Nitrogen-doped molybdenum oxide coated graphite negative electrode material and preparation method thereof

Abstract

The application provides a nitrogen-doped molybdenum oxide coated graphite negative electrode material and a preparation method thereof. The negative electrode material comprises a graphite substrate and a functional nanometer coating coated on the surface of the graphite substrate. The functional nanometer coating is prepared through a simple liquid phase coating and a low-temperature pyrolysis crystallization process, can improve the wettability of an electrolyte to the surface of the graphite, thereby improving the interface kinetics of the graphite / electrolyte, inhibiting the adverse lithium dendrite deposition side reaction, and improving the cycle stability of the negative electrode material at a high rate. Moreover, the functional nanometer coating ensures the rapid migration of lithium ions in the charging and discharging process, inhibits the additional growth of SEI films in the rapid charging and discharging process, and enables the graphite material to maintain high structural stability. In addition, the whole preparation process is simple, the raw material cost is low, and the process is easy to engineer, and the application prospect in the field of lithium ion battery negative electrode materials is extremely high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy lithium ion battery negative electrode material, and particularly relates to a nitrogen-doped molybdenum oxide coated graphite negative electrode material and a preparation method thereof. BACKGROUND

[0002] With the growth of the electric vehicle market, the demand for high-performance lithium ion batteries (LIBs) is steadily increasing, and the main indicators for investigation include energy density, safety, cycle life, cost and charging time, especially charging time and driving range, which are often considered as key factors affecting whether car owners are willing to buy new energy vehicles. The charging performance of LIBs not only depends on the charging protocol and battery configuration, but also depends on the selection of the materials used, especially the negative electrode material.

[0003] Due to the large reversible specific capacity (372 mAh / g) and low lithium intercalation / deintercalation potential (0.2 V vs Li / Li + ), graphite is widely used as a LIBs negative electrode material on a commercial scale, but due to the slow interface kinetics of the bare natural graphite negative electrode and the electrolyte, the anode voltage quickly drops below 0 V under fast charging conditions, causing lithium dendrite deposition on the surface of the graphite, which not only causes significant capacity loss, but also causes short circuits, leading to safety problems. Therefore, improving the interface kinetics of the graphite electrode / electrolyte, increasing the desolvation and migration rate of lithium ions at the interface, and stabilizing the SEI structure and chemical evolution, are important keys to improving the fast charging capability of natural graphite negative electrode materials. SUMMARY

[0004] In view of the above problems existing in the prior art, the present application provides a nitrogen-doped molybdenum oxide coated graphite negative electrode material, which comprises a graphite substrate and a functional nanocoating coated on the surface layer of the graphite substrate, and the functional nanocoating is prepared by a simple liquid phase coating and low-temperature pyrolysis crystallization process, which can improve the wettability of the electrolyte on the surface of the graphite, thereby improving the interface kinetics of the graphite / electrolyte, inhibiting the adverse lithium dendrite deposition side reaction, and improving the cycle stability of the negative electrode material at high rates.

[0005] The specific application contents are as follows:

[0006] In a first aspect, the present application provides a nitrogen-doped molybdenum oxide coated graphite negative electrode material, which comprises a graphite substrate and a functional nanocoating coated on the surface layer of the graphite substrate;

[0007] The functional nanocoating is composed of nitrogen-doped molybdenum oxide;

[0008] The weight ratio of the graphite substrate to the functional nanocoating is 100:0.01-0.5;

[0009] The nitrogen-doped molybdenum oxide comprises molybdenum element, oxygen element and nitrogen element, and the weight ratio of the molybdenum element, oxygen element and nitrogen element is 100:(16-33):(7-11).

[0010] Optionally, the average thickness of the functional nanocoating is 5-65 nm.

[0011] Optionally, the molecular formula of the nitrogen-doped molybdenum oxide is MoO x N y (1 < x < 2, 0.5 < y < 0.75).

[0012] Optionally, the weight ratio of the graphite substrate and the functional nanocoating is 100:0.2.

[0013] Optionally, the weight ratio of the molybdenum element, oxygen element and nitrogen element is 100:32.35:7.295.

[0014] Optionally, the fixed carbon content of the graphite substrate is ≥99.95%, D 50 = 5-45 μm; the graphite substrate is one or both of natural flaky graphite and spherical graphite.

