Method for preparing shape-controllable Fe3O4 / P-doped graphene oxide composite lithium ion battery negative electrode material by pH regulation and control hydrolysis method

Abstract

The invention relates to a method for preparing a shape-controllable Fe3O4 / P-doped graphene oxide composite lithium ion battery negative electrode material through a pH regulation and control hydrolysis method, and belongs to the technical field of new energy materials. According to the method, the nano Fe3O4 anchored phosphorus-doped graphene composite material (pHx-Fe3O4 / PGO, x = 7-14) of a three-dimensional conductive network is constructed through a pH regulation and control hydrolysis reaction and a phosphorus doping in-situ compounding process. The preparation method comprises the following specific implementation steps: 1) taking graphene oxide (GO) dispersion liquid as a matrix, accurately regulating and controlling the pH value (x = 7-14) of a reaction system through ammonia water, and further controlling a hydrolysis reaction to obtain a solution A with different surface charge states; 2) introducing ammonium dihydrogen phosphate into the solution A as a phosphorus source, and carrying out a coordination reaction to form a solution B; and 3) realizing uniform loading of the ferric hydroxide precursor through coordination of ferric chloride hexahydrate and hydroxyl, and performing suction filtration, drying and 300-600 DEG C argon carbonization to form the Fe3O4 / phosphorus-doped graphene heterostructure. The capacity of the obtained material can reach 930.38 mAh / g after 100 times of circulation under the high current density of 2A / g. According to the method, the conductivity and the structural stability are remarkably improved through pH regulation and control of the Fe3O4 morphology in cooperation with the phosphorus doping strategy, and the method is environmentally friendly in process and suitable for industrial production and has important application value in the field of energy storage devices.

Description

Technical Field

[0001] The present invention relates to an electrode material for a lithium-ion battery negative electrode, belonging to the technical field of new energy materials, and specifically to a method for preparing a morphology-controllable Fe3O4 / P-doped graphene oxide composite lithium-ion battery negative electrode material by a pH-controlled hydrolysis method. Background Art

[0002] With the growing demand for renewable energy, the importance of high-performance energy storage devices has become increasingly prominent. Lithium-ion batteries (LIBs) are widely used due to their high energy density and low cost. However, the low theoretical capacity of traditional graphite anode materials limits the improvement of energy density. Therefore, the research on transition metal oxides (TMOs) anode materials with high theoretical capacity and good safety has become a focus. Fe3O4, due to its high theoretical specific capacity (926mAh / g), abundant natural resources and low cost, is considered one of the potential candidates for lithium-ion battery anode materials.

[0003] Fe3O4 still faces numerous challenges and drawbacks in practical applications. First, Fe3O4 has low intrinsic conductivity, which results in slow electron transfer during charge and discharge, thus limiting its rate capability (i.e., its charge and discharge capability at high current densities). Low conductivity can exacerbate electrode polarization, reducing the battery's energy efficiency and power output. Second, during lithium ion insertion and deintercalation, Fe3O4 undergoes significant structural changes and volume expansion (approximately 200%). This volume expansion increases mechanical stress in the electrode material, leading to pulverization and shedding of the electrode material, compromising the integrity of the electrode structure. This not only reduces the battery's cycle life but can also lead to contact failure between the active material and the current collector, increasing the battery's internal resistance. Due to volume expansion and material pulverization, Fe3O4 electrodes experience rapid capacity decay after multiple charge and discharge cycles. Furthermore, Fe3O4 undergoes phase transitions and irreversible reactions during charge and discharge, resulting in loss of active material and a decrease in electrode performance. These issues severely limit the long-term stability of Fe3O4 in practical battery applications. GO is a two-dimensional carbon material whose layered structure consists of covalent carbon bonds, forming a continuous conjugated network, which gives it excellent mechanical strength and flexibility. This enables GO to effectively alleviate the volume expansion problem of Fe3O4. At the same time, GO also has excellent conductivity, which facilitates the rapid transfer of electrons. Its large surface area effectively promotes ion transport at the electrode-electrolyte interface. Previously, CN201610729938.6 prepared a lithium-ion battery anode material with an Fe3O4 / rGO sandwich structure. The combination of these two materials effectively suppressed the volume expansion and material pulverization of Fe3O4, significantly improving the electrochemical performance. However, this patent did not address the effects of the morphology and size of Fe3O4 particles and the distance between graphene layers on the performance of lithium-ion batteries. Therefore, developing a controllable preparation strategy for Fe3O4 nanoparticles with precise morphology and size control, and achieving efficient composite interface construction with the graphene matrix, has important research value for promoting the application of new electromagnetic functional materials in energy storage and conversion, environmental remediation and other fields. Summary of the Invention

