CN104393299B - Nano-silicon polythiophene conductive composite for lithium ion battery and preparation method thereof - Google Patents

Abstract

The invention provides a nano silicon-polythiophene conductive composite material, which belongs to the technical field of lithium ion batteries. The invention uses nano-silicon as the lithium intercalation active material, thiophene as the conductive monomer, chloroform as the solvent, and anhydrous ferric chloride as the oxidant, and is obtained by in-situ polymerization through a chemical oxidation method. In the composite material, conductive polythiophene is uniformly coated on the surface of silicon nanoparticles, and nano-silicon particles have lithium storage activity. Conductive polythiophene improves the cycle performance of silicon-based electrode materials from both volume effect and conductivity. Experiments have shown that the lithium-ion battery made of it has a specific capacity of about 2300mAh/g for the first discharge, and after 50 charge-discharge tests, the specific capacity still maintains 501mAh/g, so it has good electrochemical cycle performance , has a good prospect in practical applications.

Description

Nano-Si-Polythiophene Conductive Composite Materials for Li-ion Batteries and Its Preparation method

technical field

The invention belongs to the technical field of lithium-ion batteries, and relates to a silicon-based material used for negative electrode materials of lithium-ion batteries; in particular, it relates to a nano-silicon-polythiophene composite material and a preparation method thereof.

Background technique

With the development of science and technology and human progress, the energy crisis and environmental pollution have attracted widespread attention. Traditional energy not only has limited reserves and is non-renewable energy, but also seriously pollutes the environment. Scientists in related fields have been actively looking for new energy. In recent years, power lithium-ion batteries have attracted the attention of researchers. The current commercial lithium-ion battery anode material is mainly graphite with a low theoretical specific capacity (372 mAh/g), which is far from meeting the requirements of high-power electrical appliances. Therefore, electrode materials with high theoretical specific capacity, such as silicon-based and tin-based, have attracted widespread attention of scientists. Silicon-based materials are materials with the highest theoretical specific capacity (4200 mAh/g) among various alloy materials currently being studied. However, the volume change is very large (up to 420%) during the lithium intercalation process, resulting in the crushing destruction of silicon nanostructure materials, and the new energy of the battery drops sharply. Therefore, the current research on silicon-based materials is mainly focused on reducing the volume effect due to the charging and discharging process and increasing the conductivity of silicon-based materials. The main methods to improve the performance of silicon-based materials are: nanometerization, compounding, using new binders, improving current collectors and electrolytes, and the combination of nanometerization and compounding is the main way of research on silicon-based materials.

Since American and Japanese scientists won the Nobel Prize in Chemistry for their discovery of conductive polymers in 2000, research on the application of conductive polymers in electrode materials has become more and more in-depth. Introducing conductive polymers during the preparation of silicon-based electrode materials can not only increase the conductivity of the material, but also reduce the volume change of silicon particles during charge and discharge, greatly improving the cycle stability of silicon-based materials , improving the performance of the battery.

Contents of the invention

The object of the present invention is to prepare a nano-silicon-polythiophene composite material used for lithium-ion battery negative electrode materials in order to solve some problems in the prior art.

Another object of the present invention is to provide a method for preparing the above-mentioned nano-silicon-polythiophene composite material for lithium-ion battery negative electrode materials.

1. Preparation of nano-silicon-polythiophene composites

The nano-silicon-polythiophene composite material of the present invention uniformly coats a layer of conductive polythiophene on the nano-silicon particles. In order to improve the cycle performance of silicon-based materials to the greatest extent, the mass percentage of polythiophene in the composite material was controlled at 7.5-34.2%, and the mass percentage of nano-silicon particles as the active material was controlled at 65.8-92.5%.

The preparation method of the nano-silicon-polythiophene composite material of the present invention is as follows: first disperse silicon particles with a particle diameter of 20 to 160 nm and the oxidizing agent ferric chloride in chloroform, stir well and then add polymerized monomer thiophene dissolved in ethanol, Polymerize under stirring at room temperature for 3~20 hours; after the reaction is completed, filter with suction, wash with absolute ethanol, hydrochloric acid, and deionized water in turn until neutral, dry in vacuum, and grind to obtain the product.