[0015] Optionally, the graphite substrate is spherical graphite, and the D 50 = 16 μm, D 10 = 12 μm, D 80 = 18 μm.

[0016] In a second aspect, the present application provides a preparation method of the nitrogen-doped molybdenum oxide coated graphite negative electrode material of the first aspect, and the preparation method comprises the following steps:

[0017] S1, dissolving a molybdenum source in deionized water, adding a graphite substrate, stirring to obtain a suspension A;

[0018] S2, stirring the suspension A under the condition of 50-80°C to obtain a solid powder B;

[0019] S3, adding a nitrogen source to the solid powder B, then adding an appropriate amount of alcohol, grinding uniformly to obtain a mixed solid powder C;

[0020] S4, annealing the mixed solid powder C under the inert gas atmosphere of 300-600°C for 5-8h, grinding to obtain the nitrogen-doped molybdenum oxide coated graphite negative electrode material;

[0021] The mass ratio of the molybdenum source, the nitrogen source and the graphite substrate is 0.01-0.1 g:10 g:4 g; the molybdenum source is one or more of ammonium molybdate, ammonium molybdate dihydrate, ammonium molybdate tetrahydrate and molybdic acid; the nitrogen source is one or more of urea, melamine and thiourea; and the graphite substrate is one or both of natural flaky graphite and spherical graphite.

[0022] Optionally, the annealing procedure comprises: increasing the temperature to 365 DEG C at a rate of 5 DEG C / min, maintaining for 1 h; then increasing the temperature to 500 DEG C at a rate of 3 DEG C / min, maintaining for 2 h; and finally increasing the temperature to 600 DEG C at a rate of 5 DEG C / min, maintaining for 2 h.

[0023] Optionally, the molybdenum source is ammonium molybdate tetrahydrate; the nitrogen source is urea; and the graphite substrate is spherical graphite.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] (1) The nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the present application comprises a graphite substrate and a functional nanometer coating uniformly coated on the surface layer of the graphite substrate. The functional nanometer coating can improve the wettability of the electrolyte on the surface of the graphite substrate, reduce the lithium ion adsorption energy, improve the intercalation interface kinetics of the lithium ion intercalation (i.e. the interface of the graphite substrate / electrolyte), inhibit the lithium dendrite deposition phenomenon in the rapid charging process, and improve the cycle stability of the graphite material at high rates. Moreover, the functional nanometer coating ensures the rapid migration of lithium ions in the charging and discharging process, and inhibits the additional growth of the SEI film in the rapid charging and discharging process, so that the graphite material can maintain high structural stability. In addition, the functional nanometer coating can improve the lithium ion intercalation sites at a higher charging potential, thereby improving the rapid charging capacity of the natural graphite negative electrode, and maintaining high structural stability and long-term cycle stability.

[0026] (2) The preparation method of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the present application can form a stable functional nanometer coating on the surface of the natural graphite through a simple liquid coating and low-temperature pyrolysis crystallization process. The whole method is simple in process, low in raw material cost and easy to engineer. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0028] Figure 1 A flow chart of a preparation method of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment of the present application is shown.

[0029] Figure 2 An SEM image of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment 1 of the present application is shown.

[0030] Figure 3 An HRTEM image of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment of the present application is shown.

[0031] Figure 4 A rate performance result chart of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment 1 of the present application in a C2025 button half-cell is shown.

[0032] Figure 5 A cycle performance result chart of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment 1 of the present application in a C2025 button half-cell is shown.

[0033] Figure 6 A cycle performance result chart of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment 2 of the present application in a C2025 button half-cell is shown. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, any person under the inspiration of the present application or combining the present application with other prior art features to obtain any product same or similar to the present application, falls within the protection scope of the present application. In addition, all other embodiments obtained by the ordinary skilled in the art without carrying out creative labor, fall within the protection scope of the present application.

[0035] The specific experimental steps or conditions not mentioned in the embodiments can be carried out according to the conventional experimental steps or conditions described in the prior art in the field. The reagents and other instruments not mentioned by the manufacturer are all conventional reagent products that can be obtained by purchase. In addition, the drawings are only schematic illustrations of the embodiments of the present application, and are not necessarily drawn to scale. The same reference signs in the drawings represent the same or similar parts, and thus repeated description thereof will be omitted. Some block diagrams shown in the drawings are functional entities, which do not necessarily correspond to physically or logically independent entities.

