METHOD FOR PREPARING SILICON-CARBON COMPOSITE, NEGATIVE ELECTRODE, AND LITHIUM ION BATTERY

The present application provides a method for preparing silicon-carbon composite. The silicon-carbon composite prepared according to the present application is suitable to be an active material for negative electrode of lithium ion battery, which could not only ensure high capacity of silicon but also have good cycle performance and good charge and discharge performance. The present application also provides a negative electrode comprising a copper foil and a slurry including the mixture of a conductive agent, a binder, solvents and the silicon-carbon composite prepared according to the method for preparing silicon-carbon composite of the present application; and a lithium ion battery comprising a shell, a winding core positioned in the shell, electrolyte received in the shell and immersing the winding core, wherein the winding core comprising a positive electrode, separators and the negative electrode provided according to the present application.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application claims priority to Chinese patent application No. 201710039430.8 filed on Jan. 19, 2017, the whole disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present application generally relates to lithium ion batteries and, more particularly, to a method for preparing silicon-carbon composite, a negative electrode, and a lithium ion battery.

Description of the Related Art

At present, lithium ion batteries have been widely used as energy storage systems in 3C digital, electric vehicle and other fields. Lithium ion batteries are required to have high energy density, good cycle performance and safety performance, and low cost. A traditional active material for negative electrode of a lithium ion battery is graphite, however, the theoretical capacity of graphite is 372 mAh/g, resulting in a low energy density of the lithium ion battery, which is difficult to meet the current requirements.

Compared with graphite, silicon has a higher lithium insertion capacity (about 3600 mAh/g at room temperature) and a lower lithium insertion potential (<0.5V), which make silicon to be the most potential active material for negative electrode of lithium ion battery to replace graphite. However, silicon has a large volume change in process of taking off or embedding the lithium, resulting in problems of disintegration of silicon particles, poor contact between active material and negative current collector, and repetitive growth of unstable solid electrolyte interphase which may cause the consumption of electrolyte, and low charge and discharge efficiency and poor cycle performance of the lithium ion battery.

Conventional preparation and modification methods of silicon based materials, such as thermal reduction method, carbon coating method and chemical vapor deposition method, are facing problems of agglomeration of nano-particles, uneven distribution, and large volume expansion of silicon-carbon product which may cause poor cycle performance of lithium ion battery.

In view of the foregoing, what is needed, therefore, is to provide a method for preparing silicon-carbon composite, a negative electrode, and a lithium ion battery to overcome the defects as mentioned above.

SUMMARY OF THE INVENTION

One object of the present application is to provide a method for preparing silicon-carbon composite. The silicon-carbon composite prepared according to the present application is suitable to be an active material for negative electrode of lithium ion battery, which could not only ensure high capacity of silicon but also have good cycle performance and good charge and discharge performance.

According to one embodiment of the present application, a method for preparing silicon-carbon composite comprising steps of:

1) dispersing a silicon source and a carbon source in water at a molar ratio of Si:C=(5-15):1, and obtaining a silicon-carbon suspension;

2) heating the silicon-carbon suspension of step 1) and the silicon-carbon suspension reacting at 180-220° C. for 3-8 hours, cooling down to room temperature, washing and drying, and obtaining a carbon coated nano-silicon based oxide;

3) mixing and grinding the carbon coated nano-silicon based oxide of step 2) with magnesium powders, and obtaining a mixture;

4) adding the mixture of step 3) into inorganic salt and heating at 400-700° C. for 5-15 hours under protection of an inert gas, and obtaining a precursor; and

5) washing the precursor by hydrochloric acid and deionized water, soaking by hydrofluoric acid, and then washing by deionized water and drying, and obtaining a silicon-carbon composite.

The silicon-carbon composite prepared according to the present application has characteristics of uniform particles, excellent electrochemical property, and rapid in process of taking off or embedding of electrons and lithium ions.

