A silicon anode, a method for preparing the silicon anode, and a battery thereof.

Abstract

This invention discloses a silicon anode, a method for preparing the silicon anode, and a battery thereof, comprising a silicon substrate, a first coating layer, a second coating layer, and carbon nanotubes. The silicon substrate forms the core of the silicon anode, the carbon nanotubes and the first coating layer are formed on the surface of the silicon substrate, and the second coating layer coats the carbon nanotubes 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 anode of this invention adopts a double-layer coating structure with a first coating layer and a second coating layer. The first coating layer is a carbon layer, and the second coating layer is an elastic polymer layer. The elastic polymer layer can suppress the volume expansion of silicon. During the expansion process, the polymer layer can freely shrink and is not easily broken. Through the fixation effect of the first and second coating layers on the carbon nanotubes, gaps are not easily generated between the active material particles of the silicon anode and the carbon nanotubes during cycling, and good electrical contact is always maintained. Furthermore, the carbon nanotubes grow uniformly on the surface of the silicon substrate, and there is no problem of agglomeration.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery negative electrode material preparation, and particularly relates to a silicon negative electrode, a silicon negative electrode preparation method and a battery thereof. BACKGROUND

[0002] With the rapid development of the new energy industry, high-energy density, high-power and high-safety batteries are in urgent need. At present, the commercial negative electrode material is mainly graphite negative electrode, and the theoretical specific capacity thereof is only 370 mAh / g, which cannot meet the demand for energy density. The silicon negative electrode has been widely concerned and researched due to its high theoretical capacity, low lithium intercalation potential, rich raw materials, non-toxicity and environmental protection, and is expected to replace the graphite negative electrode to become the next generation of high-energy density negative electrode material.

[0003] During the charging and discharging process, the silicon will expand by 300-400%, and the carbon layer on the surface will crack under the expansion and contraction, so that the silicon is exposed to the electrolyte, causing continuous side reactions, consumption of the electrolyte and increase of the impedance, and finally leading to capacity attenuation. The huge volume expansion of the silicon will cause gaps between active material particles and between the active material and the conductive agent, resulting in loss of electrical contact. SUMMARY

[0004] The purpose of the present application is to provide a silicon negative electrode, a silicon negative electrode preparation method and a battery thereof, so as to avoid exposure of the silicon surface to the electrolyte, reduce the occurrence of side reactions, and improve the cycle performance by preventing the loss of electrical contact during the cycle process.

[0005] The present application discloses a silicon negative electrode, which comprises a silicon substrate, a first coating layer, a second coating layer and carbon nanotubes; the silicon substrate is the core of the silicon negative electrode, the carbon nanotubes and the first coating layer are formed on the surface of the silicon substrate, and the second coating layer is coated on the carbon nanotubes and the first coating layer; the first coating layer is a carbon layer, and the second coating layer is an elastic polymer layer.

[0006] Optionally, the carbon nanotubes and the first coating layer are synchronously grown on the surface of the silicon substrate.

[0007] Optionally, the thickness of the second coating layer is 5-100 nm.

[0008] Optionally, the mass fraction of the second coating layer is 2-15%.

[0009] Optionally, the diameter of the carbon nanotubes is 2-20 nm, and the length is 0.5-10 um.

[0010] Optionally, the number of the carbon nanotubes per square micrometer is 5-50.

[0011] Optionally, the thickness of the first coating layer is 1-50 nm.

[0012] Optionally, the mass fraction of the first coating layer is 1-10%.

[0013] This invention also discloses a method for preparing a silicon anode, comprising the steps described above:

[0014] By combining silicon particles with a catalyst, metal catalytic sites are formed on the silicon surface, resulting in composite particles.

[0015] The composite particles are added to an atmosphere furnace, inert gas is introduced to purge the air, and the mixture is heated to a certain temperature. Alkane gas is then introduced and the mixture is kept at that temperature for a certain time. Carbon nanotubes and the first coating layer are grown simultaneously on the surface of the composite particles to obtain a carbon-coated silicon anode.

[0016] The carbon-coated silicon anode was added to the prepared acid solution to remove the residual catalyst.

