A porous silicon-carbon composite negative electrode material and its preparation method and application, lithium-ion battery

Abstract

The present invention belongs to the field of lithium-ion battery material preparation, and specifically discloses a porous silicon-carbon composite negative electrode material, its preparation method and application, and lithium-ion battery. The present invention first combines a polymer with ethyl orthosilicate by electrospinning to form a nanofiber membrane with high strength and suitable porosity, which provides a suitable space for the subsequent embedding of nanosilicon and carbon nanotubes, and greatly alleviates the volume expansion of silicon during the charge and discharge process, thereby improving its cycle performance; the present invention fills nanosilicon and carbon nanotubes in the interlayer and pore structure of the nanofiber membrane, thereby increasing the tap density and contact area of ​​the material and reducing the electronic impedance; the present invention also utilizes the coupling effect of silane coupling agents between nanosilicon, carbon nanotubes and nanofiber membranes to improve the conductivity and structural stability of the material, and finally obtains a silicon-carbon composite negative electrode material with high porosity, large specific surface area and low expansion rate. The method of the present invention has a simple preparation process and is easy to operate, and is suitable for planned industrial production.

Description

Technical Field

[0001] The present invention belongs to the field of lithium ion battery material preparation, and specifically relates to a porous silicon-carbon composite negative electrode material, a preparation method and application thereof, and a lithium ion battery. Background Art

[0002] With the increasing market demand for high-energy-density lithium-ion batteries, lithium-ion battery negative electrode materials are required to have high specific capacity and low expansion. However, most lithium-ion battery negative electrodes on the market currently use graphite as raw material, and the theoretical capacity of graphite is only 372mAh / g, which is difficult to meet the market's higher requirements for negative electrode material performance.

[0003] Silicon materials have attracted widespread attention due to their high theoretical capacity of 4200 mAh / g, low delithiation potential, and abundant storage capacity. However, silicon materials undergo significant volume changes during charge and discharge, coupled with low electrical conductivity, severely impacting their rate and cycling performance. Over the past few decades, efforts have focused on improving the electrochemical performance of silicon-based anode materials. For example, efforts have been made to reduce silicon particle size to the nanoscale or to achieve amorphous structures to relieve the structural stress caused by the large volume changes. However, nano-silicon particles have a large surface energy and are prone to agglomeration, leading to capacity fading, which negates the advantages of nanoparticles. Furthermore, nanosizing silicon materials cannot address their poor electrical conductivity. Therefore, efforts are underway to combine silicon with other materials through suitable preparation methods to create silicon-based composites, leveraging the physical properties of the other materials to improve the electrochemical performance of elemental silicon. A promising approach is to combine silicon with structurally stable and highly conductive carbon materials. While fully utilizing the high capacity of silicon, the carbon materials mitigate silicon's volume expansion and provide transport pathways for electrons and lithium ions. However, the silicon-carbon composite material actually prepared has a low initial efficiency while reducing volume expansion, the electronic conductivity has not been significantly improved, and the silicon core and the shell carbon are prone to material peeling during long-term cycling, thereby affecting its cycling performance. In order to solve this problem, Chinese patent application CN106129367A discloses a silicon / carbon nanocomposite fiber, which is composed of carbon fiber and silicon nanoparticles. A hollow structure is formed on the surface of the carbon fiber and silicon nanoparticles are embedded, and there are gaps between the silicon nanoparticles and the carbon fiber to accommodate the volume expansion of the silicon nanoparticles. This composite material can protect individual silicon particles in the carbon fiber, and the presence of the void structure improves the structural stability of the composite material. However, the preparation process of this material is relatively complicated, and the conductivity needs to be further improved. Summary of the Invention

[0004] The purpose of the present invention is to provide a porous silicon-carbon composite negative electrode material, which solves the problems of poor conductivity and unstable structure of existing silicon-carbon materials.

[0005] Secondly, the present invention provides a method for preparing a porous silicon-carbon composite negative electrode material.

[0006] Again, the present invention provides an application of a porous silicon-carbon composite negative electrode material in the preparation of a lithium-ion battery.

[0007] Finally, the present invention provides a lithium ion battery using the porous silicon-carbon composite negative electrode material.

[0008] In order to achieve the above objectives, the technical solution adopted by the present invention is:

[0009] A porous silicon-carbon composite negative electrode material is prepared by a method comprising the following steps:

[0010] (1) mixing a polymer, tetraethyl orthosilicate, and an organic solvent to obtain a precursor solution;

[0011] The precursor solution is electrospun to obtain a nanofiber membrane;

[0012] (2) dispersing the nanofiber membrane in a silane coupling agent solution, mixing it evenly with nano-silicon and a conductive agent, and then performing a hydrothermal reaction. After the reaction, the nanofiber membrane is washed with an acid solution and dried to obtain a silicon oxide / nano-silicon composite material;

[0013] The silicon oxide compound / nano-silicon composite material is immersed in an ammonium fluoride solution, taken out and then carbonized to obtain the composite material.