[0036] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein, but should be considered part of the disclosure.

[0037] Furthermore, the technical features involved in the different embodiments of the application described below can be combined with each other as long as there is no conflict.

[0038] In the prior art, when graphite material is applied to lithium ion batteries, during the charging and discharging process, the electrolyte will decompose on the surface of the graphite and form a SEI film. Due to the slow interface kinetics between the graphite surface and the electrolyte, this easily leads to a large overpotential on the surface of the graphite material during fast charging, forming lithium dendrite deposition, causing significant capacity loss, seriously affecting the cycle stability of the battery, and leading to an increase in the internal resistance of the battery, which easily causes overheating and even a short circuit safety problem. In view of the above problems, the present application considers improving the interface kinetics between the graphite material and the electrolyte, improving the desolvation and migration rate of lithium ions at the interface, and stabilizing the structural changes caused by repeated intercalation and deintercalation, thereby improving the fast charging capability of the natural graphite negative electrode material. Based on this, the present application provides a nitrogen-doped molybdenum oxide coated graphite negative electrode material, which includes a graphite substrate and a functional nanocoating uniformly coated on the surface layer of the graphite substrate. In the case of maintaining the high tap density, compaction density and high energy density of the graphite substrate, the functional nanocoating can improve the wettability of the electrolyte on the surface of the graphite material, reduce the adsorption energy of lithium ions, improve the intercalation interface kinetics of lithium ions, inhibit the lithium dendrite deposition phenomenon caused by the overpotential on the surface of the graphite negative electrode during fast charging, and improve the cycle stability of the graphite as a negative electrode material at high rate; and ensure the rapid migration of lithium ions during the charging and discharging process, inhibit the additional growth of the SEI film during the fast charging and discharging process, and maintain the high structural stability of the graphite.

[0039] The specific embodiments are as follows:

[0040] In a first aspect, the present application provides a nitrogen-doped molybdenum oxide coated graphite negative electrode material, which includes a graphite substrate and a functional nanocoating coated on the surface layer of the graphite substrate.

[0041] The functional nanocoating is composed of nitrogen-doped molybdenum oxide.

[0042] The weight ratio of the graphite substrate to the functional nanocoating is 100:0.01-0.5.

[0043] The nitrogen-doped molybdenum oxide includes molybdenum elements, oxygen elements and nitrogen elements, and the weight ratio of the molybdenum elements, oxygen elements and nitrogen elements is 100:(16-33):(7-11).

[0044] In some embodiments, the functional nanocoating has an average thickness of 5-65 nm.

[0045] In some embodiments, the nitrogen-doped molybdenum oxide has a molecular formula of MoO x N y (1 < x < 2, 0.5 < y < 0.75).

[0046] The functional nanocoating with a composition of MoO x N y (1 < x < 2, 0.5 < y < 0.75) is conducive to improving the energy density of the graphite substrate, and can also inhibit the additional growth of SEI film in the process of rapid charging and discharging, improve the wettability of the surface of the graphite substrate, reduce the lithium ion adsorption energy, and improve the interfacial dynamics of lithium ion intercalation. In addition, the composition can improve the lithium ion intercalation sites at a higher charging potential, thereby improving the rapid charging capacity of the natural graphite negative electrode, maintaining its high structural stability and long-term cycle stability.

[0047] In some embodiments, the weight ratio of the graphite substrate to the functional nanocoating is 100:0.2.

[0048] The functional nanocoating with a very low content not only endows the graphite substrate with excellent structural stability and long-term cycle stability, but also retains the original high tap density and high compaction density of the graphite substrate, ensuring a high energy density.

[0049] In some embodiments, the weight ratio of the molybdenum element, the oxygen element, and the nitrogen element is 100:32.35:7.295.

[0050] When the weight ratio of the graphite substrate to the functional nanocoating is 100:0.2, and the weight ratio of the molybdenum element, the oxygen element, and the nitrogen element is 100:32.35:7.295, the nitrogen-doped molybdenum oxide coated graphite negative electrode material has the most stable high-rate charge-discharge cycle stability and a high energy density.

[0051] In some embodiments, the graphite substrate has a fixed carbon content of ≥99.95%, a D 50 =5-45 μm; and the graphite substrate is one or both of natural flaky graphite and spherical graphite.

