CN115995541A - Hard carbon coated nano silicon oxide composite anode material and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of lithium-ion battery electrode materials, and proposes a hard carbon-coated nano-silicon oxide composite negative electrode material and a preparation method thereof. The composite negative electrode material has a core-shell structure, and the core of the core-shell structure includes nano A silicon/metal oxide composite body, the shell includes hard carbon; the mass of the shell in the composite negative electrode material is 10-50% of the mass of the composite negative electrode material. Through the above technical solution, the problem of poor cycle performance of the battery when the silicon carbon and hard carbon composite material in the prior art is used as the negative electrode of the battery is solved.

Description

A kind of hard carbon coated nano-silicon oxide composite negative electrode material and preparation method thereof

technical field

The invention relates to the technical field of lithium-ion battery electrode materials, in particular to a hard carbon-coated nano-silicon oxide composite negative electrode material and a preparation method thereof.

Background technique

Silicon carbon material has become the preferred anode material for high energy density batteries due to its high energy density (1200-2000mAh/g) and wide range of material sources. However, its large volume expansion (300%) and low temperature performance deviation limit its wide application. The hard carbon material is used in the field of high-rate batteries such as 48V/HEV due to its zero expansion, excellent low-temperature performance, and excellent cycle performance. However, its specific capacity (300mAh/g) and compacted density (1.0g/cm ³ ) Low and can only be used in specific areas. If the silicon carbon material is combined with hard carbon, it can not only reduce the expansion, improve the low temperature, but also increase the energy density. For example, patent application number 202210704738.0 discloses hard carbon-stabilized lithium-silicon alloy negative electrodes and batteries, which mainly introduce hard carbon into LiSi alloy negative electrodes to form a uniform and almost stress-free continuum, lithium-rich phases Li1 ₅ Si ₄ , LiC ₆ The woven three-dimensional lithium-conducting conductive network can effectively increase the active area of the electrode, optimize the kinetic performance of the electrode, and improve the long-term cycle performance of the battery. However, the negative electrode material prepared by this scheme has the disadvantages of deviation in power performance and poor bonding force between materials, and the material is prone to pulverization after a long cycle to reduce cycle performance.

Contents of the invention

The invention proposes a hard carbon-coated nano-silicon oxide composite negative electrode material and a preparation method thereof, which solves the problem of poor cycle performance of the battery when the silicon carbon and hard carbon composite material is used as the negative electrode of the battery in the related art.

Technical scheme of the present invention is as follows:

A hard carbon-coated nano-silicon oxide composite negative electrode material, the composite negative electrode material has a core-shell structure, the inner core of the core-shell structure includes a nano-silicon/metal oxide composite, and the outer shell includes hard carbon; the composite negative electrode The mass of the shell in the material is 10-50% of the mass of the composite negative electrode material.

A method for preparing a hard carbon-coated nano-silicon oxide composite negative electrode material, comprising the following steps:

S1, carbonizing nano-silicon and metal salt after mixing to obtain nano-silicon/metal oxide composite material;

S2. After adding the hard carbon precursor and the nano-silicon/metal oxide composite material to the organic solvent, the mixture is obtained;

S3. After passing through the oxidizing gas, carbonize to obtain a hard carbon-coated nano-silicon oxide composite negative electrode material.

As a further technical solution, the metal salt in the S1 includes tris(2-methylpropyl)aluminum, triisobutylaluminum, aluminum oxide borate, triisopropoxytitanium chloride, titanium carbonyl, ferric ammonium citrate, One of the dihydroxyzirconium carbonates.

As a further technical solution, the mass ratio of nano-silicon to metal salt in S1 is 100:1-10.

As a further technical solution, the mass ratio of the nano-silicon/metal oxide composite material, the hard carbon precursor and the organic solvent in the S2 is 100:50-100:500-2000.

As a further technical solution, the organic solvent in the S2 includes methanol, ethanol, ethylene glycol, n-butanol, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide, and tetrahydrofuran. A kind of; hard carbon precursors include one of glucose, sucrose, lignin, starch, and cellulose.

As a further technical solution, the oxidizing gas in S3 includes one of fluorine gas and chlorine gas.

As a further technical solution, the flow rate of the oxidizing gas in the S3 is 1-10mL/min, and the feeding time is 30-120min.

As a further technical solution, after the oxidizing gas is passed through the S3, it is filtered and then carbonized to obtain a hard carbon-coated nano-silicon oxide composite negative electrode material.

As a further technical solution, the temperature of carbonization in S3 is 600-1000°C, and the time is 1-6h.