[0014] The present invention combines a polymer with ethyl orthosilicate by electrostatic spinning, and the formed nanofiber membrane has high strength and appropriate porosity, which provides suitable space for the subsequent embedding of nano-silicon, and greatly alleviates the expansion of silicon during the charge and discharge process, thereby improving its cycle performance. At the same time, the present invention fills nano-silicon between the nano-fiber membrane layers, thereby increasing the tap density and contact area of ​​the material, reducing its electronic impedance, and utilizing the bridge effect of the silane coupling agent between the nano-silicon and the nano-fiber membrane to increase the binding force between the nano-silicon and the silicon oxide compound (such as silicon dioxide), thereby improving the structural stability of the material. The present invention adds a silane coupling agent before the hydrothermal reaction, which is beneficial to increasing the dispersibility of nano-silicon and carbon nanotubes, improving the binding ability of the two with the nano-fiber membrane, and forming a network structure; during the hydrothermal reaction, the silane coupling agent can also generate silicon free radicals, which are then cooled to generate a material containing silicon oxide compounds. In other words, the hydrothermal reaction mainly generates free radicals by gasification of the material, and then when the temperature is lowered, each free radical combines to generate different compounds.

[0015] As a preferred embodiment, in step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral, and polyvinyl pyrrolidone. Further preferably, the polymer is selected from one of polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate.

[0016] As a preferred embodiment, in step (1), the organic solvent is selected from one or more of ethanol, ethylene glycol, isopropyl alcohol, glycerol, N,N-dimethylformamide, and N-methylpyrrolidone. Further preferably, the organic solvent is selected from one of ethylene glycol, isopropyl alcohol, and N,N-dimethylformamide.

[0017] As a preferred embodiment, in step (1), the mass ratio of the polymer, tetraethyl orthosilicate, and organic solvent is (1-12): (1-12):100.

[0018] As a preferred embodiment, in step (1), the process parameters of the electrospinning are: a receiving distance of 10 to 20 cm, a voltage of 10 to 20 kV, an injection speed of the spinning solution (i.e., the precursor solution) of 0.01 to 0.1 mL / min, and a rotation speed of the drum receiving device of 50 to 100 r / min.

[0019] As a preferred embodiment, in step (1), after the electrospinning, the nanofiber membrane is dried at (40-60)°C under vacuum conditions for (40-60) hours. More preferably, the nanofiber membrane is dried at 50°C under vacuum conditions for 48 hours.

[0020] As a preferred embodiment, in step (2), the silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane (KH-550), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), and γ-(methacryloyloxy)propyltrimethoxysilane (KH-570).

[0021] As a preferred embodiment, in step (2), the silane coupling agent solution is prepared using one or more of ethylene glycol, isopropyl alcohol, dichloromethane, petroleum ether, and toluene as a solvent. The concentration of the silane coupling agent solution is 0.1 to 0.4 wt%.

[0022] As a preferred embodiment, in step (2), the conductive agent is carbon nanotubes.

[0023] As a preferred embodiment, in step (2), the mass ratio of the nanofiber membrane, silane coupling agent, nano-silicon, and carbon nanotubes is (10-20): (0.5-2): (1-5): (0.5-2).

[0024] As a preferred embodiment, in step (2), the hydrothermal reaction temperature is (100-200)°C and the reaction time is (1-6) hours. Such hydrothermal reaction conditions can fully mix the materials, achieve good uniformity, high synthesis efficiency, and good consistency.

[0025] As a preferred embodiment, in step (2), the acid solution is a dilute hydrochloric acid solution with a concentration of (0.5-2) wt %, more preferably 1 wt %. The acid cleaning is performed at least twice, preferably three times. The main function of the acid cleaning is to remove the slightly alkaline silane coupling agent, while the hydrogen ions in the hydrochloric acid slightly etch the surface of the silicon compound.

[0026] As a preferred embodiment, in step (2), the drying is freeze drying, preferably freeze drying at (-20 to -40)°C for (40 to 60) hours, more preferably freeze drying at -30°C for 48 hours.

