CN115188938A - Silicon cathode, preparation method of silicon cathode and battery thereof - Google Patents

Abstract

The invention discloses a silicon cathode, a preparation method of the silicon cathode and a battery thereof, wherein the silicon cathode comprises a silicon substrate, a first coating layer, a second coating layer and a carbon nano tube; the silicon substrate is an inner core of a silicon cathode, the carbon nano tube and the first coating layer are formed on the surface of the silicon substrate, the second coating layer is coated on the carbon nano tube and the first coating layer, the first coating layer is a carbon layer, and the second coating layer is an elastic polymer layer. The silicon cathode adopts a double-layer coating structure of the first coating layer and the second coating layer, the first coating layer is a carbon layer, the second coating layer is an elastic macromolecule layer, the elastic macromolecule layer can inhibit the volume expansion of silicon, the macromolecule layer can freely contract in the expansion process and is not easy to break, through the fixing effect of the coating layer and the second coating layer on the carbon nano tube, gaps are not easy to generate between active substance particles of the silicon cathode and the carbon nano tube in the circulation process, the carbon nano tube can always keep good electric contact, and the carbon nano tube can uniformly grow on the surface of the silicon substrate, so that the agglomeration problem can not occur.

Description

Silicon cathode, preparation method of silicon cathode and battery thereof

Technical Field

The invention relates to the technical field of preparation of battery cathode materials, in particular to a silicon cathode, a preparation method of the silicon cathode and a battery thereof.

Background

With the rapid development of new energy industry, the development of high energy density, high power and high safety batteries is imminent. The current commercialized negative electrode material mainly uses graphite negative electrode, the theoretical gram capacity of the negative electrode material is only 370mAh/g, and the energy density requirement can not be met. The silicon cathode is widely concerned and researched due to the advantages of high theoretical capacity, low lithium intercalation potential, rich raw materials, no toxicity, environmental protection and the like, and is expected to replace a graphite cathode to become a next-generation high-energy-density cathode material in the future.

The silicon can generate 300-400% volume expansion in the charging and discharging process, the surface coating carbon layer can crack under the expansion and contraction effects, the side reaction is caused to continuously occur when the silicon is exposed in the electrolyte, and the consumption of the electrolyte and the increase of the impedance finally cause the capacity attenuation. The large volume expansion of silicon can cause voids between active material particles and between the active material and the conductive agent, losing electrical contact.

Disclosure of Invention

The invention aims to provide a silicon cathode, a preparation method of the silicon cathode and a battery thereof, which can prevent the surface of the silicon from being exposed in electrolyte, reduce the occurrence of side reaction, prevent the loss of electric contact in the circulation process and improve the circulation performance.

The invention discloses a silicon cathode, which comprises a silicon substrate, a first coating layer, a second coating layer and a carbon nano tube, wherein the first coating layer is arranged on the silicon substrate; the silicon substrate is an inner core of a silicon cathode, the carbon nano tube and the first coating layer are formed on the surface of the silicon substrate, and the carbon nano tube and the first coating layer are coated by the second coating layer; the first coating layer is a carbon layer and the second coating layer is an elastic polymer layer.

Optionally, the carbon nanotubes and the first coating layer are formed on the surface of the silicon substrate by synchronous growth.

Optionally, the thickness of the second cladding layer is 5-100nm.

Optionally, the second coating layer is present in an amount of 2-15% by mass.

Optionally, the carbon nanotube has a tube diameter of 2-20nm and a length of 0.5-10um.

Optionally, the number of carbon nanotubes per square micron is 5-50.

Optionally, the first cladding layer has a thickness of 1-50nm.

Optionally, the first coating layer accounts for 1-10% of the mass.

