1. A preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material is characterized by comprising the following steps:

(1) crushing black phosphorus to obtain black phosphorus powder;

(2) adding a carbon material into the mixture obtained in the step (1), transferring the mixture into a reaction kettle for solvothermal reaction, and drying and sieving a reaction product after the reaction is finished to obtain carbon-coated black phosphorus powder; the carbon material is selected from one or more of graphene oxide and carbon nanotubes;

(3) and (3) mixing and stirring the carbon-coated black phosphorus powder obtained in the step (2) and artificial graphite in an organic solvent, and simultaneously carrying out ultrasonic dispersion, drying, iron removal and screening to obtain the black phosphorus-based graphite composite lithium ion battery negative electrode material.

2. The method according to claim 1, wherein the step (1) is carried out by ultrasonic exfoliation in a cell disruptor.

3. The preparation method according to claim 2, wherein the ultrasonic power of the cell crusher is 18 to 22KHz, the ultrasonic time is 5 to 15 hours, and the ultrasonic solvent in the cell crusher is N-methylpyrrolidone during the ultrasonic process.

4. The preparation method according to claim 1, wherein in the step (1), the D50 before crushing the black phosphorus is 10-20 μm.

5. The preparation method according to claim 1, wherein in the step (2), the solvothermal reaction temperature is 100-200 ℃ and the reaction time is 3-15 h.

6. The method according to claim 1, wherein in the step (2), the amount of the carbon material added is 1 to 10% by mass of the total mass of the carbon material and the black phosphorus.

7. The preparation method according to claim 1, wherein in the step (3), the addition amount of the carbon-coated black phosphorus powder is 5 to 50% of the total mass of the carbon-coated black phosphorus powder and the artificial graphite.

8. The method according to any one of claims 1 to 7, wherein in the step (2) and the step (3), the drying temperature is 35 to 80 ℃, and the drying is performed in an oxygen-free environment.

9. The preparation method according to any one of claims 1 to 7, wherein in the step (3), the stirring speed is 500 to 1500r/min, the ultrasonic frequency is 8 to 12KHz, and the ultrasonic time is 3 to 7 hours.

Background

The lithium ion battery is a clean renewable resource, and compared with the traditional lead-acid, nickel-hydrogen and nickel-cadmium batteries, the lithium ion battery has the advantages of environmental friendliness, high energy density, long cycle life and the like. With the development of power automobiles, the requirements on the energy density of lithium ion batteries are higher and higher. The national Ministry of industry and communications requires that the energy density of the lithium ion battery in China reaches 300wH/kg by 2020. The traditional graphite material is difficult to realize the target as the lithium ion battery cathode material, and the theoretical capacity of the graphite cathode material is only 372mAh/g, so that a new cathode material is urgently needed to meet the development of power lithium ion batteries.

As a novel two-dimensional semiconductor material, the black phosphorus not only has the physical characteristics of the two-dimensional material, but also retains the ultrahigh lithium storage capacity (2595 mAh/g) of the phosphorus, which is 7 times of that of a graphite negative electrode material (372 mAh/g). Compared with red phosphorus, black phosphorus has higher ion mobility, and the hole mobility of the black phosphorus is as high as 1000 cm/v/s, so that the application of the black phosphorus in the aspect of lithium ion batteries is more advantageous. However, the pure black phosphorus material has defects, such as volume expansion of 200% in the charging and discharging process, which causes especially poor cycle life, and too low charging and discharging efficiency, which is a technical bottleneck limiting batch production of black phosphorus in lithium ion batteries. The black phosphorus is theoretically compounded with other materials, so that the performance of the battery can be improved to a certain extent, but the black phosphorus and other materials are combined in a ball milling mode in the traditional technology, the formed composite structure is unstable, the black phosphorus material expands to cause the surface structure of the black phosphorus material to be damaged in the charging and discharging process, and the coating material falls off, so that the conductivity of the material is unstable, and the cycle performance is poor.

Disclosure of Invention

The invention aims to solve the technical problem of overcoming the defects and shortcomings in the background technology and providing a preparation method of a black phosphorus-based graphite composite lithium ion battery cathode material.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

a preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material comprises the following steps:

(1) crushing black phosphorus to obtain black phosphorus powder;

(2) adding a carbon material into the mixed solution obtained in the step (1), transferring the mixed solution into a reaction kettle for solvothermal reaction, and drying and sieving a reaction product after the reaction is finished to obtain carbon-coated black phosphorus powder;

(3) and (3) mixing and stirring the carbon-coated black phosphorus powder obtained in the step (2) and artificial graphite in an organic solvent, and simultaneously carrying out ultrasonic dispersion, drying, deironing and screening to obtain the black phosphorus-based graphite composite lithium ion battery negative electrode material.

