Black phosphorus-based composite negative electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a black phosphorus-based composite negative electrode material and a preparation method and a lithium ion battery thereof, and the preparation method comprises the following steps: (1) mixing graphite and black phosphorus to obtain a composite material; (2) mixing the composite material and a saccharide compound in a solvent, and performing a hydrothermal reaction to obtain the black phosphorus-based composite negative electrode material; wherein the solvent comprises water and ethylene glycol. The hydrothermal reaction of the composite material and the saccharide compound in the solution system of water and ethylene glycol can make the system reaction more uniform, and the ethylene glycol can reduce the reaction rate, so that the carbonization reaction is more gentle, and then the black phosphorus-based composite negative electrode material with high purity, good dispersity and uniform carbon coating is obtained. In addition, the carbon coating effectively improves the conductivity of the material, and at the same time, the volume expansion of the black phosphorus is relieved, and then the cycle performance is improved, and the capacity of the prepared battery can meet the development requirements of high energy density of electric vehicles.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of battery materials, and particularly relates to a black phosphorus-based composite negative electrode material and a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Since the 1990s, lithium ion batteries have been used in portable electronic devices, and lithium ion batteries have been widely applied in the fields of mobile phones, notebook computers and electric / hybrid vehicles due to their high capacity density, good cyclic energy, low self-discharge rate and other advantages. The positive electrode materials widely used in commercial lithium ion batteries include lithium cobaltate LiCoO2, lithium manganate LiMn2O4, lithium iron phosphate LiFePO4 and ternary nickel cobalt manganese / nickel cobalt aluminum. However, most of the commercial lithium ion battery negative electrode materials are graphite materials, which have the disadvantages of low specific energy, insufficient lithium intercalation rate and cannot meet the high requirements of lithium ion batteries.

[0003] Phosphorus as a two-dimensional negative electrode material is considered to be the most promising negative electrode material due to its outstanding theoretical specific capacity (2592 mAh g -1 ). Phosphorus has three allotropes: white phosphorus, red phosphorus and black phosphorus. White phosphorus is unstable when exposed to air, and such instability may cause certain safety problems, and therefore cannot be used in the field of lithium ion batteries; Red phosphorus and black phosphorus have high theoretical specific capacity, but they will undergo >300% volume change during the lithium ion extraction / intercalation process, causing material surface interface cracking and even breaking, which will aggravate the side reaction and cause serious and rapid capacity decay of the battery. Compared with red phosphorus, black phosphorus has more outstanding thermal stability, higher carrier mobility and higher conductivity, and therefore is more promising for use in high-energy lithium ion batteries.

[0004] The modification methods for improving the material cracking caused by the volume expansion of the phosphorus negative electrode in the cycle mainly include synthesizing nano black phosphorus negative electrode and surface modification. The preparation methods of the nano particle black phosphorus material mainly include spray condensation method and high energy ball milling method. For example, CN106025194A discloses a black phosphorus-based composite negative electrode material and a preparation method thereof. The black phosphorus-based composite negative electrode material is composed of black phosphorus, germanium oxide and graphite. The flaky germanium oxide particles are uniformly dispersed on the surface of the black phosphorus material, and the graphite is coated on the surface of the germanium oxide / black phosphorus. The mass ratio of the black phosphorus and the germanium oxide is (0.25-2):1. The mass percentage of the graphite in the negative electrode material is 5-80%. The black phosphorus-based composite negative electrode material is prepared by using red phosphorus, germanium oxide and graphite as raw materials through a two-step ball milling method. CN108772079A discloses a preparation method of a nano black phosphorus / graphene composite material. The method comprises the following steps: mixing a nano black phosphorus dispersion liquid and an oxidized graphene dispersion liquid under the condition that the temperature is 5-30℃, and obtaining a nano black phosphorus / oxidized graphene dispersion liquid through ultrasonic treatment; freeze-drying the nano black phosphorus / oxidized graphene dispersion liquid to obtain a nano black phosphorus / oxidized graphene solid foam; placing the nano black phosphorus / oxidized graphene solid foam in an inert gas atmosphere for ultraviolet, infrared or visible light irradiation pretreatment for 2-72h to obtain a nano black phosphorus / pre-reduced oxidized graphene solid; and placing the nano black phosphorus / pre-reduced oxidized graphene solid in an inert gas atmosphere and reducing it under the condition of microwave with a temperature of 50-300℃ for 0.5-10h to obtain a nano black phosphorus / graphene composite material.

[0005] Although the above prior art can improve the volume expansion problem of the black phosphorus negative electrode material in the cycle to some extent, the effect is not significant, and the improved black phosphorus negative electrode material has the problems of low purity and poor dispersibility.

