Graphite negative electrode material, preparation method thereof and lithium battery

Abstract

The application relates to a graphite negative electrode material and a preparation method thereof and a lithium battery. The preparation method comprises the following steps: mixing a lithium source and a niobium source, dissolving the lithium source and the niobium source in a solvent to obtain a sol; mixing spherical graphite and the sol to obtain a graphite-gel composite; heating the graphite-gel composite to 500-800 DEG C in an inert atmosphere, and keeping the temperature for 2-4 hours, so that the gel is decomposed and crystallized into lithium niobate, and the lithium niobate coated graphite is obtained; and the lithium niobate coated graphite is coated with TiO2 on the surface in an inert atmosphere to obtain the graphite negative electrode material. The application further provides the graphite negative electrode material prepared by the above method and a lithium battery made of the material. The application can effectively improve the rate performance and cycle life of the lithium battery using the coated graphite negative electrode material, and improve the structural anti-expansion property of the material.

Description

Technical Field

[0001] This invention relates to a graphite anode material, its preparation method, and a lithium battery, belonging to the field of lithium-ion battery material technology. Background Technology

[0002] In the field of lithium-ion battery anode materials, graphite has become the most widely used choice for commercial applications due to its advantages in cost and performance, with a theoretical specific capacity of up to 372 mAh / g. However, against the backdrop of continuously rising market demand and constant technological innovation, the performance shortcomings of traditional graphite are becoming increasingly prominent, making it difficult to meet the stringent requirements of high-end application scenarios.

[0003] During battery cycling, the rate capability and cycle performance of anode materials, represented by spherical natural graphite, limit the improvement of battery performance. On the one hand, the relatively regular crystal structure of spherical natural graphite makes it prone to particle breakage due to stress changes within the crystals during lithium-ion insertion and extraction, leading to electrode structure damage and affecting cycle stability. On the other hand, the relatively low electronic conductivity of spherical natural graphite increases the resistance to lithium-ion transport within and on the surface of the particles under high-current charge and discharge conditions, thus limiting rate capability. This restricts the application expansion of graphite anodes in the field of high-performance batteries.

[0004] To address these technical bottlenecks, doping and surface coating modification have become key technical approaches for material optimization. However, currently widely used traditional coating methods have significant limitations, making it difficult to achieve uniform coating, with poor coating consistency being a particularly prominent issue.

[0005] To fully leverage the advantages of surface coating modification in enhancing material performance, it is imperative to explore novel coating processes to achieve uniform coating of graphite surfaces. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a method for preparing graphite anode materials. By synergistically coating graphite materials with lithium niobate and titanium dioxide, lithium batteries made from the resulting anode materials exhibit excellent cycle performance and rate performance.

[0007] To achieve the above objectives, the present invention first provides a method for preparing a graphite anode material, comprising: Lithium source and niobium source are mixed at a mass ratio of 1:(0.8-1.5) and dissolved in a solvent to obtain a sol; Spherical graphite is mixed with the sol to obtain a graphite-gel composite, wherein the mass ratio of the spherical graphite to the niobium source is 100:(1-5). The graphite-gel composite was heated to 500-800℃ in an inert atmosphere and held for 2-4 hours to decompose the gel and crystallize it into lithium niobate, thus obtaining graphite coated with lithium niobate. The graphite coated with lithium niobate is coated with TiO2 on the surface under an inert atmosphere to obtain a graphite anode material, wherein the mass ratio of the spherical graphite to the titanium source is 100:(1-8). The TiO2 coating process includes: vaporizing a titanium source into gaseous titanium through a thermal evaporation process, depositing the gaseous titanium onto the graphite surface coated with lithium niobate, and obtaining a graphite anode material co-coated with titanium dioxide and lithium niobate. The heating and vaporization temperature of the titanium source is 200-600℃, and the heating temperature for deposition is 400-800℃.

[0008] The preparation method provided by this invention can effectively ensure the stability of the graphite structure during cycling by controlling parameters such as temperature and heating time in the thermal evaporation deposition process, thereby improving the cycle performance of lithium batteries using this graphite anode material.

