A lithium-ion battery silicon-carbon nanowire material and its preparation method and application

Abstract

The present invention discloses a lithium-ion battery silicon-carbon nanowire material, a preparation method and an application thereof, and belongs to the field of battery material technology. The lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer, wherein the core layer is a silicon material coated with fuzzy carbon nanotubes, the tubular shell layers are interwoven into a mesh structure, the tubular shell layers are nitrogen-doped carbon fibers with a cavity structure, the fuzzy carbon nanotubes are connected to the cavity of the tubular shell layers, and the fuzzy carbon nanotubes include a transition metal element inside. The present invention can buffer the volume stress generated by the silicon material during the lithiation process by wrapping the surface of the silicon material with fuzzy nano-metal carbon nanotubes, and the fuzzy nano-metal carbon nanotubes are connected to the cavity of the tubular shell nitrogen-doped carbon fibers, thereby preventing side reactions with the electrolyte and improving the cycle stability of the silicon material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and more specifically, to a lithium-ion battery silicon-carbon nanowire material and a preparation method and application thereof. Background Art

[0002] After decades of development, the traditional negative electrode graphite has only 372mAh·g -1 The theoretical capacity of lithium ion batteries is difficult to meet the demand for high energy density, so it is particularly important to find the next generation of high energy density secondary lithium ion battery negative electrode materials. 15 Si4 has 3757mAh·g -1 It has a high theoretical capacity and a low lithium insertion and extraction voltage platform below 0.4Vv.s.Li+ / Li. It is also abundant in reserves, environmentally friendly and low in cost, so it has great development potential.

[0003] Silicon-based anodes suffer from large volume changes during charge and discharge, poor cycle performance, and low initial efficiency, limiting their commercial application. The main reasons for the poor cycle performance of silicon-based anodes are: first, silicon is a semiconductor material with poor electronic and ionic conductivity, which hinders the material's electrochemical performance. Second, during alloying with lithium, silicon expands by over 300%. This dramatic volume change can easily lead to particle pulverization and fragmentation, and damage the SEI film, severely reducing the cycle life of lithium-ion batteries. Third, the HF produced by the decomposition of the lithium salt LiPF6 reacts with silicon, creating an unstable interface between the silicon anode and the electrolyte. The solid electrolyte film (SEI film) formed on the surface of the silicon anode material cannot adapt to the significant volume changes during lithium insertion and removal, and breaks down, exposing the silicon surface to the electrolyte. This leads to continuous formation of the solid electrolyte film, consumption of active lithium, and ultimately capacity loss.

[0004] To address the above-mentioned issues, the prior art discloses a lithium-ion battery silicon-carbon anode material. This material is prepared by electrospinning nano-silicon coated with a lithium source, using polyacrylonitrile and polystyrene as the core layer, and polymethyl methacrylate, polyacrylonitrile, or polystyrene as the shell solution to obtain a pre-lithiated silicon-carbon core-shell fiber anode material. By adding lithium-source-coated nano-silicon during the spinning process, this method reduces oxidation of the nano-silicon during the pre-oxidation process and replenishes the lithium consumed by SEI formation, thereby improving the initial coulombic efficiency of the lithium-ion battery. However, this method does not address the improvement of the cycle capacity retention rate of lithium-ion batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing silicon-carbon negative electrode materials that cannot improve the cycle capacity retention rate of lithium-ion batteries, and provide a lithium-ion battery silicon-carbon nanowire material. By tightly wrapping the metal particles and the grown fuzzy carbon nanotubes on the surface of the silicon material, the contact with the silicon material inside the material is increased, the volume stress generated by the silicon material during the lithiation process is buffered, the capacity of the material during the charge and discharge process and the structural stability during the cycle process are promoted, thereby improving the cycle capacity retention rate of the lithium-ion battery, and also having a higher initial charge and discharge specific capacity.

[0006] Another object of the present invention is to provide a method for preparing silicon-carbon nanowire materials for lithium-ion batteries.

[0007] Another object of the present invention is to provide a negative electrode sheet for a lithium ion battery.

[0008] Another object of the present invention is to provide a lithium ion battery.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a fuzzy carbon nanotube-coated silicon material. The tubular shell layers are interwoven into a mesh structure. The tubular shell layers are nitrogen-doped carbon fibers with a cavity structure. The fuzzy carbon nanotubes are connected to the cavities of the tubular shell layers, and the interior of the fuzzy carbon nanotubes contains a transition metal element.