[0006] Therefore, how to effectively improve the volume expansion problem of the black phosphorus negative electrode material in the cycle and improve the purity and dispersibility of the black phosphorus negative electrode material is a technical problem to be solved. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a black phosphorus-based composite negative electrode material, a preparation method thereof and a lithium ion battery. The black phosphorus and the graphite are compounded in the present application, and the hydrothermal reaction of the composite material and the saccharide compound is carried out in the solution system of water and ethylene glycol, so that the system reaction is more uniform, and the ethylene glycol can reduce the reaction rate, so that the carbonization reaction and the nucleation reaction of carbon on the surface of the graphite / black phosphorus particles are more moderate, and then the black phosphorus-based composite negative electrode material with high purity, good dispersibility and uniform carbon coating is obtained. In addition, the carbon coating effectively improves the conductivity of the material, and at the same time, the volume expansion of the black phosphorus is relieved, and thus the cycle performance is improved, and the capacity of the prepared battery can meet the development requirements of high energy density of electric vehicles.

[0008] To achieve the object of the present application, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a preparation method of a black phosphorus-based composite negative electrode material, which comprises the following steps:

[0010] (1) mixing graphite and black phosphorus to obtain a composite material;

[0011] (2) mixing the composite material and a saccharide compound in a solvent to perform a hydrothermal reaction, thereby obtaining the black phosphorus-based composite negative electrode material;

[0012] wherein the solvent comprises water and ethylene glycol.

[0013] The present application can make the system reaction more uniform by compounding black phosphorus and graphite and performing a hydrothermal reaction of the composite material and a saccharide compound in a solution system of water and ethylene glycol, and the ethylene glycol can reduce the reaction rate, so that the carbonization reaction and the nucleation reaction of carbon on the surface of graphite / black phosphorus particles are more gentle, thereby obtaining a black phosphorus-based composite negative electrode material with high purity, good dispersity and uniform carbon coating.

[0014] The present application performs carbon coating on the graphite / black phosphorus composite material, effectively improves the conductivity of the material, improves the surface defects of the black phosphorus material, increases the diffusion channels of lithium ions in the black phosphorus material, and at the same time relieves the volume expansion of the black phosphorus during lithium extraction, thereby improving the cycle performance thereof. In addition, the presence of the carbon coating layer also separates the graphite and black phosphorus from the electrolyte, reduces the degree of occurrence of side reactions, thereby making the SEI layer formed on the surface of the particles thin and dense, increasing the cycle stability of the material, reducing the irreversible capacity of the battery, and the capacity of the prepared battery can meet the development requirements of high energy density of electric vehicles.

[0015] Preferably, the graphite in step (1) comprises artificial graphite or natural graphite, preferably artificial graphite, and further preferably mesocarbon microbeads.

[0016] Preferably, the graphite in step (1) has a median particle size D50 of 8-35 μm, for example, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, etc.

[0017] Preferably, the black phosphorus in step (1) has a median particle size D50 of 5-12 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm or 12 μm, etc.

[0018] Preferably, the mass content of the black phosphorus in step (1) is 5-15%, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, etc., based on the total mass of the graphite and the black phosphorus.

[0019] In the present application, if the mass content of the black phosphorus is too low, the capacity of the graphite negative electrode material is limited; if the mass content of the black phosphorus is too high, the material expansion will increase due to the black phosphorus, thereby causing more serious side reactions and damaging the cycle performance of the battery.

[0020] Preferably, the mixing method in step (1) is a high-energy ball milling method. The present application does not limit the specific implementation of the high-energy ball milling method, and exemplary methods include wet ball milling or dry ball milling, etc.

[0021] In the present application, the high-energy ball milling method can be used to crush the black phosphorus with a larger particle size through grinding, impact, stirring, etc., to obtain black phosphorus particles with a smaller particle size.

[0022] Preferably, the mixing time in step (1) is 5-10h, for example, 5h, 6h, 7h, 8h, 9h, or 10h, etc.

[0023] In the present application, if the mixing time is too short, the larger black phosphorus particles cannot be completely crushed; and the mesocarbon microbeads and the black phosphorus cannot be mixed sufficiently.

[0024] Preferably, after the mixing in step (1), drying is performed.

[0025] Preferably, the drying process is performed in an inert atmosphere, and the gas in the inert atmosphere includes any one or a combination of at least two of argon, nitrogen, helium, or carbon dioxide.

[0026] Preferably, the flow rate of the gas in the inert atmosphere is 15-25mL / min, for example, 15mL / min, 17mL / min, 19mL / min, 21mL / min, 23mL / min, or 25mL / min, etc.

[0027] Preferably, the drying temperature is 40-80℃, for example, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, or 80℃, etc.

[0028] Preferably, the saccharide compound in step (2) includes glucose and / or sucrose.

[0029] Preferably, the mass ratio of the composite material and the saccharide compound in step (2) is 100:(0.5-1.5), for example, it can be 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1, 100:1.1, 100:1.2, 100:1.3, 100:1.4 or 100:1.5, etc.