One embodiment of the present application provides a negative electrode comprising a copper foil and a slurry including the mixture of a conductive agent, a binder, solvents and the silicon-carbon composite prepared according to the method for preparing silicon-carbon composite of the present application; the slurry is coated on two opposite surfaces of the copper foil.

The negative electrode provided according to the present application has good chemical stability and controllable volume change.

One embodiment of the present application provides a lithium ion battery comprising a shell having an opening at one end, a winding core positioned in the shell, electrolyte received in the shell and immersing the winding core, and a cap cover positioned in the opening for enclosing the opening; wherein the winding core comprising a positive electrode, separators and the negative electrode provided according to the present application.

The lithium ion battery provided according to the present application has high energy density, good cycle performance and good charge and discharge performance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order that the objects, technical solution and technical effects of the present application can be understood more clearly, the present application will be described in more detail with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are illustrative only and are not intended to limit the present application.

According to one embodiment of the present application, a method for preparing silicon-carbon composite comprising steps of:

1) dispersing a silicon source and a carbon source in water at a molar ratio of Si:C=(5-15):1, and obtaining a silicon-carbon suspension;

2) heating the silicon-carbon suspension of step 1) and the silicon-carbon suspension reacting at 180-220° C. for 3-8 hours, cooling down to room temperature, washing and drying, and obtaining a carbon coated nano-silicon based oxide;

3) mixing and grinding the carbon coated nano-silicon based oxide of step 2) with magnesium powders, and obtaining a mixture;

4) adding the mixture of step 3) into inorganic salt and heating at 400-700° C. for 5-15 hours under protection of an inert gas, and obtaining a precursor; and

5) washing the precursor by hydrochloric acid and deionized water, soaking by hydrofluoric acid, and then washing by deionized water and drying, and obtaining a silicon-carbon composite.

Specifically, in step 1), the silicon source is SiO or SiO2.

Specifically, in step 1), the silicon source has a particle size of 50-200 nm.

Specifically, in step 1), the silicon source and the carbon source are separately dispersed in water to obtain a silicon source suspension and a carbon source suspension, and then the silicon source suspension and the carbon source suspension are mixed to obtain the silicon-carbon suspension.

Specifically, in step 1), a concentration of the carbon source suspension is 0.1-1 mol/L while the carbon source is selected from a group consisting of glucose, sucrose, citric acid and maleic acid.

Specifically, in step 1), a solid content of the carbon source suspension is 0.3-5% while the carbon source is graphene.

Specifically, in step 3), a mass ratio of the carbon coated nano-silicon based oxide to the magnesium powders is 1:(0.6-1.6)

Specifically, in step 4), the inorganic salt is selected from a group consisting of anhydrous sodium chloride, anhydrous potassium chloride, anhydrous aluminum chloride and anhydrous magnesium chloride.

Specifically, in step 4), a mass ratio of the mixture to the inorganic salt is 1:(10-20).

Specifically, in step 4), the inert gas is selected from a group consisting of nitrogen, neon, argon, krypton, xenon and radon.

Specifically, in step 4), a rate of temperature rising from room temperature to 400-700° C. is 3-5° C./min.

The silicon-carbon composite prepared according to the present application is suitable to be an active material for negative electrode of lithium ion battery, which could not only ensure high capacity of silicon but also have good cycle performance and good charge and discharge performance.

Referring toFIG. 1, one embodiment of the present application provides a negative electrode11comprising a copper foil111and a slurry112including the mixture of a conductive agent, a binder, solvents and the silicon-carbon composite prepared according to the method for preparing silicon-carbon composite of the present application; the slurry112is coated on two opposite surfaces of the copper foil111.

The negative electrode11comprising the silicon-carbon composite prepared according to the present application may have good chemical stability and controllable volume change.

Referring toFIG. 2, one embodiment of the present application provides a lithium ion battery100comprising a shell20having an opening at one end, a winding core10positioned in the shell20, electrolyte received in the shell20and immersing the winding core10, and a cap cover30positioned in the opening for enclosing the opening; wherein the winding core10comprising a positive electrode12, separators13and the negative electrode11provided according to the present application.