In the above preparation method, preferably, the step (1) is ultrasonic peeling in a cell crusher.

In the preparation method, the preferable ultrasonic power of the cell crusher is 18-22 KHz, the ultrasonic time is 5-15 h, and the ultrasonic medium in the cell crusher is N-methylpyrrolidone in the ultrasonic process.

In the preparation method, in the step (1), the D50 of the black phosphorus is preferably 10-20 μm.

In the preparation method, preferably, in the step (2), the carbon material is selected from one or more of graphene oxide and carbon nanotubes.

In the preparation method, preferably, in the step (2), the solvothermal reaction temperature is 100-200 ℃, and the reaction time is 3-15 hours.

In the preparation method, preferably, the addition amount of the carbon material accounts for 1-10% of the total mass of the carbon material and the black phosphorus; in the step (3), the addition amount of the carbon-coated black phosphorus accounts for 5-50% of the total mass of the carbon-coated black phosphorus and the artificial graphite.

In the preparation method, preferably, in the step (2) and the step (3), the drying temperature is 35-80 ℃, and the drying is carried out in an oxygen-free environment.

Preferably, in the preparation method, in the step (3), the stirring is double-helix stirring, the stirring speed is 500-1500 r/min, the ultrasonic frequency is 8-12 KHz, and the ultrasonic time is 3-7 h.

Compared with the prior art, the invention has the advantages that:

(1) according to the invention, the carbon material is fully dissolved by reaction in the reaction kettle and reaches a certain saturation degree, so that a growth base source is formed, and then the carbon-coated black phosphorus powder is obtained by nucleation and crystallization on black phosphorus particles, and the obtained powder has the characteristics of high purity, good dispersibility, compact and uniform shell layer and the like, and can effectively improve the first charge-discharge efficiency of black phosphorus and relieve volume expansion; and mixing the carbon-coated black phosphorus powder with graphite in an organic solvent, wherein the graphite is coated on the outer surface of the carbon-coated black phosphorus, so that the volume expansion of the black phosphorus can be further inhibited, and the electrochemical performance is improved.

(2) According to the invention, the carbon material and the black phosphorus are subjected to solvothermal reaction through the reaction kettle, and the carbon material is uniformly coated on the surface of the black phosphorus by using a chemical effect, so that the surface defect of the black phosphorus material is improved, channels in the lithium ion intercalation material are increased, the volume expansion caused by repeated intercalation and dissociation of lithium ions in the charging and discharging process can be effectively relieved, and the defect of poor cycle life of the material is overcome; meanwhile, due to the existence of the carbon coating layer, the direct contact between the black phosphorus material and the electrolyte can be effectively prevented, and the electrolyte and the carbon coating layer can form a thin and compact SEI (solid electrolyte interphase) film in the charging and discharging processes, so that the co-intercalation of lithium ions in a solvent can be effectively inhibited, and the falling-off of the material in the circulating process can be prevented; and an SEI film can be formed between the surface oxide of the graphene or the carbon nano tube and the electrode in a covalent manner, so that the stability of the SEI film is enhanced, the irreversible capacity is reduced, and the charge-discharge efficiency is increased.

(3) According to the invention, the graphite material is coated on the surface of the black phosphorus coated by the carbon material, the characteristics that the graphite material has small volume change and excellent cycle performance in the charging and discharging processes and the graphite material is a mixed conductor of ions and electrons are combined, the black phosphorus is used as an active substance to provide lithium storage capacity, the carbon and the graphite relieve the volume change of the black phosphorus in the charging and discharging processes, the conductivity of the black phosphorus material is improved, and the black phosphorus material can be prevented from being agglomerated in the charging and discharging cycles.

(4) According to the invention, the carbon-black phosphorus-graphite cathode material prepared by utilizing the ultrahigh conductivity and the compatibility of graphene oxide or/and the carbon nano tube and researching the carbon-black phosphorus-graphite combination technical mode successfully solves the problems of poor cycle life, low first efficiency, low capacity of the graphite cathode material and the like of the black phosphorus material.

(5) The invention breaks through the limitation that the theoretical capacity of the conventional graphite cathode is only 372mAh/g, develops the cathode material mainly comprising the black phosphorus material, relieves the dependence on the graphite cathode material, has high energy density of the prepared battery, and can meet the development requirement of a lithium-ion electric power automobile.

Drawings

FIG. 1 is an SEM photograph of a material prepared in example 1 of the present invention.