[0030] In the present application, if the mass ratio of the composite material and the saccharide compound is too large, i.e. the mass of the saccharide compound is too small, the carbon-coated carbon source is less, the composite negative electrode material is not uniformly coated, and the purpose of relieving the volume expansion of black phosphorus material and improving the conductivity of the material cannot be achieved; if the mass ratio of the composite material and the saccharide compound is too small, i.e. the mass of the saccharide compound is too large, the carbon-coated carbon source is more, the carbon layer on the surface of the material is too thick, the active material content per unit area is reduced, the battery capacity is damaged, and Li + diffusion on the surface of the active material.

[0031] Preferably, the mixing method of step (2) comprises the following steps:

[0032] (a) mixing the saccharide compound and the solvent to obtain a mixed solution;

[0033] (b) mixing the mixed solution and the composite material.

[0034] Preferably, in the solvent, the volume ratio of water and ethylene glycol is (0.3-1):(0.1-0.7), wherein the selected range of water is "0.3-1", for example, it can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., and the selected range of ethylene glycol is "0.1-0.7", for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7, etc.

[0035] In the present application, if the volume ratio of water and ethylene glycol is too small, the amount of added ethylene glycol is too large, the saccharide compound is not sufficiently dissolved, the surface of the negative electrode particles cannot be completely covered by the carbon layer, and the coating layer is discontinuous, which intensifies the side reactions in the battery and damages the battery performance; if the volume ratio of water and ethylene glycol is too large, the amount of ethylene glycol is small, which cannot inhibit the nucleation rate of carbon on the surface of the negative electrode material particles, causing unevenness of the carbon coating layer, and the uneven coating layer also becomes an active site for side reactions, thereby affecting the cycle performance of the battery.

[0036] Preferably, the temperature of the hydrothermal reaction in step (2) is 125-175℃, for example, it can be 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃ or 175℃, etc.

[0037] Preferably, the time of the hydrothermal reaction in step (2) is 8-12h, for example, it can be 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, etc.

[0038] Preferably, the black phosphorus in step (1) is subjected to a crushing treatment before being mixed with graphite.

[0039] Preferably, the crushing treatment is a high-energy ball milling method, which includes dry ball milling or wet ball milling.

[0040] Preferably, the time of the crushing treatment is 10-20h, for example, it can be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, etc.

[0041] Preferably, after the hydrothermal reaction in step (2), dispersion and drying are sequentially performed.

[0042] In the present application, after the hydrothermal reaction, the steps of dispersion and drying are performed to disperse the agglomerated particles after the hydrothermal reaction, so that the composite negative electrode material is mixed more uniformly, and the sugar compounds that are not completely reacted in the hydrothermal reaction are removed.

[0043] Preferably, the dispersion method includes ultrasonic dispersion and / or magnetic stirring dispersion.

[0044] Preferably, stirring is performed during the ultrasonic dispersion, and the stirring rate is 800-1000rad / min, for example, it can be 800rad / min, 850rad / min, 900rad / min, 950rad / min or 1000rad / min, etc.

[0045] Preferably, the time of the dispersion is 4-6h, for example, it can be 4h, 4.5h, 5h, 5.5h or 6h, etc.

[0046] Preferably, the drying atmosphere is an inert atmosphere, and the gas in the inert atmosphere includes any one or a combination of at least two of argon, nitrogen, helium or carbon dioxide, and the flow rate of the gas is 15-25mL / min, for example, it can be 15mL / min, 17mL / min, 19mL / min, 21mL / min, 23mL / min or 25mL / min, etc.

[0047] Preferably, the drying temperature is 40-80℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc.

[0048] As a preferred technical solution, the preparation method comprises the following steps:

[0049] (I) performing a crushing treatment on black phosphorus to obtain crushed black phosphorus;

[0050] (II) mixing mesocarbon microbeads with a D50 of 8-35 μm and the crushed black phosphorus for 5-10 h, and then drying in an inert atmosphere at 40-80℃ to obtain a composite material;

[0051] wherein the mass content of the black phosphorus is 5-15% based on the total mass of the graphite and the black phosphorus;

[0052] (III) mixing a saccharide compound and a solvent to obtain a solution;

[0053] wherein the solvent comprises water and ethylene glycol, and the volume ratio of water to ethylene glycol is (0.3-1):(0.1-0.7);

[0054] (IV) mixing the composite material and the solution, and hydrothermally reacting at 125-175℃ for 8-12 h, and then dispersing and drying at 40-80℃ to obtain the black phosphorus-based composite negative electrode material;

[0055] wherein the mass ratio of the composite material to the saccharide compound in the solution is 100:(0.5-1.5).

[0056] In a second aspect, the present application provides a black phosphorus-based composite negative electrode material, which is prepared by the method of the first aspect.

[0057] The black phosphorus-based composite negative electrode material comprises a graphite / black phosphorus composite material core and a carbon coating layer on the surface of the core.

[0058] In a third aspect, the present application provides a lithium ion battery, wherein the negative electrode of the lithium ion battery comprises the black phosphorus-based composite negative electrode material of the second aspect.

[0059] The numerical ranges of the present application include not only the point values listed above, but also any point values between the listed point values, and the specific point values included in the ranges are not listed in the interest of brevity and simplicity.

