathode material coated with carbon and europium co-doped lithium tungstate, which is specifically as follows: S1. Weigh lithium hydroxide, tungsten trioxide and europium oxide according to the molar ratio of Li:W:Eu of 2:0.99:0.01; Add lithium hydroxide to deionized water at 80°C to prepare 2.5 L of a 5.34 mol / L lithium hydroxide solution. Add the weighed tungsten trioxide and europium oxide to the lithium hydroxide solution, and react fully for 4 h under stirring at 400 rpm. Adjust the solid-liquid mass ratio to 0.3:1 to obtain a slurry; Add 0.02% of glucose based on the mass of the slurry to obtain a carbon- and europium-containing mixed slurry; Perform spray drying on the carbon- and europium-containing mixed slurry to obtain a mixed powder; the spray drying conditions are set as follows: the feeding rate is 8 L / h, the inlet air temperature during drying is 300°C, the outlet air temperature is 130°C, the cloth bag temperature is 80°C, and the atomizer frequency is 300 Hz.

[0033] S2. Add 1 kg of the mixed powder to a pulse tube furnace. Under a nitrogen atmosphere, heat it up to 800°C at a heating rate of 10°C / min, hold for 0.5 h, then cool it down to 650°C at a rate of 8°C / min, hold for 10 h, cool it down to room temperature in a nitrogen atmosphere, and then perform sanding in a nano sand mill for 4 h at a rotation speed of 1200 rpm. After drying, a crude product of carbon and europium co-doped lithium tungstate is obtained. Crush it with a jet mill to obtain a nano carbon and europium co-doped lithium tungstate material, carbon and europium co-doped lithium tungstate Ⅰ, whose chemical general formula is Li2W 0.99 Eu 0.01O4 / C; S3. Mix 10 g of the carbon-europium co-doped lithium tungstate Ⅰ with 1 kg of the ternary cathode material NCM622, and under an air atmosphere, heat it to 700 °C at a rate of 8 °C / min and hold for 8 h to obtain a ternary cathode material coated with carbon-europium co-doped lithium tungstate, denoted as ternary cathode composite material Ⅰ.

[0034] In this example, the microstructures of the above-provided carbon-europium co-doped lithium tungstate Ⅰ and ternary cathode composite material Ⅰ were also characterized, and the specific content is as follows: The XRD pattern of the carbon-europium co-doped lithium tungstate Ⅰ is as Figure 1 shown. From Figure 1 it can be seen that the phase of the carbon-europium co-doped lithium tungstate Ⅰ is composed of lithium tungstate, indicating that the reaction between lithium hydroxide and tungsten trioxide is complete and no other impurities are generated.

[0035] The SEM image of the carbon-europium co-doped lithium tungstate Ⅰ is as Figure 2 shown. From Figure 2 it can be seen that the morphology of the carbon-europium co-doped lithium tungstate Ⅰ is spherical-like particles, and the primary particle size is 300 nm - 500 nm; The particle size of the carbon-europium co-doped lithium tungstate Ⅰ was detected by a particle size analyzer, and the particle size distribution diagram of the carbon-europium co-doped lithium tungstate Ⅰ is as Figure 3 shown. From Figure 3 it can be seen that in the carbon-europium co-doped lithium tungstate Ⅰ, the secondary particle size range is: the particles accounting for more than 90% of the total volume have a particle size less than 1.06 μm and greater than 0.4 μm; the particles accounting for more than 50% of the total volume have a particle size less than 0.81 μm and greater than 0.4 μm. The above shows that the carbon-europium co-doped lithium tungstate Ⅰ has a uniform particle size. After measurement, the specific surface area is 5.29 m 2 / g, which is beneficial for the carbon-europium co-doped lithium tungstate Ⅰ to uniformly coat on the surface of the ternary cathode material.