The invention also discloses a preparation method of the silicon cathode, which is used for preparing the silicon cathode and comprises the following steps:

compounding silicon particles with a catalyst to form metal catalytic sites on the surface of the silicon to obtain composite particles;

adding the composite particles into an atmosphere furnace, introducing inert gas to discharge air, heating to a certain temperature, further introducing alkane gas, preserving the temperature for a certain time, and synchronously growing carbon nanotubes and a first coating layer on the surfaces of the composite particles to obtain a carbon-coated silicon cathode;

adding the carbon-coated silicon cathode into the prepared acid solution, and removing the residual catalyst;

and dissolving a high polymer material in a solvent, adding the silicon negative electrode, fully stirring, and then carrying out atomization drying to obtain the silicon negative electrode containing the high polymer coating.

The invention also discloses a battery comprising the silicon cathode.

The silicon cathode adopts a double-layer coating structure of the first coating layer and the second coating layer, the first coating layer is a carbon layer, the second coating layer is an elastic polymer layer, the elastic polymer layer can inhibit the volume expansion of silicon, the polymer layer can freely contract in the expansion process and is not easy to break, the silicon surface is prevented from being exposed in electrolyte, the occurrence of side reactions is reduced, and the cycle performance is improved. The carbon nanotubes form a three-dimensional conductive network, enhancing conductivity. Importantly, the carbon nano tube is formed on the surface of the silicon substrate, the silicon, the first coating layer and the second coating layer are tightly combined with the carbon nano tube, the method is different from simple surface contact, the coating layer and the second coating layer fix the carbon nano tube, gaps are not easy to generate between active substance particles of the silicon cathode and the carbon nano tube in the circulation process, electric contact is not easy to lose, and the carbon nano tube is not easy to agglomerate.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort. In the drawings:

fig. 1 is a schematic structural view of a silicon negative electrode according to an embodiment of the present invention.

Wherein, 1, silicon substrate; 2. a first cladding layer; 3. a second cladding layer; 4. carbon nanotubes.

Detailed Description

It is to be understood that the terminology, the specific structural and functional details disclosed herein are for the purpose of describing particular embodiments only, and are representative, but that the present invention may be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

The invention is described in detail below with reference to the figures and alternative embodiments.

As shown in fig. 1, as an embodiment of the present invention, a silicon negative electrode is disclosed, which includes a silicon substrate 1, a first coating layer 2, a second coating layer 3 and a carbon nanotube 4; the silicon substrate 1 is an inner core of a silicon cathode, the carbon nano tube 4 and the first coating layer 2 are formed on the surface of the silicon substrate 1, the second coating layer 3 is coated on the carbon nano tube 4 and the first coating layer 2, the first coating layer 2 is a carbon layer, and the second coating layer 3 is an elastic polymer layer.

The silicon cathode adopts a double-layer coating structure of the first coating layer 2 and the second coating layer 3, the first coating layer 2 is a carbon layer, the second coating layer 3 is an elastic polymer layer, the elastic polymer layer can inhibit the volume expansion of silicon, the polymer layer can freely contract and is not easy to break in the expansion process, the silicon surface is prevented from being exposed in electrolyte, the occurrence of side reactions is reduced, and the cycle performance is improved. The carbon nanotubes 4 form a three-dimensional conductive network, enhancing the conductivity. Importantly, the carbon nano tube 4 is formed on the surface of the silicon substrate 1, the silicon, the first coating layer 2, the second coating layer 3 and the carbon nano tube 4 are tightly combined, the method is different from simple surface contact, the carbon nano tube 4 is fixed through the coating layers and the second coating layer 3, gaps are not easy to generate between active material particles of a silicon cathode and the carbon nano tube in the circulation process, electric contact is not easy to lose, and the carbon nano tube 4 is not easy to agglomerate.

Specifically, the silicon substrate 1 is one or a combination of more of simple substance silicon, siOx, silicon alloy and metal doped SiOx, the granularity is 0.5-20 um, and the mass percentage is 70-95%. The first coating layer 2 is an amorphous carbon layer, and may be one or both of hard carbon and soft carbon. The second coating layer 3 is an elastic polymer layer, and may be a polymer material such as polyurethane, polyaniline, polyvinylidene fluoride, polymethyl methacrylate, polypropylene, polystyrene, polyacrylonitrile, or the like.

