CN115692662B - A kind of preparation method of aluminum and rare earth co-coated graphite negative electrode composite material - Google Patents

Abstract

The invention discloses a method for preparing an aluminum and rare earth co-coated graphite negative electrode composite material, comprising: adding aluminum powder, an aluminum-based coupling agent, a rare earth compound, and a complexing agent to a solvent to disperse uniformly to obtain a solution A; Add graphite and reducing agent to deionized water and disperse evenly to obtain solution B; add solution A, solution B and its organic alkaline solution through a three-necked flask at the same time, and at a temperature of 50‑150 ° C, a pressure of ‑0.01 to ‑0.09 Carry out coprecipitation reaction under the condition of Mpa for 1-6h, filter, vacuum-dry the filter residue, and carbonize at a temperature of 700-1100°C for 1-6h to obtain the product. The invention improves the first-time efficiency and fast charging performance of the graphite material.

Description

A kind of preparation method of aluminum and rare earth co-coated graphite negative electrode composite material

technical field

The invention belongs to the field of preparation of lithium ion battery materials, in particular to a method for preparing aluminum and rare earth co-coated graphite negative electrode composite materials.

Background technique

As the market's requirements for the energy density of lithium iron phosphate batteries increase, it is required that lithium-ion batteries have high energy density and the fast charging performance of materials should also be improved. The anode material is the key material that affects the energy density of the battery and its fast charging performance. At present, the anode material in the market is mainly artificial graphite, which mainly improves the initial efficiency by coating soft carbon or hard carbon on the graphite surface. Fast charging performance, but due to the low initial efficiency of soft carbon or hard carbon materials (80-85%), the initial efficiency of the graphite negative electrode material is about 92%, while the initial efficiency of the positive electrode material lithium iron phosphate is about 96%. Materials have become the main reason for the low efficiency of lithium iron phosphate batteries for the first time, affecting the improvement of their energy density. Therefore, in order to increase the energy density of lithium iron phosphate batteries, it is necessary to increase the first-time efficiency of graphite materials. Improve the first efficiency of graphite materials mainly through the following measures: 1) reduce the surface defects of graphite materials and reduce the lithium ions consumed by the formation of SEI film, but the increase is not large; 2) coating aluminum oxide and other metal oxides, but will cause Impedance increases and energy density is reduced; 3) Coating fast ion conductors, but processing problems are difficult and the cost is high. For example, patent application No. 202110661595.5 discloses a network-shaped γ-alumina coated modified graphite negative electrode material, its preparation method and its application, which uniformly coats aluminum salt by sol-gel method at high temperature and normal pressure On the surface of the graphite negative electrode; the obtained coated precursor is vacuum-dried; after drying, the product is obtained by calcining at a high temperature. Although the first-time efficiency and high-temperature performance are improved, the kinetic performance and rate performance of the material are reduced due to the coating of alumina, and the reaction efficiency is low under normal pressure, which is not conducive to the promotion of industrialization.

Contents of the invention

The purpose of the present invention is to overcome the above disadvantages and provide a method for preparing an aluminum and rare earth co-coated graphite negative electrode composite material that improves the first-time efficiency and fast charge performance of graphite materials.

A kind of preparation method of aluminum and rare earth co-coated graphite negative electrode composite material of the present invention, comprises the following steps:

Step S1: According to the mass ratio of 1-10: 1-10: 1-5: 1-5: 500, weigh aluminum powder, aluminum-based coupling agent, rare earth compound, complexing agent and organic solvent and disperse evenly to obtain solution A ;

Step S2: according to the mass ratio of 100:1-5:500-1000, graphite, reducing agent and organic solvent thereof are uniformly dispersed to obtain solution B;

Step S3: According to solution A:solution B:organic lye mass ratio=500:500-1000:100, add simultaneously through a three-necked flask, and react 1 at a temperature of 50-150°C and a pressure of -0.01～-0.09Mpa -6h, filter, and vacuum-dry the filter residue at 80°C for 24h, carbonize at a temperature of 700-1100°C for 1-6h, and obtain aluminum and rare earth co-coated graphite negative electrode composite material.

The aluminum-based coupling agent in the step S1 is one of distearoyloxyisopropyl aluminate, triisopropyl aluminate or tribenzyl aluminate.

The rare earth compound in the step S1 is one of the oxides of cerium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium or scandium.

The complexing agent in the step S1 is one of tetraammine copper sulfate, potassium tetraiodide mercurate or tetraammine zinc sulfate.