FIG. 2 is a graph showing the first charge and discharge curves of the material prepared in example 1 of the present invention.

FIG. 3 is a graph of the cycle performance of the material prepared in example 1 of the present invention at 25 ℃ and 0.5C/0.5C.

FIG. 4 is a graph showing the first charge and discharge curves of the material prepared in comparative example 2 according to the present invention.

FIG. 5 is a graph showing the cycle performance at 25 ℃ and 0.5C/0.5C of the comparative example 2 material of the present invention.

Detailed Description

In order to facilitate an understanding of the present invention, the present invention will be described more fully and in detail with reference to the preferred embodiments, but the scope of the present invention is not limited to the specific embodiments below.

Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.

Example 1:

the invention discloses a preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material, which comprises the following steps:

(1) putting black phosphorus with the diameter of D50=15 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 20KHz, and the ultrasonic time is 10 h;

(2) directly adding graphene oxide into the mixed solution obtained in the step (1), wherein the mass ratio of the graphene oxide to the black phosphorus is 5: 95, transferring the mixture into a hydrothermal reaction kettle for reaction at the temperature of 150 ℃ for 8 hours;

(3) drying the reaction product obtained in the step (2) at 60 ℃, introducing nitrogen for protection when drying, wherein the flow rate of the nitrogen is 20mL/min, and obtaining carbon-coated black phosphorus;

(4) mixing the carbon-coated black phosphorus obtained in the step (3) with the artificial graphite according to a mass ratio of 5: 95 adding a solvent (the mass of N methyl pyrrolidone: the mass of ethanol = 4: 6), mixing and stirring, and simultaneously carrying out ultrasonic treatment, wherein the ultrasonic frequency is 10KHz, the ultrasonic time is 4h, and the stirring speed is 800 r/min;

(5) and (3) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying is carried out, wherein the nitrogen flow is 20mL/min, and carrying out iron removal screening treatment on the product after drying is finished to obtain a finished product of the black phosphorus-based graphite composite lithium ion battery cathode material, wherein an SEM image is shown in figure 1, the black phosphorus-based material is uniformly mixed with artificial graphite, and the surface of the black phosphorus is coated with a carbon material with a small particle size, so that the lithium ion migration rate is improved.

The first charge-discharge curve of the black phosphorus-based graphite composite lithium ion battery negative electrode material of the embodiment is shown in fig. 2, the cycle performance at 25 ℃ and 0.5C/0.5C is shown in fig. 3, and as can be seen from fig. 2, the first charge capacity of the negative electrode material is close to 500mAH/g, which is greatly improved relative to the maximum 372mAH/g of artificial graphite theory; as can be seen from fig. 3, the capacity retention rate of the negative electrode material was about 95% after 250 cycles, and about 90% after 450 cycles.

Example 2:

the invention discloses a preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material, which comprises the following steps:

(1) putting black phosphorus with the diameter of D50=15 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 21KHz, and the ultrasonic time is 12 h;

(2) directly adding graphene oxide into the mixed solution obtained in the step (1), wherein the mass ratio of the graphene oxide to the black phosphorus is 5: 95, transferring the mixture into a hydrothermal reaction kettle for reaction at the temperature of 180 ℃ for 12 hours;

(3) drying the reaction product obtained in the step (2) at 60 ℃, introducing nitrogen for protection when drying, wherein the flow rate of the nitrogen is 20mL/min, and obtaining carbon-coated black phosphorus;

(4) mixing the carbon-coated black phosphorus obtained in the step (3) with the artificial graphite according to the mass ratio of 10: 90 adding the mixture into a solvent (N-methyl pyrrolidone: ethanol = 4: 6), mixing and stirring, and simultaneously carrying out ultrasonic treatment, wherein the ultrasonic frequency is 10KHz, the ultrasonic time is 4h, and the stirring speed is 100 r/min;

(5) and (3) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and after drying, carrying out iron removal screening treatment on the product to obtain a finished product of the black phosphorus-based graphite composite lithium ion battery cathode material.

