CN102593439B - Silicon-based composite material for lithium ion battery and preparation method of silicon-based composite material - Google Patents

Abstract

The invention discloses a silicon-based composite material for lithium-ion battery negative poles and a preparation method thereof, belonging to the technical field of lithium-ion battery negative pole materials. The composite material is marked as Si-MC, including nano-silicon, non-graphitizable carbon and metal, and contains trace amounts of N, S and Na elements. Its preparation method is to ultrasonically disperse silicon powder, metal phthalocyanine, pyrazine and sodium lauryl sulfate in N,N-dimethylformamide solvent; Heating in a pressure reactor; next, the above-mentioned thermal polymerization product was vacuum rotary evaporated to remove the organic solvent; the obtained solid powder was dried in a vacuum oven and then heat-treated under the protection of an argon atmosphere to finally obtain a Si-MC composite. The prepared composite material has a stable and reversible specific capacity of at least 700mAhg ^-1 in the voltage range of 0.05V-3.0V and a charge-discharge rate of 100mAg ^-1 , which has a good application prospect.

Description

Silicon-based composite material for negative electrode of lithium ion battery and preparation method thereof

technical field

The invention belongs to the field of lithium ion battery materials, and in particular relates to a silicon-based negative electrode material and a preparation method thereof.

Background technique

Lithium-ion batteries have become one of the research and development hotspots in the energy field because of their advantages such as high working voltage, high specific energy, no memory effect, and little environmental pollution. With the development of society and technology, people put forward higher requirements on the performance of lithium-ion batteries, and electrode materials play a key role in the improvement of battery performance. At present, the commercial negative electrode is mainly made of graphite materials, and its theoretical capacity is only 372mAhg ^-1 , and the capacity will be lower in practical application. In this case, it is of great significance to study anode materials for lithium-ion batteries with higher capacity and better cycle performance.

Si can form Li ₂₂ Si ₅ alloy with Li, and the theoretical capacity can reach 4200mAhg ^-1 , which is much higher than that of graphite negative electrode; the average potential of silicon to Li ⁺ /Li is 0.25V, and the pairing with the positive electrode can ensure the high voltage of the battery; Silicon is rich in reserves and environmentally friendly. Therefore, silicon is a promising anode material for lithium-ion batteries. However, during the charge-discharge cycle of silicon, the volume will change drastically, destroying the structure of the material, causing the electrode to be pulverized, and deteriorating the cycle performance of the electrode. On the other hand, the initial efficiency of silicon anodes is usually very low, which limits their practical applications. At present, the methods commonly used in the literature to improve the electrochemical performance of silicon electrodes can be divided into two categories: one is to use silicon and carbon in combination, and use the carbon layer as a protective layer and buffer matrix to inhibit the agglomeration of silicon and buffer its volume change, thereby To maintain the cycle stability of the electrode; the second is to use metal doping to provide a conductive network, thereby improving the charge transfer reaction between silicon and lithium, so as to enhance the electrochemical performance of silicon electrodes.

However, traditional carbon-coated silicon methods, such as arc discharge, laser deposition, and chemical vapor deposition, usually use complex equipment, high energy consumption, high cost, and cumbersome operations, making it difficult to achieve large-scale production. Other carbon sources are toxic organic reagents, which require high operating conditions and are likely to cause environmental pollution. Although pure metal doping improves the conductivity of the electrode, it often cannot achieve better cycle performance.

Contents of the invention

The object of the present invention is to provide a silicon-based composite material with high efficiency, high specific capacity and good cycle stability for the first time and a method for preparing the material in view of the deficiencies in the prior art.

The silicon-based composite material for the lithium ion battery negative electrode prepared by the present invention is marked as Si-M-C, mainly includes nano-silicon, non-graphitizable carbon and metal, and the mass content of silicon in the composite material is in the range of 20% to 60%. It also contains trace elements of N, S and Na, and the mass ratio of these three elements in the composite material is less than 1%. Among them, the average particle size of silicon is 50nm, which is the main active material for lithium intercalation and desorption, and is evenly dispersed in the non-graphitized carbon layer; non-graphitized carbon is not only an active material, but also buffers the volume change when silicon intercalates and delithiates Function; M is Co, Fe or Mn, and exists in the form of metal element or Si-M alloy, which improves the conductivity of the electrode.

The preparation method of Si-M-C composite material provided by the invention specifically comprises the following steps:

1) Mix silicon powder and metal phthalocyanine according to a certain mass ratio, add a certain amount of pyrazine and sodium lauryl sulfate, and ultrasonically disperse them in N,N-dimethylformamide solvent;

2) Transfer the liquid obtained in step (1) into a self-pressurized reaction kettle with a polytetrafluoroethylene liner, and then place the reaction kettle in an oven at 150° C. to 180° C. for 3 to 6 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) The solid powder obtained in step 3) is heat-treated for 1 h under the protection of an argon atmosphere at a temperature of 600° C. to 800° C. to finally obtain a Si-M-C composite.

