Lithium niobate-coated graphite composite negative electrode material and preparation method and application thereof

Abstract

The application discloses a lithium niobate-coated graphite composite negative electrode material and a preparation method and application thereof. x NbO y , wherein 0 ‑ 1 S / cm-10 ‑8 S / cm; the thickness of the lithium niobate is 0.01 nm-200 nm; and the lithium niobate-coated graphite composite negative electrode material is applied in a lithium ion battery, so that the rate performance of the lithium ion battery can be effectively improved, and the fast charging performance is improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium battery materials, in particular to a lithium niobate-coated graphite composite negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] Graphite is a commonly used negative electrode material of a commercialized lithium ion battery. The graphite has a low lithium intercalation potential, a stable charge / discharge platform and reversible lithium ion intercalation / deintercalation capability. Meanwhile, the graphite is abundant in resources and low in cost. With the continuous development of electronic equipment and new energy automobile industries, fast charging technology is paid more and more attention. The traditional graphite negative electrode material has problems such as low capacity and lithium precipitation when fast charging due to slow lithium intercalation speed, which seriously limits the fast charging performance of the current lithium ion battery.

[0003] In order to solve the problem of insufficient fast charging performance of the graphite, researchers use methods such as surface modification, surface coating and material structure design for modification.

[0004] For example, Chinese invention patent CN114864916A (publication date: August 5, 2022) uses a sol-gel method to prepare a niobium pentoxide-coated graphite composite negative electrode material; niobium pentachloride is dissolved in anhydrous ethanol to form a niobium alcohol solution; deionized water is added dropwise, stirred uniformly, and a mixed solvent is formed; graphite is added in a certain molar ratio, stirred uniformly, dried under water bath, placed in an oven for drying, and ground into powder; the prepared powder is sintered at 700 DEG C to 900 DEG C under a tubular furnace argon atmosphere to obtain a niobium pentoxide-coated graphite composite negative electrode material; the preparation method of this patent needs to be sintered at high temperature, the energy consumption cost is high, and the discharge specific capacity of the prepared material at 2C rate is 100 mAh / g, and the discharge specific capacity at 5C rate is 55 mAh / g, so the fast charging performance is not obviously improved.

[0005] Chinese invention patent CN114122392A (publication date: March 1, 2022) proposes a preparation method of a high-capacity fast-charging graphite composite material, first adopts a liquid nitrogen immersion method to introduce defects between graphite layers and improve the interlayer spacing of the material, then introduces tin source between the materials through a hydrothermal method to improve the specific capacity of the material and the active points for storing lithium at the defects, and finally deposits titanium niobate on the surface of the material through an atomic layer vapor deposition method (ALD) to obtain a high-capacity fast-charging graphite composite material. The graphite composite material coated with titanium niobate prepared by the above method has a high production cost and harsh production conditions, and only the performance of the graphite at 0.1C rate is displayed, the performance of the graphite at a high rate is not displayed, and the rate performance mainly displays the performance of a soft package battery, which cannot completely reflect the improvement of the rate performance of the graphite.

[0006] Chinese invention patent CN114864897A (publication date August 5, 2022) proposes a fast-charging graphite composite material composed of a core and an outer layer, and the outer layer covers the core. The core is graphite, and the outer layer is composed of Li5FeO4, metal oxide and amorphous carbon. The preparation method is to use graphite as the substrate, metal oxide and Li5FeO4 as the reaction source, and use atomic vapor deposition method to repeatedly deposit metal oxide and Li5FeO4 on graphite to obtain graphite precursor material. After uniformly dispersing the precursor material in the resin solution, spray drying, and then high-temperature graphitization at 800-1200°C for 1-6 hours, the graphite composite material is obtained. The atomic vapor deposition method used in this patent requires corresponding production line equipment, has harsh requirements, and the designed structure is complex, the processing procedure is more, the production cost is higher, and only the performance of graphite at 0.1C rate is displayed, the performance of graphite alone at high rate is not displayed, and the rate performance mainly displays the performance of soft pack battery, which cannot fully reflect the improvement of the rate performance of graphite.