[0011] The lithium-ion battery silicon-carbon nanowire material of the present invention is characterized in that the surface of the silicon material is wrapped with fuzzy nano-metal carbon nanotubes, and the fuzzy nano-metal carbon nanotubes are connected to the cavity of the tubular shell nitrogen-doped carbon fiber, which can buffer the volume stress generated by the silicon material during the lithiation process, prevent the internal silicon material from having side reactions with the electrolyte, improve the structural stability of the material, and improve the cycle stability of the silicon material; the fuzzy carbon nanotubes include transition metal elements inside, and the carbon nanotubes and metal nanoparticles can increase the contact area and conductivity with the silicon inside the cavity, promote the capacity of silicon, improve the conductivity and rate performance of the silicon material, and effectively reduce the use of conductive agents for the silicon negative electrode; the tubular shell has a nitrogen-doped carbon fiber with a cavity structure, which can provide a continuous conductive network and have space to alleviate the volume expansion of the silicon material, prevent the SEI film from repeatedly growing on the surface of the silicon material, and protect the stability of the capacity of the material during the charge and discharge process, thereby improving the cycle performance of the battery.

[0012] Preferably, the transition metal is iron, cobalt, nickel, manganese or copper.

[0013] Preferably, the silicon material is one or more of silicon powder, silicon monoxide or silicon dioxide.

[0014] The present invention also protects a method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material, comprising the following steps:

[0015] S1. The silicon source, carbon source and solvent are mixed uniformly to obtain a core solution;

[0016] S2. The metal salt, carbon-nitrogen source and solvent are mixed to obtain a shell solution;

[0017] S3. Coaxially electrospinning the core solution and the shell solution to obtain a core-shell fiber layer;

[0018] S4. Pre-oxidizing the core-shell fiber layer and carbonizing it in a non-oxidizing atmosphere to obtain a lithium-ion battery silicon carbon nanowire material;

[0019] Wherein, in S1, the carbon source is one or more of polystyrene, polyacrylonitrile, polyvinyl pyrrolidone or polymethyl methacrylate;

[0020] The mass ratio of silicon source to carbon source is 1:(3-6);

[0021] In S2, the metal salt is one or more of iron salt, cobalt salt, nickel salt, manganese salt or copper salt;

[0022] The carbon-nitrogen source is one or more of polyacrylonitrile, polypyrrole, asphalt, polyamide, urea or melamine;

[0023] The mass ratio of the metal salt to the carbon-nitrogen source is 1:(1.5-7);

[0024] In S3, the electrospinning voltage was 8–30 kV, the receiving distance was 10–25 cm, and the mass ratio of the core solution to the shell solution output was 1:(1.5–2.5);

[0025] In S4, the pre-oxidation temperature is 120-150°C, the carbonization temperature is 700-1000°C, and the carbonization time is 2-5 hours.

[0026] The present invention comprises the following steps: (1) adding metal salts to the shell solution of coaxial electrospinning, wherein the metal salts in situ grow fuzzy nano-metal-carbon nanotubes during the carbonization and pyrolysis process, which can effectively wrap the silicon material, buffer the volume stress generated by the silicon source during the lithiation process, prevent the silicon source from reacting with the electrolyte, and improve the structural stability of the silicon-carbon material during the lithium ion insertion and extraction process, thereby ensuring the performance of the cycle capacity of the lithium-ion battery during the charge and discharge process. (2) The nano-metal-carbon nanotubes in the core layer are a "fuzzy carbon nanotube" structure generated by the pyrolysis catalysis of the transition metal in the carbon source atmosphere, tightly wrapped on the surface of the silicon material, increasing the contact with the silicon material inside the fiber, improving the conductivity and rate performance of the silicon material, and effectively reducing the use of conductive agents for the silicon negative electrode; (3) by adding carbon-nitrogen sources to the shell solution to prepare nitrogen-doped carbon fibers containing "carbon-nitrogen" elements and having a cavity structure, a continuous conductive network can be provided while having space to alleviate the volume expansion of the silicon material, preventing the SEI film from growing repeatedly on the surface of the silicon material, protecting the stability of the capacity of the material during the charge and discharge process, thereby improving the battery performance.

[0027] Preferably, in the S2 shell solution, the mass ratio of the metal salt to the carbon-nitrogen source is 1:(1.5-3).

[0028] Preferably, the metal salt is one or more of acetate, acetylacetonate, nitrate, sulfate or phosphate.

[0029] The metal salt includes at least one of nickel acetate, iron acetate, copper acetate, cobalt acetate, manganese acetate, nickel acetylacetonate, iron acetylacetonate, copper acetylacetonate, cobalt acetylacetonate, manganese acetylacetonate, nickel nitrate, iron nitrate, cobalt nitrate, copper nitrate, manganese nitrate, nickel sulfate, iron sulfate, copper sulfate, cobalt sulfate, manganese sulfate, nickel phosphate, iron phosphate, cobalt phosphate, copper phosphate, and manganese phosphate.