[0036] The SEM image of the ternary cathode composite material Ⅰ is as Figure 4 shown. Figure 4 In it, the ternary cathode composite material Ⅰ contains large particles and small particles, which is due to the large difference in particle size of the ternary cathode material itself. From Figure 4 it can be seen that the surfaces of the large particles and small particles in the ternary cathode composite material Ⅰ are uniformly coated with the carbon-europium co-doped lithium tungstate Ⅰ. From the above, it can be known that the carbon-europium co-doped lithium tungstate Ⅰ provided by the present invention can uniformly coat on the surface of the ternary cathode material, which is beneficial to improving the transport rate of lithium ions and electrons and the electronic conductivity of the cathode material, reducing the side reactions on the surface of the cathode material, and acting as a sintering aid to make the cathode material denser and maintain the structural stability of the lithium-ion battery cathode material.

[0037] Example 2 This embodiment provides a ternary cathode material coated with carbon-europium co-doped lithium tungstate, which is a composite material prepared by uniformly coating nano carbon-europium co-doped lithium tungstate on the surface of the ternary cathode material; Among them, the chemical general formula of the nano carbon-europium co-doped lithium tungstate is Li6W 1.97 Eu 0.03 O9 / C.

[0038] This embodiment also provides a preparation method of the above-mentioned ternary cathode material coated with carbon-europium co-doped lithium tungstate, which is specifically as follows: S1. Weigh lithium hydroxide, ammonium tungstate and europium oxide according to the molar ratio of Li:W:Eu of 6:1.97:0.03; At 20 °C, add lithium hydroxide to deionized water to prepare 3 L of 3 mol / L lithium hydroxide solution. Add the weighed ammonium tungstate and europium hydroxide to the lithium hydroxide solution, and react fully for 2 h under stirring at 800 rpm. Adjust the solid-liquid mass ratio to 0.5:1 to obtain a slurry; Add 0.05% of starch based on the mass of the slurry to obtain a mixed slurry containing carbon and europium; Spray dry the mixed slurry containing carbon and europium to obtain a mixed powder. The spray drying conditions are set as follows: the feeding rate is 15 L / h, the inlet air temperature during drying is 200 °C, the outlet air temperature is 150 °C, the cloth bag temperature is 100 °C, and the atomizer frequency is 350 Hz.

[0039] S2. Add 1 kg of the mixed powder to a pulse tube furnace. Under a nitrogen atmosphere, heat it to 900 °C at a heating rate of 8 °C / min, keep it warm for 2 h, then cool it at a rate of 6 °C / min to 700 °C, keep it warm for 5 h, and cool it to room temperature in a nitrogen atmosphere. Then, carry out sand grinding in a nano sand mill. The sand grinding time is 3 h and the rotation speed is 1500 rpm. After drying, obtain a crude product of carbon-europium co-doped lithium tungstate. Crush it with a jet mill to obtain a nano carbon-europium co-doped lithium tungstate material, carbon-europium co-doped lithium tungstate II, whose chemical general formula is Li6W 1.97 Eu 0.03 O9 / C; S3. Mix 15 g of the carbon-europium co-doped lithium tungstate II with 1 kg of the ternary cathode material NCM523. Under an air atmosphere, heat it to 650 °C at a rate of 10 °C / min and keep it warm for 10 h to obtain a ternary cathode material coated with carbon-europium co-doped lithium tungstate, denoted as ternary cathode composite material II.

[0040] This embodiment also characterizes the microstructure of the above-provided carbon-europium co-doped lithium tungstate II. The SEM image of the carbon-europium co-doped lithium tungstate II is as shown in Figure 5As shown. It was measured that the morphology of the carbon-europium co-doped lithium tungstate II was spherical-like particles with a primary particle size of 300 nm to 500 nm; the secondary particle size range was: particles accounting for more than 90% of the total volume had a particle size less than 0.953 μm and greater than 0.517 μm; particles accounting for more than 50% of the total volume had a particle size less than 0.736 μm and greater than 0.517 μm, and the specific surface area was 6.23 m 2 / g.