[0027] As a preferred embodiment, in step (2), the ammonium fluoride solution is an aqueous solution of ammonium fluoride. The concentration of the ammonium fluoride solution is 40-60%, preferably 50%. One purpose of soaking in the ammonium fluoride solution is to utilize the nitrogen element in the ammonium fluoride to dope and improve the electronic conductivity of the material. On the other hand, the aqueous solution of ammonium fluoride is an acidic solution, which can slightly etch the surface of the silicon-based material.

[0028] As a preferred embodiment, in step (2), the soaking time is (24 to 72) hours.

[0029] As a preferred embodiment, in step (2), before the carbonization treatment, the product is dried at (70-90)°C under vacuum conditions for (24-48) hours, preferably at 80°C under vacuum conditions.

[0030] As a preferred embodiment, in step (2), the carbonization treatment conditions are: in an inert atmosphere, heating to (600-1000)°C at a heating rate of (1-10)°C / min, and keeping warm for (1-24)h.

[0031] As a preferred embodiment, in step (2), after the carbonization treatment, the material is naturally cooled to room temperature under an inert atmosphere, and then ball-milled and crushed to obtain a porous silicon-carbon composite negative electrode material. The inert atmosphere is an argon atmosphere. The particle size of the porous silicon-carbon composite negative electrode material is (1-15) μm, preferably (5-10) μm.

[0032] A method for preparing a porous silicon-carbon composite negative electrode material comprises the following steps:

[0033] (1) mixing a polymer, tetraethyl orthosilicate, and an organic solvent to obtain a precursor solution;

[0034] The precursor solution is electrospun to obtain a nanofiber membrane;

[0035] (2) dispersing the nanofiber membrane in a silane coupling agent solution, mixing it evenly with nano-silicon and a conductive agent, and then performing a hydrothermal reaction. After the reaction, the nanofiber membrane is washed with an acid solution and dried to obtain a silicon oxide / nano-silicon composite material;

[0036] The silicon oxide compound / nano-silicon composite material is immersed in an ammonium fluoride solution, taken out and then carbonized to obtain the composite material.

[0037] As a preferred embodiment, in step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral, and polyvinyl pyrrolidone. Further preferably, the polymer is selected from one of polyvinyl alcohol, polyethylene oxide, and polyvinyl acetate.

[0038] As a preferred embodiment, in step (1), the organic solvent is selected from one or more of ethanol, ethylene glycol, isopropyl alcohol, glycerol, N,N-dimethylformamide, and N-methylpyrrolidone. Further preferably, the organic solvent is selected from one of ethylene glycol, isopropyl alcohol, and N,N-dimethylformamide.

[0039] As a preferred embodiment, in step (1), the mass ratio of the polymer, tetraethyl orthosilicate, and organic solvent is (1-12): (1-12):100.

[0040] As a preferred embodiment, in step (1), the process parameters of the electrospinning are: a receiving distance of 10 to 20 cm, a voltage of 10 to 20 kV, an injection speed of the spinning solution (i.e., the precursor solution) of 0.01 to 0.1 mL / min, and a rotation speed of the drum receiving device of 50 to 100 r / min.

[0041] As a preferred embodiment, in step (1), after the electrospinning, the nanofiber membrane is dried at (40-60)°C under vacuum conditions for (40-60) hours. More preferably, the nanofiber membrane is dried at 50°C under vacuum conditions for 48 hours.

[0042] As a preferred embodiment, in step (2), the silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane (KH-550), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), and γ-(methacryloyloxy)propyltrimethoxysilane (KH-570).

[0043] As a preferred embodiment, in step (2), the silane coupling agent solution is prepared using one or more of ethylene glycol, isopropyl alcohol, dichloromethane, petroleum ether, and toluene as a solvent. The concentration of the silane coupling agent solution is 0.1 to 0.4 wt%.

[0044] As a preferred embodiment, in step (2), the conductive agent is carbon nanotubes.

[0045] As a preferred embodiment, in step (2), the mass ratio of the nanofiber membrane, silane coupling agent, nano-silicon, and carbon nanotubes is (10-20): (0.5-2): (1-5): (0.5-2).

[0046] As a preferred embodiment, in step (2), the temperature of the hydrothermal reaction is (100-200)°C, and the reaction time is (1-6)h.

[0047] As a preferred embodiment, in step (2), the acid solution is a dilute hydrochloric acid solution with a concentration of (0.5-2) wt%, more preferably 1 wt%. The cleaning with the acid solution is performed at least twice, preferably three times.

[0048] As a preferred embodiment, in step (2), the drying is freeze drying, preferably freeze drying at (-20 to -40)°C for (40 to 60) hours, more preferably freeze drying at -30°C for 48 hours.

[0049] As a preferred embodiment, in step (2), the ammonium fluoride solution is an aqueous solution of ammonium fluoride. The concentration of the ammonium fluoride solution is 40-60%, preferably 50%.