The reducing agent in the step S2 is one of anhydrous hydrazine, methyl hydrazine or ethyl hydrazine.

The organic solvent in the step S1 and step S2 is one of isopropanol, butanediol or xylene.

The organic lye in the step S3 is one of dimethylamine, trimethylamine and N,N-dimethylethanolamine.

Compared with the prior art, the present invention has obvious beneficial effects. It can be seen from the above technical schemes that: the present invention deposits alumina on the graphite surface by co-deposition to improve the first efficiency, and through the deposition of metal aluminum and rare earth compounds with strong electronic conductivity characteristics, reduce impedance and improve power performance; at the same time, use aluminum-based coupling agent to form a three-dimensional network structure of metal aluminum and rare earth compounds, improve the structural stability of the material during charge and discharge, and improve cycle performance. Through the chemical reaction of complexing agent, reducing agent and organic base, alkaline colloid is deposited on the surface of graphite, carbonized to obtain metal oxide, and coated on the surface of graphite to form a thin film structure, which reduces impedance and improves cycle performance.

Description of drawings

FIG. 1 is a SEM image of the aluminum-coated graphite negative electrode composite material prepared in Example 1.

Detailed ways

Example 1

A preparation method of aluminum and rare earth co-coated graphite negative electrode composite material, comprising the steps: Step S1: taking 5g of aluminum powder, 5g of distearoyloxyisopropylaluminate, 3g of cerium oxide, 3g of tetraammonium sulfate After copper alloy and 500g isopropanol are uniformly dispersed, solution A is obtained;

Step S2: After weighing 100g of artificial graphite, 3g of anhydrous hydrazine and 800g of isopropanol and mixing them uniformly, obtain solution B;

Step S3: Add 500g of solution A, 800g of solution B and 100g of dimethylamine solution simultaneously through a three-necked flask, react at a temperature of 100°C and a pressure of -0.05Mpa for 3h, filter, and vacuum-dry the filter residue at 80°C for 24h , and carbonized at a temperature of 900°C for 3h, that is.

Example 2

A preparation method of aluminum and rare earth co-coated graphite negative electrode composite material, comprising the steps of:

Step S1: After weighing 1g of aluminum powder, 1g of triisopropyl aluminate, 1g of samarium oxide, 1g of potassium tetraiodide mercurate and 500ml of butanediol and dispersing evenly, a solution A was obtained;

Step S2: Mix 100g artificial graphite, 1g methylhydrazine and 500g butanediol thereof to obtain solution B;

Step S3: Add 500g of solution A, 500g of solution B and 100g of trimethylamine solution simultaneously through a three-necked flask, and react at a temperature of 50°C and a pressure of -0.09Mpa for 6h, then filter, and vacuum-dry the filter residue at 80°C for 24h , and carbonized at a temperature of 700 ° C for 6 hours, that is.

Example 3

A preparation method of aluminum and rare earth co-coated graphite negative electrode composite material, comprising the steps of:

Step S1: After weighing 10g of aluminum powder, 10g of tribenzyl aluminate, 5g of europium oxide, 5g of tetraamminezinc sulfate and 500g of xylene and dispersing them uniformly, a solution A was obtained;

Step S2: 100g artificial graphite, 5g ethylhydrazine and 1000g xylene are mixed uniformly to obtain solution B;

Step S3: Add solution A, solution B and 100 g of N,N-dimethylethanolamine simultaneously through a three-necked flask, and react at a temperature of 150°C and a pressure of -0.01Mpa for 1h, filter, and vacuum the filter residue at 80°C Dry for 24 hours, and carbonize for 1 hour at a temperature of 1100°C.

Comparative example 1:

A preparation method of graphite negative electrode composite material, comprising the steps of:

Step S1: after weighing 3g of cerium oxide, 3g of tetraammine copper sulfate and 500g of isopropanol and dispersing evenly, obtain solution A;

Step S2: take 100g artificial graphite, 3g anhydrous hydrazine and 800g isopropanol and mix them uniformly to obtain solution B;

Step S3: Then add 500g of solution A, 800g of solution B and 100g of dimethylamine solution simultaneously through a three-necked flask, and react at a temperature of 100°C and a pressure of -0.05Mpa for 3h, then filter and vacuum dry at 80°C for 24h , and carbonized at a temperature of 900° C. for 3 hours to obtain a graphite negative electrode composite material.