[0030] Preferably, in S4, the carbonization temperature is 750-750°C.

[0031] Preferably, in the core solution, the mass fraction of the silicon source and the carbon source is 40% to 80%; in the shell solution, the mass fraction of the metal salt and the carbon-nitrogen source is 55% to 85%.

[0032] In the present invention, the solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and dichloromethane.

[0033] The non-oxidizing atmosphere is at least one of argon, a hydrogen-argon mixture, or nitrogen.

[0034] The present invention also protects a lithium ion battery negative electrode sheet, comprising the above-mentioned lithium ion battery silicon-carbon nanowire material.

[0035] The lithium ion battery silicon carbon nanowire material and conductive agent powder are dry-mixed to obtain a mixed powder; a binder is added to the mixed powder, and the mixture is stirred evenly to obtain a slurry and prepare a lithium ion battery negative electrode sheet.

[0036] The present invention also protects a lithium ion battery, comprising the above-mentioned lithium ion battery negative electrode sheet.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention discloses a silicon-carbon nanowire material for lithium-ion batteries. The surface of the silicon material is wrapped with fuzzy nano-metal carbon nanotubes, and the fuzzy nano-metal carbon nanotubes are connected to the cavity of the tubular shell nitrogen-doped carbon fiber. The fuzzy nano-metal carbon nanotubes can buffer the volume stress generated by the silicon material during the lithiation process, prevent side reactions with the electrolyte, and improve the cycle stability of the silicon material. In addition, the contact between the nitrogen-doped carbon fiber and the silicon material is increased inside, thereby improving the conductivity and rate performance of the silicon material and effectively reducing the use of conductive agents in the silicon negative electrode. The tubular shell has a nitrogen-doped carbon fiber with a cavity structure, which can provide a continuous conductive network while having space to alleviate the volume expansion of the silicon material, prevent the repeated growth of the SEI film on the surface of the silicon material, and protect the stability of the material's capacity during the charge and discharge process, thereby improving battery performance.

[0039] The lithium-ion battery prepared by using the lithium-ion silicon-carbon nanowire as the negative electrode material of the lithium-ion battery has a capacity higher than 1000 mAh g -1 The first discharge specific capacity is high, and after 1000 cycles, it still has a high discharge specific capacity, and the capacity retention rate can reach more than 84%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a scanning electron microscope (SEM) image of the lithium-ion battery silicon-carbon nanowire material of Example 1 of the present invention.

[0041] Figure 2 This is a scanning electron microscope (SEM) image of the cross section of the lithium-ion battery silicon-carbon nanowire material according to Example 1 of the present invention.

[0042] Figure 3 Transmission electron microscopy and EDS element distribution diagrams of the lithium-ion battery silicon-carbon nanowire material of Example 1 of the present invention.

[0043] Figure 4 This is a transmission electron microscope (TEM) image of the lithium-ion battery silicon-carbon nanowire material of Example 1 of the present invention.

[0044] Figure 5 The X-ray diffraction (XRD) patterns of the materials of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are shown.

[0045] Figure 6 These are Raman spectra of the materials of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention.

[0046] Figure 7 This is a BET specific surface area diagram of the lithium-ion battery silicon-carbon nanowire material of Example 1 of the present invention.

[0047] Figure 8 This is a schematic structural diagram of the lithium-ion battery silicon-carbon nanowire material according to Example 1 of the present invention.

[0048] Figure 9 DFT calculation of the energy barrier for the adsorption-diffusion of lithium ions using nickel, nitrogen, and graphitized carbon in the material of Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0050] Example 1

[0051] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fiber with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, nickel.

[0052] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0053] S1. Add silicon powder and polystyrene powder to N,N-dimethylformamide in a mass ratio of 1:6, mix thoroughly and stir to prepare a core solution with a mass fraction of 40%.

[0054] S2. Add nickel acetylacetonate and polyacrylonitrile powder in a mass ratio of 2:3 to N,N-dimethylformamide, mix and stir thoroughly, and prepare a shell solution with a mass fraction of 65% after complete dissolution.

[0055] S3. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 15 kV, the receiving distance was 20 cm, and the receiving device was release paper.

[0056] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 130℃ to maintain the fiber morphology, and then heated to 750℃ under argon protection and carbonized for 4 hours to fully carbonize the fiber layer. Fluffy nickel-carbon nanotubes (Ni-CNTs) are in situ grown inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of silicon powder to obtain lithium-ion battery silicon-carbon nanowire material.

[0057] Example 2

[0058] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fiber with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, which is iron.