Wherein, the silicon described in step 1) is nano-silicon powder with an average particle diameter of 50nm; the metal phthalocyanine is one of iron phthalocyanine, cobalt phthalocyanine or manganese phthalocyanine; the purity of metal phthalocyanine is more than 90%. The mass ratio of silicon powder to metal phthalocyanine is between 1:2 and 1:8; the molar ratio of metal phthalocyanine to pyrazine is 1:2; the molar ratio of metal phthalocyanine to sodium lauryl sulfate is 10 : 1. The argon purity described in step 4) is above 99%.

Compared with the prior art, the present invention has the following advantages:

1) In the Si-MC composite material prepared by the present invention, the combination of Si and metal and its C is more firm, so that Si has a good conductive network and is present in a good buffer matrix, ensuring that the composite material It has good electrochemical performance; if the prepared composite material is in the voltage range of 0.05V ~ 3.0V, under the charge and discharge rate of 100mAg ^-1 , its stable and reversible specific capacity can reach at least 700mAhg ^-1 , which has a good Application prospect.

2) The process of preparing the Si-M-C composite material in the present invention is simple, and the metal doping and carbon coating of silicon can be realized in one step, which is suitable for large-scale production.

Description of drawings

The X-ray diffraction figure of prepared sample and commercial nano silicon powder in Fig. 1, embodiment 1,2,3;

The transmission electron microscope figure of prepared sample and commercial nano silicon powder in Fig. 2, embodiment 1,2,3;

(a) Si; (b) Si-Co-C; (c) Si-Fe-C and (d) Si-Mn-C;

The charge-discharge cycle performance figure of prepared sample and commercial nano-silicon powder in Fig. 3, embodiment 1, 2, 3;

Figure 4, the charge-discharge cycle performance graph of the sample prepared in Example 4.

Detailed ways

Example 1

1) Weigh about 0.11g of silicon powder, 0.55g of cobalt phthalocyanine, 0.16g of pyrazine and 0.028g of sodium dodecylsulfonate, dissolve them in 35mL of N,N-dimethylformamide, and stir them ultrasonically for 60 minutes ;

2) Transfer the liquid obtained in step (1) into a self-pressurized reaction kettle with a polytetrafluoroethylene liner, and then place the reaction kettle in an oven at 160° C. for 4.5 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) The solid powder obtained in step 3) was heat-treated for 1 h under the protection of an argon atmosphere at a temperature of 700° C. to finally obtain a Si-Co-C composite.

Example 2

1) Weigh about 0.11 g of silicon powder, 0.55 g of iron phthalocyanine, 0.16 g of pyrazine and 0.028 g of sodium dodecylsulfonate, dissolve them in 35 mL of N,N-dimethylformamide, and stir them ultrasonically for 60 minutes ;

2) Transfer the liquid obtained in step (1) into a self-pressurized reaction kettle with a polytetrafluoroethylene liner, and then place the reaction kettle in an oven at 160° C. for 4.5 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) The solid powder obtained in step 3) is heat-treated for 1 h under the protection of an argon atmosphere at a temperature of 700° C. to finally obtain a Si-Fe-C composite.

Example 3

1) Weigh about 0.11 g of silicon powder, 0.55 g of manganese phthalocyanine, 0.16 g of pyrazine and 0.028 g of sodium dodecylsulfonate, dissolve them in 35 mL of N,N-dimethylformamide, and stir them ultrasonically for 60 minutes ;

2) Transfer the liquid obtained in step (1) into a self-pressurized reaction kettle with a polytetrafluoroethylene liner, and then place the reaction kettle in an oven at 160° C. for 4.5 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) The solid powder obtained in step 3) was heat-treated for 1 h under the protection of an argon atmosphere at a temperature of 700° C. to finally obtain a Si-Mn-C composite.

Example 4

1) Weigh about 0.07 g of silicon powder, 0.56 g of cobalt phthalocyanine, 0.16 g of pyrazine and 0.028 g of sodium dodecylsulfonate and dissolve them in 35 mL of N,N-dimethylformamide, and stir ultrasonically for 60 minutes ;

2) Transfer the liquid obtained in step (1) into a self-pressurized reaction kettle with a polytetrafluoroethylene liner, and then place the reaction kettle in an oven at 160° C. for 5 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) The solid powder obtained in step 3) is heat-treated for 1 h under the protection of an argon atmosphere at a temperature of 700 ° C to finally obtain a Si-Co-C composite

Example 5

1) Weigh about 0.55 g, 0.11 g of silicon powder, 0.11 g of iron phthalocyanine, 0.16 g of pyrazine and 0.028 g of sodium dodecylsulfonate, dissolve them in 35 mL of N,N-dimethylformamide, and stir them ultrasonically for 60 minutes ;

2) Transfer the liquid obtained in step (1) into a self-pressurized reactor with a polytetrafluoroethylene liner, and then place the reactor in an oven at 180° C. for 4.5 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) The solid powder obtained in step 3) is heat-treated for 1 h under the protection of an argon atmosphere at a temperature of 700° C. to finally obtain a Si-Fe-C composite.