Comparative example 2:

A preparation method of an aluminum-coated graphite negative electrode composite material, comprising the steps of:

Step S1: Weigh 5g of aluminum powder and 5g of distearoyloxyisopropyl aluminate and add it to 500g of isopropanol to disperse evenly to obtain solution A;

Step S2: take 100g artificial graphite and add to 800g isopropanol and mix uniformly to obtain solution B;

Step S3: Add solution A, solution B and 100 g of dimethylamine solution simultaneously through a three-necked flask, and react at a temperature of 100°C and a pressure of -0.05Mpa for 3h, then filter, vacuum dry at 80°C for 24h, and Carbonize at a temperature of 900° C. for 3 hours to obtain an aluminum-coated graphite negative electrode composite material.

Performance Testing:

(1) SEM test

Figure 1 is the SEM image of the aluminum and rare earth co-coated graphite negative electrode composite material prepared in Example 1. It can be seen from the figure that the surface of the material has a microporous structure with a uniform size and a particle size D50 of about 15 μm.

(2) Physical and chemical performance test

The oil absorption values of the graphite negative electrode composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were tested to characterize the ability of the materials to absorb electrolyte. Measure according to the method in GB/T-7046-2003 "Determination of Absorption Value of Pigment Carbon Black Dibutyl Phthalate", and test the composite material according to GB/T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries" The specific surface area, tap density and electrical conductivity of the powder. The test results are shown in Table 1.

Table 1

As can be seen from Table 1, the oil absorption value of the aluminum and rare earth co-coated graphite negative electrode composite material prepared by the present invention is significantly higher than that of the comparative example, which can improve the ability of the material to absorb electrolyte, so that the lithium-ion battery has better cycle performance and rate performance. At the same time, because the embodiment is doped with metal aluminum powder and its rare earth metal compound with high electronic conductivity, the conductivity of the powder is improved.

(3) Button battery charge and discharge performance test

The graphite negative electrode composite materials in Examples 1-3 and Comparative Examples 1-2 were assembled into button batteries respectively. The assembly method included: adding binder and solvent to the composite materials, stirring and pulping, and then coating on copper foil After being dried and rolled, pole pieces are obtained. Wherein, the binder used is PVDF binder, the solvent is NMP, and its dosage ratio is graphite: PVDF:NMP=80g:20g:300ml; Electrolyte is LiPF ₆ /EC+DEC (EC, DEC volume ratio 1:1 , the concentration of LiPF ₆ is 1.3mol/L), the metal lithium sheet is used as the counter electrode, and the separator is made of polyethylene propylene (PEP) composite film, which is assembled in an argon-filled glove box.

The electrochemical performance was carried out on a Wuhan Landian 5V/10mA battery tester, the charge and discharge voltage range was 0.005V to 2.0V, and the charge and discharge rate was 0.1C. At the same time, the rate and cycle performance of the material are tested, the discharge rate is 0.1C/0.2C/0.5C/1.0C, and the rate performance of 1C/0.1C is calculated; at the same time, it is tested at 0.2C/0.2C, 0.005V -2V, 25±3℃ cycle performance. The test results are shown in Table 2.

Table 2

It can be seen from Table 2 that the discharge capacity and efficiency of the batteries made of the composite materials obtained in Examples 1-3 are significantly higher than those of the comparative examples. This is because doping the rare earth compound and its aluminum powder in the composite material reduces its irreversible capacity loss and improves the electronic conductivity of the material, which improves the first efficiency and rate performance of the material; at the same time, the embodiment material has a high specific surface area and improves liquid retention. Performance, and improve the recycling performance of materials.

(4) Soft pack battery test

The graphite negative electrode composite materials obtained in Examples 1-3 and Comparative Examples 1-2 were used as the negative electrode material, lithium iron phosphate was used as the positive electrode material, and LiPF ₆ /EC+DEC (volume ratio 1:1) was used as the electrolyte, Celgard 2400 The membrane is a separator, and 5Ah pouch batteries C1, C2, C3, D1, and D2 are prepared. And test the cycle performance, rate performance and safety performance of its pouch battery.

4.1 Rate performance test conditions: charge rate: 1C/2C/3C/5C, discharge rate 1C; voltage range: 2.5-3.65V, test the charging constant current ratio of the battery, the test results are shown in 3.