[0059] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0060] S1. Add silicon powder and polymethyl methacrylate powder to N,N-dimethylacetamide in a mass ratio of 1:5, mix thoroughly and stir evenly to prepare a core solution with a mass fraction of 45%.

[0061] S2. Add ferric phosphate and (polyacrylonitrile: urea = 8:1) to N,N-dimethylacetamide in a mass ratio of 1:3, mix and stir thoroughly, and prepare a shell solution with a mass fraction of 80% after complete dissolution.

[0062] S3. The core solution and shell solution were introduced into the coaxial needle respectively. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 2:5, the applied voltage was 8 kV, the receiving distance was 15 cm, and the receiving device was release paper.

[0063] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 120℃ to maintain the fiber morphology, and then heated to 850℃ under nitrogen protection and carbonized for 5 hours to fully carbonize the fiber layer. Fluffy iron-carbon nanotubes (Fe-CNTs) are in situ grown inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of silicon powder to obtain lithium-ion battery silicon-carbon nanowire material.

[0064] Example 3

[0065] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fibers with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, which is cobalt.

[0066] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0067] S1. Silicon oxide powder and polymethyl methacrylate powder were added to dimethyl sulfoxide in a mass ratio of 1:4, and the mixture was thoroughly mixed and stirred to prepare a core solution with a mass fraction of 65%.

[0068] S2. Cobalt sulfate and polyamide were added to dimethyl sulfoxide in a mass ratio of 1:4, and the mixture was thoroughly mixed and stirred to form a shell solution with a mass fraction of 65% after complete dissolution.

[0069] S3. The core solution and shell solution were introduced into the coaxial needle respectively. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 2:3, the applied voltage was 12 kV, the receiving distance was 25 cm, and the receiving device was release paper.

[0070] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 135℃ to maintain the fiber morphology, and then heated to 850℃ for carbonization for 3 hours under the protection of hydrogen-argon mixed gas to fully carbonize the fiber layer. Fluffy cobalt-carbon nanotubes (Co-CNTs) are in situ grown inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of silicon oxide to obtain lithium-ion battery silicon-carbon nanowire material.

[0071] Example 4

[0072] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fiber with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, nickel.

[0073] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0074] S1. Add silicon oxide powder and polyvinyl pyrrolidone powder in a mass ratio of 1:3 to dichloromethane solvent, mix thoroughly and stir evenly to prepare a core solution with a mass fraction of 75%.

[0075] S2. Nickel acetate and (polyacrylonitrile: melamine = 7:1) powder were added to dichloromethane in a mass ratio of 1:5, and the mixture was thoroughly mixed and stirred until completely dissolved to prepare a shell solution with a mass fraction of 75%.

[0076] S3. The core solution and shell solution were introduced into a coaxial needle respectively. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 18 kV, the receiving distance was 17 cm, and the receiving device was release paper.

[0077] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 135℃ to maintain the fiber morphology, and then heated to 750℃ under argon protection and carbonized for 2 hours to fully carbonize the fiber layer. Fluffy nickel-carbon nanotubes (Ni-CNTs) are in situ grown inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of silicon oxide to obtain lithium-ion battery silicon-carbon nanowire material.

[0078] Example 5

[0079] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fibers with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, which is cobalt.

[0080] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0081] S1. Add silicon dioxide powder and polyvinyl pyrrolidone powder to N,N-dimethylformamide in a mass ratio of 1:4, mix thoroughly and stir to prepare a core solution with a mass fraction of 75%.

[0082] S2. Cobalt nitrate and (polypyrrole: urea = 8:1) were added to N,N-dimethylformamide in a mass ratio of 1:3, and the mixture was thoroughly mixed and stirred until completely dissolved to prepare a shell solution with a mass fraction of 85%.

[0083] S3. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 2:5, the applied voltage was 20 kV, the receiving distance was 20 cm, and the receiving device was release paper.

[0084] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 140℃ to maintain the fiber morphology, and then heated to 1000℃ in an argon-hydrogen atmosphere for carbonization for 5 hours to fully carbonize the fiber layer, reduce the oxygen value of silicon dioxide and reduce it to silicon dioxide, and in situ grow fluffy cobalt-carbon nanotubes (Co-CNTs) inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of the particles to obtain lithium-ion battery silicon-carbon nanowire material.

[0085] Example 6

[0086] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fiber with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, which is iron.

[0087] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0088] S1. Add silica powder and polystyrene in a mass ratio of 1:5 to dimethyl sulfoxide, mix thoroughly and stir evenly to prepare a core solution with a mass fraction of 65%.