Example 3:

the invention discloses a preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material, which comprises the following steps:

(1) putting black phosphorus with the diameter of D50=15 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 20KHz, and the ultrasonic time is 10 h;

(2) directly adding graphene oxide into the mixed solution obtained in the step (1), wherein the mass ratio of the graphene oxide to the black phosphorus is 5: 95, transferring the mixture into a hydrothermal reaction kettle for reaction at the temperature of 150 ℃ for 8 hours;

(3) drying the reaction product obtained in the step (2) at 60 ℃, introducing nitrogen for protection when drying, wherein the flow rate of the nitrogen is 20mL/min, and obtaining carbon-coated black phosphorus;

(4) mixing the carbon-coated black phosphorus obtained in the step (3) with the artificial graphite according to a mass ratio of 8: 92, adding the mixture into a solvent (N-methyl pyrrolidone: ethanol = 4: 6), mixing and stirring, and simultaneously carrying out ultrasonic treatment, wherein the ultrasonic frequency is 10KHz, the ultrasonic time is 4h, and the stirring speed is 800 r/min;

(5) and (3) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and after drying, carrying out iron removal screening treatment on the product to obtain a finished product of the black phosphorus-based graphite composite lithium ion battery cathode material.

Example 4:

the invention discloses a preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material, which comprises the following steps:

(1) putting black phosphorus with the diameter of D50=10 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 18KHz, and the ultrasonic time is 14 h;

(2) directly adding graphene oxide into the mixed solution obtained in the step (1), wherein the mass ratio of the graphene oxide to the black phosphorus is 8: 92, transferring the mixture into a hydrothermal reaction kettle for reaction at the temperature of 200 ℃ for 18 hours;

(3) drying the reaction product obtained in the step (2) at 60 ℃, introducing nitrogen for protection when drying, wherein the flow rate of the nitrogen is 20mL/min, and obtaining carbon-coated black phosphorus;

(4) and (3) mixing the carbon-coated black phosphorus obtained in the step (3) with the artificial graphite according to a mass ratio of 15: 85 adding solvent (N-methyl pyrrolidone: ethanol = 4: 6), mixing and stirring, and simultaneously performing ultrasonic treatment, wherein the ultrasonic frequency is 12KHz, the ultrasonic time is 6h, and the stirring speed is 1000 r/min;

(5) and (3) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and after drying, carrying out iron removal screening treatment on the product to obtain a finished product of the black phosphorus-based graphite composite lithium ion battery cathode material.

Example 5:

the invention discloses a preparation method of a black phosphorus-based graphite composite lithium ion battery negative electrode material, which comprises the following steps:

(1) putting black phosphorus with the diameter of D50=8 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 21KHz, and the ultrasonic time is 18 h;

(2) directly adding graphene oxide and carbon nanotubes in a mass ratio of 1:1 into the mixed solution obtained in the step (1), wherein the mass ratio of the carbon material to the black phosphorus is 7: 93, then transferring the mixture into a hydrothermal reaction kettle for reaction at the temperature of 200 ℃ for 16 hours;

(3) drying the reaction product obtained in the step (2) at 60 ℃, introducing nitrogen for protection when drying, wherein the flow rate of the nitrogen is 20mL/min, and obtaining carbon-coated black phosphorus;

(4) mixing the carbon-coated black phosphorus obtained in the step (3) with the artificial graphite according to a mass ratio of 20: 80 adding the prepared solvent (N methyl pyrrolidone: ethanol = 4: 6), mixing and stirring, and simultaneously carrying out ultrasonic treatment, wherein the ultrasonic frequency is 12KHz, the ultrasonic time is 7h, and the stirring speed is 1500 r/min;

(5) and (3) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and after drying, carrying out iron removal screening treatment on the product to obtain a finished product of the black phosphorus-based graphite composite lithium ion battery cathode material.

Comparative example 1:

the preparation method of the negative electrode material of the lithium ion battery of the comparative example comprises the following steps:

(1) adding artificial graphene into a mixed solution of N-methyl pyrrolidone and ethanol (the mass ratio of the N-methyl pyrrolidone to the ethanol is 4: 6), mixing and stirring while performing ultrasonic treatment, wherein the ultrasonic frequency is 10KHz, the ultrasonic time is 5 hours, and the stirring speed is 1200 r/min;

(2) and (2) drying the material obtained in the step (1) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and performing iron removal screening treatment on the product after drying to obtain a finished product of the lithium ion battery cathode material.

Comparative example 2:

the preparation method of the negative electrode material of the lithium ion battery of the comparative example comprises the following steps:

(1) putting black phosphorus with the diameter of D50=15 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 20KHz, and the ultrasonic time is 10 h;

(2) directly adding germanium oxide into the mixed solution obtained in the step (1), wherein the mass ratio of the germanium oxide to the black phosphorus is 5: 95, transferring the mixture into a hydrothermal reaction kettle for reaction at the temperature of 150 ℃ for 8 hours;

(3) drying the reaction product obtained in the step (2) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and obtaining germanium oxide coated black phosphorus;

(4) and (3) mixing the germanium oxide coated black phosphorus obtained in the step (3) with the artificial graphite according to the mass ratio of 5: 95 adding into prepared solvent (N methyl pyrrolidone: ethanol = 4: 6) to prepare solution with solid content of 35%, mixing and stirring while performing ultrasonic treatment, wherein the ultrasonic frequency is 10KHz, the ultrasonic time is 4h, and the stirring speed is 800 r/min;

(5) and (4) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and after drying, performing iron removal screening treatment on the product to obtain a finished product of the lithium ion battery cathode material.