[0009] According to a specific embodiment of the present invention, preferably, the lithium source is selected from one or a combination of two of lithium nitrate and lithium acetate.

[0010] According to a specific embodiment of the present invention, preferably, the niobium source is one or a combination of two or more of niobium pentachloride, niobium oxalate, and niobium ethoxide.

[0011] According to a specific embodiment of the present invention, preferably, a dispersant is added to the sol, and the dispersant is one or a combination of two of polyvinylpyrrolidone and citric acid.

[0012] According to a specific embodiment of the present invention, preferably, the titanium source is one or a combination of two or more of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, and isopropyl titanate.

[0013] According to a specific embodiment of the present invention, preferably, the mass ratio of lithium source to niobium source is 1:1.

[0014] According to a specific embodiment of the present invention, preferably, the mass ratio of the spherical graphite to the niobium source is 100:(3-5).

[0015] According to a specific embodiment of the present invention, preferably, the mass ratio of the spherical graphite to the titanium source is 100:(4-6).

[0016] According to a specific embodiment of the present invention, preferably, the spherical graphite is natural graphite, and the particle size of the spherical graphite is 10-20 micrometers.

[0017] According to a specific embodiment of the present invention, preferably, the heating and vaporization temperature of the titanium source is 400-500℃.

[0018] According to a specific embodiment of the present invention, preferably, the heating temperature for depositing the titanium source is 700-800°C.

[0019] According to a specific embodiment of the present invention, preferably, the gas flow rate after the titanium source is vaporized is 10-30 L / min, and the deposition time is 1-6 h, more preferably 1-3 h. According to a specific embodiment of the present invention, preferably, the inert gas includes at least one of nitrogen and argon.

[0020] According to a specific embodiment of the present invention, preferably, the above preparation method includes the following specific steps: Spherical graphite was sieved to obtain spherical graphite A; Lithium source and niobium source are dissolved in solvent at a mass ratio of 1:(0.8-1.5), dispersant is added, and the mixture is stirred at 40-80℃ for 1-3 hours to form a transparent and stable sol B; The spherical graphite A was added to sol B and mixed, and stirred in an inert gas atmosphere for 2-6 hours to allow the sol to be uniformly adsorbed on the graphite surface, thus obtaining a graphite-gel composite. The composite was vacuum dried at 80-120℃ for 6-12h, and then transferred to a box furnace. The temperature was raised to 500-800℃ in an inert atmosphere and held for 2-4h to decompose the gel and crystallize it into lithium niobate (LiNbO3), which at the same time enhanced the bonding force between the coating layer and graphite. The lithium niobate-coated graphite was placed in a rotary furnace under an inert atmosphere for surface TiO2 coating to obtain a graphite anode material; The specific preparation method of the TiO2 coating includes: vaporizing a titanium source into gaseous titanium through a thermal evaporation process, and depositing the gaseous titanium onto the surface of lithium niobate-coated spherical graphite to obtain a graphite anode material co-coated with titanium dioxide and lithium niobate.

[0021] This invention utilizes a titanium source to perform surface thermal evaporation deposition coating on lithium niobate-coated graphite, forming a synergistic coating layer of titanium dioxide and lithium niobate on the graphite surface. This effectively improves the reversible capacity of the graphite material, enhances cycle and rate performance, and improves the structural anti-expansion properties of the graphite anode. Furthermore, the titanium source thermal evaporation deposition process effectively increases the uniformity of the coating, reduces porosity and defects on the graphite surface, and achieves uniform titanium dioxide coating on the graphite surface. This invention addresses the shortcomings of single coatings (such as poor electronic conductivity of lithium niobate and low ionic conductivity of TiO2) through the synergistic coating of two materials, while retaining their respective advantages (high ionic conductivity / high stability of lithium niobate and high electronic conductivity / low expansion of TiO2), ultimately achieving "synergistic enhancement" of the graphite anode.