[0089] S2. Add ferric acetylacetonate and (polyamide: melamine = 8:1) to dimethyl sulfoxide in a mass ratio of 1:2, mix and stir thoroughly, and prepare a shell solution with a mass fraction of 75% after complete dissolution.

[0090] S3. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 25 kV, the receiving distance was 17 cm, and the receiving device was release paper.

[0091] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 150℃ to maintain the fiber morphology, and then heated to 1000℃ in an argon-hydrogen atmosphere for carbonization for 5 hours to fully carbonize the fiber layer, reduce the oxygen value of silicon dioxide and reduce it to silicon monoxide, and in situ grow fluffy iron-carbon nanotubes (Fe-CNTs) inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of the particles to obtain lithium-ion battery silicon-carbon nanowire material.

[0092] Example 7

[0093] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fibers with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, which is manganese.

[0094] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0095] S1. Add silicon powder and polystyrene powder to N,N-dimethylformamide in a mass ratio of 1:6, mix thoroughly and stir to prepare a core solution with a mass fraction of 40%.

[0096] S2. Manganese acetylacetonate and polyacrylonitrile powder were added to N,N-dimethylformamide in a mass ratio of 2:3, and the mixture was thoroughly mixed and stirred to form a shell solution with a mass fraction of 65% after complete dissolution.

[0097] S3. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 15 kV, the receiving distance was 20 cm, and the receiving device was release paper.

[0098] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 130℃ to maintain the fiber morphology, and then heated to 750℃ under argon protection and carbonized for 4 hours to fully carbonize the fiber layer. Villi-like manganese-carbon nanotubes (Mn-CNTs) are in situ grown inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of silicon powder to obtain lithium-ion battery silicon-carbon nanowire material.

[0099] Example 8

[0100] A lithium-ion battery silicon-carbon nanowire material comprises a core layer and a tubular shell layer. The core layer is a silicon material coated with fuzzy carbon nanotubes. The tubular shell layer is interwoven into a mesh structure. The tubular shell layer is nitrogen-doped carbon fiber with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer. The fuzzy carbon nanotubes contain a transition metal element, which is copper.

[0101] The method for preparing the above-mentioned lithium-ion battery silicon-carbon nanowire material comprises the following steps:

[0102] S1. Add silicon powder and polystyrene powder to N,N-dimethylformamide in a mass ratio of 1:6, mix thoroughly and stir to prepare a core solution with a mass fraction of 40%.

[0103] S2. Add copper acetylacetonate and polyacrylonitrile powder in a mass ratio of 2:3 to N,N-dimethylformamide, mix and stir thoroughly, and prepare a shell solution with a mass fraction of 65% after complete dissolution.

[0104] S3. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 15 kV, the receiving distance was 20 cm, and the receiving device was release paper.

[0105] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 130℃ to maintain the fiber morphology, and then heated to 750℃ under argon protection and carbonized for 4 hours to fully carbonize the fiber layer. Fluffy copper-carbon nanotubes (Cu-CNTs) are in situ grown inside the cavity of nitrogen-doped carbon fiber (NHCF) with a cavity structure and on the surface of silicon powder to obtain lithium-ion battery silicon-carbon nanowire material.

[0106] Examples 9 to 16

[0107] A lithium-ion battery negative electrode sheet comprises the silicon-carbon nanowire negative electrode material of embodiments 1 to 8.

[0108] The method for preparing the above-mentioned lithium-ion battery negative electrode sheet comprises the following steps:

[0109] The silicon carbon nanowire negative electrode material of Examples 1 to 8, the conductive agent, and the binder were mixed in a ratio of 0.77:0.015:0.015, stirred evenly, and the viscosity was adjusted to 1200 cP. The mixture was coated on a current collector and dried thoroughly to prepare a lithium ion battery negative electrode sheet.

[0110] The conductive agent is Ketjen black and the binder is polyacrylic acid (PAA).

[0111] Example 17

[0112] A lithium-ion battery negative electrode sheet comprises the silicon-carbon nanowire negative electrode material of embodiment 1.

[0113] The method for preparing the above-mentioned lithium-ion battery negative electrode sheet comprises the following steps:

[0114] The silicon carbon nanowire negative electrode material of Example 1, the conductive agent, and the binder were mixed in a ratio of 0.8:0.1:0.1, stirred evenly, and the viscosity was adjusted to 1200 cP. The mixture was coated on a current collector and dried thoroughly to prepare a lithium ion battery negative electrode sheet.

[0115] The conductive agent is Ketjen black and the binder is polyacrylic acid (PAA).

[0116] Examples 18 to 26

[0117] A lithium ion battery comprises the lithium ion battery negative electrode sheets of embodiments 7 to 16.