[0007] Lee, S. M. et al. A cooperative biphasic MoO x -MoP x promoter enables a fast-charging lithium-ion battery. Nat. Commun. 12, 6578 (2021). x -MoP x coated graphite material, the preparation process is: using H2O2 to dissolve MoO3, then mixing and stirring with graphite, removing the solvent at 80°C to obtain powder, then treating the obtained powder in a tube furnace containing phosphorus gas at 600°C for two hours, wherein the phosphorus gas is obtained by heating and decomposing NaH2PO2 powder; the preparation conditions of the preparation process in this article are relatively complex, and the specific composition ratio of phosphorus in the treatment gas is unknown; the prepared MoO x -MoP x coated graphite material is used to prepare a full battery, and the discharge capacity is 160mAh / g at 6C charge / 1C discharge, and 145mAh / g after 300 cycles, which shows that the rate performance improvement is not obvious.

[0008] The soft carbon / hard carbon and metal oxides and other substances used in the above conventional surface coating have no obvious improvement on the interface dynamics of graphite materials, and have limited effect on improving the fast-charging performance of graphite.

[0009] On the contrary, by coating inorganic lithium salt with certain ion conductivity on the surface of graphite, the reaction kinetics performance of graphite negative electrode can be more effectively promoted, and the fast-charging performance of the material can be improved. SUMMARY

[0010] The embodiment of the present application provides a lithium niobate coated graphite composite negative electrode material and a preparation method and application thereof.

[0011] The preparation method of the lithium niobate coated graphite composite negative electrode material provided by the embodiment of the present application realizes modification under relatively milder conditions, is relatively simple in process, can reduce cost, and can be used for large-scale industrial production.

[0012] In a first aspect, the embodiment of the present application provides a lithium niobate coated graphite composite negative electrode material, which comprises: graphite particles, and lithium niobate coated on the surface of the graphite particles.

[0013] The chemical general formula of the lithium niobate is Li x NbO y , wherein 0

[0014] The mass percentage of the lithium niobate in the composite negative electrode material is 0.001%-10%;

[0015] The electrical conductivity of the lithium niobate is 10 -1 S / cm-10 -8 S / cm;

[0016] The thickness of the lithium niobate is 0.01 nm-200 nm.

[0017] Preferably, the mass percentage of the lithium niobate in the composite negative electrode material is 1%-5%;

[0018] The electrical conductivity of the lithium niobate is 10 -5 S / cm-10 -2 S / cm;

[0019] The thickness of the lithium niobate is 1 nm-20 nm.

[0020] Preferably, the lithium niobate comprises one or more coexistences of amorphous lithium niobate or crystalline lithium niobate.

[0021] The lithium niobate is coated on the surface of the graphite particles in an island shape and / or a continuous and uniform film shape.

[0022] In a second aspect, the embodiment of the present application provides a preparation method of the lithium niobate coated graphite composite negative electrode material in the first aspect, and the preparation method comprises:

[0023] Step S1, mixing a lithium source material and a niobium source material, sealing in a glass tube containing a rubber plug, injecting a solvent, placing the glass tube in an ultrasonic disperser for ultrasonic dispersion, forming a mixed alcohol solution;

[0024] Step S2, adding the mixed alcohol solution dropwise to dilute, obtaining a diluted mixed alcohol solution;

[0025] Step S3, adding graphite particles to the diluted mixed alcohol solution, continuing ultrasonic dispersion, obtaining a precursor solution;

[0026] Step S4, placing the precursor solution on a heating stirring table, heating and stirring until the solvent evaporates, then placing it in an oven for baking, grinding to obtain a precursor powder;

[0027] Step S5, placing the precursor powder in a high-temperature furnace for sintering treatment, obtaining a lithium niobate-coated graphite composite negative electrode material.

[0028] Preferably, the lithium source material includes lithium foil or lithium oxalate;

[0029] The niobium source material includes niobium ethoxide or niobium oxalate;

[0030] The solvent includes anhydrous ethanol or deionized water;

[0031] The molar mass ratio of lithium to niobium in the mixed alcohol solution is 1.05:(0-1];

[0032] The graphite particles are flaky or spherical particles with an average particle size of 5-10μm.

[0033] Preferably, the ultrasonic dispersion time is 10-20min;

[0034] The ultrasonic dispersion frequency is 28-200KHz.