[0017] The polymer material is dissolved in a solvent, added to the silicon anode, stirred thoroughly, and then atomized and dried to obtain a silicon anode with a polymer coating.

[0018] The present invention also discloses a battery comprising a silicon anode as described above.

[0019] The silicon anode of this invention employs a double-layer coating structure with a first coating layer and a second coating layer. The first coating layer is a carbon layer, and the second coating layer is an elastic polymer layer. The elastic polymer layer can suppress the volume expansion of silicon, and during the expansion process, the polymer layer can freely contract without easily breaking, preventing the silicon surface from being exposed to the electrolyte, reducing side reactions, and improving cycle performance. Carbon nanotubes form a three-dimensional conductive network, enhancing conductivity. Importantly, the carbon nanotubes are formed on the surface of the silicon substrate, achieving a tight bond between the silicon, the first coating layer, the second coating layer, and the carbon nanotubes. Unlike simple surface contact, the fixation of the carbon nanotubes by the first and second coating layers prevents the formation of voids between the active material particles of the silicon anode and the carbon nanotubes during cycling, reducing the likelihood of loss of electrical contact, and also preventing the carbon nanotubes from agglomerating. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of the invention and illustrate implementation methods, and together with the textual description, explain the principles of the invention. Obviously, the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings:

[0021] Figure 1 This is a schematic diagram of the silicon anode structure in an embodiment of the present invention.

[0022] Among them, 1. silicon substrate; 2. first coating layer; 3. second coating layer; 4. carbon nanotubes. Detailed Implementation

[0023] It should be understood that the terminology, specific structural and functional details used herein are merely for describing particular embodiments and are representative. However, the invention can be implemented in many alternative forms and should not be construed as being limited to the embodiments set forth herein.

[0024] The present invention will now be described in detail with reference to the accompanying drawings and optional embodiments.

[0025] like Figure 1 As shown, as an embodiment of the present invention, a silicon anode is disclosed, including a silicon substrate 1, a first coating layer 2, a second coating layer 3, and a carbon nanotube 4; the silicon substrate 1 is the core of the silicon anode, the carbon nanotube 4 and the first coating layer 2 are formed on the surface of the silicon substrate 1, and the second coating layer 3 coats the carbon nanotube 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.

[0026] The silicon anode of this invention employs a double-layer coating structure with a first coating layer 2 and a second coating layer 3. The first coating layer 2 is a carbon layer, and the second coating layer 3 is an elastic polymer layer. The elastic polymer layer can suppress the volume expansion of silicon. During the expansion process, the polymer layer can freely contract and is not easily broken, preventing the silicon surface from being exposed to the electrolyte, reducing the occurrence of side reactions, and improving cycle performance. Carbon nanotubes 4 form a three-dimensional conductive network, enhancing conductivity. Importantly, the carbon nanotubes 4 are formed on the surface of the silicon substrate 1, achieving a tight bond between the silicon, the first coating layer 2, the second coating layer 3, and the carbon nanotubes 4. Unlike simple surface contact, the carbon nanotubes 4 are fixed by the first and second coating layers 3, making it less likely for voids to form between the active material particles of the silicon anode and the carbon nanotubes during cycling, thus preventing loss of electrical contact, and also preventing the carbon nanotubes 4 from agglomerating.

[0027] Specifically, the silicon substrate 1 is one or more combinations of elemental silicon, SiOx, silicon alloy, and metallic doped SiOx, with a particle size of 0.5µm-20µm and a mass percentage of 70-95%. The first coating layer 2 is an amorphous carbon layer, which can be one or two types of hard carbon and soft carbon. The second coating layer 3 is an elastic polymer layer, which can be a polymer material such as polyurethane, polyaniline, polyvinylidene fluoride, polymethyl methacrylate, polypropylene, polystyrene, or polyacrylonitrile.

[0028] Specifically, carbon nanotubes 4 are partially infiltrated and doped onto the silicon substrate 1. In this scheme, because the carbon nanotubes 4 are grown in situ on the silicon substrate 1, they will partially infiltrate and dop into the silicon substrate 1, increasing the bonding strength.