[0052] In some embodiments, the graphite substrate is spherical graphite, the spherical graphite has a D 50 =16 μm, a D 10 =12 μm, and a D 80 =18 μm.

[0053] In a second aspect, the present application provides a preparation method of the multi-nitrogen-doped molybdenum oxide coated graphite negative electrode material according to the first aspect, Figure 1 A flow chart of the preparation method of the multi-nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the embodiment of the present application is shown in FIG. 2. Figure 1 As shown in FIG. 2, the preparation method comprises the following steps:

[0054] S1, dissolving a molybdenum source in deionized water, adding a graphite substrate, stirring to obtain a suspension A.

[0055] In the implementation of the present step, the molybdenum source is one or more of ammonium molybdate, ammonium molybdate dihydrate, ammonium molybdate tetrahydrate and molybdate. The graphite substrate is one or both of natural flaky graphite and spherical graphite. Preferably, the molybdenum source is ammonium molybdate tetrahydrate, and the graphite substrate is spherical graphite. Ammonium molybdate can be pyrolyzed under inert atmosphere to obtain solid phase molybdenum trioxide and other volatile gaseous components, and the volatile gaseous components have little effect on the element doping of the nano coating.

[0056] S2, stirring the suspension A at 50-80℃ to obtain a solid powder B.

[0057] In the implementation of the present step, the suspension A is slowly stirred at 50-80℃ to evaporate the deionized water and obtain the solid powder B.

[0058] S3, adding a nitrogen source to the solid powder B, then adding an appropriate amount of alcohol, and grinding uniformly to obtain a mixed solid powder C.

[0059] In the implementation of the present step, the nitrogen source is one or more of urea, melamine and thiourea. Preferably, the nitrogen source is urea. In steps S1-S3, the mass ratio of the molybdenum source, the nitrogen source and the graphite substrate is 0.01-0.1g:10g:4g. The nitrogen source can be recrystallized to generate g-C3N4 under inert atmosphere.

[0060] S4, annealing the mixed solid powder C under inert gas atmosphere at 300-600℃ for 5-8h, and grinding to obtain the nitrogen-doped molybdenum oxide coated graphite negative electrode material.

[0061] The annealing procedure includes: increasing temperature to 365℃ at 5℃ / min, keeping for 1h; then increasing temperature to 500℃ at 3℃ / min, keeping for 2h; finally increasing temperature to 600℃ at 5℃ / min, keeping for 2h. Under the above annealing conditions, the ammonium molybdate is pyrolyzed at 365℃ in inert atmosphere to obtain solid-phase molybdenum trioxide. Then, the nitrogen source is pyrolyzed and recrystallized at 500℃ in inert atmosphere to generate g-C3N4. Finally, g-C3N4 replaces part of oxygen elements in molybdenum trioxide with nitrogen elements at 400-600℃ in inert atmosphere to form MoO x N y (1<x<2, 0.5<y<0.75), i.e. a component of the functional nano-coating.

[0062] When the molybdenum source is ammonium molybdate tetrahydrate, the nitrogen source is urea, the graphite substrate is spherical graphite, and the D 50 =16μm, D 10 =12μm, D 80 =18μm, the prepared nitrogen-doped molybdenum oxide coated graphite negative electrode material has the best charge-discharge cycle stability and fast charge-discharge performance.

[0063] The nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the application is prepared through a simple liquid phase coating and a low-temperature pyrolysis crystallization process. The functional nano-coating with specific components on the surface of the negative electrode material has excellent stability, and can make lithium ions migrate quickly during the charge-discharge process, maintain the high structural stability of the graphite substrate, improve the surface wettability of the active material, further inhibit the adverse lithium dendrite deposition side reaction by improving the interface kinetics of graphite / electrolyte, and improve the cycle stability of graphite as a negative electrode material at high rate. The obtained negative electrode material has high tap density and excellent fast charge-discharge performance. The process of the application is simple, the raw material cost is low, and the process is easy to engineer.

[0064] To make those skilled in the art more clearly understand the application, the following examples and test examples are used to illustrate the nitrogen-doped molybdenum oxide coated graphite negative electrode material and the preparation method thereof.