[0035] Preferably, the heating stirring table temperature is 70-110℃, the stirring speed is 300-400r / min, and the stirring time is 1-2 hours;

[0036] The oven temperature is 50-80℃, and the baking time is 1-2 hours.

[0037] Preferably, the high-temperature furnace includes any of a tube furnace or a muffle furnace;

[0038] The sintering treatment method is specifically: heating at a rate of 5-10℃ / min to 200-450℃ in an air atmosphere, and holding for 2-3 hours.

[0039] In a third aspect, the embodiments of the present application provide a negative electrode sheet, which comprises the lithium niobate-coated graphite composite negative electrode material of the first aspect.

[0040] In a fourth aspect, the embodiments of the present application provide a lithium ion battery, which comprises the negative electrode sheet of the third aspect; and the lithium ion battery comprises any one of a liquid lithium ion battery, a solid-state lithium ion battery or a polymer lithium ion battery.

[0041] The embodiments of the present application provide a lithium niobate-coated graphite composite negative electrode material, a preparation method and application thereof. Since the inorganic salt lithium niobate, especially amorphous lithium niobate, has a high lithium ion conduction rate, the coating of the lithium niobate layer on the graphite negative electrode material is beneficial to the lithium ion transmission on the surface of the graphite, thereby effectively reducing the interface impedance and improving the rate performance of the material, and further improving the fast charging performance of the material.

[0042] The preparation method of the lithium niobate-coated graphite composite negative electrode material provided by the embodiments of the present application does not need the traditional atomic layer vapor deposition method (ALD) and a complex modification process. The lithium niobate is coated on the surface of the graphite material through a simple and low-cost sol-gel method and a milder sintering condition. The preparation method is simple, the cost is low, and the method can be suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0043] The technical solutions of the embodiments of the present application are further described in detail below with reference to the drawings and examples.

[0044] Figure 1 is a flow chart of the preparation method of the lithium niobate-coated graphite composite negative electrode material provided by the embodiments of the present application.

[0045] Figure 2 is a scanning electron microscope (SEM) image of the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 of the present application.

[0046] Figure 3 is an X-ray diffraction (XRD) image of the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 of the present application.

[0047] Figure 4 is a transmission electron microscope energy dispersive X-ray spectrum (TEM-EDS) image of the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 of the present application.

[0048] Figure 5 is a rate performance comparison chart of the three-electrode battery assembled by the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 of the present application and the graphite of Comparative Example 1.

[0049] Figure 6 is a rate performance comparison chart of a three-electrode battery assembled by the lithium niobate-coated graphite composite negative electrode material prepared in Example 2 of the present application and the graphite of Comparative Example 2.

[0050] Figure 7 is an X-ray diffraction (XRD) chart of the lithium niobate-coated graphite composite negative electrode material prepared in Example 3 of the present application and the graphite of Comparative Example 1.

[0051] Figure 8 is a transmission electron microscope-energy dispersive X-ray spectroscopy (TEM-EDS) chart of the lithium niobate-coated graphite composite negative electrode material prepared in Example 3 of the present application.

[0052] Figure 9 is a transmission electron microscope-energy loss spectroscopy (TEM-EELS) chart of the lithium niobate-coated graphite composite negative electrode material prepared in Example 3 of the present application.

[0053] Figure 10 is a rate performance comparison chart of a three-electrode battery assembled by the lithium niobate-coated graphite composite negative electrode material prepared in Example 3 of the present application and the graphite of Comparative Example 1. DETAILED DESCRIPTION

[0054] The present application will be further described in the following with reference to the accompanying drawings and specific examples, but it should be understood that these examples are only for a more detailed illustration and should not be understood as limiting the present application in any form, i.e. are not intended to limit the protection scope of the present application.

[0055] The present application provides a lithium niobate-coated graphite composite negative electrode material, comprising: graphite particles, and lithium niobate coated on the surface of the graphite particles.

[0056] wherein the chemical general formula of the lithium niobate is Li x NbO y , wherein 0 < x ≤ 1, 2 ≤ y ≤ 3.