[0060] Compared with the prior art, the present application has the following beneficial effects:

[0061] (1) The present application effectively improves the capacity of the material by compounding black phosphorus and graphite, and by carrying out the hydrothermal reaction of the composite material and the saccharide compound in the solution system of water and ethylene glycol, the system reaction can be more uniform, and the ethylene glycol can reduce the reaction rate, so that the carbonization reaction and the nucleation reaction of carbon on the surface of the graphite / black phosphorus particles are more moderate, and then the black phosphorus-based composite negative electrode material with high purity, good dispersity and uniform carbon coating is obtained.

[0062] (2) The present application carries out carbon coating on the graphite / black phosphorus composite material, effectively improves the conductivity of the material, improves the surface defects of the black phosphorus material, increases the diffusion channel of lithium ions in the black phosphorus material, and at the same time relieves the volume expansion of the black phosphorus in the process of lithium extraction, thereby improving the cycle performance, in addition, the existence of the carbon coating layer also separates the graphite and the black phosphorus from the electrolyte, reduces the degree of occurrence of the side reaction, thereby making the SEI layer formed on the surface of the particles thin and dense, increasing the cycle stability of the material, reducing the irreversible capacity of the battery, and the capacity of the prepared battery can meet the development requirements of high energy density of electric vehicles. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 The first charge-discharge curve diagram of the black phosphorus-based composite negative electrode material prepared in Example 1 of the present application.

[0064] Figure 2 The cycle performance diagram of the black phosphorus-based composite negative electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0065] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0066] Example 1

[0067] The present embodiment provides a preparation method of a black phosphorus-based composite negative electrode material, which comprises the following steps:

[0068] (1) The black phosphorus with a D50 of 16 μm is placed in a ball mill jar, and a planetary ball mill is used for ball milling with anhydrous ethanol as a medium, the ball milling time is 15 h, and the pulverized black phosphorus with a D50 of 10 μm is obtained;

[0069] (2) The mesocarbon microbead with a D50 of 8 μm and the pulverized black phosphorus are placed in a ball mill jar, and a planetary ball mill is used for mixing ball milling with anhydrous ethanol as a medium, the mixing time is 8 h, and then drying is carried out in an argon gas at 60℃, the flow rate of the gas is 20 mL / min, and the composite material is obtained;

[0070] The mass content of the black phosphorus is 10% based on the total mass of the mesocarbon microbead and the black phosphorus;

[0071] (3) mixing glucose and solvent to obtain a solution;

[0072] The solvent is composed of deionized water and ethylene glycol, and the volume ratio of water to ethylene glycol is 1:1.

[0073] (4) mixing the composite material and the solution, and performing hydrothermal reaction on the composite material in an oven at 150 DEG C for 10h to obtain a black phosphorus-based composite negative electrode material;

[0074] The mass ratio of the composite material to glucose in the solution is 100:1.

[0075] (5) placing the black phosphorus-based composite negative electrode material in an ultrasonic disperser, using ethylene glycol as an ultrasonic medium, using magnetic stirring as stirring, setting the stirring speed to 900 rad / min, setting the ultrasonic frequency to 13 kHz, and performing ultrasonic dispersion for 5h;

[0076] (6) drying the black phosphorus-based composite negative electrode material dispersed in step (5) in an oven at 60 DEG C, using argon gas to protect the drying process, setting the gas flow rate to 20 mL / min, and obtaining a target product, i.e., a black phosphorus-based composite negative electrode material with mesocarbon microbead / black phosphorus composite material as a core and a carbon layer as a coating layer, after drying.

[0077] Figure 1 A first charge-discharge curve of the black phosphorus-based composite negative electrode material prepared in this embodiment is shown in the figure, and it can be seen from the figure that the first charge capacity of the negative electrode material is close to 550 mAh / g, which is greatly improved compared with the theoretical maximum 372 mAh / g of artificial graphite.

[0078] Figure 2 A cycle performance graph of the black phosphorus-based composite negative electrode material prepared in this embodiment is shown in the figure, and it can be seen from the figure that the capacity retention rate of the negative electrode material is about 89.2% after 100 cycles.

[0079] Embodiment 2

[0080] The embodiment provides a preparation method of a black phosphorus-based composite negative electrode material, and the preparation method comprises the following steps:

[0081] (1) placing black phosphorus with a D50 of 16 μm in a ball mill jar, using anhydrous ethanol as a medium, and using a planetary ball mill to perform ball milling, wherein the ball milling time is 10h, and the D50 of the pulverized black phosphorus is 12 μm;

[0082] (2) Put the mesocarbon microbead with a D50 of 15 pm and the crushed black phosphorus into a ball mill tank, use a planetary ball mill to ball mill the mixture with anhydrous ethanol as the medium, the mixing time is 5 h, then dry in an argon gas at 60 DEG C, the flow rate of the gas is 20 mL / min, to obtain a composite material;

[0083] wherein, based on the total mass of the mesocarbon microbead and the black phosphorus, the mass content of the black phosphorus is 5%;

[0084] (3) Mix the glucose and the solvent to obtain a solution;

[0085] wherein, the solvent is composed of deionized water and ethylene glycol, the volume ratio of water to ethylene glycol is 1:1;

[0086] (4) Mix the composite material and the solution, and perform a hydrothermal reaction in an oven at 150 DEG C for 8 h to obtain a black phosphorus-based composite negative electrode material;

[0087] wherein, the mass ratio of the composite material to the glucose in the solution is 100:0.5.