[0041] Example 3 This example provides a ternary cathode material coated with carbon-europium co-doped lithium tungstate, which is a composite material prepared by uniformly coating nano-carbon-europium co-doped lithium tungstate on the surface of the ternary cathode material; Among them, the chemical general formula of the nano-carbon-europium co-doped lithium tungstate is Li2W 1.95 Eu 0.05 O7 / C.

[0042] This example also provides a preparation method of the above-mentioned ternary cathode material coated with carbon-europium co-doped lithium tungstate, which is specifically as follows: S1. Weigh lithium nitrate, tungstic acid and europium carbonate according to the molar ratio of Li:W:Eu of 2:1.95:0.05; At 50 °C, add lithium nitrate to deionized water to prepare 3 L of 4 mol / L lithium hydroxide solution. Add the weighed tungstic acid and europium carbonate to the lithium nitrate solution, and react fully for 1 h under stirring at 1200 rpm. Adjust the solid-liquid mass ratio to 0.2:1 to obtain a slurry; Add 0.03% of sucrose based on the mass of the slurry to obtain a carbon- and europium-containing mixed slurry; Perform spray drying on the carbon- and europium-containing mixed slurry to obtain a mixed powder; the spray drying conditions are set as follows: the feeding rate is 10 L / h, the inlet air temperature during drying is 200 °C, the outlet air temperature is 100 °C, the cloth bag temperature is 50 °C, and the atomizer frequency is 200 Hz.

[0043] S2. Add 1 kg of the mixed powder to a pulse tube furnace. Under a nitrogen atmosphere, heat it to 850 °C at a heating rate of 12 °C / min, hold for 1.5 h, then cool it at a rate of 10 °C / min to 500 °C, hold for 2 h, cool it to room temperature in a nitrogen atmosphere, and then perform sanding in a nano sand mill for 6 h at a rotation speed of 800 rpm. After drying, obtain a crude product of carbon-europium co-doped lithium tungstate. Crush it through a jet mill to obtain a nano-carbon-europium co-doped lithium tungstate material, carbon-europium co-doped lithium tungstate III, whose chemical general formula is Li2W 1.95 Eu 0.05 O7 / C; S3. Mix 12 g of the carbon-europium co-doped lithium tungstate III with 1 kg of the ternary positive electrode material NCM111, heat the mixture to 750°C at a rate of 12°C / min in an air atmosphere and keep the mixture warm for 7 hours to obtain a carbon-europium co-doped lithium tungstate coated ternary positive electrode material, which is recorded as ternary positive electrode composite material III.

[0044] This embodiment also characterizes the microstructure of the carbon-europium co-doped lithium tungstate III provided above. The SEM image of the carbon-europium co-doped lithium tungstate III is as follows: Figure 6 As shown. According to the measurement, the carbon-europium co-doped lithium tungstate III has a spherical particle shape, a primary particle size of 300nm~500nm; the secondary particle size range is: more than 90% of the total volume has a particle size less than 1.123μm and greater than 0.486μm; more than 50% of the total volume has a particle size less than 0.837μm and greater than 0.486μm, and the specific surface area is 6.89m 2 / g.

[0045] Comparative Example 1 This comparative example provides a method for preparing a ternary positive electrode composite material coated with europium, which is basically the same as step S3 of Example 1. The specific preparation method includes the following steps: 10 g of the europium oxide was mixed with 1 kg of the ternary positive electrode material NCM622, and the temperature was raised to 700° C. at a rate of 8° C. / min and kept at this temperature for 8 h in an air atmosphere to obtain a europium-coated ternary positive electrode composite material, which was recorded as ternary positive electrode composite material pair I.