The mass ratio of nano silicon particles to thiophene monomer is 9:1~1:1; the molar ratio of ferric chloride to thiophene monomer is 2:1~6:1.

In the nano-silicon-polymer composite material of the present invention, the nano-silicon particles have lithium storage activity, and the conductive polythiophene improves the cycle performance of the silicon-based electrode material from both volume effect and conductivity.

2. Structural characterization of nano-silicon-polymer composites

1. Infrared spectral analysis

Fig. 1 is the infrared spectrogram of Si, PTh/Si, PTh of the present invention. It can be seen from Figure 1 that 784 cm ^-1 is the CH out-of-plane bending vibration absorption peak of 2,5-disubstituted polythiophene, 1109 cm ^-1 is the CH stretching vibration absorption peak of thiophene ring, 1028 cm ^-1 , 692 cm ^{- 1} are the asymmetric and symmetric stretching vibration absorption peaks of CS, respectively, and 1319 cm ⁻¹ is the asymmetric stretching vibration absorption peak of CC. The absorption peak at 784 cm ^-1 indicates that the oxidative polymerization of thiophene occurs at the α position, and polythiophene polymerized at the α position has better conductivity than the polymerized polythiophene at the β position.

2. XRD spectrum analysis

Fig. 2 is the XRD spectrum of the composite material nano-silicon-polythiophene (Si/PTh), polythiophene (PTh) and Si prepared in the present invention. It can be seen from the spectrum of silicon in Figure 2 that 2θ = 28.4°, 47.2°, 56.1°, 69.1° and 76.3° correspond to (111), (220), (311), (400) and (331 ) crystal plane diffraction peaks. The Si/PTh composite material only shows the crystal plane diffraction peaks of elemental silicon, indicating that the prepared polythiophene is completely amorphous.

3. Thermogravimetric (TG) analysis

Fig. 3 is the thermal weight loss curve of the composite material prepared in the present invention under the flowing air component. It can be seen from Figure 3 that the mass ratio of thiophene monomer in the feeding ratio is 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% and 50 wt.%, respectively, and only 1.0 wt% is actually coated. .% , 7.5 wt.% , 15.2 wt.% , 25.2 wt.% and 34.2 wt.%, the temperature range of the test is from room temperature to 800°C, the test is carried out under the flowing air component, and the heating rate is 10°C/min. It can be seen from the curve that only part of the thiophene monomer undergoes oxidative polymerization. It shows that the Si/PTh composite material has good thermal stability.

4. Scanning electron microscope analysis

Fig. 4 is a scanning electron microscope image of the silicon-based material prepared in the present invention, (a) SEM of Si, (b) SEM of Si/PTh. Comparing Figures a and b, it can be clearly seen that thiophene is uniformly coated on the surface of silicon nanoparticles after polymerization.

5. Transmission electron microscope analysis

Fig. 5 is the transmission and scanning transmission electron microscope images of the composite material prepared in the present invention. (a) is the transmission electron microscope image of the composite material Si/PTh, (b) the scanning transmission electron microscope image of the composite material Si/PTh. (a) The lighter color in the picture is polythiophene, and the darker color and diffraction patterns are nano-silicon particles; (b) The white bright spots in the picture are nano-silicon particles, and the darker material around the bright spots is conductive polythiophene . It is further proved from Fig. 5 that thiophene uniformly covers the surface of silicon particles after polymerization.

3. Electrochemical performance test of nano-silicon conductive polythiophene composites

The prepared silicon polythiophene composite material is smeared on the copper foil according to the mass ratio: composite material: conductive acetylene black: binder=70:20:10 as electrode material, and lithium sheet is used as the counter electrode to make buttons Battery. The electrochemical cycle performance test was carried out at a current density of 100mA/g, and the charge and discharge test was carried out 100 times, and the test voltage range was 0.02~1.5V.