[0118] The method for preparing the lithium-ion battery comprises the following steps:

[0119] Preparation of electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and 1 mol / L LiPF6 were mixed in a volume ratio of 1:1:1 to obtain an electrolyte;

[0120] Then, a 2025 button-type lithium-ion battery was assembled using metallic lithium as the counter electrode, electrolyte and Celgard2400 separator.

[0121] Comparative Example 1

[0122] A method for preparing a silicon-carbon material comprises the following steps:

[0123] S1. Add silicon powder and polystyrene powder to N,N-dimethylformamide in a mass ratio of 1:6, mix thoroughly and stir to prepare a core solution with a mass fraction of 40%.

[0124] S2. Add polyacrylonitrile powder to N,N-dimethylformamide, stir evenly, and prepare a shell solution with a mass fraction of 65% after it is completely dissolved.

[0125] S3. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 15 kV, the receiving distance was 20 cm, and the receiving device was release paper.

[0126] S4. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 130°C to maintain the fiber morphology, and then heated to 750°C for carbonization for 4 hours under argon protection to fully carbonize the fiber layer to obtain a silicon-carbon material.

[0127] Comparative Example 2

[0128] A method for preparing a silicon-carbon material comprises the following steps:

[0129] S1. Add silicon powder and polyacrylonitrile powder to N,N-dimethylformamide in a mass ratio of 1:6, mix thoroughly and stir to prepare a core solution with a mass fraction of 65%, which also serves as the shell solution.

[0130] S2. The core solution and shell solution were respectively introduced into a coaxial needle. The thickness ratio of the inner and outer layers of the coaxial needle was 17:22, the ratio of the inner and outer layer liquid output was 1:2, the applied voltage was 15 kV, the receiving distance was 20 cm, and the receiving device was release paper.

[0131] S3. The composite nanofiber layer of core structure and shell structure is pre-oxidized at 130°C to maintain the fiber morphology, and then heated to 750°C under argon protection and carbonized for 4 hours to fully carbonize the fiber layer to obtain a silicon-carbon material.

[0132] Result detection

[0133] The lithium ion battery silicon carbon nanowire material prepared in Example 1 was characterized by scanning electron microscopy, X-ray diffractometer, Raman spectroscopy, and BET surface area tester. The test results are as follows: Figures 1 to 7 shown.

[0134] The silicon-carbon materials of Comparative Examples 1 and 2 were prepared using the same preparation method as in Examples 14 to 20 to obtain lithium-ion batteries.

[0135] The test was conducted at room temperature using the Xinwei battery test system from Wuhan Jinnuo Electronics Co., Ltd. The test conditions were as follows:

[0136] (1) First charge and discharge I = 1C, cycle I = 1C, voltage range 0.005-2.0V vs Li+ / Li.

[0137] (2) First charge and discharge I = 0.5C, cycle I = 0.5C, voltage range 0.005-2.0V vs Li+ / Li.

[0138] (3) First charge and discharge I = 2C, cycle I = 2C, voltage range 0.005-2.0V vs Li+ / Li.

[0139] The specific test results are shown in Tables 1 and 2 below:

[0140] Table 1

[0141]

[0142]

[0143] Table 2

[0144]

[0145] above Figures 1 to 7 The analysis of Tables 1 and 2 is as follows:

[0146] Figure 1 This is a scanning electron microscope (SEM) image of the lithium-ion battery silicon-carbon nanowire material of Example 1 of the present invention. Figure 2 This is a scanning electron microscope (SEM) image of the cross section of the lithium-ion battery silicon-carbon nanowire material according to Example 1 of the present invention. Figure 3 Transmission electron microscopy and EDS element distribution diagrams of the lithium-ion battery silicon-carbon nanowire material of Example 1 of the present invention. Figure 4 This is a transmission electron microscope (TEM) image of the lithium-ion battery silicon carbon nanowire material of Example 1 of the present invention. Figures 1 to 4 The lithium-ion battery silicon-carbon nanowire material prepared by the present invention comprises a core layer and a tubular shell layer. The core layer is silicon-coated with fuzzy carbon nanotubes, while the tubular shell layer is interwoven into a network structure. The tubular shell layer is composed of nitrogen-doped carbon fibers with a hollow structure. The fuzzy carbon nanotubes are connected to the cavities of the tubular shell and contain a transition metal element. The fuzzy carbon nanotubes are in close contact with the silicon material, allowing the active material to rapidly incorporate more lithium at high current densities.

[0147] Figure 5 The X-ray diffraction (XRD) patterns of the materials of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are shown in FIG. 1 , where the PDF card number of Si is PDF#75-0587 and the PDF card number of Ni is PDF#87-0712. Figure 5 It can be seen that the material of the present invention has a characteristic lattice diffraction peak of metallic nickel, indicating the presence of nickel in the material.