[0065] Example 1

[0066] A nitrogen-doped molybdenum oxide-coated graphite anode material is disclosed. The anode material comprises a graphite substrate and a functional nano-coating coated on the surface of the graphite substrate. The functional nano-coating is composed of nitrogen-doped molybdenum oxide. The weight ratio of the graphite substrate to the functional nano-coating is 100:0.2. The nitrogen-doped molybdenum oxide comprises molybdenum, oxygen, and nitrogen, with a weight ratio of 100:32.35:7.295. The average thickness of the functional nano-coating is 9 nm. The molecular formula of the nitrogen-doped molybdenum oxide is MoO. x N y (1 < x < 2, 0.5 < y < 0.75). The graphite substrate is spherical graphite with a fixed carbon content of 99.95% and D. 50 =16μm, D 10 =12μm, D 80 =18μm.

[0067] Figure 2 , Figure 3 The SEM and HRTEM images of the nitrogen-doped molybdenum oxide-coated graphite anode material provided in this embodiment are shown respectively. As shown in the figure, the functional nanocoating is approximately 50 nm thick and uniformly coats the graphite surface.

[0068] Figure 4 The figure shows the rate performance results of the nitrogen-doped molybdenum oxide-coated graphite anode material provided in this embodiment in a C2025 button half-cell. As shown in the figure, the anode material achieves an initial discharge capacity of 402.3 mAh / g at 0.2C, 392.1 mAh / g at 0.5C, 386.2 mAh / g at 1C, 370.6 mAh / g at 2C, 366.6 mAh / g at 3C, 339.2 mAh / g at 4C, 320.8 mAh / g at 5C, and 298.7 mAh / g at 6C. It is evident that the anode material in this embodiment exhibits excellent rate cycling performance.

[0069] Figure 5 The figure shows the cycling performance results of the nitrogen-doped molybdenum oxide-coated graphite anode material provided in this embodiment in a C2025 button half-cell. As shown in the figure, the anode material has an initial discharge capacity of 376.1 mAh / g at a current density of 0.75C, and retains a capacity of 392.2 mAh / g after 1000 cycles. At a current density of 1.5C, the anode material has an initial discharge capacity of 212.8 mAh / g, and retains a capacity of 370.1 mAh / g after 1000 cycles. It is evident that the anode material in this embodiment exhibits excellent cycling stability.

[0070] Example 2

[0071] Based on the same inventive concept, the embodiment provides a preparation method of the nitrogen-doped molybdenum oxide coated graphite negative electrode material in Example 1, which specifically comprises the following steps:

[0072] S1: Dissolve 0.02 g of ammonium molybdate tetrahydrate in 10 ml of deionized water, add 4 g of high-purity spherical graphite (fixed carbon content = 99.96%, D 50 = 16 μm), stir to obtain a suspension A;

[0073] S2: Place the suspension A in a water bath at 80°C, slowly stir to evaporate the deionized water, and obtain a solid powder B;

[0074] S3: Add 10 g of urea to the solid powder B, then add 5 ml of alcohol, and fully grind and mix in a agate mortar to obtain a mixed solid powder C;

[0075] S4: Place the mixed solid powder C in an argon atmosphere, heat to 365°C at a rate of 5°C / min in a tube furnace, keep for 1 h; then continue to heat to 500°C at a rate of 3°C / min, keep for 2 h; finally, continue to heat to 600°C at a rate of 5°C / min, keep for 2 h, and fully grind to obtain the nitrogen-doped molybdenum oxide coated graphite negative electrode material.

[0076] Example 3

[0077] A nitrogen-doped molybdenum oxide coated graphite negative electrode material, the negative electrode material comprising a graphite substrate and a functional nanocoating coated on the surface layer of the graphite substrate; the functional nanocoating is composed of nitrogen-doped molybdenum oxide; the weight ratio of the graphite substrate to the functional nanocoating is 100:0.26; the nitrogen-doped molybdenum oxide comprises molybdenum element, oxygen element and nitrogen element, and the weight ratio of the molybdenum element, the oxygen element and the nitrogen element is 100:25.10:8.75; the average thickness of the functional nanocoating is 9 nm; the molecular formula of the nitrogen-doped molybdenum oxide is MoO x N y (1 < x < 2, 0.5 < y < 0.75). The graphite substrate is spherical graphite, the fixed carbon content = 99.99%, D 50 = 17 μm, D 10 = 13 μm, D 80 = 18 μm.

[0078] Figure 6The cycle performance result diagram of the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided in the embodiment in a C2025 button half battery is shown, and as shown, the first discharge capacity of the negative electrode material is 211.8 mAh / g at a current density of 6C, and the remaining capacity is 340.3 mAh / g after 4000 cycles.