1. Cycle performance test analysis

Fig. 6 is a diagram of the electrochemical cycle performance of the electrode material prepared in the present invention. It can be seen from the cycle curve in Figure 6 that due to the large volume change of the pure nano-silicon electrode during charging and discharging, structural crushing occurs, and the new cycle energy drops sharply; compared with pure silicon nano-silicon electrode material The cycle performance of the electrode has been significantly improved: the first charge-discharge Coulombic efficiency reached 77.9%, and the specific capacity was still close to 501 mAh/g after 50 cycles. The specific capacity decayed rapidly in the first 10 cycles, and the subsequent cycles showed Very good cycle stability.

2. Cyclic voltammetry analysis

Fig. 7 is a cyclic voltammogram of the electrode material prepared in the present invention at a scan rate of 0.1 mv. It can be seen from the curve in Figure 7 that there is an obvious peak at 0.4 V during the first discharge process, which is mainly due to the formation of a solid electrolyte protective film (SEI) during the first lithium intercalation process, which can prevent subsequent cycles due to the electrode material Decomposition of electrolyte and corrosion of nano-silicon due to direct contact with electrolyte. The process of lithium ions and elemental silicon gaining electrons to form lithium-silicon alloy produces a reduction peak; the process of lithium-silicon alloy losing electrons to form lithium ions and elemental silicon produces an oxidation peak. The curves of the first and second cycles are quite different. The difference between the second cycle and the third cycle decreases, indicating that the cycle performance of the electrode material is becoming more and more stable.

In summary, the nano-silicon-polythiophene composite material prepared by the present invention exhibits better cycle performance. The coating layer polythiophene improves the performance of the electrode material from both the volume effect and the conductivity, and its specific capacity is much higher than the theoretical specific capacity of the current commercial negative electrode material graphite, and the preparation process of the electrode material is simple and environmentally friendly. It has the prospect of commercialization in the future.

Description of drawings

Fig. 1 is the infrared spectrogram of Si of the present invention, PTh/Si, PTh;

Fig. 2 is the XRD spectrum of materials Si/PTh, PTh and Si prepared by the present invention;

Fig. 3 is the thermal weight loss curve figure of the composite material prepared by the present invention under the flowing air component;

Fig. 4 is the scanning electron micrograph of the silicon-based material prepared by the present invention;

Fig. 5 is the transmission and the scanning transmission electron micrograph of composite material prepared by the present invention;

Fig. 6 is the electrochemical cycle performance diagram of the prepared electrode material of the present invention;

Fig. 7 is a cyclic voltammogram of the electrode material prepared in the present invention at a scan rate of 0.1 mv.

detailed description

Example 1

The preparation method with a thiophene feeding ratio of 30%: Add 1.7505g nano-silicon powder and 5.7836g anhydrous ferric chloride to 150mL chloroform, stir for 30 minutes, the solution is dark green; dissolve 0.7509g thiophene in 50mL chloroform Use a peristaltic pump to slowly add to the above mixed solution and stir fully at a stirring speed of 350r/min; then oxidatively polymerize at room temperature for 10 hours; after the reaction is completed, filter with suction, wash with absolute ethanol for 3 times, and then wash with 1mol/L hydrochloric acid. Then wash with a large amount of deionized water for several times until the solution becomes neutral, and finally vacuum dry at 50° C. for 10 h to obtain a composite material.

Weigh 0.2810g of composite material, 0.0795g of conductive acetylene black, and 0.0406g of methylcellulose sodium, grind them thoroughly, put the mixed powder in a small beaker, add a little deionized water, stir for 12 hours, and smear on copper foil. Use 2025 button battery case, the separator is PP/PE/PP, 1mol/L LiPF ₆ is used as the electrolyte, the solvent is dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate (molar ratio 1:1:1) And add vinylene carbonate (CV) with a volume ratio of 3% as a stabilizer, use a lithium sheet as a counter electrode, and assemble it into a button battery with a glove box under the protection of argon; the voltage range is 0.02~1.5V, 100mA/ The electrochemical cycle performance test was carried out under g current density. After 50 charge and discharge tests, the specific capacity still remains 501mAh/g.