[0148] Figure 6 The Raman spectra of the lithium ion battery silicon carbon nanowire materials of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention are as follows: Figure 6 Through the ratio of the D peak to the G peak of the Raman spectrum, it was found that the ID / IG value of Example 1 was 0.73, the ID / IG value of Comparative Example 1 was 1.182, and the ID / IG value of Comparative Example 2 was 1.171. The ID / IG value of Example 1 was the smallest, which further verified that due to the presence of metal-carbon nanotubes, the overall graphitization degree of the material was significantly improved, the conductivity of the material was better, and the performance of the silicon material could be stably exerted while reducing the use of conductive agents.

[0149] Figure 7 This is a BET specific surface area diagram of the lithium ion battery silicon carbon nanowire material of Example 1 of the present invention, Figure 7 It can be seen that the BET specific surface area is 276.42 m 2 / g, pore volume is 0.546cm 3 / g, and the pore size distribution is mainly within the range of 10 nanometers, which is conducive to the rapid insertion and extraction of lithium ions. This shows that the composite material has a large specific surface area, and the presence of mesopores is conducive to the migration of lithium ions, which can exert good capacity at high current density.

[0150] Figure 8 This is a schematic structural diagram of the lithium-ion battery silicon carbon nanowire material according to an embodiment of the present invention. Figure 8It can be seen that the lithium-ion battery silicon-carbon nanowire material prepared by the present invention includes a core layer and a tubular shell layer. The core layer is a fuzzy carbon nanotube-coated silicon material. The tubular shell layers are interwoven into a network structure. The tubular shell layers are nitrogen-doped carbon fibers with a cavity structure. The fuzzy carbon nanotubes are connected to the cavity of the tubular shell layer, and the fuzzy carbon nanotubes (-CNTs) include transition metal elements inside.

[0151] Figure 9 The DFT calculation of the energy barrier of lithium ion adsorption-diffusion of nickel, nitrogen, and graphitized carbon in the material of Example 1 of the present invention is performed, wherein: Figure 9 a is the adsorption energy of Ni, graphitized nitrogen, and graphitized carbon for lithium ions in the material of Comparative Example 1, which are -2.87 eV, -1.08 eV, and -0.77 eV, respectively. It can be found by comparison that Ni and graphitized nitrogen can facilitate the adsorption of lithium ions and promote the lithiation rate of silicon; Figure 9 b, c, and d correspond to the diffusion energy barriers of Ni's 111 crystal plane, graphitized nitrogen, and graphitized carbon for lithium ions, which are 0.0112 eV, 0.0698 eV, and 0.22 eV, respectively, which are conducive to the migration and storage of lithium ions. Therefore, it can be verified that the composite nanowire material has an advantageous effect on the embedding and storage of lithium ions.

[0152] As can be seen from Table 1, the lithium-ion battery prepared by the lithium-ion battery silicon carbon nanowire material of the present invention has a capacity higher than 1000 mAh·g -1 The first discharge specific capacity is high, and after 1000 cycles, it still has a high discharge specific capacity, and the capacity retention rate can reach more than 84%.

[0153] It can be seen from Examples 18 to 23 in Table 1 that the silicon material of the silicon-carbon nanowire material for lithium-ion batteries of the present invention can be silicon powder, silicon oxide or silicon dioxide, all of which can fully exert their own capacity, so the lithium-ion battery has a higher charge and discharge specific capacity.

[0154] As can be seen from Examples 18 and 26 in Table 1, in Example 18, the amount of conductive agent in the negative electrode sheet was 1.5% of the negative electrode slurry, while in Example 26, the amount of conductive agent in the negative electrode sheet was 10% of the negative electrode slurry. The cycle capacity retention rate of Example 18 was higher than that of Example 26, indicating that the lithium-ion battery silicon-carbon nanowire material of the present invention has excellent conductivity, thus reducing the amount of conductive agent. This is because conventional proportions produce a low areal loading (the amount of active material per unit area), resulting in a relatively low energy density for the assembled battery. The lithium-ion battery silicon-carbon nanowire material of the present invention can increase the proportion of negative electrode active material in the slurry while ensuring a stable material structure. As a result, the prepared electrode sheet and assembled battery have higher areal loading and energy density.