[0088] (5) Put the black phosphorus-based composite negative electrode material into an ultrasonic disperser for ultrasonic dispersion, the ultrasonic medium is ethylene glycol, the stirring is magnetic stirring, the stirring speed is 900 rad / min, the ultrasonic frequency is 13 kHz, and the ultrasonic time is 4 h;

[0089] (6) Dry the dispersed black phosphorus-based composite negative electrode material in an oven at 60 DEG C, the drying process is protected by using argon gas, the flow rate of the gas is 20 mL / min, and the target product, i.e. the black phosphorus-based composite negative electrode material with mesocarbon microbead / black phosphorus composite material as the core and carbon layer as the coating layer, is obtained after drying.

[0090] Example 3

[0091] The embodiment provides a preparation method of a black phosphorus-based composite negative electrode material, and the preparation method comprises the following steps:

[0092] (1) Put the black phosphorus with a D50 of 16 pm into a ball mill tank, use a planetary ball mill to ball mill with anhydrous ethanol as the medium, the ball milling time is 20 h, to obtain crushed black phosphorus with a D50 of 9 pm;

[0093] (2) Put the mesocarbon microbead with a D50 of 10 pm and the crushed black phosphorus into a ball mill tank, use a planetary ball mill to ball mill the mixture with anhydrous ethanol as the medium, the mixing time is 10 h, then dry in an argon gas at 60 DEG C, the flow rate of the gas is 20 mL / min, to obtain a composite material;

[0094] The mass content of the black phosphorus is 15% based on the total mass of the mesocarbon microbead and the black phosphorus;

[0095] (3) mixing glucose and a solvent to obtain a solution;

[0096] The solvent is composed of deionized water and ethylene glycol, and the volume ratio of water to ethylene glycol is 1:1.

[0097] (4) mixing the composite material and the solution, and performing a hydrothermal reaction on the composite material in an oven at 150 DEG C for 12 h to obtain a black phosphorus-based composite negative electrode material;

[0098] The mass ratio of the composite material to glucose in the solution is 100:1.5.

[0099] (5) placing the black phosphorus-based composite negative electrode material in an ultrasonic disperser, using ethylene glycol as an ultrasonic medium, using magnetic stirring as stirring, setting the stirring speed to 900 rad / min, setting the ultrasonic frequency to 13 kHz, and performing ultrasonic dispersion for 6 h;

[0100] (6) drying the black phosphorus-based composite negative electrode material dispersed in step (5) in an oven at 60 DEG C, using argon gas to protect the drying process, setting the gas flow rate to 20 mL / min, and obtaining a target product, i.e., a black phosphorus-based composite negative electrode material with mesocarbon microbead / black phosphorus composite material as a core and a carbon layer as a coating layer.

[0101] Example 4

[0102] The embodiment provides a preparation method of a black phosphorus-based composite negative electrode material.

[0103] (1) placing black phosphorus with a D50 of 16 μm in a ball mill jar, using a planetary ball mill with anhydrous ethanol as a medium to perform ball milling, setting the ball milling time to 15 h, and obtaining crushed black phosphorus with a D50 of 10 μm;

[0104] (2) placing mesocarbon microbeads with a D50 of 20 μm and the crushed black phosphorus in a ball mill jar, using a planetary ball mill with anhydrous ethanol as a medium to perform ball milling and mixing, setting the mixing time to 8 h, and then drying in nitrogen gas at 40 DEG C, with a gas flow rate of 15 mL / min, to obtain a composite material;

[0105] The mass content of the black phosphorus is 15% based on the total mass of the mesocarbon microbead and the black phosphorus;

[0106] (3) mixing glucose and a solvent to obtain a solution;

[0107] The solvent is composed of deionized water and ethylene glycol, and the volume ratio of water to ethylene glycol is 1:1.

[0108] (4) mixing the composite material and the solution, and performing a hydrothermal reaction in an oven at 125 DEG C for 12 h to obtain a black phosphorus-based composite negative electrode material;

[0109] wherein the mass ratio of the composite material to glucose in the solution is 100:1.

[0110] (5) placing the black phosphorus-based composite negative electrode material in an ultrasonic disperser, using ethylene glycol as an ultrasonic medium, performing magnetic stirring, a stirring speed being 800 rad / min, an ultrasonic frequency being 13 kHz, and an ultrasonic time being 6 h;

[0111] (6) drying the black phosphorus-based composite negative electrode material dispersed in step (5) in an oven at 40 DEG C, using nitrogen gas to protect during the drying process, a gas flow being 15 mL / min, and obtaining a target product, i.e. a black phosphorus-based composite negative electrode material with mesocarbon microbeads / black phosphorus composite material as a core and a carbon layer as a coating layer, after drying.