Example 6

1) Weigh about 0.11 g of silicon powder, 0.55 g of manganese phthalocyanine, 0.16 g of pyrazine and 0.028 g of sodium dodecylsulfonate, dissolve them in 35 mL of N,N-dimethylformamide, and stir them ultrasonically for 60 minutes ;

2) Transfer the liquid obtained in step (1) into a self-pressurized reaction kettle with a polytetrafluoroethylene liner, and then place the reaction kettle in an oven at 160° C. for 4.5 hours;

3) The above thermal polymerization product is vacuum rotary evaporated to remove the organic solvent, and then dried in a vacuum oven at 80°C;

4) Heat-treat the solid powder obtained in step 3) under the protection of an argon atmosphere for 1 h at a temperature of 800° C. to finally obtain a Si-Mn-C composite

Fig. 1 is the X-ray diffraction pattern of sample and commercial nano silicon powder prepared in embodiment 1,2,3. It can be seen from the figure that there are six characteristic diffraction peaks of silicon, and the 2θ values are 28.6°, 47.5°, 56.2°, 69.3°, 76.6° and 88.2° respectively. The broad diffraction peak marked by △ corresponds to non-graphitizable carbon; the diffraction peak marked by * corresponds to Co; the diffraction peak marked by ◆ corresponds to Fe ₂ Si; The marked diffraction peaks correspond to MnSi.

Fig. 2 is the transmission electron microscope picture of the sample prepared in embodiment 1, 2, 3 and commercial nano silicon powder. It can be seen from the figure that Si nanoparticles are dispersedly embedded in the carbon layer of the prepared Si-M-C composite.

The electrochemical performance evaluation of the silicon-based composite material prepared in the present invention and commercial silicon powder as a reference is carried out on a Xinwei tester by using a CR2032 button cell. In the electrode preparation, the obtained Si-MC material (or commercial silicon powder), carbon black (Super P) and sodium alginate were uniformly mixed and slurry-coated on the stainless steel current collector according to the mass ratio of 70:20:10, and then 80 ℃ vacuum oven for 12h. The assembly of the button cell was carried out in a glove box full of argon (the content of water and oxygen was kept below 0.5ppm), the metal lithium sheet was used as the counter electrode and the reference electrode, and the EC/DMC (1: 1wt%) containing _1M LiPF6 ) as the electrolyte, and Whatman GF/D borosilicate glass fiber filter paper as the diaphragm.

Fig. 3 is the charge-discharge cycle performance diagram of samples prepared in Examples 1, 2, and 3 and commercial nano-silicon powder. It can be seen from the figure that compared with the commercial silicon powder, the Si-M-C composite material prepared by the present invention exhibits good cycle stability and can provide a much higher specific capacity than the commercial graphite carbon anode.

FIG. 4 is a charge-discharge cycle performance graph of the sample prepared in Example 4. FIG. It can be seen from the figure that when the mass ratio of silicon powder and cobalt phthalocyanine is 1:8, the prepared composite electrode has a specific capacity of 70 at a charge and discharge rate of 100 mAg ^-1 within a voltage range of 0.05 V to 3.0 V. After the second cycle, it can still keep above 700mAhg ^-1 ; the first efficiency of the electrode is 65%, and it approaches and maintains at 100% from the second cycle.

Claims (3)

1. the preparation method of lithium ionic cell cathode silicon based compound material, described lithium ionic cell cathode silicon based compound material, be labeled as Si-M-C, mainly comprise nano-silicon, ungraphitised carbon and metal, the mass content of silicon in composite material is 20%～60%, the average grain diameter of silicon is 50nm, for main doff lithium active material, is dispersed in non-graphitized carbon-coating; Ungraphitised carbon had both belonged to active material, and the change in volume during again to silicon doff lithium plays cushioning effect; M is Co, Fe or Mn, and existence form is metal simple-substance or Si-M alloy, it is characterized in that, comprises the following steps:

(1) silica flour and metal phthalocyanine are mixed according to certain mass ratio, and add a certain amount of pyrazine and lauryl sodium sulfate, ultrasonic being dispersed in DMF solvent; The mass ratio of silica flour and metal phthalocyanine is between 1:2～1:8; The mol ratio of metal phthalocyanine and pyrazine is 1:2; The mol ratio of metal phthalocyanine and lauryl sodium sulfate is 10:1;

(2) step (1) gained liquid rotating is moved in the self-pressure reactor of polytetrafluoroethylliner liner, then reactor is placed in to 150 ℃～180 ℃ baking ovens and is incubated 3～6 hours;

(3) above-mentioned thermal polymerization product vacuum is revolved to steaming, remove organic solvent, then in 80 ℃ of vacuum drying ovens, dry;

(4) gained pressed powder in step (3) is heat-treated to 1h under argon gas atmosphere protection, temperature is 600 ℃-800 ℃, finally obtains Si-M-C compound.

2. according to the preparation method of claim 1, it is characterized in that, the silicon described in step 1) is nano silica fume, and average grain diameter is 50nm; Metal phthalocyanine is a kind of in iron-phthalocyanine, cobalt phthalocyanine or manganese phthalocyanine; The purity of metal phthalocyanine is more than 90%.

3. according to the preparation method of claim 1, it is characterized in that, the purity of argon described in step 4) is more than 99%.