[0057] The mass percentage of the lithium niobate in the composite negative electrode material is 0.001%-10%, preferably 1%-5%; the electrical conductivity of the lithium niobate is 10 -1 S / cm-10 -8 S / cm, preferably 10 -5 S / cm-10 -2 S / cm; the thickness of the lithium niobate is 0.01 nm-200 nm, preferably 1 nm-20 nm.

[0058] The lithium niobate comprises one or more of amorphous lithium niobate or crystalline lithium niobate coexisting; the lithium niobate is coated on the surface of the graphite particles in the form of islands and / or continuous uniform thin film.

[0059] The embodiment of the present application provides a preparation method of the lithium niobate-coated graphite composite negative electrode material, as shown in the formula (I), and specifically comprises the following steps. Figure 1

[0060] In step S1, a lithium source material and a niobium source material are mixed, sealed in a glass tube containing a rubber plug, injected with a solvent, and subjected to ultrasonic dispersion in an ultrasonic dispersion machine to form a mixed alcohol solution.

[0061] The lithium source material includes lithium foil or lithium oxalate; the niobium source material includes niobium ethoxide or niobium oxalate; and the solvent includes anhydrous ethanol or deionized water.

[0062] In this step, the raw materials are selected in two schemes, one of which is to mix lithium foil and niobium ethoxide, and use anhydrous ethanol as the solvent; the other is to mix lithium oxalate and niobium oxalate, and use deionized water as the solvent; the molar mass ratio of lithium element to niobium element in the obtained mixed alcohol solution is 1.05:(0-1].

[0063] The ultrasonic dispersion time is 10 min-20 min, and the ultrasonic dispersion frequency is 28 KHz-200 KHz.

[0064] In step S2, the mixed alcohol solution is diluted by dropwise adding a solvent to obtain a diluted mixed alcohol solution.

[0065] Similarly, the solvent used for dilution in this step is the same as that used in step S1.

[0066] In step S3, graphite particles are added to the diluted mixed alcohol solution, and ultrasonic dispersion is continued to obtain a precursor solution.

[0067] The graphite particles are flaky or spherical particles with an average particle size of 5-10 μm.

[0068] The ultrasonic dispersion time in this step is 10 min-20 min, and the ultrasonic dispersion frequency is 28 KHz-200 KHz.

[0069] In step S4, the precursor solution is placed on a heating stirring table, heated and stirred until the solvent evaporates, then placed in an oven for baking, and ground to obtain a precursor powder.

[0070] The heating stirring table has a temperature of 70-110°C, a stirring speed of 300-400 r / min, and a stirring time of 1-2 hours.

[0071] The oven has a temperature of 50-80°C, and the baking time is 1-2 hours.

[0072] ​Step S5, the precursor powder is placed in a high-temperature furnace for sintering treatment to obtain the lithium niobate-coated graphite composite negative electrode material.

[0073] The high-temperature furnace is selected from any one of a tube furnace or a muffle furnace.

[0074] The sintering treatment method is specifically as follows: in an air atmosphere, the temperature is raised at a temperature raising rate of 5℃ / min-10℃ / min to 200℃-450℃, and the temperature is kept for 2-3 hours.

[0075] In the present application, it is found that when the sintering temperature is less than or equal to 375℃, the lithium niobate coated on the surface of the graphite is amorphous lithium niobate, and the amorphous lithium niobate has better lithium ion conductivity, thereby making the lithium niobate-coated graphite composite negative electrode material have better fast-charging performance.

[0076] The lithium niobate-coated graphite composite negative electrode material prepared by the preparation method can be used as a negative active material to prepare a negative electrode sheet, and the negative electrode sheet can be applied in a lithium ion battery, wherein the lithium ion battery includes any one of a liquid lithium ion battery, a solid-state lithium ion battery or a polymer lithium ion battery.

[0077] To better understand the technical solutions provided by the present application, the following describes the preparation process and properties of the lithium niobate-coated graphite composite negative electrode material with multiple specific examples.