[0050] As a preferred embodiment, in step (2), the soaking time is (24 to 72) hours.

[0051] As a preferred embodiment, in step (2), before the carbonization treatment, the product is dried at (70-90)°C under vacuum conditions for (24-48) hours, preferably at 80°C under vacuum conditions.

[0052] As a preferred embodiment, in step (2), the carbonization treatment conditions are: in an inert atmosphere, heating to (600-1000)°C at a heating rate of (1-10)°C / min, and keeping warm for (1-24)h.

[0053] As a preferred embodiment, in step (2), after the carbonization treatment, the material is naturally cooled to room temperature under an inert atmosphere, and then ball-milled and crushed to obtain a porous silicon-carbon composite negative electrode material. The inert atmosphere is an argon atmosphere. The particle size of the porous silicon-carbon composite negative electrode material is (1-15) μm, preferably (5-10) μm.

[0054] The present invention combines a polymer with ethyl orthosilicate through electrospinning. The resulting nanofiber membrane has the advantages of high strength and moderate porosity, providing suitable space for the subsequent embedding of nanosilicon and carbon nanotubes. It also significantly reduces the volume expansion of silicon during charge and discharge, improving its cycling performance. Furthermore, the present invention hydrothermally incorporates nanosilicon and carbon nanotubes into the interlayers of the nanofiber network. The coupling effect of a silane coupling agent between the nanosilicon, carbon nanotubes, and the nanofiber membrane is utilized to improve the material's conductivity and structural stability. The result is a silicon-carbon composite negative electrode material with high porosity, large specific surface area, and low expansion rate.

[0055] The invention discloses an application of a porous silicon-carbon composite negative electrode material in the preparation of a lithium-ion battery.

[0056] A lithium-ion battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode comprises a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector. The negative electrode material layer comprises a negative electrode material, a conductive agent, and a binder. The negative electrode material adopts the above-mentioned porous silicon-carbon composite negative electrode material.

[0057] Beneficial effects of the present invention:

[0058] In the porous silicon-carbon composite negative electrode material of the present invention, nano-silicon is evenly dispersed in the mesh of the framework formed by nanofibers, and the fibers are intertwined and penetrated to form pores, which can reduce the volume expansion of silicon; at the same time, the present invention utilizes the network structure formed by the coupling effect of silane coupling agent between nano-silicon, carbon nanotubes, and nanofiber membranes to improve the conductivity and structural stability of the material, and ultimately obtains a silicon-carbon composite negative electrode material with high porosity, large specific surface area, low expansion rate, and high specific capacity.

[0059] The method first prepares a polymer / ethyl orthosilicate nanofiber membrane, which is then immersed in a dispersed solution of nanosilicon and carbon nanotubes. The membrane undergoes a hydrothermal reaction, freeze-drying, and carbonization to produce a porous silicon-carbon composite anode material. This method is simple to prepare and operate, suitable for planned industrial production, and aligns with modern green environmental protection concepts. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a SEM image (10 μm) of the porous silicon-carbon composite negative electrode material in Example 1 of the present invention;

[0061] Figure 2 This is the SEM image (3 μm) of the porous silicon-carbon composite negative electrode material in Example 1 of the present invention.

[0062] To more clearly illustrate the technical solutions of the embodiments of the present invention, the above briefly introduces the drawings obtained in the experimental examples. It should be understood that the above drawings only illustrate certain experimental examples of the present invention and should not be construed as limiting the scope of protection of the claims. Those skilled in the art can also derive other relevant drawings based on these drawings without inventive effort. DETAILED DESCRIPTION

[0063] In order to make the technical problems to be solved by the present invention, the technical solutions adopted, and the technical effects achieved easier to understand, the technical solutions of the present invention are clearly and completely described below in conjunction with specific embodiments, comparative examples, and experimental examples. It should be noted that if specific conditions are not specified in the embodiments, comparative examples, and experimental examples, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents, instruments, etc. used in the embodiments, comparative examples, and experimental examples can all be purchased through commercial channels.

