A carbonaceous honeycomb skeleton-based magnesium fluoride interfacial modified SiOC composite negative electrode material

Abstract

A magnesium fluoride interface-modified SiOC composite anode material based on a carbon honeycomb framework belongs to the field of lithium-ion battery anode materials. The composite material macroscopically comprises an interconnected three-dimensional porous honeycomb structure, consisting of, from the inside out: a graphene-like carbon matrix forming a three-dimensional ordered macroporous (3DOM) structure; Ni / NiO nanoparticles in situ embedded in the pore walls of the carbon matrix; a carbon nanofiber (CNF) conductive network interspersed and distributed within the pores and grown in situ; an amorphous SiOC ceramic phase active material uniformly coated on the pore wall surface and the overall honeycomb structure, forming a three-dimensional interconnected porous structure; and a magnesium fluoride (MgF2) nanoprotective layer generated in situ and coated on the outermost surface of the composite material. This material can be directly used as an integrated electrode and is suitable for high-energy-density, long-cycle-life lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium-ion battery anode materials, specifically relating to a magnesium fluoride interface-modified SiOC composite anode material based on a carbon honeycomb framework and its preparation method. This invention is particularly suitable for high-energy-density, long-cycle-life lithium batteries, and can effectively solve the interface failure problem of silicon-based anodes during cycling. Background Technology

[0002] With the rapid development of smart grids, electric vehicles, and portable electronic products, the market has placed unprecedented demands on the energy density and cycle life of lithium-ion batteries. The theoretical capacity of traditional graphite anodes (372 mAh / g) is nearing its limit, while silicon-based materials, although possessing high capacity advantages, face the challenge of interfacial failure due to volume expansion. Silicon-oxygen-carbon (SiOC) ceramic materials have become highly promising anode materials due to their high theoretical capacity (1000–2500 mAh / g), moderate volume expansion (~120%), and tunable chemical composition. However, SiOC still exhibits significant volume changes during cycling, leading to repeated rupture and regeneration of the surface solid electrolyte interface (SEI). Traditional SEIs are rich in organic components (such as ROCO₂Li), have low mechanical strength and poor ionic conductivity, and cannot adapt to cyclic stress, resulting in continuous consumption of active lithium and rapid capacity decay.

[0003] To address these issues, current technologies primarily seek breakthroughs at two levels: structural design and interface engineering. At the structural design level, the inventors' team previously developed "SiO..." x C y The "Coated Integrated Carbon Honeycomb Structure (OMGC) Material" (Patent Publication No.: CN120854497A) constructs a three-dimensional ordered macroporous (3DOM) structure using a co-sacrificial template method. It employs N and O co-doped graphene-like carbon as a framework, in-situ composite SiOC, and grows a carbon nanofiber (CNF) conductive network. While this structure provides excellent mechanical support and electronic conduction at the macroscale, it fails to address the instability of the solid-liquid interface at the nanoscale, and interfacial side reactions remain the root cause of performance degradation.

[0004] At the interface engineering level, introducing magnesium fluoride (MgF2) as a functional precursor is a recent breakthrough strategy. It can be converted in situ during the early stages of electrochemical cycling: MgF2 + 2Li + + 2e −→ 2LiF + Mg generates a lithium fluoride (LiF)-rich SEI with embedded nano-sized Mg. LiF provides high ionic conductivity and high modulus to resist stress, while the highly ductile metallic Mg acts as a "toughening phase" to release stress and prevent crack propagation, giving the SEI "mechanically adaptive" properties. However, applying the MgF2 coating process to complex three-dimensional porous integrated electrodes faces challenges: the precursor solution is difficult to uniformly wet on the hydrophobic carbon framework, and the heat treatment process easily damages the original fine structure. Therefore, there is an urgent need to develop an innovative technology that combines a mechanically adaptive interface protective layer with a high-performance integrated structure.