4.2 The cycle test conditions are 1C/1C, 2.5-3.65V, temperature: 25±3°C, and the number of cycles is 500 cycles. The test results are shown in Table 3.

table 3

It can be seen from Table 3 that the capacity and capacity retention rate of the pouch battery prepared by using the graphite negative electrode composite materials obtained in Examples 1 to 3 after multiple cycles are higher than those of the comparative example, and the capacity decay rate and decay rate are significantly lower than those of the comparative example. Proportion. The experimental results show that the battery obtained by using the negative electrode material of the present invention has good cycle performance. The reason is that: the oxide with high density and its metal element doping are deposited on the graphite surface by the precipitation method, which reduces the impedance and improves the constant current ratio; simultaneously deposits The material has structurally stable properties, thereby improving cycle performance. At the same time, the material of the embodiment has the characteristic of high electrical conductivity of the powder, and the constant current ratio is improved, that is, the rate performance is improved.

4.3 Acupuncture experiment

Take 10 batteries each of Example 1-3 and Comparative Example 1-2. After the battery is fully charged, use a nail with a diameter of 5mm to pass through the center of the battery, and install a temperature tester at the pole of the battery, and put the nail Stay in the battery, observe the battery condition and measure the battery temperature. The test results are shown in Table 4.

Table 4

Example temperature(℃) Is it on fire Example 1 105 no Example 2 109 no Example 3 112 no Comparative example 1 204 yes Comparative example 2 156 yes

It can be seen from Table 4 that because the materials in Examples 1 to 3 contain flame-retardant materials such as alumina and its aluminum powder, the reason is that the local temperature of the battery is too high when the battery is in abnormal use such as short circuit, while the materials in Examples Poor thermal diffusion performance, thus improving the temperature rise during acupuncture experiments.

4.4 Impact test:

Take 10 batteries of each of Example 1-3 and Comparative Example 1-2. After fully charged, place a hard rod with a diameter of 16.0mm horizontally on the battery, and drop it with a 20-pound weight from a height of 610mm. On the hard stick, observe the condition of the battery. The test results are detailed in Table 5.

table 5

As can be seen from Table 5, the lithium-ion battery prepared by the embodiment is obviously inferior to the comparative example in the impact test. The reason is that the negative electrode graphite material of the embodiment battery contains aluminum oxide compounds. When the battery temperature is too high during the battery impact process, the battery The impedance of the battery increases instantaneously, blocking the thermal runaway of the battery and improving its safety performance.

The above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (6)

1. The preparation method of the aluminum and rare earth co-coated graphite negative electrode composite material comprises the following steps:

step S1, according to the mass ratio of 1-10:1-10:1-5:1-5: weighing aluminum powder, an aluminum-based coupling agent, a rare earth compound, a complexing agent and an organic solvent, and uniformly dispersing to obtain a solution A;

step S2, according to the mass ratio of 100:1-5: dispersing graphite, a reducing agent and an organic solvent of the reducing agent uniformly in 500-1000 to obtain a solution B;

step S3, according to the solution A: solution B: organic lye mass ratio = 500:500-1000:100 is added through a three-neck flask at the same time, reacts for 1-6h under the conditions that the temperature is 50-150 ℃ and the pressure is minus 0.01-minus 0.09Mpa, is filtered, and filter residues are dried for 24h under the vacuum condition at 80 ℃ and carbonized for 1-6h at the temperature of 700-1100 ℃ to obtain the composite material;

wherein: the rare earth compound in the step S1 is one of oxides of cerium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium or scandium.

2. The method for preparing the aluminum and rare earth co-coated graphite anode composite material according to claim 1, wherein: the aluminum-based coupling agent in the step S1 is one of distearyl oxyisopropyl aluminate, triisopropyl aluminate or tribenzyl aluminate.

3. The method for preparing the aluminum and rare earth co-coated graphite anode composite material according to claim 1, wherein: the complexing agent in the step S1 is one of copper tetramine sulfate, potassium mercuric tetraiodide or zinc tetramine sulfate.

4. The method for preparing the aluminum and rare earth co-coated graphite anode composite material according to claim 1, wherein: the reducing agent in the step S2 is one of anhydrous hydrazine, methyl hydrazine or ethyl hydrazine.

5. The method for preparing the aluminum and rare earth co-coated graphite anode composite material according to claim 1, wherein: the organic solvent in the step S1 and the step S2 is one of isopropanol, butanediol or xylene.

6. The method for preparing the aluminum and rare earth co-coated graphite anode composite material according to claim 1, wherein: the organic alkali liquor in the step S3 is one of dimethylamine, trimethylamine and N, N-dimethylethanolamine.