[0112] Example 5

[0113] The embodiment provides a preparation method of a black phosphorus-based composite negative electrode material, and the preparation method comprises the following steps:

[0114] (1) placing black phosphorus with a D50 of 16 pm in a ball mill jar, using a planetary ball mill with anhydrous ethanol as a medium to perform ball milling, a ball milling time being 15 h, and obtaining crushed black phosphorus with a D50 of 10 pm;

[0115] (2) placing mesocarbon microbeads with a D50 of 35 pm and the crushed black phosphorus in a ball mill jar, using a planetary ball mill with anhydrous ethanol as a medium to perform ball milling mixing, a mixing time being 8 h, and then performing drying in carbon dioxide gas at 80 DEG C, a gas flow being 25 mL / min, to obtain a composite material;

[0116] wherein, based on the total mass of the mesocarbon microbeads and the black phosphorus, the mass content of the black phosphorus is 10%;

[0117] (3) mixing sucrose and a solvent to obtain a solution;

[0118] wherein the solvent is composed of deionized water and ethylene glycol, and the volume ratio of water to ethylene glycol is 0.4:0.6;

[0119] (4) mixing the composite material and the solution, and performing a hydrothermal reaction in an oven at 175 DEG C for 8 h to obtain a black phosphorus-based composite negative electrode material;

[0120] wherein the mass ratio of the composite material to sucrose in the solution is 100:1.

[0121] (5) The black phosphorus-based composite negative electrode material is placed in an ultrasonic disperser for ultrasonic dispersion, the ultrasonic medium is ethylene glycol, the stirring is magnetic stirring, the stirring speed is 1000 rad / min, the ultrasonic frequency is 13 kHz, and the ultrasonic time is 4 h;

[0122] (6) The black phosphorus-based composite negative electrode material dispersed in step (5) is dried in an oven at 80°C, nitrogen gas is used for protection during the drying process, the gas flow is 25 mL / min, and the target product, i.e., the black phosphorus-based composite negative electrode material with mesocarbon microbead / black phosphorus composite material as the core and a carbon layer as the cladding layer, is obtained after drying.

[0123] Example 6

[0124] The difference between this example and Example 1 is that the mass content of black phosphorus in step (2) is 3%.

[0125] The rest of the preparation method and parameters remain the same as those in Example 1.

[0126] Example 7

[0127] The difference between this example and Example 1 is that the mass content of black phosphorus in step (2) is 20%.

[0128] The rest of the preparation method and parameters remain the same as those in Example 1.

[0129] Example 8

[0130] The difference between this example and Example 1 is that the mixing method of mesocarbon microbeads and crushed black phosphorus in step (2) is mechanical stirring.

[0131] The rest of the preparation method and parameters remain the same as those in Example 1.

[0132] Example 9

[0133] The difference between this example and Example 1 is that the mixing time in step (2) is 3 h.

[0134] The rest of the preparation method and parameters remain the same as those in Example 1.

[0135] Example 10

[0136] The difference between this example and Example 1 is that the mixing time in step (2) is 12 h.

[0137] The rest of the preparation method and parameters remain the same as those in Example 1.

[0138] Example 11

[0139] The difference between this example and Example 1 is that the volume ratio of water to ethylene glycol in step (3) is 1.2:0.1.

[0140] The remaining preparation method and parameters are consistent with Example 1.

[0141] Example 12

[0142] The difference between this example and Example 1 is that the volume ratio of water to ethylene glycol in step (3) is 0.1:0.9.

[0143] The remaining preparation method and parameters are consistent with Example 1.

[0144] Example 13

[0145] The difference between this example and Example 1 is that the mass ratio of composite material to glucose in the solution in step (4) is 100:2.

[0146] The remaining preparation method and parameters are consistent with Example 1.

[0147] Example 14

[0148] The difference between this example and Example 1 is that the mass ratio of composite material to glucose in the solution in step (4) is 100:0.2.

[0149] The remaining preparation method and parameters are consistent with Example 1.

[0150] Example 15

[0151] The difference between this example and Example 1 is that steps (5) and (6) are not performed.

[0152] The remaining preparation method and parameters are consistent with Example 1.

[0153] Comparative Example 1

[0154] The difference between this comparative example and Example 1 is that the solvent in step (3) is deionized water.

[0155] The remaining preparation method and parameters are consistent with Example 1.

[0156] Comparative Example 2

[0157] The difference between this comparative example and Example 1 is that the solvent in step (3) is ethylene glycol.

[0158] The remaining preparation method and parameters are consistent with Example 1.