[0005] This invention aims to fill this gap by combining a MgF2-based interface protective layer with an OMGC-based SiOC composite anode to develop a new generation of lithium-ion battery anode materials with high capacity, high first-cycle efficiency, and ultra-long cycle stability. Its features include: (1) a three-dimensional ordered macroporous conductive framework: a highly ordered honeycomb structure composed of N and O co-doped graphene-like carbon, with Ni / NiO nanoparticles embedded in the pore walls and a CNF conductive network grown in situ; (2) a high-capacity active material layer: an amorphous SiOC ceramic phase bonded to the surface of the carbon framework by chemical vapor deposition (CVD); and (3) an interface functional protective layer: a uniformly coated nanoscale MgF2 coating with controllable thickness and high integrity. Summary of the Invention

[0006] To address the core issue of insufficient interfacial electrochemical stability at the nanoscale in existing integrated silicon-carbon anode materials, this invention provides an innovative interfacial protection strategy and a high-performance composite anode material based on this strategy. This invention modifies the surface of the SiOC / Ni / OMGC integrated anode substrate by using a MgF2-based protective layer that can be in situ transformed into a highly stable, mechanically adaptive SEI during electrochemical cycling. This achieves a synergistic enhancement of macroscopic structural stability and nanoscale interfacial stability, significantly improving the rate performance and cycle life of the battery.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions: (1) preparing a carbon honeycomb architecture-based SiOC composite anode material with a 3DOM structure and a CNF conductive network; (2) uniformly loading a MgF2 precursor on its surface by quantitative solution impregnation method; (3) converting the precursor into a dense and uniform MgF2 protective layer in situ by mild heat treatment.

[0008] A magnesium fluoride interface-modified SiOC composite anode material based on an integrated carbon honeycomb architecture is characterized in that the composite material is macroscopically an interconnected three-dimensional porous honeycomb architecture, comprising, from the inside out: a graphene carbon matrix constituting a three-dimensional ordered macroporous (3DOM) structure; Ni / NiO nanoparticles in situ embedded in the pore walls of the graphene carbon matrix; a carbon nanofiber (CNF) conductive network interspersed and distributed within the pores and grown in situ; an amorphous SiOC ceramic phase active material uniformly coated on the pore wall surface and the overall honeycomb architecture, forming a three-dimensional interconnected porous structure; and a magnesium fluoride (MgF2) nanoprotective layer generated in situ and coated on the outermost surface of the composite material.

[0009] This invention provides a method for preparing a magnesium fluoride interface-modified SiOC composite anode material based on a carbon honeycomb framework, characterized by the following steps:

[0010] (1) Prepare a precursor impregnation solution by mixing a complexing agent (such as citric acid) and a metal salt (such as nickel nitrate) in a certain proportion; wherein the concentration of citric acid is 0.5-2 mol / L (preferably 1 mol / L) and the concentration of metal salt is 1-3 mol / L (preferably 2 mol / L).

[0011] (2) The random-shaped organic colloidal crystal (such as polymethyl methacrylate PMMA) microsphere template is fully impregnated in the solution of step (1), filtered and dried to obtain the primary precursor; wherein, the impregnation conditions are 3-16 h at room temperature (preferably 12 h).

[0012] (3) The primary precursor is placed in a mold and pressed into a sheet with a pressure of 6-15 MPa (preferably 10 MPa) and held for 10-60 s (preferably 30 s) to obtain a block precursor with a diameter of centimeters and uniform thickness; wherein the thickness is from several hundred nanometers to millimeters (preferably 100-1000 micrometers).

[0013] (4) The bulk precursor is placed in the high-temperature zone of a dual-temperature tube furnace, and the silane coupling agent (KH-560, with a mass of 0.1-10 times that of the precursor, preferably 2 times) is placed in the low-temperature zone. The mixture is then calcined in an inert atmosphere (nitrogen, argon, or a hydrogen-argon mixture, preferably a hydrogen-argon mixture). The low-temperature zone is 350 °C, and the high-temperature zone is 600 °C, held for 0.5-5 h (preferably 0.5 h) to obtain an integrated carbon honeycomb structure and a SiOC composite matrix. This matrix has a 3DOM structure, with the pore walls being a graphene carbon matrix inlaid with metallic nickel and coated with SiOC. Dense CNFs are grown in situ on the pore walls. The heating rates in the low-temperature and high-temperature zones are 1-30 °C / min, with the high-temperature zone heating rate preferably 10 °C / min. o C / min, which simultaneously ensures that the heat preservation time in the low temperature zone and the high temperature zone is synchronized.

[0014] (5) Dissolve the soluble magnesium fluoride complex (preferably magnesium hexafluorosilicate MgSiF6·6H2O, concentration 1-5 mg / mL, preferably 3 mg / mL) in anhydrous ethanol / water mixed solvent (volume ratio 5-10:1, preferably 9:1) to prepare a homogeneous and transparent precursor solution.