[0064] Example 1

[0065] The porous silicon-carbon composite negative electrode material of the present invention is prepared by a method comprising the following steps:

[0066] (1) Preparation of nanofiber membrane:

[0067] Dissolve 5 g of polyvinyl alcohol and 5 g of tetraethyl orthosilicate in 100 mL of ethylene glycol organic solvent to obtain a precursor solution;

[0068] The precursor solution was electrospun (receiving distance 15 cm, voltage 15 kV, spinning solution injection rate 0.05 mL / min, roller receiving device speed 80 rpm), and then dried under vacuum conditions at 50 °C for 48 h to obtain a nanofiber membrane;

[0069] (2) Preparation of porous silicon-carbon composite negative electrode materials:

[0070] 15 g of nanofiber membrane was dispersed in 500 mL of ethylene glycol organic solvent with a concentration of 0.2 wt% of γ-aminopropyltriethoxysilane, followed by adding 3 g of nanosilicon and 1 g of carbon nanotubes. The mixture was evenly mixed and transferred to an autoclave for reaction at 150°C for 3 h. The mixture was then washed three times with 1 wt% dilute hydrochloric acid and freeze-dried at -30°C for 48 h to obtain a silicon oxide / nanosilicon composite material.

[0071] The silicon oxide compound / nano-silicon composite material was transferred to a 50% ammonium fluoride solution and soaked for 48 hours, then filtered and vacuum dried (80°C, 36 hours), and heated to 700°C at a heating rate of 5°C / min under an argon inert atmosphere, kept warm for 12 hours, and then naturally cooled to room temperature under an argon inert atmosphere, ball milled and crushed to obtain a porous silicon-carbon composite negative electrode material.

[0072] Example 2

[0073] The porous silicon-carbon composite negative electrode material of the present invention is prepared by a method comprising the following steps:

[0074] (1) Preparation of nanofiber membrane:

[0075] Dissolve 1 g of polyethylene oxide and 1 g of ethyl orthosilicate in 100 mL of isopropyl alcohol to obtain a precursor solution.

[0076] The precursor solution was electrospun (receiving distance 10 cm, voltage 10 kV, spinning solution injection rate 0.01 mL / min, roller receiving device speed 50 rpm), and then dried under vacuum conditions at 50 °C for 48 h to obtain a nanofiber membrane;

[0077] (2) Preparation of porous silicon-carbon composite negative electrode materials:

[0078] 10 g of the nanofiber membrane was dispersed in 500 mL of an isopropanol organic solvent containing 0.1 wt% of γ-(methacryloyloxy)propyltrimethoxysilane, followed by addition of 1 g of nanosilicon and 0.5 g of carbon nanotubes. The mixture was mixed well and transferred to an autoclave for reaction at 100°C for 6 h. The mixture was then washed three times with 1 wt% dilute hydrochloric acid and freeze-dried at -30°C for 48 h to obtain a silicon oxide / nanosilicon composite material.

[0079] The silicon oxide compound / nano-silicon composite material was transferred to a 50% ammonium fluoride solution and soaked for 24 hours, then filtered and vacuum dried (80°C, 36 hours), and heated to 600°C at a heating rate of 1°C / min under an argon inert atmosphere, kept warm for 24 hours, and then naturally cooled to room temperature under an argon inert atmosphere, ball milled and crushed to obtain a porous silicon-carbon composite negative electrode material.

[0080] Example 3

[0081] The porous silicon-carbon composite negative electrode material of the present invention is prepared by a method comprising the following steps:

[0082] (1) Preparation of nanofiber membrane:

[0083] Dissolve 10 g of polyvinyl acetate and 10 g of tetraethyl orthosilicate in 100 mL of N,N-dimethylformamide organic solvent to obtain a precursor solution;

[0084] The precursor solution was electrospun (receiving distance 20 cm, voltage 20 kV, spinning solution injection rate 0.1 mL / min, roller receiving device speed 100 rpm), and then dried under vacuum conditions at 50 °C for 48 h to obtain a nanofiber membrane;

[0085] (2) Preparation of porous silicon-carbon composite negative electrode materials:

[0086] 20 g of the nanofiber membrane was dispersed in 500 mL of a dichloromethane organic solvent containing 0.4 wt% γ-(2,3-epoxypropoxy)propyltrimethoxysilane, followed by addition of 5 g of nanosilicon and 2 g of carbon nanotubes. The mixture was mixed evenly and transferred to an autoclave for reaction at 200 ° C for 1 h. The mixture was then washed three times with 1 wt% dilute hydrochloric acid and freeze-dried at -30 ° C for 48 h to obtain a silicon oxide / nanosilicon composite material.

[0087] The silicon oxide compound / nano-silicon composite material was transferred to a 50% ammonium fluoride solution and soaked for 72 hours, then filtered and vacuum dried (80°C, 36 hours), and heated to 1000°C at a heating rate of 10°C / min under an argon inert atmosphere, kept warm for 1 hour, and then naturally cooled to room temperature under an argon inert atmosphere, ball milled and crushed to obtain a porous silicon-carbon composite negative electrode material.