Working principle of the present invention and beneficial effect are:

1. The present invention mixes nano-silicon with metal oxides, which can reduce the electronic impedance of nano-silicon, thereby improving the rate performance. At the same time, the outer layer is coated with hard carbon. On the one hand, the characteristics of low self-expansion and excellent low-temperature performance of hard carbon materials are used. Improve the low temperature and expansion of silicon carbon materials. On the other hand, the outer layer passes fluorine or chlorine gas to the hard carbon material to form C-F or C-Cl chemical bonds on the surface, improving the structural stability and defectivity of the material, and improving high-temperature storage. performance and its cycle performance.

2. The metal and amorphous carbon obtained by carbonizing the metal salt in the present invention can improve the electronic conductivity of the material, and the one obtained by polymerization and carbonization has the characteristics of high isotropy and stable structure, which can improve the rate and cycle performance .

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

FIG. 1 is an SEM image of the hard carbon-coated nano-silicon oxide composite negative electrode material prepared in Example 1.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts all involve the protection scope of the present invention.

Example 1

A method for preparing a hard carbon-coated nano-silicon oxide composite negative electrode material, comprising the following steps:

S1, 100g nano-silicon, 100g concentration are obtained suspension in the methanol solution of tris(2-methylpropyl)aluminum of 5wt%, after suspension is spray-dried, carbonize 3h at 950 ℃, obtain nano-silicon/ Alumina composite materials;

S2. After adding 80 g of glucose to 1000 g of methanol to dissolve and disperse evenly, add 100 g of the nano-silicon/alumina composite material prepared above and disperse evenly again to obtain a mixture;

S3. Feed fluorine gas at a flow rate of 5mL/min. After 60 minutes, stop the gas flow, filter and transfer to a tube furnace, carbonize at 800°C for 3 hours, and pulverize to obtain a hard carbon-coated nano-silicon oxide composite negative electrode. Material.

Example 2

A method for preparing a hard carbon-coated nano-silicon oxide composite negative electrode material, comprising the following steps:

S1. Put 100g of nano-silicon and 100g of triisobutylaluminum in a dimethylformamide solution with a concentration of 1wt% to obtain a suspension. After the suspension is spray-dried, it is carbonized at 700°C for 6h to obtain nano-silicon/oxidized Aluminum composite materials;

S2. After adding 50 g of lignin to 500 g of dimethylformamide to dissolve and disperse evenly, add 100 g of the nano-silicon/alumina composite material prepared above and disperse evenly again to obtain a mixture;

S3. Introduce chlorine gas at a gas flow rate of 1 mL/min. After 120 minutes, stop the inflow of gas, filter and transfer to a tube furnace, carbonize at 600°C for 6 hours, and pulverize to obtain a hard carbon-coated nano-silicon oxide composite negative electrode material. .

Example 3

A method for preparing a hard carbon-coated nano-silicon oxide composite negative electrode material, comprising the following steps:

S1, 100g nano-silicon, 100g concentration is obtained in the n-butanol solution of the triisopropoxy titanium chloride of 10wt%, after the suspension is spray-dried, carbonized 1h at 1100 ℃, obtains nano-silicon/ Alumina composite materials;

S2. After adding 100g of cellulose to 2000g of n-butanol solvent to dissolve and disperse evenly, add 100g of the nano-silicon/alumina composite material prepared above and disperse evenly again to obtain a mixture;

S3. Introduce chlorine gas at a gas flow rate of 10mL/min. After 30 minutes, stop the introduction of gas, filter and transfer to a tube furnace, carbonize at 1000°C for 1 hour, and pulverize to obtain a hard carbon-coated nano-silicon oxide composite negative electrode material. .

Example 4

Compared with Example 1, the difference of Example 4 is that the added amount of the methanol solution of tris(2-methylpropyl)aluminum is 300 g.

Comparative example 1

Add 100g of nano-silicon and 80g of glucose into 1000g of methanol organic solvent to dissolve and disperse evenly. After spray drying, carbonize at 800°C for 3h under an argon atmosphere to obtain a silicon-carbon composite material.

Comparative example 2

A method for preparing a hard carbon-coated nano-silicon oxide composite negative electrode material, comprising the following steps:

S1, 100g nano-silicon, 100g concentration are obtained suspension in the methanol solution of tris(2-methylpropyl)aluminum of 5wt%, after suspension is spray-dried, carbonize 3h at 950 ℃, obtain nano-silicon/ Alumina composite materials;

S2. After adding 80 g of glucose to 1000 g of methanol to dissolve and disperse evenly, add 100 g of the nano-silicon/alumina composite material prepared above and disperse evenly again to obtain a mixture;

S3. Transfer the mixture to a tube furnace, feed the mixed gas and carbonize it at 800°C for 3 hours. Carbon-coated nano-silicon oxide composite negative electrode material; the mixed gas is argon and fluorine, and the volume ratio of argon and fluorine is 3:1.