[0159] Performance Test

[0160] The black phosphorus-based composite negative electrode material prepared in the above examples 1-15 and comparative examples 1-2 was mixed with a conductive agent (conductive carbon black, SP) and a binder (polyvinylidene fluoride, PVDF) (solid content 10%) at a mass ratio of 90:2:8 to prepare a slurry, which was then uniformly coated on a 6 μm thick copper foil, pressed into a sheet, punched into a 14 mm diameter electrode, and dried in a vacuum drying oven at 120°C for 10 h to prepare an electrode.

[0161] The electrode prepared above was used as a working electrode, a lithium metal sheet was used as an auxiliary electrode and a reference electrode, and an electrolyte of 1 mol / L LiPF6 in EC / DMC / EMC (volume ratio 1:1:1) was used to assemble a CR2430 type button cell in an Itex glove box.

[0162] The button cell prepared was subjected to electrochemical performance testing.

[0163] Test conditions: constant current charge and discharge experiment was carried out at a current density of 0.01C, the voltage range was 0.005V-2.5V, the initial charge and discharge capacity and the initial coulombic efficiency of the material were measured, the cycle test was carried out at 25°C under the standard of 0.5C / 0.5C constant current charge and discharge, and the cycle number was 100 cycles.

[0164] The test results are shown in Table 1.

[0165] Table 1

[0166]

[0167]

[0168] Analysis:

[0169] As can be seen from the above table, the black phosphorus-based composite negative electrode material prepared by the preparation method provided by the application has excellent electrochemical performance, the initial charge capacity and the initial coulombic efficiency are obviously improved, and the cycle stability is also significantly improved.

[0170] As can be seen from the comparison of the data results of examples 1 and 6-7, if the mass content of black phosphorus is too low, the capacity improvement of the graphite negative electrode material is limited; if the mass content of black phosphorus is too high, the material will expand due to black phosphorus, thereby causing more serious side reactions and damaging the cycle performance of the battery.

[0171] From the comparison of the data results of Example 1 and Example 8, if only the conventional mechanical stirring method is used, the mechanical stirring energy is not as good as the high-energy ball milling, the crushing and grinding effect is not good, and the black phosphorus particles cannot be better crushed. The particle size of the black phosphorus material is large, the particle surface is rough, and the SEI layer continuously reorganizes and causes serious side reactions in the cycle process, thereby damaging the battery performance. Therefore, the crushing degree of the black phosphorus particles is low, and appropriate size black phosphorus particles cannot be obtained to alleviate the side reactions and improve the performance of the negative electrode material.

[0172] From the comparison of the data results of Example 1 and Example 9-10, if the mixing time is too short, the larger black phosphorus particles cannot be effectively ground and refined, thereby affecting the cycle life of the battery material; if the mixing time is too long, the particle size of the ground particles exceeds the limit, which causes waste of manpower, material resources, and energy resources.

[0173] From the comparison of the data results of Example 1 and Example 11-12, if the volume ratio of water to ethylene glycol is too small, that is, the content of deionized water is too low, the sugar compound required for carbon coating in the experiment cannot be fully dissolved, the coating layer is discontinuous and uneven, and the coating effect is affected; if the volume ratio of water to ethylene glycol is too large, that is, the content of ethylene glycol is too low, the carbon atoms nucleate on the surface of the negative electrode particles at a faster speed, which easily causes the carbon coating layer to agglomerate on the surface of the particles, resulting in uneven carbon coating layer; the faster nucleation speed of carbon atoms on the surface of the negative electrode particles also causes the adhesion between the carbon coating layer and the particles to be insufficient, and the carbon coating layer is easily detached during the cycle process.

[0174] From the comparison of the data results of Example 1 and Example 13-14, if the mass ratio of the composite material to the solution of glucose is too small, that is, the content of the sugar compound is too low, the carbon coating layer will be too thin, and even the carbon coating layer cannot exist continuously on the surface of the negative electrode particles, thereby causing the continuously repaired and reorganized SEI layer to consume the limited active lithium ions in the battery, and thereby damaging the cycle life of the battery; if the mass ratio of the composite material to the solution of glucose is too large, that is, the content of the sugar compound is too large, the carbon coating layer will be too thick, Li + After passing through the carbon layer resistance, the polarization degree of the battery is increased, and the battery performance is damaged.

[0175] From the comparison of the data results of Example 1 and Example 15, if the obtained black phosphorus-based composite negative electrode material is not subjected to the dispersion and drying steps, the residual sugar after the hydrothermal reaction cannot be removed, and impurities are formed in the battery.

[0176] As can be seen from the data results of Example 1 and Comparative Examples 1-2, if the solvent of the saccharide compound is only deionized water, the nucleation speed of carbon atoms on the surface of the negative electrode particles is faster and is not easy to control, and then the carbon layer on the surface of the negative electrode material aggregates, the adhesion of the carbon coating layer to the particles is insufficient, a dense coating layer cannot be formed, the carbon coating layer is easy to fall off, and thus the volume expansion of black phosphorus in the cycle process and the degree of occurrence of side reactions cannot be alleviated; if the solvent of the saccharide compound is only ethylene glycol, the saccharide cannot be fully dissolved, and thus a uniform carbon coating layer cannot be formed, resulting in the worst cycle performance.