Specifically, the carbon nanotubes 4 are partially permeation-doped on the silicon substrate 1. In this embodiment, since the carbon nanotubes 4 are grown in situ on the silicon substrate 1, they partially penetrate and dope the silicon substrate 1, thereby increasing the bonding strength.

Specifically, the carbon nanotubes 4 are partially embedded in the second coating layer 3. In the scheme, the second coating layer 3 is coated on the carbon nano tube 4 and the first coating layer 2 through atomization and drying, and the carbon nano tube 4 can be partially embedded into the second coating layer 3, so that the bonding firmness of the carbon nano tube 4 is increased.

Specifically, the thickness of the first clad layer 2 is 1 to 50nm, and the mass ratio of the first clad layer 2 is 1 to 10%.

Specifically, the thickness of the second cladding layer 3 is 5-100nm, and the mass ratio of the second cladding layer 3 is 2-15%.

Specifically, the carbon nanotube 4 has a tube diameter of 2-20nm and a length of 0.5-10um. The number of carbon nanotubes 4 per square micrometer is 5-50. Specifically, the tube diameter and length of each carbon nanotube 4 can be adjusted according to the size of the catalyst and process parameters.

Specifically, the carbon nanotube 4 and the first coating layer 2 are synchronously grown on the surface of the silicon substrate 1, the carbon nanotube 4 and the first coating layer 2 grow in situ, the carbon nanotube 4 is fixed through the first coating layer 2 and the second coating layer 3, the silicon substrate 1 and the carbon nanotube 4 are tightly combined, the electric contact is not easily lost in the circulating process, meanwhile, the carbon nanotube 4 does not need to be added into slurry, and the cost and the difficulty of a dispersion process are reduced.

The invention also discloses a preparation method of the silicon cathode, which is used for preparing the silicon cathode and is characterized by comprising the following steps:

s100: compounding silicon particles with a catalyst to form metal catalytic sites on the surface of the silicon to obtain composite particles;

s200: adding the composite particles into an atmosphere furnace, introducing inert gas to discharge air, heating to a certain temperature, further introducing alkane gas, preserving the temperature for a certain time, and synchronously growing carbon nanotubes and a first coating layer on the surfaces of the composite particles to obtain a carbon-coated silicon cathode;

s300: adding the carbon-coated silicon cathode into the prepared acid solution, and removing the residual catalyst;

s400: and dissolving a high polymer material in a solvent, adding the silicon negative electrode, fully stirring, and then carrying out atomization drying to obtain the silicon negative electrode containing the high polymer coating.

Specifically, in the S100 step, the metal catalyst may be one or a mixture of Fe, co, ni, tiO2, znO, mgO. The proportion of the silicon particles to the catalyst is 1.001-1, and the composite treatment can be ball milling, high-speed mixing and jet milling.

Specifically, in the S200 step, the heating furnace may be a tube furnace, a batch rotary kiln, or a continuous rotary kiln. The inert gas can be nitrogen, argon, helium or mixed gas, and the flow rate is 0.5-5L/min. The alkane gas can be methane, ethane, acetylene, propyne and mixed gas, and the flow rate can be 0.2-3L/min. The heating rate can be 1-10 ℃/min, the heating temperature can be 600-1100 ℃/min, and the heat preservation time can be 0.5-5h. The carbon element of the carbon nanotube 4 and the first coating layer 2 is alkane gas, the carbon nanotube 4 grows at the position of the silicon substrate 1 with the metal catalyst, and the first coating layer 2 grows at the position of the silicon substrate 1 without the metal catalyst. The carbon nanotube 4 and the first coating layer 2 are synchronously grown and formed on the surface of the silicon substrate 1, the carbon nanotube 4 is grown and formed on the silicon substrate 1 in situ, and is not directly added, the first coating layer 2 is also grown and formed on the silicon substrate 1 in situ, the carbon nanotube 4 is fixed through the first coating layer 2 and the second coating layer 3, the silicon substrate 1 and the carbon nanotube 4 are tightly combined, the electrical contact is not easily lost in the circulation process, the carbon nanotube 4 uniformly grows on the surface of the silicon substrate, and the agglomeration problem cannot occur. Meanwhile, the carbon nano tube 4 is not required to be added into the slurry, so that the cost and the difficulty of a dispersing process are reduced.