[0004] In order to solve the problems described in the background technology, the present invention provides a preparation method of Fe3O4 anchored P-doped graphene oxide composite material based on pH optimization. Ammonia water is used as a precipitant to provide OH - , adjust the pH value, add ferric chloride hexahydrate to introduce iron source, ammonia as a weak base will promote Fe 3+ Hydrolyze to ferric hydroxide. This process will affect the Fe in ferric chloride hexahydrate 3+The formation of nucleation centers affects the nucleation and growth of Fe3O4 nanoparticles. Then, ammonium dihydrogen phosphate is used as the phosphorus source for phosphorus doping. At high temperature, ammonium dihydrogen phosphate decomposes and releases phosphorus. In this process, phosphorus can enter the structure of graphene and form doping. Due to the atomic radius of phosphorus (P), the Larger than the atomic radius of carbon (C) Phosphorus doping can form PC bonds in graphene. The formation of these bonds leads to structural distortion of the hexagonal carbon frame, increasing the interlayer spacing, improving conductivity, and increasing the specific surface area. These factors work together to improve the electrochemical performance of the material. The amount of ammonia added plays a crucial role in the whole process, because Fe 3+ Under alkaline conditions, it will hydrolyze to form ferric hydroxide, which is the key factor in the formation of Fe3O4 nanoparticle nucleation centers. The amount of ammonia can be controlled by the pH value. When the pH value is too low, Fe 3+ and Fe 2+ The hydrolysis reaction is not sufficient, which may lead to incomplete formation of Fe3O4 phase and the generation of undesirable Fe2O3 phase. In addition, the lower pH value slows down the nucleation rate and accelerates the crystal growth rate, which may cause the particle size to increase. However, when the pH value is too high, it may cause particle aggregation and precipitation because of excessive OH - Ions may give the particle surface a stronger negative charge, leading to increased repulsion between particles. At the same time, under extremely alkaline conditions, changes in the morphology and size distribution of Fe3O4 nanoparticles may be observed, such as from spherical to octahedral or needle-shaped. Finally, a pHx-Fe3O4 / PGO composite anode material was successfully prepared through an annealing process. Compared with the Fe3O4 / GO composite material without pH optimization and P doping, the prepared Fe3O4 / particle morphology is more regular, showing a uniform spherical shape and reaching the nanoscale (~340nm) in size. In addition, the successful doping of phosphorus increases the interlayer spacing of graphene (expanded by 108%), allowing the nanoscale Fe3O4 to be successfully anchored into the graphene sheets, which can better alleviate the volume expansion problem of Fe3O4.

[0005] The method comprises the following steps:

[0006] Step 1: diluting the graphene oxide dispersion: diluting the graphene oxide dispersion by adding deionized water to obtain solution A;

[0007] Step 2: pH adjustment: add aqueous ammonia to solution A while adding dropwise while stirring to adjust the pH to different values ​​to obtain solution B;

[0008] Step 3, phosphorus doping process: adding ammonium dihydrogen phosphate to solution B to obtain solution C;

[0009] Step 4: Adding an iron source: Prepare ferric chloride hexahydrate solutions of different concentrations, slowly add them to solution C, and stir thoroughly to obtain solution D; then, under alkaline conditions, the ferric chloride hexahydrate reacts with the components in solution D to generate a Fe(OH)3 precursor;

[0010] Step 5. Preparation of a composite material of nano-sized ferroferric oxide particles anchored with phosphorus-doped graphene oxide: The obtained solution D is filtered to separate the solid product, and the solid powder is then dried and annealed in a tube furnace under an argon atmosphere. The obtained composite is ground, then washed several times with anhydrous ethanol and deionized water, and dried for later use.

[0011] Furthermore, in the step 1, the graphene oxide aqueous solution is diluted to 0.2-0.8% wt., and is subjected to ultrasound and stirring for 1 hour each to fully disperse it.

[0012] Furthermore, in the step 2, ammonia water is added to the graphene oxide to adjust the pH value to different values ​​of 7-14.

[0013] Furthermore, in step 3, the amount of ammonium dihydrogen phosphate added is 1-10 wt.% of the mass fraction of the substances involved in the entire process.