[0177] The applicant declares that the process of the present application is illustrated by the above examples, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the selected raw materials of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A preparation method of a black phosphorus-based composite negative electrode material, characterized in that, The preparation method comprises the following steps: (1) mixing graphite and black phosphorus to obtain a composite material; (2) mixing the composite material and a saccharide compound in a solvent to perform a hydrothermal reaction to obtain the black phosphorus-based composite negative electrode material; the mass ratio of the composite material to the saccharide compound in step (2) is 100:(0.5-1.5); The solvent comprises water and ethylene glycol; in the solvent, the volume ratio of water to ethylene glycol is (0.3-1):(0.1-0.7).

2. The production method according to claim 1, characterized by, The graphite in step (1) comprises artificial graphite or natural graphite.

3. The production method according to claim 1, characterized by, The graphite in step (1) is artificial graphite.

4. The method of claim 1, wherein, The graphite in step (1) is mesocarbon microbeads.

5. The preparation method according to claim 1, characterized in that, The graphite in step (1) has a median particle size D50 of 8-35 μm.

6. The method of claim 1, wherein, The black phosphorus in step (1) has a median particle size D50 of 5-12 μm.

7. The preparation method according to claim 1, characterized in that, The mass content of the black phosphorus in step (1) is 5-15% based on the total mass of the graphite and the black phosphorus.

8. The method of claim 1, wherein, The mixing method in step (1) is high-energy ball milling.

9. The method of claim 1, wherein, The mixing time in step (1) is 5-10 h.

10. The method of claim 1, wherein, After the mixing in step (1), drying is performed.

11. The method of claim 10, wherein, The drying process is performed in an inert atmosphere, and the gas in the inert atmosphere comprises any one or a combination of at least two of argon, nitrogen, helium or carbon dioxide.

12. The method of claim 11, wherein, The flow rate of the gas in the inert atmosphere is 15-25 mL / min.

13. The preparation method according to claim 10, characterized in that, The drying temperature is 40-80 °C.

14. The method of claim 1, wherein, The saccharide compound in step (2) comprises glucose and / or sucrose.

15. The method of claim 1, wherein, The mixing manner in step (2) comprises the following steps: (a) mixing a saccharide compound and a solvent to obtain a solution; (b) mixing the solution and a composite material.

16. The method of claim 1, wherein, The hydrothermal reaction in step (2) is performed at a temperature of 125-175 °C.

17. The method of claim 1, wherein, The hydrothermal reaction in step (2) is performed for a time of 8-12 h.

18. The method of claim 1, wherein, The black phosphorus in step (1) is subjected to a crushing treatment before being mixed with graphite.

19. The method of claim 18, wherein, The crushing treatment is performed for a time of 10-20 h.

20. The method of claim 1, wherein, After the hydrothermal reaction in step (2), dispersion and oven drying are further performed in sequence.

21. The method of claim 20, wherein, The dispersion manner comprises ultrasonic dispersion and / or magnetic stirring dispersion.

22. The method of claim 20, wherein, The dispersion is performed for a time of 4-6 h.

23. The preparation method according to claim 20, characterized in that, The oven drying is performed in an inert atmosphere, and the gas in the inert atmosphere comprises any one or a combination of at least two of argon, nitrogen, helium or carbon dioxide, and the flow rate of the gas is 15-25 mL / min.

24. The method of claim 20, wherein, The oven drying is performed at a temperature of 40-80 °C.

25. The method of claim 1, wherein, The preparation method comprises the following steps: (I) crushing black phosphorus to obtain crushed black phosphorus; (II) mixing mesocarbon microbeads with a D50 of 8-35 μm and the crushed black phosphorus for 5-10 h, and then performing drying in an inert atmosphere at a temperature of 40-80 °C to obtain a composite material; The mass content of the black phosphorus is 5-15% based on the total mass of the graphite and the black phosphorus; (III) mixing a saccharide compound and a solvent to obtain a solution; The solvent comprises water and ethylene glycol, and the volume ratio of water to ethylene glycol is (0.3-1):(0.1-0.7). (IV) mixing the composite material and the solution, and hydrothermally reacting at 125-175 ℃ for 8-12 h, then dispersing and drying at 40-80 ℃ to obtain the black phosphorus-based composite negative electrode material; The mass ratio of the composite material to the sugar compound in the solution is 100:(0.5-1.5).

26. A black phosphorus-based composite anode material, characterized in that, The black phosphorus-based composite negative electrode material is prepared by the preparation method in any one of claims 1-25. The black phosphorus-based composite negative electrode material comprises a graphite / black phosphorus composite material core and a carbon coating layer on the surface of the core.

27. A lithium-ion battery, characterized by The lithium ion battery comprises the black phosphorus-based composite negative electrode material in the negative electrode.

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