[0022] The present invention also provides a graphite anode material, which is prepared by the above-described preparation method. This graphite anode material comprises a graphite body coated with lithium niobate and titanium dioxide distributed on its surface, wherein the titanium dioxide is uniformly deposited on the surface of the lithium niobate coating after being thermally evaporated and vaporized from a titanium source.

[0023] The present invention also provides a synthesis apparatus for the above preparation method, wherein the synthesis apparatus includes a gas phase titanium synthesis apparatus and a coated graphite synthesis apparatus, the gas phase titanium synthesis apparatus is equipped with an injection pump and a heated reaction vessel, and the coated graphite synthesis apparatus is one of a tube furnace or a rotary furnace. The heating reactor is equipped with a titanium source inlet, an inert gas inlet, and a mixed atmosphere outlet. The coated graphite synthesis apparatus is equipped with a mixing atmosphere inlet, a feed inlet, and a product outlet; The outlet of the injection pump is connected to the titanium source inlet of the heated reactor; The mixing atmosphere outlet of the heated reactor is connected to the mixing atmosphere inlet of the graphite-coated synthesis device.

[0024] According to a specific embodiment of the present invention, in the above-mentioned synthesis equipment, an injection pump is used to realize the vaporization of the titanium source. The injection pump can precisely control the delivery parameters of the liquid material. By controlling the flow rate, metering the dosage, and maintaining stable pressure, a "standardized" liquid material input is provided for the subsequent vaporization process, ultimately ensuring that the generation rate, concentration, and purity of gaseous titanium fully meet the synthesis requirements, achieving high-precision and high-stability gas-phase synthesis.

[0025] The present invention also provides a lithium battery, wherein the negative electrode of the lithium battery is made of the above-mentioned graphite negative electrode material.

[0026] By forming a uniform coating layer on the graphite surface, the structural integrity of the material during electrochemical cycling can be effectively enhanced, thereby significantly improving several key indicators of the battery, such as cycle performance and rate performance.

[0027] Compared with the prior art, the beneficial effects of the present invention include: effectively improving the rate performance and cycle life of lithium batteries using graphite-coated anode materials, and improving the structural resistance to expansion of the materials. Attached Figure Description

[0028] Figure 1 A schematic diagram of the apparatus structure for synthesizing lithium niobate co-coated graphite is shown.

[0029] Figure 2 A comparison graph showing charge-discharge cycle data of the coin cells in each embodiment and the comparative example is provided.

[0030] Figure 3A comparison chart showing the charge / discharge rate data of the coin cells in each embodiment and the comparative example is provided.

[0031] Figure 4 The GITT voltage curves of the coin cells of Example 3 and Comparative Example 3, along with the corresponding calculated lithium-ion diffusion coefficients, are shown. Detailed Implementation

[0032] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0033] The structures of the synthesis equipment used in the embodiments and comparative examples are as follows: Figure 1 As shown, it includes a gas-phase titanium synthesis device and a graphite-coated synthesis device. The gas phase titanium synthesis device is equipped with an injection pump 1 and a heated reaction vessel 2, and the graphite coating synthesis device is a rotary furnace 3; The heating reactor 2 is equipped with a titanium source inlet 21, an inert gas inlet 22, and a mixed atmosphere outlet 23, which are used to input gaseous titanium source, input inert gas, and output mixed atmosphere, respectively. The rotary kiln 3 is equipped with a mixed atmosphere inlet 31, a feed inlet 32 ​​and a product outlet 33, which are used to input a mixed atmosphere, input graphite coated with lithium niobate, and output graphite anode material co-coated with titanium dioxide and lithium niobate, respectively. The outlet of injection pump 1 is connected to the titanium source inlet 21 of the heated reaction vessel 2; The mixing atmosphere outlet 23 of the heating reactor 2 is connected to the mixing atmosphere inlet 31 of the rotary furnace 3.