[0014] Furthermore, in step 4, the concentration of ferric chloride hexahydrate is 50-200 mg / ml, and the stirring time is 12-24 hours.

[0015] Furthermore, in step five, the argon gas flow rate is 0.3-1.8 m / s, the tubular furnace heating rate is 1-15°C / min, the annealing temperature is set at 300-600°C, the holding time is 2-6h, the obtained composite is ground, and then washed several times with anhydrous ethanol and deionized water, and dried for use.

[0016] Compared with the prior art, the present invention uses ammonia as a precipitant to provide OH - , thereby promoting Fe 3+ Hydrolyze to ferric hydroxide. Ammonium dihydrogen phosphate is used as a doping phosphorus source. The addition of ammonia water will affect the Fe content in ferric chloride hexahydrate. 3+The pHx-Fe3O4 / PGO composite material finally prepared by the present invention provides a new means for Fe3O4-based lithium-ion batteries. It not only solves the problem that the particles cannot be successfully anchored between the layers due to the small interlayer spacing of graphene oxide, but are instead aggregated on the surface, but also solves the volume expansion problem caused by the uneven morphology and size of the particles of ferroferric oxide, significantly improving the electrochemical stability of the material as a negative electrode material for lithium-ion batteries, and promoting the further development of research and industrialization of nanomaterials in the fields of electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow diagram of the present invention.

[0018] Figure 2 This is the XRD pattern of Example 1 of the present invention.

[0019] Figure 3 This is the SEM of Example 1 of the present invention and a diagram showing the fitting analysis of the particle size. DETAILED DESCRIPTION

[0020] The following describes the implementation of the present invention in detail with reference to specific embodiments. However, these embodiments do not limit the present invention and are merely examples. By way of illustration, the advantages of the present invention will be more clearly understood. All variations that can be directly derived or imagined by a person of ordinary skill in the art from the disclosure of the present invention should be considered to be within the scope of protection of the present invention. The positional relationships described in the embodiments are consistent with those shown in the accompanying drawings, and other parts not described in detail in the embodiments are all prior art.

[0021] Example 1

[0022] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.2 wt.% to obtain solution A;

[0023] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 8 to obtain solution B;

[0024] (3) Then, ammonium dihydrogen phosphate (4 wt.%) was added to solution B to obtain solution C;

[0025] (4) Then, ferric chloride hexahydrate (60 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 12 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0026] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 300°C for 4 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH8-Fe3O4 / PGO composite material.

[0027] (6) The pH8-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0028] Example 2

[0029] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.8 wt.% to obtain solution A;

[0030] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 14 to obtain solution B;

[0031] (3) then adding ammonium dihydrogen phosphate (5 wt.%) to solution B to obtain solution C;

[0032] (4) Then, ferric chloride hexahydrate (70 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 5 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0033] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 300°C for 2 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH14-Fe3O4 / PGO composite material.

[0034] (6) The pH14-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare a negative electrode material. The mixed solution was coated on a copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0035] Example 3

[0036] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.7 wt.% to obtain solution A;

[0037] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 8.5 to obtain solution B;

[0038] (3) Then, ammonium dihydrogen phosphate (4 wt.%) was added to solution B to obtain solution C;

[0039] (4) Then, ferric chloride hexahydrate (100 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 12 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0040] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 500°C for 2 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH8.5-Fe3O4 / PGO composite material.

[0041] (6) The pH8.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0042] Example 4

[0043] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting it to 0.9 wt.% to obtain solution A;

[0044] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 9.5 to obtain solution B;

[0045] (3) Then, ammonium dihydrogen phosphate (3 wt.%) was added to solution B to obtain solution C;

[0046] (4) Then, ferric chloride hexahydrate (90 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 4 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0047] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 500°C for 3 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH9.5-Fe3O4 / PGO composite material.

[0048] (6) The pH9.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0049] Example 5

[0050] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.2 wt.% to obtain solution A;

[0051] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 11.5 to obtain solution B;

[0052] (3) Then, ammonium dihydrogen phosphate (7 wt.%) was added to solution B to obtain solution C;

[0053] (4) Then, ferric chloride hexahydrate (60 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 9 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0054] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 600°C for 3 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH11.5-Fe3O4 / PGO composite material.