Specifically, in the step S300, the acid solution may be hydrochloric acid, sulfuric acid, nitric acid, or a mixed acid. The temperature can be 20-50 ℃ and the time can be 1-10h.

Specifically, in the step S400, the stirring speed can be 500-3000r/min, the time can be 0.5-5h, the air inlet temperature of spray drying can be 90-200 ℃/min, and the air outlet temperature can be 50-120 ℃/min.

The invention also discloses a battery comprising the silicon cathode.

The following description is given with reference to specific examples.

Example 1

The method comprises the following steps: adding 1kg of silicon monoxide and 0.01kg of iron powder into a planetary ball mill, and carrying out ball milling for 3 hours at the rotating speed of 200r/min to obtain silicon monoxide and iron composite particles;

step two: adding the composite particles obtained in the step one into a rotary furnace, introducing 2L/min nitrogen for 30min to exhaust air, heating to 850 ℃ at 5 ℃/min, further introducing 0.5L/min acetylene, preserving heat for 3h, cooling to room temperature, and synchronously growing carbon nanotubes 4 and a first coating layer 2 on the surface of the composite particles to obtain a carbon-coated silicon cathode;

step three: adding the obtained silicon cathode into 0.9mol/L hydrochloric acid solution, continuously stirring for 5 hours at the temperature of 40 ℃, dissolving simple substance iron, then carrying out suction filtration and drying;

step four: dispersing 0.08Kg of polyurethane in 5Kg of THF solvent, adding 0.8Kg of the obtained silicon negative electrode, stirring at 2000r/min for 2h, performing spray drying, wherein the air inlet temperature is 130 ℃, the air outlet temperature is 70 ℃ to obtain powdery particles, and further sieving to obtain the silicon negative electrode coated by the macromolecule layer.

Example 2

The method comprises the following steps: adding 1kg of lithium doped silica and 0.02kg of magnesium oxide into a planetary ball mill, and ball-milling for 2 hours at the rotating speed of 300r/min to obtain silica and magnesium oxide composite particles;

step two: adding the composite particles obtained in the step one into a rotary furnace, introducing 2L/min nitrogen for 30min to exhaust air, heating to 900 ℃, further introducing 0.5L/min acetylene, preserving heat for 3h, cooling to room temperature, and synchronously growing carbon nanotubes 4 and a first coating layer 2 on the surface of the composite particles to obtain a carbon-coated silicon cathode;

step three: adding the obtained silicon cathode into 0.5mol/L hydrochloric acid solution, continuously stirring for 5 hours at the temperature of 30 ℃, removing magnesium impurities, then carrying out suction filtration and drying;

step four: dissolving 0.08Kg of polymethyl methacrylate in 5Kg of acetone solvent, adding 0.8Kg of the obtained silicon negative electrode, stirring at 2000r/min for 2 hours, performing spray drying at the air inlet temperature of 120 ℃ and the air outlet temperature of 60 ℃ to obtain powdery particles, and further sieving to obtain the silicon negative electrode coated by the macromolecule layer.

Comparative example 1

No metal catalyst was added relative to example 1.

Comparative example 2

No polymer coating was performed as compared to example 1.

Comparative example 3

No metal catalyst was added relative to example 2.

Comparative example 4

No polymer coating was performed as compared to example 2.

And assembling the silicon-carbon composite negative electrode material into a CR 2016-button type half cell to evaluate the electrochemical performance of the cell.