[0029] Specifically, the carbon nanotube 4 is partially embedded in the second coating layer 3. In this scheme, the second coating layer 3 is wrapped on the carbon nanotube 4 and the first coating layer 2 by atomization drying, and the carbon nanotube 4 is partially embedded in the second coating layer 3, thereby increasing the binding strength of the carbon nanotube 4.

[0030] Specifically, the thickness of the first coating layer 2 is 1-50 nm, and the mass fraction of the first coating layer 2 is 1-10%.

[0031] Specifically, the thickness of the second coating layer 3 is 5-100 nm, and the mass fraction of the second coating layer 3 is 2-15%.

[0032] Specifically, the carbon nanotube 4 has a tube diameter of 2-20 nm and a length of 0.5-10 um. 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 the process parameters.

[0033] 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 are grown in situ, and the carbon nanotube 4 is fixed by the first coating layer 2 and the second coating layer 3, thereby realizing the close combination of the silicon substrate 1 and the carbon nanotube 4, not easily losing electrical contact in the cycle process, and without the need to add carbon nanotubes 4 in the slurry, thereby reducing the cost and the difficulty of the dispersion process.

[0034] The application also discloses a silicon negative electrode preparation method for preparing the silicon negative electrode.

[0035] S100: composite treatment of silicon particles and a catalyst to form metal catalytic sites on the surface of the silicon to obtain composite particles;

[0036] S200: adding the composite particles into an atmosphere furnace, introducing inert gas to discharge air, heating to a certain temperature, further introducing an alkane gas, and incubating for a certain time to synchronously grow carbon nanotubes and a first coating layer on the surface of the composite particles to obtain a carbon-coated silicon negative electrode;

[0037] S300: adding the carbon-coated silicon negative electrode into prepared acid liquor to remove residual catalyst;

[0038] S400: dissolving a high polymer material in a solvent, adding the above silicon negative electrode, fully stirring, and then atomizing and drying to obtain a silicon negative electrode containing a high polymer coating layer.

[0039] Specifically, in the S100 step, the metal catalyst can be Fe, Co, Ni, TiO2, ZnO, MgO or a mixture thereof. The silicon particles and the catalyst are mixed at a ratio of 1:0.001-1:0.03, and the composite treatment can be ball milling, high-speed mixing or jet milling.

[0040] Specifically, in the step S200, the heating furnace can be a tube furnace, an intermittent rotary furnace or a continuous rotary furnace. The inert gas can be nitrogen, argon, helium or a mixture thereof, and the flow rate can be 0.5-5L / min. The alkane gas can be methane, ethane, acetylene, propyne or a mixture thereof, 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 holding time can be 0.5-5h. The carbon nanotubes 4 and the first coating layer 2 are grown on the silicon substrate 1 by the alkane gas, and the carbon nanotubes 4 are grown on the position of the silicon substrate 1 with the metal catalyst, and the first coating layer 2 is grown on the position of the silicon substrate 1 without the metal catalyst. In this way, the carbon nanotubes 4 and the first coating layer 2 are synchronously grown on the surface of the silicon substrate 1, the carbon nanotubes 4 are in-situ grown on the silicon substrate 1, and the first coating layer 2 is in-situ grown on the silicon substrate 1. The carbon nanotubes 4 are fixed by the first coating layer 2 and the second coating layer 3, the silicon substrate 1 and the carbon nanotubes 4 are tightly combined, the electrical contact is not easily lost in the cycle process, the carbon nanotubes 4 are uniformly grown on the surface of the silicon substrate 1, and the agglomeration problem does not occur. In addition, the carbon nanotubes 4 do not need to be added in the slurry, and the cost and the dispersion process difficulty are reduced.

[0041] Specifically, in the step S300, the acid solution can be hydrochloric acid, sulfuric acid, nitric acid or a mixture thereof. The temperature can be 20-50℃, and the time can be 1-10h.

[0042] Specifically, in the step S400, the stirring speed can be 500-3000r / min, the time can be 0.5-5h, the inlet air temperature of the spray drying can be 90-200℃ / min, and the outlet air temperature can be 50-120℃ / min.

[0043] The application also discloses a battery comprising the silicon anode as described above.

[0044] The application will be described in detail below with reference to specific examples.