The lithium ion battery100comprising the negative electrode11may have high energy density, good cycle performance and good charge and discharge performance.

1. dispersing 5 g SiO2in 40 mL deionized water and mixing with 1.51 g aqueous solution of glucose to obtain a silicon-carbon suspension, wherein a concentration of the aqueous solution of glucose is 0.1-1 mol/L, and SiO2and glucose are mixed in a molar ratio of Si:C=(5-15):1;

2. heating the silicon-carbon suspension in a water-bath heater and the silicon-carbon suspension reacting at 180° C. for 4 hours, cooling down to room temperature, washing by deionized water and drying in a vacuum oven to obtain a carbon coated SiO2;

3. mixing and grinding the carbon coated SiO2and magnesium powders in a mass ratio of 1:0.88 to obtain a mixture;

4. adding the mixture into inorganic salt comprising anhydrous sodium chloride and anhydrous potassium chloride, and heating at 700° C. for 10 hours under the protection of an inert gas to obtain a precursor, wherein a mass ratio of the mixture to the inorganic salt is 1.88:20, a mass ratio of the sodium chloride to the anhydrous potassium chloride is 1:1 and a rate of temperature rising from room temperature to 700° C. is 3° C./min;

5. washing the precursor by hydrochloric acid and deionized water, soaking by hydrofluoric acid, and then washing by deionized water and drying in the vacuum oven to obtain a silicon-carbon composite;

6. mixing the silicon-carbon composite, a conductive agent, a binder and solvents to form a slurry112and coating the slurry112on two opposite surfaces of a copper foil111to obtain a negative electrode11;

7. winding the negative electrode11, a positive electrode12and separators13into a winding core10and sealing the winding core10into a shell20after injecting electrolyte to obtain a lithium ion battery100.

1. dispersing 5 g SiO2in 40 mL deionized water and mixing with 1.70 g aqueous solution of glucose to obtain a silicon-carbon suspension, wherein a concentration of the aqueous solution of glucose is 0.1-1 mol/L, and SiO2and glucose are mixed in a molar ratio of Si:C=(5-15):1;

2. heating the silicon-carbon suspension in a water-bath heater and the silicon-carbon suspension reacting at 190° C. for 6 hours, cooling down to room temperature, washing by deionized water and drying in a vacuum oven to obtain a carbon coated SiO2;

3. mixing and grinding the carbon coated SiO2and magnesium powders in a mass ratio of 1:0.84 to obtain a mixture;

4. adding the mixture into inorganic salt comprising anhydrous sodium chloride and anhydrous magnesium chloride, and heating at 650° C. for 8 hours under the protection of an inert gas to obtain a precursor, wherein a mass ratio of the mixture to the inorganic salt is 1.84:20, a mass ratio of the sodium chloride to the anhydrous magnesium chloride is 1:1.23 and a rate of temperature rising from room temperature to 650° C. is 3° C./min;

5. washing the precursor by hydrochloric acid and deionized water, soaking by hydrofluoric acid, and then washing by deionized water and drying in the vacuum oven to obtain a silicon-carbon composite;

6. mixing the silicon-carbon composite, a conductive agent, a binder and solvents to form a slurry112and coating the slurry112on two opposite surfaces of a copper foil111to obtain a negative electrode11;

7. winding the negative electrode11, a positive electrode12and separators13into a winding core10and sealing the winding core10into a shell20after injecting electrolyte to obtain a lithium ion battery100.