The button cell manufacturing process comprises the following steps: the mass ratio of the active material (Si/C), the acetylene black, the CMC and the SBR is 80: 5:5, wherein the CMC is a 1.2% aqueous solution. The slurry was dispersed for 30min with a high shear mixer at 2000 rpm. Then, the homogenized slurry was uniformly coated on a copper foil 8 μm thick with a coating areal density of 5mg/cm2. Drying the pole piece in a drying oven at 80 ℃ for 10 hours, and compacting the dried pole piece by using a roller press; the pole pieces were punched and cut into disks 14mm in diameter. Assembling a half cell in a glove box protected by high-purity argon, wherein a counter electrode sheet adopts metal lithium foil, a diaphragm adopts a polypropylene porous membrane, and the volume ratio of ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate is 1:1: 1mol/L LiPF6 was added to the mixed solution obtained in 1 as an electrolyte. First charge-discharge system: 0.1C-0.02C/0.1C, voltage range 0.005-2V, charge-discharge mode for 2-50 cycles: 0.2C-0.02C/0.2C, voltage range 0.005-2V, thickness expansion calculation mode: the thickness of the pole piece is fully charged for the first time/the thickness of the pole piece after rolling. The test results are given in table 1 below:

TABLE 1

From the test results it can be seen that: the carbon nano tube 4 grown in situ has obvious cycle improvement, the second coating layer 3 has obvious expansion inhibition by coating, and the cycle is also improved.

It should be noted that, the limitations of the steps involved in the present disclosure are not considered to limit the order of the steps without affecting the implementation of the specific embodiments, and the steps written in the foregoing may be executed first, or executed later, or even executed simultaneously, and as long as the present disclosure can be implemented, all should be considered to belong to the protection scope of the present disclosure.

The foregoing is a more detailed description of the invention in connection with specific alternative embodiments, and the practice of the invention should not be construed as limited to those descriptions. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (10)

1. A silicon cathode is characterized by comprising a silicon substrate, a first coating layer, a second coating layer and a carbon nano tube; the silicon substrate is the inner core of the silicon cathode, the carbon nano tube and the first coating layer are formed on the surface of the silicon substrate, and the carbon nano tube and the first coating layer are coated by the second coating layer; the first coating layer is a carbon layer, and the second coating layer is an elastic polymer layer.

2. The silicon negative electrode of claim 1, wherein the carbon nanotubes and the first cladding layer are formed by simultaneous growth on the surface of the silicon substrate.

3. The silicon negative electrode according to claim 1 or 2, wherein the thickness of the second cladding layer is 5 to 100nm.

4. The silicon negative electrode as claimed in claim 1 or 2, wherein the second coating layer accounts for 2 to 15% by mass.

5. The silicon negative electrode as claimed in claim 1 or 2, wherein the carbon nanotubes have a tube diameter of 2-20nm and a length of 0.5-10um.

6. The silicon anode according to claim 1 or 2, wherein the number of the carbon nanotubes per square micron is 5 to 50.

7. The silicon negative electrode according to claim 1 or 2, wherein the thickness of the first coating layer is 1 to 50nm.

8. The silicon negative electrode as claimed in claim 8, wherein the first coating layer is 1 to 10% by mass.

9. A silicon anode production method for producing the silicon anode according to any one of claims 1 to 8, comprising the steps of:

compounding silicon particles with a catalyst to form metal catalytic sites on the surface of the silicon to obtain composite particles;

adding the composite particles into an atmosphere furnace, introducing inert gas to discharge air, heating to a certain temperature, further introducing alkane gas, preserving the temperature for a certain time, and synchronously growing carbon nanotubes and a first coating layer on the surfaces of the composite particles to obtain a carbon-coated silicon cathode;

adding the carbon-coated silicon cathode into the prepared acid solution, and removing the residual catalyst;

dissolving a high polymer material in a solvent, adding the silicon cathode, fully stirring, and then carrying out atomization drying to obtain the silicon cathode containing the high polymer coating layer.

10. A battery comprising the silicon negative electrode according to any one of claims 1 to 8.

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