[0045] Example 1

[0046] Step one: 1kg of silicon monoxide and 0.01kg of iron powder are added into a planetary ball mill, and ball milling is carried out at a speed of 200r / min for 3h to obtain silicon monoxide and iron composite particles;

[0047] Step two: the composite particles obtained in step one are added into a rotary furnace, 2L / min of nitrogen is introduced for 30min to discharge air, heating is carried out at a speed of 5℃ / min to 850℃, 0.5L / min of acetylene is further introduced, and holding is carried out for 3h, and then cooling is carried out to room temperature. The carbon nanotubes 4 and the first coating layer 2 are synchronously grown on the surface of the composite particles to obtain a carbon-coated silicon anode.

[0048] Step three: the above obtained silicon negative electrode was added into 0.9 mol / L hydrochloric acid solution, and was continuously stirred at 40°C for 5 h to dissolve elemental iron, and then was filtered and dried;

[0049] Step four: 0.08 kg of polyurethane was dispersed in 5 Kg of THF solvent, 0.8 Kg of the above obtained silicon negative electrode was added, and was stirred at 2000 r / min for 2 h, and then was spray dried with an inlet temperature of 130°C and an outlet temperature of 70°C to obtain powder particles, and further sieving obtained the silicon negative electrode coated with a high molecular layer.

[0050] Example 2

[0051] Step one: 1 kg of lithium-containing silicon monoxide and 0.02 kg of magnesium oxide were added into a planetary ball mill, and were ball milled at a rotation speed of 300 r / min for 2 h to obtain silicon monoxide and magnesium oxide composite particles;

[0052] Step two: the composite particles obtained in step one were added into a rotary furnace, 2 L / min of nitrogen was introduced for 30 min to discharge air, and then was heated to 900°C, and further 0.5 L / min of acetylene was introduced, and was kept for 3 h, and then was cooled to room temperature, and the carbon nanotube 4 and the first coating layer 2 were synchronously grown on the surface of the composite particles to obtain a carbon-coated silicon negative electrode;

[0053] Step three: the above obtained silicon negative electrode was added into 0.5 mol / L hydrochloric acid solution, and was continuously stirred at 30°C for 5 h to remove magnesium impurities, and then was filtered and dried;

[0054] Step four: 0.08 kg of polymethyl methacrylate was dissolved in 5 Kg of acetone solvent, 0.8 Kg of the above obtained silicon negative electrode was added, and was stirred at 2000 r / min for 2 h, and then was spray dried with an inlet temperature of 120°C and an outlet temperature of 60°C to obtain powder particles, and further sieving obtained the silicon negative electrode coated with a high molecular layer.

[0055] Comparative Example 1

[0056] No metal catalyst was added relative to Example 1.

[0057] Comparative Example 2

[0058] No high molecular material coating was performed relative to Example 1.

[0059] Comparative Example 3

[0060] No metal catalyst was added relative to Example 2.

[0061] Comparative Example 4

[0062] No high molecular material coating was performed relative to Example 2.

[0063] The silicon-carbon composite negative electrode material is assembled into a CR2016-dedicated half battery to evaluate its electrochemical performance.

[0064] The process of making the dedicated battery is as follows: the mass ratio of active material (Si / C), acetylene black, CMC, and SBR is 80:10:5:5, wherein the CMC is a 1.2% aqueous solution. The slurry is dispersed by a high-speed shearing mixer at 2000 rpm for 30 min. Then the well-mixed slurry is uniformly coated on a copper foil with a thickness of 8 μm, and the coating surface density is 5 mg / cm2. The electrode sheet is placed in a drying oven at 80°C for 10 h, and the dried electrode sheet is compacted by a roller press; the electrode sheet is punched and cut into a circular sheet with a diameter of 14 mm. The half battery is assembled in a glove box under the protection of high-purity argon, the electrode sheet is made of a lithium foil, the separator is made of a polypropylene porous film, and 1 mol / L LiPF6 is added to a mixed solution obtained by mixing ethylene carbonate / dimethyl carbonate / methyl ethyl carbonate in a volume ratio of 1:1:1 as the electrolyte. The first charge-discharge mode is 0.1C-0.02C / 0.1C, the voltage range is 0.005-2 V, and the 2-50 cycle charge-discharge mode is 0.2C-0.02C / 0.2C, the voltage range is 0.005-2 V, and the thickness expansion calculation method is: the thickness of the fully charged electrode sheet / the thickness of the electrode sheet after rolling. The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from the test results, the in-situ grown carbon nanotubes 4 have a significant improvement in cycle, and the second coating layer 3 has a more obvious inhibition on expansion, and the cycle is also improved.