[0034] Example 1: This embodiment provides a method for preparing lithium niobate-coated graphite anode material using a thermal evaporation deposition process, comprising: 0.5 g of lithium acetate and 0.5 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 18 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace and heated to 600 °C, held at that temperature for 3 h (heating rate 5 °C / min) to decompose the gel and crystallize it into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, thus obtaining lithium niobate-coated graphite.

[0035] A mixture of 0.4 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, nitrogen gas was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced. The flow rate of the titanium source gas was 25 L / min. The deposition reaction was carried out in the rotary furnace at 800 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0036] Example 2: This embodiment provides a method for preparing lithium niobate-coated graphite anode material using a thermal evaporation deposition process, comprising: 0.4 g of lithium acetate and 0.4 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 16 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace and heated to 600 °C, held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, resulting in lithium niobate-coated graphite.

[0037] A mixture of 0.6 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, nitrogen gas was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced simultaneously. The flow rate of the titanium source gas was 20 L / min. The deposition reaction was carried out in the rotary furnace at 800 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0038] Example 3: This embodiment provides a method for preparing lithium niobate-coated graphite anode material using a thermal evaporation deposition process, comprising: 0.3 g of lithium acetate and 0.3 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 18 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace, heated to 600 °C, and held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, resulting in lithium niobate-coated graphite.

[0039] A mixture of 0.5 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, nitrogen gas was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced. The flow rate of the titanium source gas was 25 L / min. The deposition reaction was carried out in the rotary furnace at 800 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0040] Example 4: This embodiment provides a method for preparing lithium niobate-coated graphite anode material using a thermal evaporation deposition process, comprising: 0.3 g of lithium acetate and 0.3 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 18 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace, heated to 500 °C, and held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, resulting in lithium niobate-coated graphite.

[0041] A mixture of 0.5 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, nitrogen gas was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced. The flow rate of the titanium source gas was 20 L / min. The deposition reaction was carried out in the rotary furnace at 700 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0042] Comparative Example 1: 1000g of spherical graphite and 40g of titanium powder were mixed in a ball mill at a speed of 150r / min for 30min. The particle size of the spherical graphite was D. 50 = 18 micrometers; the above mixture was placed in a rotary furnace and reacted at 800°C for 4 hours to obtain the prepared graphite anode material.

[0043] Comparative Example 2: 0.3 g of lithium acetate and 0.3 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 16 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace, heated to 600 °C, and held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, thus obtaining a lithium niobate-coated graphite anode material.

[0044] Comparative Example 3: 0.8 g of lithium acetate and 0.8 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 18 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace, heated to 600 °C, and held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, resulting in lithium niobate-coated graphite.

[0045] A mixture of 0.5 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, nitrogen gas was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced. The flow rate of the titanium source gas was 20 L / min. The deposition reaction was carried out in the rotary furnace at 800 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0046] Comparative Example 4: 0.8 g of lithium acetate and 0.8 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 16 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace, heated to 600 °C, and held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, resulting in lithium niobate-coated graphite.

[0047] A mixture of 1 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, the mixture was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced. The flow rate of the titanium source gas was 20 L / min. The deposition reaction was carried out in the rotary furnace at 800 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0048] Comparative Example 5: 0.3 g of lithium acetate and 0.3 g of niobate were added to 100 ml of anhydrous ethanol and stirred at room temperature for 0.5 h to dissolve completely. An appropriate amount of polyvinylpyrrolidone was added, and the mixture was stirred at 60 °C for 2 h to obtain a transparent and stable sol. 10 g of spherical graphite powder (particle size D50 = 18 μm) was added to the sol, and the mixture was stirred under a nitrogen atmosphere for 4 h to allow the gel to fully adsorb onto the graphite surface, forming a composite. The composite was vacuum dried at 110 °C for 10 h to remove the solvent. It was then transferred to a box furnace, heated to 600 °C, and held at that temperature for 3 h (heating rate 5 °C / min) to decompose and crystallize the gel into LiNbO3, simultaneously enhancing the bonding force between the coating layer and the graphite, resulting in lithium niobate-coated graphite.