[0078] Embodiment 1

[0079] The present embodiment provides a preparation process and performance test of a lithium niobate-coated graphite composite negative electrode material, and the specific steps include:

[0080] Step S1, in a glove box, 1.43136 mg of lithium foil 50ul (0.3982 mmol) and niobium ethoxide (niobium ethoxide is a liquid with a density of 1.25 g / ml and a relative molecular mass of 318.21) are weighed, i.e. the molar mass ratio of lithium element to niobium element is 1.05:1; the lithium foil and the niobium ethoxide are mixed and sealed in a glass tube containing a rubber plug, anhydrous ethanol is injected, the glass tube is placed in an ultrasonic disperser, the frequency is set to 40 KHz, and the ultrasonic dispersion is carried out for 10 min in water, to form a mixed alcohol solution.

[0081] Step S2, the mixed alcohol solution is diluted by adding 20 ml of anhydrous ethanol dropwise to obtain a diluted mixed alcohol solution.

[0082] Step S3, 1.161 g of graphite particles is added to the diluted mixed alcohol solution, and ultrasonic dispersion is continued for 10 min to obtain a precursor solution, wherein the graphite particles are flaky particles with an average particle size of 5-10 um.

[0083] Step S4, the precursor solution was placed on a heating stirrer to heat and stir at a speed of 350 r / min for 1 hour at 80°C until the solvent evaporated, and then placed in an oven to bake at 55°C for 1 hour to obtain a precursor powder.

[0084] Step S5, the precursor powder was placed in a muffle furnace, heated to 450°C at a rate of 10°C / min in an air atmosphere, and held for 2 hours to obtain a lithium niobate-coated graphite composite negative electrode material, wherein the mass percentage of lithium niobate in the composite negative electrode material was 5%.

[0085] The SEM image of the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 is shown in FIG. 1, and it can be seen that the particle size of the composite negative electrode material is about 5-10 μm. Figure 2

[0086] The XRD pattern of the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 (abbreviated as 450-5wt% LNO-G) is shown in FIG. 2, and it can be seen that the characteristic peaks of 450-5wt% LNO-G coincide with those of lithium niobate LiNbO3 and graphite, indicating that the surface of the graphite is coated with LiNbO3 having lithium ion conductivity. Figure 3

[0087] The TEM-EDS distribution map of the lithium niobate-coated graphite composite negative electrode material prepared in Example 1 is shown in FIG. 3, and it can be seen that the lithium niobate-coated graphite composite negative electrode material contains graphite (C) and niobium (Nb), i.e. there is a niobium signal on the surface of the graphite, indicating the presence of lithium niobate, and the lithium niobate is island-shaped coated on the surface of the graphite. Figure 4

[0088] The lithium niobate-coated graphite composite negative electrode material prepared in Example 1 was used to prepare a three-electrode battery and perform performance tests, and the specific process was as follows:

[0089] The preparation of the negative electrode sheet was as follows: the lithium niobate-coated graphite composite negative electrode material was mixed with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, and then the mixture was dispersed in N-methyl pyrrolidone to form a uniform slurry using a de-foaming stirrer; the slurry was coated on a copper foil using a doctor blade, and the copper foil coated with the slurry was placed in a forced air oven to dry at 55°C, then cut into an electrode sheet with a diameter of 10 mm, and finally dried in a vacuum oven at 120°C for 6 hours to remove water, obtaining a negative electrode sheet.

[0090] ​​​The assembly of the three-electrode battery is as follows: the three-electrode battery is assembled in an argon glove box using conventional methods. The negative electrode uses the negative electrode sheet prepared above, the lithium metal sheet is used as the counter electrode, the lithium foil is used as the reference electrode, the glass fiber membrane is used as the separator, and the electrolyte is a LiPF6 solution containing 1 mol / L. The solvent of the electrolyte is fluoroethylene carbonate (FEC) / dimethyl carbonate (DMC) (volume ratio = 1:1).

[0091] The three-electrode battery assembled above was subjected to rate performance testing at room temperature. Specifically, the battery was cycled for 5 cycles under charge / discharge rates of 1C, 1.5C, 2C, 2.5C, 3C, 3.5C, 4C, 4.5C, and 5C, with a test voltage range of 0-3V.

[0092] The rate performance diagram of the three-electrode battery assembled in Example 1 is shown below. Figure 5 As shown, the discharge specific capacity at a 5C rate is 236.2 mAh / g.

[0093] To better illustrate the effects of the embodiments of the present invention, Comparative Example 1 is compared with Embodiment 1 above.