[0088] Comparative Example

[0089] The silicon-carbon composite negative electrode material of this comparative example is prepared by a method comprising the following steps:

[0090] 15 g of silica and 3 g of nano-silicon were added to 100 mL of ethylene glycol, mixed evenly by ball milling, and then transferred to a tube furnace. Under an argon inert atmosphere, the temperature was increased to 700 ° C at a heating rate of 5 ° C / min and kept warm for 12 hours. Then, the temperature was naturally cooled to room temperature under an argon inert atmosphere, ball milled and crushed to obtain a silicon-carbon composite negative electrode material.

[0091] Experimental example

[0092] 1. SEM test

[0093] The silicon-carbon composite negative electrode material of Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 and Figure 2 shown.

[0094] Depend on Figure 1 It can be seen that the particle size of the silicon-carbon composite negative electrode material is 5 to 10 μm, and the size distribution is uniform and reasonable.

[0095] Depend on Figure 2 It can be seen that the silicon-carbon composite negative electrode material has a porous structure.

[0096] 2. Physical and chemical testing

[0097] According to the method in the national standard GBT-245332009 "Graphite-based negative electrode materials for lithium-ion batteries", the silicon-carbon composite negative electrode materials of Examples 1 to 3 and the silicon-carbon composite negative electrode material of Comparative Example 1 were subjected to physical and chemical tests to test their specific surface area, powder conductivity and porosity, respectively. The test results are shown in Table 1.

[0098] Table 1 Physical and chemical test results

[0099] sample <![CDATA[Specific surface area (m 2 / g)]]> Conductivity (S / CM) Porosity (%) Example 1 9.9 9.6 28.5 Example 2 8.8 9.1 26.7 Example 3 7.5 8.3 25.4 Comparative Example 1 2.9 1.5 15.5

[0100] As can be seen from Table 1, the silicon-carbon composite negative electrode material of the present invention has a large porosity and specific surface area due to the porous structure between the layers of the nanofiber membrane. At the same time, the hydrothermal method can fully mix the silicon oxide compound and the nano-silicon and achieve good contact. It also contains carbon nanotubes with high conductivity, which improves the conductivity.

[0101] 3. Button battery performance test

[0102] The silicon-carbon composite negative electrode materials of Examples 1 to 3 and the silicon-carbon composite negative electrode material of Comparative Example 1 were respectively used as one of the active materials to prepare pole pieces. The specific preparation method was as follows: 9 g of active material, 0.5 g of conductive agent SP, and 0.5 g of binder LA136D were added to 220 mL of deionized water and stirred evenly to obtain a slurry; the slurry was coated on a copper foil current collector to obtain the product.

[0103] The pole piece using the silicon-carbon composite negative electrode material of Example 1 doped with 80% artificial graphite as the active material is marked as A, the pole piece using the silicon-carbon composite negative electrode material of Example 2 doped with 80% artificial graphite as the active material is marked as B, the pole piece using the silicon-carbon composite negative electrode material of Example 3 doped with 80% artificial graphite as the active material is marked as C, and the pole piece using the silicon-carbon composite material of Comparative Example 1 doped with 80% artificial graphite as the active material is marked as D.

[0104] The prepared electrode sheet served as the positive electrode and was assembled into button cells with a lithium sheet, electrolyte, and separator in a glove box maintained at oxygen and water concentrations below 0.1 ppm. The separator was Celebard 2400; the electrolyte was a LiPF6 solution with a concentration of 1 mol / L, and the solvent was a mixture of ethylene carbonate (EC) and diethyl carbonate (DMC) (1:1 weight ratio). The button cells were labeled A-1, B-1, C-1, and D-1, respectively. Their performance was then tested using a blue battery tester under the following conditions: a 0.1C charge-discharge rate over a voltage range of 0.05 to 2 V, with a 3-cycle cycle. The test results are shown in Table 2.

[0105] Table 2 Button battery performance test results

[0106] lithium-ion batteries First discharge capacity (mAh / g) First efficiency (%) A-1 1568.4 84.9 B-1 1531.6 84.1 C-1 1498.9 84.3 D-1 1139.4 77.1

[0107] As can be seen from Table 2, the button cell prepared using the silicon-carbon composite negative electrode material of the present invention has a high first discharge capacity and first efficiency. On the one hand, this is because the electronic conductivity of the silicon-carbon composite negative electrode material is high, which improves the specific capacity of the material; on the other hand, the hydrothermal method can make the nano-silicon and the silicon oxide compound fully contact and mix evenly, and then generate materials such as silicon monoxide during the sintering process (nano-silicon and silicon dioxide can undergo a disproportionation reaction at 900°C to generate silicon monoxide, and the ICP elemental analysis of the material shows that the composite material contains silicon oxide and other silicon oxide compounds), thereby improving the discharge capacity of the material.