[0055] (6) The pH11.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0056] Example 6

[0057] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.6 wt.% to obtain solution A;

[0058] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 9 to obtain solution B;

[0059] (3) then adding ammonium dihydrogen phosphate (2 wt.%) to solution B to obtain solution C;

[0060] (4) Then, ferric chloride hexahydrate (150 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 10 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0061] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 450°C for 3 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH9-Fe3O4 / PGO composite material.

[0062] (6) The pH9-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0063] Example 7

[0064] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.5 wt.% to obtain solution A;

[0065] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 7.5 to obtain solution B;

[0066] (3) then adding ammonium dihydrogen phosphate (8 wt.%) to solution B to obtain solution C;

[0067] (4) Then, ferric chloride hexahydrate (80 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 10 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0068] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 350°C for 2 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH7.5-Fe3O4 / PGO composite material.

[0069] (6) The pH7.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0070] Example 8

[0071] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.5 wt.% to obtain solution A;

[0072] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 13.5 to obtain solution B;

[0073] (3) then adding ammonium dihydrogen phosphate (5 wt.%) to solution B to obtain solution C;

[0074] (4) Then, ferric chloride hexahydrate (80 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 15 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0075] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 400°C for 4 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH13.5-Fe3O4 / PGO composite material.

[0076] (6) The pH13.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0077] Example 9

[0078] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.8 wt.% to obtain solution A;

[0079] (2) adding aqueous ammonia to solution A dropwise while stirring, adjusting the pH to 10.5 to obtain solution B;

[0080] (3) then adding ammonium dihydrogen phosphate (2 wt.%) to solution B to obtain solution C;

[0081] (4) Then, ferric chloride hexahydrate (120 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 10 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0082] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 550°C for 5 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH10.5-Fe3O4 / PGO composite material.

[0083] (6) The pH10.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0084] Example 10

[0085] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.5 wt.% to obtain solution A;

[0086] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 11 to obtain solution B;

[0087] (3) then adding ammonium dihydrogen phosphate (5 wt.%) to solution B to obtain solution C;

[0088] (4) Then, ferric chloride hexahydrate (50 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 20 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0089] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 400°C for 3 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH11-Fe3O4 / PGO composite material.

[0090] (6) The pH11-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0091] Example 11

[0092] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.4 wt.% to obtain solution A;

[0093] (2) adding aqueous ammonia to solution A dropwise while stirring, adjusting the pH to 7 to obtain solution B;

[0094] (3) Then, ammonium dihydrogen phosphate (3 wt.%) was added to solution B to obtain solution C;

[0095] (4) Then, ferric chloride hexahydrate (200 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 15 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0096] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 450°C for 2 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH7-Fe3O4 / PGO composite material.

[0097] (6) The pH7-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0098] Example 12

[0099] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.5 wt.% to obtain solution A;

[0100] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 12.5 to obtain solution B;

[0101] (3) Then, ammonium dihydrogen phosphate (1 wt.%) was added to solution B to obtain solution C;

[0102] (4) Then, ferric chloride hexahydrate (200 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 5 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0103] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed at 550°C in a tube furnace under argon atmosphere for 3 h. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH12.5-Fe3O4 / PGO composite material.

[0104] (6) The pH12.5-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0105] Example 13

[0106] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.8 wt.% to obtain solution A;

[0107] (2) adding aqueous ammonia to solution A dropwise while stirring to adjust the pH to 13 to obtain solution B;

[0108] (3) Then, ammonium dihydrogen phosphate (3 wt.%) was added to solution B to obtain solution C;

[0109] (4) Then, ferric chloride hexahydrate (180 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 15 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0110] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 350°C for 3 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH13-Fe3O4 / PGO composite material.

[0111] (6) The pH13-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0112] Example 14

[0113] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 0.3 wt.% to obtain solution A;

[0114] (2) adding aqueous ammonia to solution A dropwise while stirring, adjusting the pH to 10 to obtain solution B;

[0115] (3) then adding ammonium dihydrogen phosphate (8 wt.%) to solution B to obtain solution C;

[0116] (4) Then, ferric chloride hexahydrate (180 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 5 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0117] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed in a tube furnace at 450°C for 5 h under argon atmosphere. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH11-Fe3O4 / PGO composite material.