Comparative example 3

Add 100g of nano-silicon and 80g of glucose to 1000g of methanol to dissolve and disperse evenly. After spray drying, fluorine gas is introduced, and then carbonized at 800°C for 3 hours to obtain a silicon-carbon composite material; the flow rate of fluorine gas is 5mL/min. Pass through for 60min.

Test case

(1) SEM test

The hard carbon-coated nano-silicon oxide composite negative electrode material prepared in Example 1 was subjected to SEM testing, and the test results are shown in Figure 1. From Figure 1, it can be seen that the hard carbon-coated nano-silicon oxide composite negative electrode material prepared in Example 1 The negative electrode material is granular and slightly bonded, and the particle size is between 5-10 μm.

(2) Physical and chemical tests

The hard carbon-coated nano-silicon oxide composite negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-3 were tested according to the method in GB/T 38823-2020 "Silicon Carbon" for specific surface area and powder conductivity. Rate and tap density, the results are shown in Table 1.

(3) Physical and chemical tests

Take the composite materials obtained in Examples 1-4 and Comparative Examples 1-3 as negative electrode materials, and test according to the following method: add binder, conductive agent and solvent to the negative electrode material, stir and make slurry, and coat on copper On the foil, the negative electrode sheet is obtained by drying and rolling; the binder used is PVDF, the conductive agent is conductive carbon black (SP), the solvent is N-methylpyrrolidone (NMP), the negative electrode material, SP, PVDF, NMP The dosage ratio is 95g: 1g: 4g: 220mL.

In the electrolyte used, LiPF ₆ is the electrolyte, the concentration is 1.3mol/L, the solvent is a mixture of EC and DEC with a volume ratio of 1:1; the metal lithium sheet is the counter electrode, and the diaphragm is made of polypropylene (PP) film. Assemble the coin cells in a gas-free glove box.

The electrochemical performance was tested on the Wuhan Landian CT2001A battery tester. The charge and discharge voltage range was 0.005V-2.0V, the charge and discharge rate was 0.1C, and the rate performance (2C/0.1C) was tested. The test results As shown in Table 1.

Table 1 Test results

As can be seen from Table 1, the specific capacity and first-time efficiency of the hard carbon-coated nano-silicon oxide composite negative electrode material prepared in Examples 1-3 are significantly better than those of Comparative Example 1 and Comparative Example 3. The reason may be that Examples 1-3 3 The prepared nano-silicon and metal oxide can be fully mixed and uniform, which can reduce the electronic impedance of nano-silicon, improve the rate performance, and improve the specific capacity of the material. Compared with Example 1, Example 4 changed the amount of metal salt added. As a result, the specific capacity and first-time efficiency of the composite material prepared in Example 4 were lower than those in Example 1. Compared with Example 1, fluorine gas and carbonization were carried out simultaneously in Comparative Example 2. As a result, the electrochemical performance of the composite material prepared in Comparative Example 2 was lower than that of Example 1, indicating that carbonization was performed after introducing fluorine gas. The composite material has good electrochemical performance.

(4) Soft pack battery test

The composite material prepared in Examples 1-4 and Comparative Examples 1-3 and artificial graphite are mixed according to the mass ratio of 1:9 as the negative electrode material to make the negative electrode sheet, and the ternary material (Li(Ni _0.6 Co _0.2 Mn _0.2 )O ₂ ) Prepare the positive plate for the positive electrode material; the electrolyte is LiPF ₆ solution, wherein the concentration of electrolyte LiPF ₆ is 1.3mol/L, and the solvent is ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 ) mixture; using Celgard 2400 film as a diaphragm, a 5Ah soft pack battery was prepared.

1) Test of liquid absorption capacity and liquid retention rate

Use a 1mL burette to absorb the electrolyte VmL, drop a drop on the surface of the above-mentioned negative electrode, and count the time until the electrolyte is absorbed, record the time t, and calculate the liquid absorption speed V/t of the electrode. The test results are shown in Table 2.