[0094] Comparative Example 1

[0095] This comparative example uses the same graphite particles as in Example 1 as the negative electrode active material to prepare the negative electrode sheet. The preparation process of the negative electrode sheet and the assembly process of the three-electrode battery are the same as in Example 1.

[0096] The rate performance diagram of the three-electrode battery assembled in Comparative Example 1 is shown below. Figure 5 As shown, the discharge specific capacity at 5C rate is 188.7 mAh / g, which is much smaller than the discharge specific capacity of Example 1, indicating that the battery of Example 1 has a better ability for lithium ions to quickly enter the negative electrode during discharge.

[0097] Example 2

[0098] This embodiment provides a preparation process and performance testing of a lithium niobate-coated graphite composite anode material, the specific steps of which include:

[0099] Step S1: In a glove box, weigh 50 μL (0.3982 mmol) of lithium foil and niobium ethanol (niobium ethanol is a liquid with a density of 1.25 g / ml and a relative molecular mass of 318.21), i.e., the molar mass ratio of lithium to niobium is 1.05:1; mix the lithium foil and niobium ethanol, seal them in a glass tube with a rubber stopper, inject anhydrous ethanol, place the glass tube in an ultrasonic disperser, set the frequency to 40 kHz, and perform ultrasonic dispersion for 10 min in a water-resistant environment to form a mixed alcohol solution.

[0100] Step S2, dilute the mixed alcohol solution by adding 20 ml of anhydrous ethanol dropwise.

[0101] Step S3, add 2.322 g of graphite particles to the diluted mixed alcohol solution and continue ultrasonic dispersion for 20 min to obtain a precursor solution, wherein the graphite particles are flaky particles with an average particle size of 5-10 μm.

[0102] Step S4, place the precursor solution on a heating stirring table, heat and stir at a speed of 350 r / min at 80°C for 1 hour until the solvent evaporates, then place it in an oven and bake at 55°C for 1 hour, and grind to obtain a precursor powder.

[0103] Step S5, place the precursor powder in a muffle furnace, heat to 450°C at a rate of 10°C / min in an air atmosphere, and keep the temperature for 2 hours to obtain a lithium niobate-coated graphite composite negative electrode material, wherein the mass percentage of lithium niobate in the composite negative electrode material is 2.5%.

[0104] Use the lithium niobate-coated graphite composite negative electrode material (abbreviated as 450-2.5wt% LNO-G) prepared in this embodiment 2 to prepare a negative electrode sheet and assemble a battery, and the preparation process of the negative electrode sheet is the same as that of embodiment 1, and the electrolyte used in the battery assembly process is different from that of embodiment 1, which is a solution containing 1 mol / L of LiPF6, and the solvent of the electrolyte is ethylene carbonate EC / dimethyl carbonate DMC (volume ratio = 1:1), and the other assembly process and test process are the same as those of embodiment 1.

[0105] The rate performance graph of the three-electrode battery assembled in this embodiment 2 is shown in Figure 6 , and the discharge specific capacity at 5C rate is 150.9 mAh / g.

[0106] To better illustrate the effect of the embodiment of the present application, comparative example 2 is compared with the above embodiment 2.

[0107] Comparative Example 2

[0108] This comparative example uses the same graphite particles as the negative electrode active material as in embodiment 2 to prepare a negative electrode sheet, wherein the preparation of the negative electrode sheet and the assembly process of the three-electrode battery are the same as those of embodiment 2.

[0109] The rate performance graph of the three-electrode battery assembled in this comparative example 2 is shown in Figure 6 , and the discharge specific capacity at 5C rate is 120.9 mAh / g, which is much smaller than that of embodiment 2, indicating that the lithium ions in the battery of embodiment 2 have better rapid entry into the negative electrode during the discharge process.

[0110] Embodiment 3

[0111] This embodiment provides a preparation process and performance testing of a lithium niobate-coated graphite composite anode material, the specific steps of which include:

[0112] Step S1: In a glove box, weigh 50 μL (0.3982 mmol) of lithium foil and niobium ethanol (niobium ethanol is a liquid with a density of 1.25 g / ml and a relative molecular mass of 318.21), i.e., the molar mass ratio of lithium to niobium is 1.05:1; mix the lithium foil and niobium ethanol, seal them in a glass tube with a rubber stopper, inject anhydrous ethanol, place the glass tube in an ultrasonic disperser, set the frequency to 40 kHz, and perform ultrasonic dispersion for 10 min in a water-resistant environment to form a mixed alcohol solution.