[0108] 4. Soft pack battery performance test

[0109] The prepared electrode sheet is used as the negative electrode and the positive electrode ternary material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 5Ah soft-pack batteries were assembled using a celegard 2400 separator and a LiPF6 solution (the solvent was a mixture of EC and DEC in a 1:1 volume ratio, with a LiPF6 concentration of 1.3 mol / L). The resulting soft-pack batteries were labeled A-2, B-2, C-2, and D-2.

[0110] The following performance tests are performed on soft pack batteries:

[0111] (1) The thickness D1 of the negative electrode sheets of the fixed-capacity soft-pack batteries A-2, B-2, C-2, and D-2 was dissected and tested. After each soft-pack battery was cycled 100 times (1C / 1C, 25±3°C, 2.8-4.2V), the soft-pack battery was fully charged and dissected again to test the thickness D2 of the negative electrode sheet after the cycle. The expansion rate was then calculated, and the results are shown in Table 3. The liquid absorption capacity of each electrode was also tested, and the results are shown in Table 3.

[0112]

[0113] Table 3 Negative electrode expansion rate test results

[0114] lithium-ion batteries D1(μm) D2(μm) Expansion rate (%) Electrode liquid absorption (mL / min) A-2 105 155 47.6 9.7 B-2 104 154.8 48.8 9.1 C-2 106 156.1 47.3 8.9 E-2 105 182.7 74 2.5

[0115] As can be seen from Table 3, the expansion rate of the negative electrode sheet of the soft-pack battery using the silicon-carbon composite negative electrode material of the present invention is significantly lower than that of the comparative example. The reason is that the composite material of the present invention contains a network structure formed by silicon oxide (mainly silicon dioxide) fibers with high mechanical strength, which can buffer the volume expansion during the charge and discharge process. At the same time, the carbon nanotubes have a high specific surface area, which is beneficial to improving the liquid absorption capacity of the negative electrode sheet.

[0116] (2) The soft-pack batteries A-2, B-2, C-2, and D-2 were subjected to cycle performance tests respectively. The test conditions were: charge and discharge voltage range of 2.8 to 4.2 V, temperature of 25 ± 3.0 ° C, and charge and discharge rate of 1.0 C / 1.0 C. The test results are shown in Table 4.

[0117] Table 4 Soft pack battery cycle performance test results

[0118]

[0119] As can be seen from Table 4, the cycle performance of the soft-pack battery prepared using the silicon-carbon composite negative electrode material of the present invention is better than that of the comparative example at all stages of the cycle. The reason is that the network structure in the composite material of the present invention reduces its expansion rate and improves the cycle performance.

[0120] The present invention first combines a polymer with ethyl orthosilicate through an electrospinning method to form a nanofiber membrane with high strength and suitable porosity. This provides suitable space for the subsequent embedding of nanosilicon and carbon nanotubes, greatly alleviates the volume expansion of silicon during the charge and discharge process, and improves its cycle performance. At the same time, the present invention fills the interlayers of the nanofiber membrane with nanosilicon and carbon nanotubes, increasing the material's tap density and contact area, and reducing electronic impedance. The present invention also utilizes the coupling effect of a silane coupling agent between the nanosilicon, carbon nanotubes, and the nanofiber membrane to improve the material's conductivity and structural stability, ultimately obtaining a silicon-carbon composite negative electrode material with high porosity, large specific surface area, and low expansion rate. In this composite material, nanosilicon and carbon nanotubes are evenly dispersed in the framework mesh formed by the nanofibers, and the fibers intersect and penetrate to form pores, which can effectively reduce the volume expansion of silicon and improve the material's conductivity and structural stability.

[0121] The method of the present invention utilizes porous technology, which can, on the one hand, restrain the multi-directional expansion of silicon during the cycle and reduce the consumption of lithium ions. At the same time, the multi-dimensional structure can expand in more directions, reducing the expansion of silicon in the vertical direction, and utilizing silicon and carbon composite technology to reduce the electronic conductivity of the material. The method first prepares a polymer / ethyl orthosilicate nanofiber membrane, which is then immersed in a dispersed solution of nano-silicon and carbon nanotubes, and then undergoes hydrothermal reaction, freeze drying, and carbonization treatment to obtain a porous silicon-carbon composite negative electrode material. The method has a simple preparation process and is easy to operate, suitable for planned industrial production. The obtained composite material has the characteristics of high porosity, large specific surface area, low expansion rate, high specific capacity, etc. The lithium-ion battery prepared therefrom has good rate performance and cycle performance.