[0079] Embodiment 4

[0080] Based on the same inventive concept, the embodiment provides a preparation method of the nitrogen-doped molybdenum oxide coated graphite negative electrode material in Embodiment 3, and specifically includes the following steps:

[0081] S1: 0.015g of ammonium molybdate tetrahydrate is dissolved in 10ml of deionized water, 4g of high-purity spherical graphite (fixed carbon content of 99.6%, D 50 = 17μm) is added, and stirring is performed to obtain a suspension A;

[0082] S2: The suspension A is placed in a water bath at 80℃, and the deionized water is slowly stirred and evaporated to obtain a solid powder B;

[0083] S3: 10g of urea is added to the solid powder B, and then 5ml of alcohol is added, and the mixture is fully ground in a agate mortar to obtain a mixed solid powder C;

[0084] S4: The mixed solid powder C is placed in an argon atmosphere, and is heated to 365℃ at a rate of 5℃ / min in a tube furnace, and is kept at 365℃ for 1h; then it is continuously heated to 500℃ at a rate of 3℃ / min, and is kept at 500℃ for 2h; finally, it is continuously heated to 600℃ at a rate of 5℃ / min, and is kept at 600℃ for 2h, and is fully ground to obtain the nitrogen-doped molybdenum oxide coated graphite negative electrode material.

[0085] Embodiment 5

[0086] Based on the same inventive concept, the embodiment provides a preparation method of a nitrogen-doped molybdenum oxide coated graphite negative electrode material, and specifically includes the following steps:

[0087] S1: 0.03g of ammonium molybdate is dissolved in 10ml of deionized water, 4g of high-purity spherical graphite (fixed carbon content of 99.62%, D 50 = 17μm) is added, and stirring is performed to obtain a suspension A;

[0088] S2: The suspension A is placed in a water bath at 70℃, and the deionized water is slowly stirred and evaporated to obtain a solid powder B;

[0089] S3: 10g of melamine is added to the solid powder B, and then 5ml of alcohol is added, and the mixture is fully ground in a agate mortar to obtain a mixed solid powder C;

[0090] S4: The mixed solid powder C is placed in an argon atmosphere, heated to 365℃ at a rate of 5℃ / min in a tube furnace, kept for 1h; then heated to 500℃ at a rate of 3℃ / min, kept for 2h; finally heated to 600℃ at a rate of 5℃ / min, kept for 2h, and fully ground to obtain the nitrogen-doped molybdenum oxide coated graphite negative electrode material.

[0091] Example 6

[0092] Based on the same inventive concept, the embodiment provides a preparation method of a nitrogen-doped molybdenum oxide coated graphite negative electrode material, which specifically comprises the following steps:

[0093] S1: 0.03g of ammonium molybdate is dissolved in 10ml of deionized water, 4g of high-purity spherical graphite (fixed carbon content of 99.78%, D 50 = 17μm) is added, stirred to obtain a suspension A;

[0094] S2: The suspension A is placed in a water bath at 80℃, and the deionized water is slowly stirred and evaporated to obtain a solid powder B;

[0095] S3: 10g of thiourea is added to the solid powder B, then 5ml of alcohol is added, and the mixture is fully ground in a agate mortar to obtain a mixed solid powder C;

[0096] S4: The mixed solid powder C is placed in an argon atmosphere, heated to 365℃ at a rate of 5℃ / min in a tube furnace, kept for 1h; then heated to 500℃ at a rate of 3℃ / min, kept for 2h; finally heated to 600℃ at a rate of 5℃ / min, kept for 2h, and fully ground to obtain the nitrogen-doped molybdenum oxide coated graphite negative electrode material.

[0097] In summary, the results of Example 1 and Example 3 show that the nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the present application has a high energy density, as well as the most stable high-rate charge-discharge cycle stability and fast charge-discharge performance.