1. dispersing 5 g SiO2in 40 mL deionized water and mixing with 1.95 g aqueous solution of glucose to obtain a silicon-carbon suspension, wherein a concentration of the aqueous solution of glucose is 0.1-1 mol/L, and SiO2and glucose are mixed in a molar ratio of Si:C=(5-15):1;

2. heating the silicon-carbon suspension in a water-bath heater and the silicon-carbon suspension reacting at 200° C. for 5 hours, cooling down to room temperature, washing by deionized water and drying in a vacuum oven to obtain a carbon coated SiO2;

3. mixing and grinding the carbon coated SiO2and magnesium powders in a mass ratio of 1:1 to obtain a mixture;

4. adding the mixture into inorganic salt comprising anhydrous sodium chloride and anhydrous aluminum chloride, and heating at 550° C. for 10 hours under the protection of an inert gas to obtain a precursor, wherein a mass ratio of the mixture to the inorganic salt is 2:20, a mass ratio of the sodium chloride to the anhydrous aluminum chloride is 1:2.79 and a rate of temperature rising from room temperature to 550° C. is 5° C./min;

5. washing the precursor by hydrochloric acid and deionized water, soaking by hydrofluoric acid, and then washing by deionized water and drying in the vacuum oven to obtain a silicon-carbon composite;

6. mixing the silicon-carbon composite, a conductive agent, a binder and solvents to form a slurry112and coating the slurry112on two opposite surfaces of a copper foil111to obtain a negative electrode11;

7. winding the negative electrode11, a positive electrode12and separators13into a winding core10and sealing the winding core10into a shell20after injecting electrolyte to obtain a lithium ion battery100.

1. dispersing 5 g SiO2in 40 mL deionized water and mixing with 2.27 g aqueous solution of glucose to obtain a silicon-carbon suspension, wherein a concentration of the aqueous solution of glucose is 0.1-1 mol/L, and SiO2and glucose are mixed in a molar ratio of Si:C=(5-15):1;

2. heating the silicon-carbon suspension in a water-bath heater and the silicon-carbon suspension reacting at 200° C. for 6 hours, cooling down to room temperature, washing by deionized water and drying in a vacuum oven to obtain a carbon coated SiO2;

3. mixing and grinding the carbon coated SiO2and magnesium powders in a mass ratio of 1:0.84 to obtain a mixture;

4. adding the mixture into inorganic salt comprising anhydrous sodium chloride and anhydrous magnesium chloride, and heating at 650° C. for 10 hours under the protection of an inert gas to obtain a precursor, wherein a mass ratio of the mixture to the inorganic salt is 1.84:20, a mass ratio of the sodium chloride to the anhydrous magnesium chloride is 1:1.23 and a rate of temperature rising from room temperature to 650° C. is 3° C./min;

5. washing the precursor by hydrochloric acid and deionized water, soaking by hydrofluoric acid, and then washing by deionized water and drying in the vacuum oven to obtain a silicon-carbon composite;

6. mixing the silicon-carbon composite, a conductive agent, a binder and solvents to form a slurry112and coating the slurry112on two opposite surfaces of a copper foil111to obtain a negative electrode11;

7. winding the negative electrode11, a positive electrode12and separators13into a winding core10and sealing the winding core10into a shell20after injecting electrolyte to obtain a lithium ion battery100.

Discharge capacity in the first charge and discharge cycle, coulomb efficiency in the first charge and discharge cycle, and coulomb efficiency after one hundred charge and discharge cycles of lithium ion batteries provided according to the examples of the present application are shown in the following table.

Referring toFIG. 3andFIG. 4, the silicon-carbon composite prepared according to the present application has uniform particles and gap channels beneficial to the taking off or embedding process of electrons and lithium ions.

Referring toFIG. 5andFIG. 6, the lithium ion battery provided according to the present application has good charge and discharge performance and good cycle performance. The discharge capacity of the lithium ion battery in the first charge and discharge cycle could reach 2800 mAh/g, the charge capacity after one hundred charge and discharge cycles remains 1600 mAh/g, and the coulomb efficiency within one hundred charge and discharge cycles remains around 100%.

It should be understood that the above examples are only used to illustrate the technical concept and feature of the present application, and the purpose to thereof is familiarize the person skilled in the art to understand the content of the present application and carry it out, which cannot restrict the protection scope of the present invention based on above. Any equivalent transformation or modification made in the spirit of the present invention should all be included within the protection scope of the present application.