[0113] Step S2: Add 20 mL of anhydrous ethanol dropwise to the mixed alcohol solution to dilute it, thus obtaining a diluted mixed alcohol solution.

[0114] Step S3: Add 1.161g of graphite particles to the diluted mixed alcohol solution and continue ultrasonic dispersion for 10 min to obtain a precursor solution, wherein the graphite particles are scaly particles with an average particle size between 5μm and 10μm.

[0115] Step S4: Place the precursor solution on a heated stirring table and heat and stir at 350 r / min at 80°C for 1 hour until the solvent evaporates. Then place it in an oven and bake at 55°C for 1 hour. Grind to obtain precursor powder.

[0116] Step S5: The precursor powder is placed in a muffle furnace and heated to 375°C at a heating rate of 10°C / min under an air atmosphere. The temperature is then maintained for 2 hours to obtain a composite anode material of lithium niobate coated with graphite, wherein the mass percentage of lithium niobate in the composite anode material is 5%.

[0117] The XRD pattern of the lithium niobate-coated graphite composite anode material (abbreviated as 375-5wt% LNO-G) prepared in Example 3 is as follows: Figure 7 As shown, the characteristic peak of 375-5wt% LNO-G coincides with the characteristic peak of graphite, but there is no crystalline Li NbO3 signal. This indicates that the Li NbO3 on the graphite surface is not crystalline Li NbO3, but amorphous Li NbO3. Amorphous Li NbO3 has better lithium-ion conductivity.

[0118] The TEM-EDS distribution diagram of the lithium niobate-coated graphite composite anode material prepared in Example 3 is shown below. Figure 8 As shown, the composite anode material of lithium niobate coated with graphite contains graphite (C) and niobium (Nb), meaning that niobium signals exist on the graphite surface.

[0119] The TEM-EELS distribution diagram of the lithium niobate-coated graphite composite anode material prepared in Example 3 is shown below. Figure 9 As shown, the composite anode material of lithium niobate coated graphite contains graphite (C), lithium (Li), and niobium (Nb), indicating the presence of lithium and niobium signals on the graphite surface, thus confirming the presence of lithium niobate. It should be noted that... Figure 9 The image is processed in grayscale. The shade of grayscale represents the intensity of the signal of the corresponding element. The closer to white (lighter color), the stronger the signal of the corresponding element.

[0120] pass Figure 8 Combination Figure 9 This further illustrates that the composite negative electrode material in Example 3 contains graphite and lithium niobate, and the lithium niobate is island-shaped coated on the graphite surface.

[0121] The composite negative electrode material of lithium niobate coated with graphite prepared in Example 3 was used to prepare a negative electrode sheet and assemble a battery. The preparation of the negative electrode sheet, the battery assembly process and the testing process were the same as in Example 1.

[0122] The rate performance diagram of the three-electrode battery assembled in Example 3 is shown below. Figure 10 As shown, the discharge specific capacity at 5C rate is 259.9 mAh / g, which is higher than the discharge specific capacity of Example 1. This is because the sintering temperature of Example 3 is 375°C. At this temperature, the surface of the material in Example 3 is coated with amorphous lithium niobate, which is more conducive to the conduction of lithium ions.

[0123] To better illustrate the effects of the embodiments of the present invention, Comparative Example 3 is compared with Example 3 above.

[0124] Comparative Example 3

[0125] This comparative example uses the same graphite particles as in Example 3 as the negative electrode active material to prepare the negative electrode sheet. The preparation process of the negative electrode sheet and the assembly process of the three-electrode battery are the same as in Example 3.

[0126] The rate performance diagram of the three-electrode battery assembled in Comparative Example 3 is shown below. Figure 10 As shown, the discharge specific capacity at 5C rate is 188.7 mAh / g, which is much smaller than that of Example 3, indicating that the battery of Example 3 has a better ability for lithium ions to quickly enter the negative electrode during discharge.