[0098] The nitrogen-doped molybdenum oxide coated graphite negative electrode material provided by the application is coated with a functional nanometer coating on the surface of a natural graphite base, does not affect the high tap density and compacted density of the bare natural graphite, and is also beneficial to improving the energy density; the functional nanometer coating plays a role in inhibiting the additional growth of SEI films in the process of rapid charging and discharging, improves the wettability of the surface of the active material, reduces the lithium ion adsorption energy, and improves the interface dynamics of lithium ion intercalation; and the functional nanometer coating improves the lithium ion intercalation sites at a higher charging potential, thereby improving the rapid charging capacity of the natural graphite negative electrode, maintaining a high structural stability and long-term cycle stability. In addition, the functional nanometer coating improves the lithium ion intercalation sites at a higher charging potential, thereby improving the rapid charging capacity of the natural graphite negative electrode, maintaining a high structural stability and long-term cycle stability. The graphite negative electrode material coated with the coating has both high energy density and long-term cycle stability under high-rate charging and discharging.

[0099] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0100] For the method embodiments, for the sake of simple description, they are all expressed as a combination of a series of actions, but those skilled in the art should know that the present application is not limited by the order of the described actions, because according to the present application, certain steps can be performed in other order or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily necessary for the present application.

[0101] The nitrogen-doped molybdenum oxide coated graphite negative electrode material and the preparation method thereof provided by the application are described in detail above, specific examples are applied in this paper to describe the principles and implementation modes of the application, and the above embodiment description is only used to help understand the method and core idea of the application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the above description should not be understood as limiting the present application.

Claims

1. A nitrogen-doped molybdenum oxide-coated graphite anode material, characterized in that, The negative electrode material includes a graphite substrate and a functional nano-coating covering the surface of the graphite substrate. The functional nanocoating is composed of nitrogen-doped molybdenum oxide; The weight ratio of the graphite substrate to the functional nanocoating is 100:0.01-0.

5. The nitrogen-doped molybdenum oxide comprises molybdenum, oxygen and nitrogen, wherein the weight ratio of molybdenum, oxygen and nitrogen is 100:(16-33):(7-11).

2. The negative electrode material according to claim 1, characterized in that, The average thickness of the functional nanocoating is 5-65 nm.

3. The negative electrode material according to claim 1, characterized in that, The nitrogen-doped molybdenum oxide has the molecular formula MoO. x N y (1<x<2, 0.5<y<0.75).

4. The negative electrode material according to claim 1, characterized in that, The weight ratio of the graphite substrate to the functional nanocoating is 100:0.

2.

5. The negative electrode material according to claim 1, characterized in that, The weight ratio of molybdenum, oxygen and nitrogen is 100:32.35:7.

295.

6. The negative electrode material according to claim 1, characterized in that, The graphite substrate has a fixed carbon content ≥99.95%, D 50 =5-45μm; the graphite substrate is one or both of natural flake graphite and spherical graphite.

7. The negative electrode material according to claim 6, characterized in that, The graphite substrate is spherical graphite, and the D of the spherical graphite 50 =16μm, D 10 =12μm, D 80 =18μm.

8. A method for preparing the nitrogen-doped molybdenum oxide-coated graphite anode material according to any one of claims 1 to 7, characterized in that, The preparation method includes the following steps: S1. Dissolve the molybdenum source in deionized water, add the graphite substrate, stir, and obtain suspension A; S2. The suspension A is stirred at 50-80°C to obtain solid powder B; S3. Add a nitrogen source to the solid powder B, then add an appropriate amount of alcohol, grind evenly to obtain mixed solid powder C; S4. Anneal the mixed solid powder C in an inert gas atmosphere at 300-600℃ for 5-8 hours, and grind it to obtain the nitrogen-doped molybdenum oxide-coated graphite anode material. The mass ratio of the molybdenum source, nitrogen source, and graphite substrate is 0.01-0.1g:10g:4g; the molybdenum source is one or more of ammonium molybdate, ammonium molybdate dihydrate, ammonium molybdate tetrahydrate, and molybdic acid; the nitrogen source is one or more of urea, melamine, and thiourea; and the graphite substrate is one or two of natural flake graphite and spherical graphite.

9. The method for preparing the negative electrode material according to claim 8, characterized in that, The annealing process includes: increasing the temperature to 365°C at 5°C / min and holding for 1 hour; then increasing the temperature to 500°C at 3°C / min and holding for 2 hours; and finally increasing the temperature to 600°C at 5°C / min and holding for 2 hours.

10. The method for preparing the negative electrode material according to claim 8, characterized in that, The molybdenum source is ammonium molybdate tetrahydrate; the nitrogen source is urea; and the graphite substrate is spherical graphite.

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