[0046] Comparative Example 2 This comparative example provides a method for preparing a ternary positive electrode composite material coated with carbon-containing lithium tungstate. The preparation method is basically the same as that of Example 2, except that tungsten is used in an equal amount of substance to replace europium when preparing the coating layer. The specific preparation method includes the following steps: S1. Weigh lithium hydroxide and ammonium tungstate in a Li:W molar ratio of 6:2; Add lithium hydroxide to deionized water at 20°C to prepare 3L of 3 mol / L lithium hydroxide solution, add the above-weighed ammonium tungstate to the lithium hydroxide solution, fully react for 2h under stirring at 800rpm, and adjust the solid-liquid mass ratio to 0.5:1 to obtain a slurry; Adding 0.05% starch by mass of the slurry to obtain a carbon-containing mixed slurry; The carbon-containing mixed slurry is spray-dried to obtain a mixed powder; the spray drying conditions are set as follows: a feed rate of 15 L / h, an air inlet temperature of 200°C during drying, an air outlet temperature of 150°C, a bag temperature of 100°C, and an atomizer frequency of 350 Hz.

[0047] S2. Add 1 kg of the mixed powder into a pulse tube furnace. Under a nitrogen atmosphere, heat it to 900 °C at a heating rate of 8 °C / min, hold for 2 h, then cool it to 700 °C at a rate of 6 °C / min and hold for 5 h. Cool it to room temperature in a nitrogen atmosphere, and then carry out sand grinding in a nano sand mill for 3 h at a rotation speed of 1500 rpm. After drying, a crude product of lithium tungstate carbide is obtained. Crush it with a jet mill to obtain a nano lithium tungstate carbide material with a chemical general formula of Li6W2O9 / C; S3. Mix 15 g of the nano lithium tungstate carbide material with 1 kg of the ternary cathode material NCM523. Under an air atmosphere, heat it to 650 °C at a rate of 10 °C / min and hold for 10 h to prepare a ternary cathode composite material coated with lithium tungstate carbide, denoted as ternary cathode composite material pair II.

[0048] Effect example Assemble the ternary cathode composite materials prepared in Examples 1-3 and Comparative Examples 1-2 into 2025-type button batteries to obtain button batteries I-III and button battery pairs I-II respectively. The specific assembly method is as follows: In a glove box, assemble in the order of negative electrode shell, negative electrode material, separator, electrode sheet, gasket, elastic sheet, and positive electrode shell, and drop an appropriate amount of electrolyte during the assembly process to moisten the separator and electrode sheet. After assembly, seal it with a battery sealer and let it stand for 12 h before performing electrochemical performance tests.

[0049] Among them, in the present invention, a lithium sheet is used as the negative electrode material, the electrode sheet is the ternary cathode composite material prepared in the example or comparative example, and the electrolyte is a lithium hexafluorophosphate solution with a concentration of 1 mol / L.

[0050] Test the electrochemical performances such as the reversible capacity, DC resistance, and capacity retention rate of the above-prepared button batteries. The specific test results are shown in Table 1.

[0051] Among them, the test conditions for the reversible capacity are: 0.1C, 3.0 - 4.5 V; The test conditions for the DC resistance are: 1.0 C, 3.0 - 4.5 V, 50 cycles at room temperature; The test conditions for the capacity retention rate are: 1.0 C, 3.0 - 4.5 V, 50 cycles at room temperature.

[0052] Table 1

[0053] As can be seen from Table 1, compared with the batteries assembled with the ternary cathode composite materials prepared in Comparative Examples 1-2, the button batteries assembled with the ternary cathode composite materials I-III prepared in Examples 1-3 of the present invention as the cathode materials have excellent electrochemical performance, with higher reversible capacity, cycle capacity retention rate and lower internal resistance. The reason may be that: compared with the nano lithium tungstate carbide material as the cathode material, the advantages of the nano europium-carbon co-doped lithium tungstate-coated ternary cathode composite material in battery performance can be attributed to the mechanism of multi-dimensional synergistic effect: (1) Carbon doping improves the electronic conductivity of the material by forming a three-dimensional conductive network, and the introduction of europium can further optimize the internal charge distribution of the lattice, reduce the hindrance of lattice defects to the diffusion of lithium ions, and reduce the migration activation energy of Li + to improve the conductivity; (2) Europium doping can induce the formation of a non-stoichiometric Li2-xWO4 structure in the coating layer, generating more lithium vacancies and increasing the interfacial lithium ion diffusion coefficient; (3) There are significant differences in the radii of europium ions and nickel ions, manganese ions. Its doping will cause lattice strain, but by forming strong Eu-O bonds, it can effectively anchor the transition metal layer, reduce the degree of cation mixing during cycling, inhibit lattice distortion, and improve the cycling performance; at the same time, the lithium tungstate coating layer reduces surface side reactions and improves structural stability; (4) The Lewis acidity of europium can chemically adsorb the residual lithium on the surface. During high-temperature sintering, the replacement reaction of Eu 3+ with Li + can reduce the content of residual lithium on the surface and significantly reduce the interfacial impedance, thereby reducing the DC resistance.