[0049] A mixture of 0.5 mL of isopropyl titanate and 10 mL of anhydrous ethanol was added to a syringe pump. After purging nitrogen gas into the heated reactor for 30 min, nitrogen gas was pumped into the heated reactor at a rate of 4 mL / min. The temperature of the heated reactor was 400 °C, and the reaction time was 1 h. 10 g of lithium niobate-coated graphite was placed in a rotary furnace, and a mixture of inert gas and titanium source was introduced. The flow rate of the titanium source gas was 25 L / min. The deposition reaction was carried out in the rotary furnace at 1100 °C for 4 h to obtain a graphite anode material co-coated with lithium niobate and titanium dioxide.

[0050] Electrochemical tests were conducted on CR2032 coin cells assembled with the negative electrode materials of the examples and comparative examples. The electrochemical tests were performed according to the following steps: The test materials were mixed uniformly at a mass ratio of negative electrode material: conductive agent (Super P): binder (LA133) = 90:5:5, coated onto copper foil to a thickness of 150 μm, and dried in a vacuum oven at 80°C for 12 h to obtain the negative electrode sheet. CR2032 coin cells were assembled in a glove box (water and oxygen levels less than 0.01 ppm), with lithium foil as the counter electrode and 1 mol / L LiF6 dissolved in DMC:DEC:EC (volume ratio 1:1:1) as the electrolyte. The assembled coin cells were then subjected to charge-discharge cycle tests at a 1C current density on a Blue Electric system. The test results are shown in Table 1 and [Table data missing]. Figure 2 As shown. Charge / discharge rate performance was tested at current densities of 0.1C / 0.3C / 0.5C / 1C / 3C / 5C / 0.1C / 1C, and the test results are as follows. Figure 3 As shown. The degree of lithium-ion diffusion was tested using GITT (30 min pulse, 2 h relaxation), and the results are as follows. Figure 4 As shown.

[0051] Table 1

[0052] The experimental data in Table 1 show that: The anode material in this embodiment exhibits superior reversible capacity and cycling performance compared to the comparative example. This is because the layered composite coating effectively addresses issues such as electron / ion transport imbalance and insufficient structural stability inherent in single-coating systems, resulting in outstanding cycling and rate performance. The high lithium niobate ratio in the inner layer enhances ionic conductivity, while the high titanium dioxide ratio in the outer layer enhances electronic conductivity and mechanical properties. The coating introduces new active lithium storage sites on the graphite surface, improving the material's reversible capacity. Simultaneously, the sol-gel process and thermal evaporation deposition process ensure the integrity and uniformity of the coating on the graphite surface. The mechanically superior titanium dioxide coating prevents direct contact between the graphite and the electrolyte, inhibiting graphite sheet peeling during cycling and improving cycling performance.

[0053] according to Figure 2 The data from the various embodiments and comparative examples shown, cyclically at a current density of 1C (5 cycles of 0.1C activation), demonstrate that: The negative electrode material of Example 3 exhibits the best electrochemical performance, with the highest reversible capacity and cycle retention rate after charge-discharge cycles. This is due to the increased lithium storage sites provided by the uniform deposition of an appropriate amount of titanium dioxide, which in turn increases the reversible capacity.

[0054] The low capacity of the negative electrode material in Comparative Example 1 is due to the fact that although an appropriate amount of titanium dioxide is coated, the coating uniformity of the ordinary solid-phase heating coating process is poor, the coating layer is prone to agglomeration, the bonding force with graphite is poor, and a continuous coating layer cannot be formed. This results in differences in the distribution of active sites on the graphite surface and inconsistent electron transport resistance, ultimately manifesting as poor coating uniformity, which affects the charge and discharge performance of the battery.

[0055] Comparative Example 2 uses only a single lithium niobate coating process. Due to the structural and performance limitations of a single coating layer, its improvement on material interface stability is limited, making it difficult to effectively alleviate volume expansion and side reactions during charge and discharge. The first-cycle coulombic efficiency and capacity are low, resulting in poor cycle performance. Furthermore, the compatibility control between lithium niobate coating and titanium dioxide coating also affects material performance.