[0155] From Example 1 and Comparative Example 1, it can be seen that without adding metal salt to S2, the first cycle discharge capacity is 716 mAh·g -1 , and the capacity retention rate after 1000 cycles is 47%. This is because compared with Example 1, in Comparative Example 1, since no metal salt is added to the precursor solution, metal-carbon nanotubes cannot be pyrolyzed and catalytically grown during the carbonization process; the structure of silicon powder embedded in the fiber cavity formed cannot well ensure that the embedded silicon powder is fully in contact with the conductive medium. The silicon powder is easily separated from the tube wall during the lithiation and delithiation process, and it is difficult to exert a stable capacity.

[0156] It can be seen from Comparative Example 2 and Example 1 that the discharge specific capacity in the first cycle is significantly reduced, and the capacity retention rate after 1000 cycles is only 28%. This is because compared with Comparative Example 1, the core-shell solution in Comparative Example 2 contains only carbon-nitrogen sources, and the core solution does not have a carbon source with a low carbonization yield. Compared with Example 1, the shell solution does not have the addition of metal salts, and the material prepared after sintering does not have cavities and grown metal-carbon nanotubes inside. It is a fiber material with a solid structure of carbon-nitrogen nanofibers wrapped around silicon, which has poor conductivity and does not leave room for the silicon material to expand in volume, so the silicon material cannot be completely coated. This will lead to poor capacity of the battery and rapid decay during the cycle.

[0157] As can be seen from Table 2, the lithium-ion battery prepared from the lithium-ion battery silicon-carbon nanowire material of the present invention has good rate performance and has a high capacity retention rate at 0.5C, 1C and 2C.

[0158] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A lithium-ion battery silicon-carbon nanowire material, characterized in that: The material includes a core layer and a tubular shell layer, wherein the core layer is a fuzzy carbon nanotube-coated silicon material, the tubular shell layers are interwoven with each other to form a mesh structure, the tubular shell layers are nitrogen-doped carbon fibers with a cavity structure, the fuzzy carbon nanotubes are connected to the cavity of the tubular shell layers, and the interior of the fuzzy carbon nanotubes contains a transition metal element; The preparation method of the lithium ion battery silicon carbon nanowire material comprises the following steps: S1. The silicon source, carbon source and solvent are mixed to obtain a core solution; S2. The metal salt, carbon-nitrogen source and solvent are mixed to obtain a shell solution; S3. Coaxially electrospinning the core solution and the shell solution to obtain a core-shell fiber layer; S4. Pre-oxidizing the core-shell fiber layer and carbonizing it in a non-oxidizing atmosphere to obtain a lithium-ion battery silicon carbon nanowire material; Wherein, in S1, the carbon source is one or more of polystyrene, polyacrylonitrile, polyvinyl pyrrolidone or polymethyl methacrylate; The mass ratio of silicon source to carbon source is 1:(3~6); In S2, the metal salt is one or more of iron salt, cobalt salt, nickel salt, manganese salt or copper salt; The carbon-nitrogen source is one or more of polyacrylonitrile, polypyrrole, asphalt, polyamide, urea or melamine; The mass ratio of metal salt to carbon-nitrogen source is 1:(1.5~7); In S3, the electrospinning voltage was 8–30 kV, the receiving distance was 10–25 cm, and the mass ratio of the core solution to the shell solution output was 1:(1.5–2.5); In S4, the pre-oxidation temperature is 120~150℃, the carbonization temperature is 700~1000℃, and the carbonization time is 2~5h.

2. The lithium-ion battery silicon-carbon nanowire material according to claim 1, wherein: The transition metal is iron, cobalt, nickel, manganese or copper.

3. The lithium-ion battery silicon-carbon nanowire material according to claim 1, wherein: The silicon material is one or more of silicon powder, silicon monoxide or silicon dioxide.

4. The lithium-ion battery silicon-carbon nanowire material according to claim 1, wherein: In the S2 shell solution, the mass ratio of metal salt to carbon-nitrogen source is 1:(1.5~3).

5. The lithium-ion battery silicon-carbon nanowire material according to claim 1, wherein: The metal salt is one or more of acetate, acetylacetonate, nitrate, sulfate or phosphate.

6. The lithium-ion battery silicon-carbon nanowire material according to claim 1, wherein: In S4, the carbonization temperature is 750~950℃.

7. The lithium-ion battery silicon-carbon nanowire material according to claim 1, wherein: In the core solution, the mass fraction of the silicon source and the carbon source is 40%~80%; in the shell solution, the mass fraction of the metal salt and the carbon-nitrogen source is 55%~85%.

8. A lithium-ion battery negative electrode sheet, characterized in that: The lithium-ion battery silicon-carbon nanowire material comprises the silicon-carbon nanowire material according to any one of claims 1 to 7.

9. A lithium-ion battery, characterized in that: Including the lithium-ion battery negative electrode sheet as claimed in claim 8.

Images