Example 2

The preparation method with a thiophene feeding ratio of 20%: add 3.0002g nano-silicon powder and 5.7842g anhydrous ferric chloride to 150mL chloroform, stir for 30 minutes, the solution is dark green; dissolve 0.7513g thiophene in 50mL chloroform Use a peristaltic pump to slowly add to the above mixed solution and fully stir at a stirring speed of 350r/min; then oxidatively polymerize at room temperature for 10h. After the reaction, filter with suction, wash with absolute ethanol three times, then wash with 1mol/L hydrochloric acid, and then wash with a large amount of deionized water several times until the solution becomes neutral, and finally vacuum dry at 50°C for 10 hours to obtain a composite material.

Weigh 0.2820g of composite material, 0.0810g of conductive acetylene black, and 0.0410g of methylcellulose sodium, grind them thoroughly, put the mixed powder in a small beaker, add a little deionized water, stir for 12 hours, and smear on copper foil. Use 2025 button battery case, the separator is PP/PE/PP, 1mol/L LiPF ₆ is used as the electrolyte, the solvent is dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate (molar ratio 1:1:1) A 3% volume ratio of vinylene carbonate (CV) was added as a stabilizer, a lithium sheet was used as a counter electrode, and a button battery was assembled in a glove box under the protection of argon. The electrochemical cycle performance test was carried out under the voltage range of 0.02~1.5V and the current density of 100mA/g. After 50 charge and discharge tests, the specific capacity still remains 375mAh/g.

Example 3

The preparation method with a thiophene feeding ratio of 40%: Add 1.1258g of nano silicon powder and 5.7827g of anhydrous ferric chloride into 150mL of chloroform, and stir for 30 minutes to make the solution dark green; dissolve 0.7500g of thiophene in 50mL of chloroform Finally, use a peristaltic pump to slowly add to the above mixed solution and fully stir at a stirring speed of 350r/min; then oxidatively polymerize at room temperature for 10h. After the reaction, filter with suction, wash with absolute ethanol for 3 times, wash with 1mol/L hydrochloric acid, and then wash with a large amount of deionized water for several times until the solution becomes neutral, and finally vacuum-dry at 50°C for 10 hours to obtain a composite material.

Weigh 0.2815g of composite material, 0.0800g of conductive acetylene black, and 0.0399g of methylcellulose sodium, grind them thoroughly, put the mixed powder in a small beaker, add a little deionized water, stir for 12 hours, and smear on copper foil. Use 2025 button battery case, the separator is PP/PE/PP, 1mol/L LiPF ₆ is used as the electrolyte, the solvent is dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate (molar ratio 1:1:1) A 3% volume ratio of vinylene carbonate (CV) was added as a stabilizer, a lithium sheet was used as a counter electrode, and a button battery was assembled in a glove box under the protection of argon. The electrochemical cycle performance test was carried out under the voltage range of 0.02~1.5V and the current density of 100mA/g. After 50 charge and discharge tests, the specific capacity still remains at 224mAh/g.

Claims (2)

1. a kind of preparation method of the nano-silicon-polythiophene conductive composite for lithium ion battery, it is characterised in that：Will 1.7505g nano silica fumes are added in 150mL chloroforms with 5.7836g anhydrous ferric trichlorides, electric stirring 30 minutes, and solution is in dark Green；0.7509g thiophene is dissolved in after 50mL chloroforms and is slowly added in above-mentioned mixed liquor and is sufficiently stirred for using peristaltic pump, stir speed For 350r/min；Then in Oxidation at room temperature polymerization 10h；Reaction terminates rear sucking filtration, with absolute ethanol washing 3 times, then uses 1mol/L Salt pickling, is then most vacuum dried 10h after 50 DEG C, is combined for several times to the aobvious neutrality of solution with a large amount of deionized water wash Material.

2. the preparation method of the nano-silicon-polythiophene conductive composite of lithium ion battery is used for as claimed in claim 1, and which is special Levy and be：The particle diameter of nano silica fume is 20 ~ 160nm.