[0056] In Comparative Example 3, the lithium niobate coating of the anode material was too high, resulting in poor interlayer structural stability and insufficient electronic conductivity. At this point, an appropriate amount of titanium dioxide coating was insufficient to maintain the overall structural stability of the material, thus leading to the worst cycle performance.

[0057] Considering that excessive lithium niobate coating leads to a porous structure, excessive titanium dioxide coating was applied to graphite after excessive lithium niobate coating: Comparative Example 4 involved coating excessive titanium dioxide after excessive lithium niobate coating. However, increasing the titanium dioxide coating amount resulted in an excessively thick coating layer, significantly increasing transport resistance. Lithium ions could not be intercalated into the graphite in time, and lithium dendrites were easily deposited on the coating surface (especially when the titanium dioxide content was high, its own lithium intercalation capacity was low and ion transport was slow, further hindering lithium migration). This manifested as a decrease in battery charge / discharge capacity and a deterioration in rate performance. Therefore, an appropriate ratio of lithium niobate to titanium dioxide coating can enhance the synergistic effect and simultaneously improve cycle and rate performance.

[0058] In Comparative Example 5, the excessively high heating temperature during the thermal evaporation deposition step damaged the titanium dioxide structure formed on the surface, coarsened the grains, and led to cracks and peeling of the coating layer, resulting in a decrease in the material's specific surface area and interfacial adhesion. Excessively high temperatures easily trigger interfacial side reactions, generating other compounds that both crowd out lithium intercalation sites and form a high-resistivity layer, leading to a significant decrease in capacity. During cycling, the unstable interface accelerates electrolyte decomposition and SEI film damage, exacerbating irreversible lithium-ion loss and accelerating the capacity decay rate.

[0059] Figure 3 The rate performance test data of Example 3 and various comparative examples are shown. The high ionic conductivity of lithium niobate can promote the rapid migration of lithium ions and improve rate performance.

[0060] Example 3 involved coating the graphite with an appropriate amount of titanium dioxide in addition to a suitable lithium niobate coating. The extra titanium dioxide, with its good electronic conductivity, forms a transport bridge on the graphite surface, reducing transport resistance and thus improving the response speed during high-current charging and discharging. Comparative Example 1, without lithium niobate coating, exhibited the worst rate performance.

[0061] Comparative Example 2, which is coated with a single lithium niobate, showed improved rate performance compared to Comparative Example 1, but had higher interface impedance, and its rate performance was still inferior to that of Example 3.

[0062] Comparative Example 3 showed that the lithium niobate coating ratio was too high. Although the rate performance was improved to some extent after coating with an appropriate amount of titanium dioxide, the cycle performance was poor due to the poor stability of the material structure.

[0063] In Comparative Example 4, excessive titanium dioxide coating after excessive lithium niobate coating resulted in an excessively thick insulating layer, which increased the resistance to ion / electron transport, reduced electronic conductivity, and further aggravated polarization at high rates, leading to insufficient capacity utilization.

[0064] In Comparative Example 5, the high-resistivity layer generated by the side reaction at excessively high temperatures hinders the rapid transport of lithium ions, reduces the specific surface area and decreases the response efficiency of active sites, significantly reduces the capacity retention rate during high-current charging and discharging, and continuously deteriorates the rate performance of the material.

[0065] Figure 4 Example 3 and Comparative Example 3 were tested using the intermittent galvanostatic titration (GITT) technique. This test involves applying a short-duration constant current pulse and then allowing the sample to stand, recording the voltage change during the pulse, and calculating the lithium-ion diffusion coefficient using Fick's second law. This accurately reflects the migration efficiency of lithium ions within the electrode material and is a core kinetic indicator for evaluating the fast-charging performance of a battery.