[0068] It should be noted that the limitations of each step involved in the present scheme do not constitute a limitation on the order of the steps without affecting the implementation of the specific scheme. The steps written in the front can be executed first, or executed later, or even executed simultaneously, as long as the present scheme can be implemented, it should be considered to belong to the protection scope of the present invention.

[0069] The above content is a further detailed description of the present invention in combination with specific optional embodiments, and cannot be considered as a limitation of the specific implementation of the present invention. For ordinary skilled persons in the technical field to which the present invention belongs, without departing from the concept of the present invention, a number of simple deductions or substitutions can be made, which should be considered to belong to the protection scope of the present invention.

Claims

1. A silicon negative electrode, characterized by, The silicon negative electrode comprises a silicon substrate, a first coating layer, a second coating layer and carbon nanotubes; the silicon substrate is the core of the silicon negative electrode; the carbon nanotubes and the first coating layer are formed on the surface of the silicon substrate; and the second coating layer is coated on the carbon nanotubes and the first coating layer; the first coating layer is a carbon layer; and the second coating layer is an elastic polymer layer. The elastic polymer layer is polyurethane, polyaniline, polymethyl methacrylate, polypropylene, polystyrene or polyacrylonitrile; the second coating layer is wrapped on the carbon nanotubes and the first coating layer by atomization drying, so that the carbon nanotubes are partially embedded in the second coating layer and partially permeate and dope on the silicon substrate; The carbon nanotubes and the first coating layer are synchronously and in situ grown on the surface of the silicon substrate; The silicon negative electrode is prepared by the following steps: The silicon particles are compounded with a catalyst to form metal catalytic sites on the surface of the silicon, thereby obtaining composite particles; The composite particles are added into an atmosphere furnace, inert gas is introduced to discharge air, heated to a certain temperature, further introduced with alkane gas, and kept warm for a certain time, so that the carbon nanotubes and the first coating layer are synchronously grown on the surface of the composite particles, thereby obtaining a carbon-coated silicon negative electrode; The carbon-coated silicon negative electrode is added into prepared acid solution to remove residual catalyst; The polymer material is dissolved in a solvent, the above-mentioned silicon negative electrode is added, fully stirred, and then atomized and dried to obtain a silicon negative electrode containing a polymer coating layer.

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

3. The silicon negative electrode according to claim 1, wherein The mass ratio of the second coating layer is 2-15%.

4. The silicon negative electrode of claim 1, wherein The carbon nanotubes have a diameter of 2-20 nm and a length of 0.5-10 um.

5. The silicon negative electrode of claim 1, wherein The number of carbon nanotubes per square micron is 5-50.

6. The silicon negative electrode of claim 1, wherein The thickness of the first coating layer is 1-50 nm.

7. The silicon negative electrode of claim 1, wherein The mass ratio of the first coating layer is 1-10%.

8. A method for producing a silicon negative electrode for producing the silicon negative electrode according to any one of claims 1 to 7, characterized by, The method comprises the following steps: The silicon particles are compounded with a catalyst to form metal catalytic sites on the surface of the silicon, thereby obtaining composite particles; The composite particles are added into an atmosphere furnace, inert gas is introduced to discharge air, heated to a certain temperature, further introduced with alkane gas, and kept warm for a certain time, so that the carbon nanotubes and the first coating layer are synchronously grown on the surface of the composite particles, thereby obtaining a carbon-coated silicon negative electrode; The carbon-coated silicon negative electrode is added into prepared acid solution to remove residual catalyst; The polymer material is dissolved in a solvent, the above-mentioned silicon negative electrode is added, fully stirred, and then atomized and dried to obtain a silicon negative electrode containing a polymer coating layer.

9. A battery, characterized by The silicon negative electrode is as claimed in any one of claims 1 to 7.

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