[0122] The above are only preferred embodiments and experimental examples of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various changes and modifications when it is specifically implemented. Any modification, replacement (equivalence), improvement, etc. made within the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A porous silicon-carbon composite negative electrode material, characterized in that: The composite negative electrode material is prepared by a method comprising the following steps: (1) mixing a polymer, tetraethyl orthosilicate, and an organic solvent to obtain a precursor solution; The precursor solution is electrospun to obtain a nanofiber membrane; (2) the nanofiber membrane is dispersed in a silane coupling agent solution, mixed evenly with nano-silicon and a conductive agent, and then subjected to a hydrothermal reaction. After the reaction, the mixture is washed with an acid solution and dried to obtain a silicon oxide compound / nano-silicon composite material; the silicon oxide compound / nano-silicon composite material is immersed in an ammonium fluoride solution, taken out and carbonized to obtain the nano-silicon; the nano-silicon is filled between the nanofiber membrane layers; In step (2), the silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; the conductive agent is carbon nanotubes, and the mass ratio of the nanofiber membrane, silane coupling agent, nanosilicon, and carbon nanotubes is (10-20):(0.5-2):(1-5):(0.5-2); the temperature of the hydrothermal reaction is 100-200°C, and the reaction time is 1-6h; the concentration of the ammonium fluoride solution is 40-60%, and the immersion time is 24-72h; the conditions for the carbonization treatment are: in an inert atmosphere, heating to 600-1000°C at a heating rate of 1-10°C / min, and keeping warm for 1-24h.

2. The porous silicon-carbon composite negative electrode material according to claim 1, wherein: In step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral, and polyvinyl pyrrolidone; and / or the organic solvent is selected from one or more of ethanol, ethylene glycol, isopropyl alcohol, glycerol, N,N-dimethylformamide, and N-methylpyrrolidone; and / or the mass ratio of the polymer, tetraethyl orthosilicate, and the organic solvent is (1-12):(1-12):

100.

3. The porous silicon-carbon composite negative electrode material according to any one of claims 1 to 2, characterized in that: The particle size of the composite negative electrode material is 1 to 15 μm.

4. A method for preparing a porous silicon-carbon composite negative electrode material, characterized in that: The following steps are involved: (1) mixing a polymer, tetraethyl orthosilicate, and an organic solvent to obtain a precursor solution; The precursor solution is electrospun to obtain a nanofiber membrane; (2) dispersing the nanofiber membrane in a silane coupling agent solution, uniformly mixing with nano-silicon and a conductive agent, and then performing a hydrothermal reaction. After the reaction, the nano-silicon is washed with an acid solution and dried to obtain a silicon oxide compound / nano-silicon composite material; soaking the silicon oxide compound / nano-silicon composite material in an ammonium fluoride solution, taking it out and carbonizing it to obtain a nano-silicon filled between the nanofiber membrane layers; In step (2), the silane coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane; the conductive agent is carbon nanotubes, and the mass ratio of the nanofiber membrane, silane coupling agent, nanosilicon, and carbon nanotubes is (10-20):(0.5-2):(1-5):(0.5-2); the temperature of the hydrothermal reaction is 100-200°C, and the reaction time is 1-6h; the acid solution is a dilute hydrochloric acid solution with a concentration of 0.5-2wt%; In step (2), the concentration of the ammonium fluoride solution is 40-60%, and the immersion time is 24-72 hours; the conditions of the carbonization treatment are: in an inert atmosphere, heating to 600-1000° C. at a heating rate of 1-10° C. / min, and keeping warm for 1-24 hours.

5. The method for preparing the porous silicon-carbon composite negative electrode material according to claim 4, wherein: In step (1), the polymer is selected from one or more of polyvinyl alcohol, polyvinylidene fluoride, polyethylene oxide, polyvinyl acetate, polyvinyl butyral, and polyvinyl pyrrolidone; and / or the organic solvent is selected from one or more of ethanol, ethylene glycol, isopropyl alcohol, glycerol, N,N-dimethylformamide, and N-methylpyrrolidone; and / or the mass ratio of the polymer, tetraethyl orthosilicate, and the organic solvent is (1-12):(1-12):

100.

6. Use of the porous silicon-carbon composite negative electrode material according to any one of claims 1 to 2 or the porous silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 4 to 5 in preparing a lithium-ion battery.

7. A lithium-ion battery, characterized in that: The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode material layer coated on the surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode material, a conductive agent, and a binder. The negative electrode material is a porous silicon-carbon composite negative electrode material according to any one of claims 1 to 2 or a porous silicon-carbon composite negative electrode material prepared by the preparation method according to any one of claims 4 to 5.

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