The first charge-discharge curve of the negative electrode material of the black phosphorus-based graphite composite lithium ion battery of the present example is shown in fig. 4, the cycle performance at 25 ℃ and 0.5C/0.5C is shown in fig. 5, it can be seen from fig. 4 that the first charge capacity of the negative electrode material is about 425mAH/g, and as can be seen from fig. 5, the capacity retention rate of the negative electrode material is about 80% after the cycle of 500 weeks.

Comparative example 3:

the preparation method of the negative electrode material of the lithium ion battery of the comparative example comprises the following steps:

(1) putting black phosphorus with the diameter of D50=15 μm into a 1000mL closed container, taking N-methyl pyrrolidone as a solvent, and then putting the container into a cell crusher for ultrasonic stripping, wherein the ultrasonic frequency is 20KHz, and the ultrasonic time is 10 h;

(2) transferring the mixed solution obtained in the step (1) into a hydrothermal reaction kettle for reaction at the temperature of 150 ℃ for 8 hours;

(3) drying the reaction product in the step (2) at 60 ℃, and introducing nitrogen for protection when drying, wherein the flow rate of the nitrogen is 20 mL/min;

(4) mixing the material obtained in the step (3) with the artificial graphite according to the mass ratio of 5: 95 adding into prepared solvent (N-methyl pyrrolidone: ethanol = 4: 6) to prepare solution with solid content of 35%, mixing and stirring while performing ultrasonic treatment, wherein the ultrasonic frequency is 10KHZ, the ultrasonic time is 4h, and the stirring speed is 800 r/min;

(5) and (4) drying the material obtained in the step (4) at 60 ℃, introducing nitrogen for protection when drying, wherein the nitrogen flow is 20mL/min, and after drying, performing iron removal screening treatment on the product to obtain a finished product of the lithium ion battery cathode material.

The performance of the negative electrode materials in the examples and comparative examples was measured, and the results are shown in table 1, and the average particle diameter thereof was measured by a malvern 3000E laser particle size distribution instrument; the specific surface area test is carried out by adopting a BET nitrogen adsorption method and using a 3H-2000BET-A full-automatic nitrogen adsorption specific surface area instrument; the tap density is measured by a BT-1000 powder comprehensive characteristic tester.

The lithium ion battery negative electrode materials prepared in the above examples and comparative examples, the conductive agent SP and the binder PVDF (solid content is 10%) are mixed according to the mass ratio of 88:2:10 to prepare slurry, then the slurry is uniformly coated on copper foil with the thickness of 9 μm, the copper foil is pressed into a sheet and then punched into a pole piece with the diameter of 1.4cm, and the sheet piece is dried in a vacuum drying oven at 120 ℃ for 10 hours to prepare the pole piece. The prepared pole piece is used as a working electrode, a metal lithium piece is used as an auxiliary electrode and a reference electrode, and 1mol/LLIPF is adopted as electrolyte₆Is assembled into a CR2430 button cell in a German Braun glove box. At a current of 0.08CA constant current charge and discharge experiment is carried out on the density, the voltage range is 0.005V-2.5V, the first reversible lithium intercalation capacity and the first coulombic efficiency of the material are measured, a winding process is adopted to prepare 1100mAh square lithium ion batteries from the lithium ion battery cathode materials prepared in the examples and the comparative examples, constant current and constant voltage charge and discharge are carried out at the current density of 1.0C, the voltage range is 2.75V-4.2V, the cycle performance of the material is measured, and the result is shown in Table 1.

The physical and chemical properties and electrochemical properties of the materials of Table 1 are shown in the following Table

The table shows that the black phosphorus-based graphite composite lithium ion battery cathode material prepared by the invention can effectively improve the capacity of the cathode material, has the characteristics of high capacity, high first efficiency, long cycle and the like, can effectively inhibit the technical problems of volume expansion, poor cycle and the like of the black phosphorus-based material, and can enhance the lithium insertion amount of the graphite cathode by virtue of the ultrahigh electrical conductivity of the carbon material, thereby improving the multiplying power and the first efficiency.