[0127] This invention provides a composite anode material of lithium niobate coated with graphite, its preparation method, and its application. Since inorganic salt lithium niobate, especially amorphous lithium niobate, has a high lithium-ion conductivity, by coating the graphite anode material with a lithium niobate layer, the lithium niobate on the graphite surface is conducive to lithium-ion transport, thereby effectively reducing interface impedance, improving the rate performance of the material, and thus improving the fast-charging performance of the material.

[0128] The method for preparing lithium niobate-coated graphite composite anode material provided in this invention does not require traditional atomic layer vapor deposition (ALD) and complex modification processes. Instead, it uses a simple and low-cost sol-gel method with milder sintering conditions to coat lithium niobate onto the surface of graphite material. The preparation method is simple, low-cost, and suitable for large-scale industrial production.

[0129] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite anode material of lithium niobate coated with graphite, characterized in that, The composite anode material includes: graphite particles, and lithium niobate coated on the surface of the graphite particles; The general chemical formula of the lithium niobate is Li x NbO y Where 0 < x ≤ 1, 2 ≤ y ≤ 3; The mass percentage of lithium niobate in the composite anode material is 0.001%-10%. The conductivity of the lithium niobate is 10. -1 S / cm-10 -8 S / cm; The thickness of the lithium niobate is 0.01nm-200nm.

2. The composite anode material of lithium niobate coated with graphite according to claim 1, characterized in that, The mass percentage of lithium niobate in the composite anode material is 1%-5%. The conductivity of the lithium niobate is 10. -5 S / cm-10 -2 S / cm; The thickness of the lithium niobate is 1nm-20nm.

3. The composite anode material of lithium niobate coated with graphite according to claim 1, characterized in that, The lithium niobate includes one or more of amorphous lithium niobate or crystalline lithium niobate; The lithium niobate is coated on the surface of the graphite particles in an island-like and / or continuous uniform film form.

4. A method for preparing a composite anode material of lithium niobate coated with graphite according to any one of claims 1-3, characterized in that, The preparation method includes: Step S1: Mix the lithium source material and the niobium source material, seal them in a glass tube with a rubber stopper, inject solvent, and place the glass tube in an ultrasonic disperser for ultrasonic dispersion to form a mixed alcohol solution. Step S2: Dilute the mixed alcohol solution by adding solvent dropwise to obtain a diluted mixed alcohol solution; Step S3: Add graphite particles to the diluted mixed alcohol solution and continue ultrasonic dispersion to obtain the precursor solution; Step S4: Place the precursor solution on a heated stirring table, heat and stir until the solvent evaporates, then bake it in an oven and grind it to obtain precursor powder. Step S5: The precursor powder is placed in a high-temperature furnace and sintered to obtain a composite anode material of lithium niobate coated with graphite.

5. The preparation method according to claim 4, characterized in that, The lithium source material includes: lithium foil or lithium oxalate; The niobium source material includes: niobium ethanol or niobium oxalate; Solvents include: anhydrous ethanol or deionized water; The molar mass ratio of lithium to niobium in the mixed alcohol solution is 1.05:(0-1); The graphite particles are scaly or spherical particles with an average particle size between 5 μm and 10 μm.

6. The preparation method according to claim 4, characterized in that, The ultrasonic dispersion time is 10 min to 20 min; the ultrasonic dispersion frequency is 28 kHz to 200 kHz.

7. The preparation method according to claim 4, characterized in that, The temperature of the heating and stirring table is 70℃-110℃, the stirring speed is 300r / min-400r / min, and the stirring time is 1 hour-2 hours; The oven temperature is 50℃-80℃, and the baking time is 1 hour-2 hours.

8. The preparation method according to claim 4, characterized in that, The high-temperature furnace includes either a tubular furnace or a muffle furnace; The sintering process is specifically as follows: in an air atmosphere, the temperature is increased to 200℃-450℃ at a heating rate of 5℃ / min-10℃ / min, and held for 2-3 hours.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the composite negative electrode material of lithium niobate coated with graphite as described in any one of claims 1-3.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9; the lithium-ion battery includes any one of liquid lithium-ion battery, solid lithium-ion battery or polymer lithium-ion battery.

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