Calculate the theoretical liquid absorption m ₁ of the negative electrode according to the parameters of the electrode, and weigh the weight of the negative electrode m ₂ , then place the negative electrode in the electrolyte for 24 hours, weigh the weight of the negative electrode as m ₃ , and calculate The liquid absorption capacity of the negative electrode sheet is m ₃ -m ₂ , and is calculated according to the following formula: liquid retention rate=(m ₃ -m ₂ )*100%/m1, and the test results are shown in Table 2.

Table 2 liquid absorption capacity, liquid retention rate test results

It can be seen from Table 2 that the hard carbon-coated nano-silicon oxide composite negative electrode material prepared in Examples 1-3 has significantly higher liquid absorption and retention capacity than Comparative Example 1 and Comparative Example 3, which is mainly due to the fact that Example 1 -3 The prepared hard carbon-coated nano-silicon oxide composite negative electrode material has a high specific surface area, and its carbonization can form a porous structure, thereby improving the liquid absorption and retention capacity of the material. The liquid absorption speed and liquid retention rate of the composite materials prepared in Example 4 and Comparative Example 2 were lower than those in Example 1.

2) Cycle performance test

Test the cycle performance of Examples 1-4 and Comparative Examples 1-3:

The cycle performance of the battery was tested at a temperature of 25±3°C with a charge-discharge rate of 1C/1C and a voltage range of 2.8V-4.2V. The test results are shown in Table 3.

Carry out constant current + constant voltage charging at a rate of 2C, and calculate the constant current ratio of the material, that is, the constant current charging power/(constant current + constant voltage charging power). The test results are shown in Table 3.

Table 3 Cycle performance test results

500 cycles capacity retention (%) 2C constant current ratio Example 1 91.64 93.1% Example 2 90.77 92.8% Example 3 92.39 93.9% Example 4 91.98 91.9% Comparative example 1 85.21 85.6% Comparative example 2 84.23 86.5% Comparative example 3 85.01 84.9%

As can be seen from Table 3, the cycle performance and rate performance of the battery made of the hard carbon-coated nano-silicon oxide composite negative electrode material prepared in Examples 1-3 are significantly better than those of Comparative Example 1, which may be due to the fact that hard carbon materials generally Fluorine gas is added to form C-F chemical bonds on the surface, which can improve the structural stability of the material and improve its cycle performance. However, although comparative example 2 and comparative example 3 were fed with fluorine gas, the cycle performance of the composite material prepared by feeding fluorine gas and carbonization in comparative example 2 and directly mixing all raw materials in comparative example 3 was lower than that of the embodiment. 1. It shows that the composite material prepared by the preparation method of the present invention has good cycle performance.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention within.

Claims (10)

1. The hard carbon coated nano silicon oxide composite anode material is characterized by comprising a core-shell structure, wherein the inner core of the core-shell structure comprises a nano silicon/metal oxide composite body, and the outer shell comprises hard carbon; the mass of the shell in the composite anode material is 10-50% of the mass of the composite anode material.

2. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 1, which is characterized by comprising the following steps:

s1, mixing nano silicon and metal salt, and carbonizing to obtain a nano silicon/metal oxide composite material;

s2, adding a hard carbon precursor and a nano silicon/metal oxide composite material into an organic solvent, and mixing to obtain a mixture;

and S3, introducing oxidizing gas, and carbonizing to obtain the hard carbon coated nano silicon oxide composite anode material.

3. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the metal salt in S1 comprises one of tris (2-methylpropyl) aluminum, triisobutylaluminum, aluminum oxide, triisopropoxytitanium chloride, carbonyl titanium, ferric ammonium citrate and dihydroxydioxyzirconium carbonate.

4. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the mass ratio of nano silicon to metal salt in the S1 is 100:1-10.

5. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the mass ratio of the nano silicon/metal oxide composite material, the hard carbon precursor and the organic solvent in the S2 is 100:50-100:500-2000.

6. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the organic solvent in S2 comprises one of methanol, ethanol, ethylene glycol, N-butanol, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran; the hard carbon precursor comprises one of glucose, sucrose, lignin, starch and cellulose.

7. The method for preparing a hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the oxidizing gas in S3 comprises one of fluorine gas and chlorine gas.

8. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the air flow rate of the oxidizing gas in the step S3 is 1-10mL/min, and the introducing time is 30-120min.

9. The method for preparing the hard carbon coated nano silicon oxide composite negative electrode material according to claim 2, wherein the step S3 is performed with filtering and carbonization after the oxidizing gas is introduced, so as to obtain the hard carbon coated nano silicon oxide composite negative electrode material.

10. The method for preparing the hard carbon coated nano silicon oxide composite anode material according to claim 2, wherein the carbonization temperature in the S3 is 600-1000 ℃ and the time is 1-6h.

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