[0066] from Figure 4 The test results show that the lithium-ion diffusion coefficient of Example 3 is significantly better than that of Comparative Example 3. In the lithium niobate-titanium dioxide cascade composite coating layer of Example 3, titanium dioxide acts as an "electron transport channel," effectively compensating for the electronic insulation defects of lithium niobate and forming a dual-channel system of "lithium niobate-dominated ion transport + titanium dioxide-assisted electron transport." This reduces the migration resistance of lithium ions within the coating layer and the interfacial charge transfer impedance. Simultaneously, the microstructure of the composite coating layer is denser and more tightly bonded to graphite, avoiding microcracks that may occur in single coating layers or excessively thick coating layers, further reducing the "path loss" of lithium-ion transport.

[0067] The above results demonstrate that the two-step coating scheme of this invention achieves the performance target of "high rate and long cycle" for natural graphite anodes through the complementary functions of "lithium niobate optimized kinetics + titanium dioxide enhanced stability" and the precise control advantages of thermal evaporation deposition process. This provides a feasible technical path for the development of anode materials for high-power lithium-ion batteries (such as fast-charging power batteries and long-life energy storage batteries).

Claims

1. A method for preparing a graphite anode material, characterized in that, include: Lithium source and niobium source are mixed at a mass ratio of 1:(0.8-1.5) and dissolved in a solvent to obtain a sol; Spherical graphite is mixed with the sol to obtain a graphite-gel composite, wherein the mass ratio of the spherical graphite to the niobium source is 100:(3-5). The graphite-gel composite was heated to 500-800℃ in an inert atmosphere and held for 2-4 hours to decompose the gel and crystallize it into lithium niobate, thus obtaining graphite coated with lithium niobate. The graphite coated with lithium niobate is coated with TiO2 on the surface under an inert atmosphere to obtain a graphite anode material, wherein the mass ratio of the spherical graphite to the titanium source is 100:(4-6). The TiO2 coating process includes: vaporizing a titanium source into gaseous titanium through a thermal evaporation process, depositing the gaseous titanium onto the graphite surface coated with lithium niobate, and obtaining a graphite anode material co-coated with titanium dioxide and lithium niobate. The heating and vaporization temperature of the titanium source is 200-600℃, and the heating temperature for deposition is 400-800℃.

2. The preparation method according to claim 1, characterized in that, The lithium source is selected from one or a combination of two of lithium nitrate and lithium acetate.

3. The preparation method according to claim 1, characterized in that, The niobium source is one or a combination of two or more of niobium pentachloride, niobium oxalate, and niobium ethoxide.

4. The preparation method according to claim 1, characterized in that, The sol contains a dispersant, which is one or a combination of two of polyvinylpyrrolidone and citric acid.

5. The preparation method according to claim 1, characterized in that, The titanium source is one or a combination of two or more of tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate, and isopropyl titanate.

6. The preparation method according to claim 1, characterized in that, The spherical graphite is natural graphite, and the particle size of the spherical graphite is 10-20 micrometers.

7. The preparation method according to claim 1, characterized in that, The gas flow rate after the titanium source is vaporized is 10-30 L / min, and the deposition time is 1-6 h.

8. A graphite anode material, characterized in that, It is prepared according to any one of claims 1 to 7.

9. A synthetic apparatus for use in the preparation method according to any one of claims 1-7, characterized in that, The synthesis equipment includes a gas-phase titanium synthesis device and a graphite-coated synthesis device. The gas-phase titanium synthesis device is equipped with an injection pump and a heated reaction vessel. The graphite-coated synthesis device is one of a tube furnace or a rotary furnace. The heating reactor is equipped with a titanium source inlet, an inert gas inlet, and a mixed atmosphere outlet. The coated graphite synthesis apparatus is equipped with a mixing atmosphere inlet, a feed inlet, and a product outlet; The outlet of the injection pump is connected to the titanium source inlet of the heated reactor; The mixing atmosphere outlet of the heated reactor is connected to the mixing atmosphere inlet of the graphite-coated synthesis device.

10. A lithium battery, characterized in that, The negative electrode of the lithium battery is made of the graphite negative electrode material as described in claim 8.

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