[0054] The electrochemical performance of the lithium ion battery assembled with the ternary cathode material coated with europium-carbon co-doped lithium tungstate provided by the present invention is significantly improved. Within the scope of the present invention, its reversible capacity is 203 mAh / g to 209 mAh / g, the DCR is 249 to 265 mΩ, and the cycle capacity retention rate after 50 cycles is not less than 91%.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A carbon-europium co-doped lithium tungstate coated ternary positive electrode material, characterized in that: The chemical formula of the carbon-europium co-doped lithium tungstate is Li x W y-m Eu m O z / C, x=2~6, y=1~2, z=4~9, m=0.01~0.

05.

2. The carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to claim 1, characterized in that: The carbon-europium co-doped lithium tungstate is a spherical particle with a primary particle size of ≤500nm and a secondary particle size range of: more than 90% of the total volume of the particles have a particle size of less than 1.123μm and greater than 0.4μm, and a specific surface area of ​​≥5.2m 2 / g.

3. The carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to claim 1, characterized in that: The ternary positive electrode material includes at least one of NCM622, NCM111, NCM523 or NCM811.

4. The method for preparing the carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1. A lithium source, a tungsten source, a europium source, a template and water are prepared into a slurry, and then dried to obtain a mixed powder; S2. In a protective gas atmosphere, the mixed powder is heated to 800°C~900°C, kept warm for 0.5h~2h, then cooled to 500°C~700°C, kept warm for 2h~10h, and crushed to obtain carbon-europium co-doped lithium tungstate; S3, mixing the carbon-europium co-doped lithium tungstate with a ternary positive electrode material, and subjecting the mixture to heat treatment to obtain a carbon-europium co-doped lithium tungstate coated ternary positive electrode composite material.

5. The method for preparing the carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to claim 4, characterized in that: The lithium source includes any one of lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate; and / or The tungsten source includes any one of tungsten trioxide, tungstic acid or ammonium tungstate; and / or The europium source includes any one of europium oxide, europium carbonate or europium hydroxide; and / or The template agent includes any one of glucose, sucrose, starch or citric acid.

6. The method for preparing the carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to claim 4, characterized in that: The solid-liquid mass ratio of the slurry is 0.2:1 to 0.5:1; and / or The mass proportion of the template in the slurry is 0.02%-0.05%.

7. The method for preparing the carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to claim 4, characterized in that: In S1, the drying comprises any one of spray drying, microwave drying or convection drying; and / or In S2, the crushing includes crushing by a jet crusher; and / or In S3, the heat treatment is performed at a temperature of 650°C to 750°C and for a time of 7h to 10h.

8. The method for preparing the carbon-europium co-doped lithium tungstate coated ternary positive electrode material according to claim 7, characterized in that: The inlet air temperature of the spray drying is 200°C to 300°C, the outlet air temperature is 100°C to 150°C, the bag temperature is 50°C to 100°C, and the atomizer frequency is 200Hz to 350Hz.

9. Use of the carbon-europium co-doped lithium tungstate coated ternary positive electrode material as claimed in any one of claims 1 to 3 in a lithium ion battery.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the carbon-europium co-doped lithium tungstate coated ternary positive electrode material as described in any one of claims 1 to 3, or the carbon-europium co-doped lithium tungstate coated ternary positive electrode material obtained by the preparation method as described in any one of claims 4 to 8.

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