[0118] (6) The pH10-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0119] Example 15

[0120] (1) mixing a commercial graphene oxide dispersion with deionized water and diluting the mixture to 1 wt.% to obtain solution A;

[0121] (2) adding aqueous ammonia to solution A dropwise while stirring, adjusting the pH to 12 to obtain solution B;

[0122] (3) Then, ammonium dihydrogen phosphate (10 wt.%) was added to solution B to obtain solution C;

[0123] (4) Then, ferric chloride hexahydrate (200 mg / ml) was added to solution C to obtain solution D. The obtained solution D was stirred for 24 h. Under alkaline conditions, it can react with ferric chloride hexahydrate to form ferric hydroxide;

[0124] (5) The obtained solution D was filtered to separate the solid product, and then the solid powder was dried and annealed at 600°C in a tube furnace under argon atmosphere for 4 h. The obtained material was washed several times with anhydrous ethanol and deionized water, and dried to obtain a pH12-Fe3O4 / PGO composite material.

[0125] (6) The pH12-Fe3O4 / PGO composite material, acetylene black and PVDF were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare the negative electrode material. The mixed solution was coated on copper foil, and the coated copper foil was placed in a vacuum oven at 80°C and dried for 12 hours to obtain a battery electrode.

[0126] The particle size and cycle performance of Fe3O4 in the pHx-Fe3O4 / PGO composite materials prepared in Examples 1-15 are shown in Table 1, and the comparative sample is a Fe3O4 / GO sample.

[0127]

[0128] Example 10 0.34 930.38 Example 11 3.39 392.37 Example 12 1.46 360.97 Example 13 1.73 202.43 Example 14 0.59 531.43 Example 15 1.06 435.92 Comparison sample 4.09 360.97

[0129] Table 1

[0130] Note:

[0131] 1. The cycle current density is 2A / g.

[0132] 2.Fe3O4 / GO is a sample that has not been pH optimized and P doped.

[0133] The above specific embodiments describe in detail the preferred implementation methods of the present invention. However, the present invention is not limited to the specific details in the above implementation methods. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a morphology-controllable Fe3O4 / P-doped graphene oxide composite lithium-ion battery negative electrode material by pH-controlled hydrolysis, which comprises reacting ferric chloride hexahydrate with OH- to achieve controlled growth of an iron hydroxide precursor and increasing the interlayer spacing of the graphene oxide by phosphorus doping. The specific steps are as follows: Step 1: diluting the GO dispersion with deionized water to obtain solution A; Step 2: Add ammonia water to solution A, add dropwise while stirring, and adjust to different pH values ​​to obtain solution B; Step 3, adding ammonium dihydrogen phosphate to solution B to obtain solution C; Step 4: preparing ferric chloride hexahydrate solutions of different concentrations, slowly adding them to solution C, and thoroughly stirring to obtain solution D; then, under alkaline conditions, the ferric chloride hexahydrate reacts with the components in solution D to generate a Fe(OH)3 precursor; Step 5: The obtained solution D is filtered to separate the solid product, and then the solid powder is dried and annealed in a tube furnace under argon atmosphere. The obtained material is washed several times with anhydrous ethanol and deionized water, and dried to obtain pHx-Fe3O4 / PGO; Step 6: The composite material, acetylene black and PVDF are mixed with N-methylpyrrolidone (NMP) in a certain mass ratio to prepare a negative electrode material.

2. The method for preparing the pHx-Fe3O4 / PGO composite material according to claim 1, characterized in that: In the step 1, the graphene oxide aqueous solution is diluted to 0.2-0.8 wt.%, and is subjected to ultrasound and stirring for 1 hour each to fully disperse it.

3. The method for preparing the pHx-Fe3O4 / PGO composite material according to claim 1, wherein: In the step 2, ammonia water is added to the graphene oxide to adjust different pH values ​​(x=7-14).

4. The method for preparing the pHx-Fe3O4 / PGO composite material according to claim 1, characterized in that: In the step 3, the amount of ammonium dihydrogen phosphate added is 1-10 wt.% of the mass fraction of the substances involved in the entire process.

5. The method for preparing the pHx-Fe3O4 / PGO composite material according to claim 1, characterized in that: In the step 4, the concentration of ferric chloride hexahydrate is 50-200 mg / ml, and the stirring time is 12-24 hours.

6. The method for preparing the pHx-Fe3O4 / PGO composite material according to claim 1, characterized in that: In the step 5, the argon gas flow rate is 0.5-1.5 m / s, the tubular furnace heating rate is 1-15° C. / min, the annealing temperature is set at 300-600° C., and the holding time is 2-6 h.

7. The method for preparing the pHx-Fe3O4 / PGO composite material according to claim 1, characterized in that: In the step 1, the composite material, acetylene black and PVDF are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare a negative electrode material.

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