[0015] (6) The solution from step (5) is fully permeated into the three-dimensional porous structure of the composite matrix from step (4) by dripping. The permeation amount per single disc is 0.5-2 mL (preferably 1 mL).

[0016] (7) The composite matrix loaded with magnesium fluorine complex obtained in step (6) is vacuum dried at a temperature of 40-100℃ for 6-12 h (preferably 80℃ for 8 h) to obtain an intermediate product loaded with MgSiF6 precursor.

[0017] (8) The above intermediate product is heat-treated in an inert atmosphere (nitrogen, argon or hydrogen-argon mixture, preferably argon; gas flow rate of 1-500 sccm, preferably 50 sccm) at a temperature of 300-500℃ (preferably 400℃), a heating rate of 1-30℃ / min (preferably 10℃ / min), and held for 0.5-5 h (preferably 2 h); this process yields a uniform and dense MgF2 nano-coating (thickness of 2-10 nm, preferably 5 nm), which is then cooled in the furnace to obtain the final integrated SiOC composite anode material modified by MgF2.

[0018] During the heat treatment process in step (8) above, the metallic Ni in the composite matrix is ​​converted into NiO.

[0019] The preparation method provided by this invention has the following beneficial effects:

[0020] (1) Combination of process inheritance and innovation: Based on the mature integrated matrix synthesis process, a high-performance interface protection layer is introduced through only two post-treatment steps: solution loading and mild heat treatment. The route is simple, has good compatibility, and is easy to scale up for production. The heat treatment process simultaneously realizes the formation of MgF2 coating and partial oxidation of Ni nanocrystals, optimizing the interface chemical environment.

[0021] (2) Three-level synergistic protection mechanism: realize multi-level synergy of "OMGC framework (buffer and conduction) - SiOC / CNF composite layer (lithium storage and conduction) - MgF2 interface layer (electrochemical protection)"; the carbon framework copes with macroscopic volume changes and provides three-dimensional continuous ion / electron transport channels, and the MgF2-derived SEI film copes with nanoscale interface stress, jointly ensuring structural integrity and interface stability during long-term cycling.

[0022] (3) Imparting adaptive mechanical properties to the interface: During the first charge and discharge of the battery, the MgF2 coating is transformed in situ into a composite SEI composed of high modulus LiF (~65 GPa) and high toughness metal Mg (ductility 15-20%). This "rigid-flexible" property enables it to adapt to the volume change of the active material, effectively suppressing the repeated cracking and proliferation of the SEI, and significantly reducing irreversible capacity loss. This is the key to improving the first-cycle coulombic efficiency and cycle life.

[0023] (4) Parameters are controllable and there is a large optimization space: By precisely controlling the concentration, penetration amount and heat treatment temperature and time of MgSiF6 in the precursor solution, the thickness (2-10 nm), crystallinity and coverage (>90%) of MgF2 coating can be effectively optimized, thus providing the possibility for fine-tuning the performance for different application needs.

[0024] The chemical composition, crystal structure, morphology, and other physical properties of the prepared materials were determined using instruments such as a SmartLab X-ray diffractometer (XRD), a Raman spectrometer, an S4800 field emission scanning electron microscope (SEM), and a JEM F200 field emission transmission electron microscope (TEM). The lithium-ion battery performance of the prepared materials was tested using the Xinwei Battery Testing System.

[0025] For lithium-ion battery applications, 2032-type button cells were assembled in an argon-protected glove box (H2O < 0.5 ppm, O2 < 0.5 ppm) to test the electrochemical lithium storage performance of the prepared materials. The prepared composite anode material does not require the use of traditional copper current collectors and can be directly used as an integrated electrode in battery assembly. In the assembled half-cell, lithium foil is used as the counter electrode, Whatman glass fiber is used as the battery separator, and a LiPF6 solution (concentration of 1 mol / L) dissolved in a mixture of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1 is used as the electrolyte. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the embodiments will be briefly described below. The following drawings are only some embodiments of the present invention; based on these drawings, those skilled in the art can obtain other related drawings without creative effort.

[0027] Figure 1 Optical photographs of the integrated carbon honeycomb structure SiOC composite anode material prepared for Comparative Example 1 (original sample) and Example 1 (MgF2 modified sample).

[0028] Figure 2(a) X-ray diffraction (XRD) spectra and (b) Raman spectra of the original sample and the modified sample.

[0029] Figure 3 Scanning electron microscope (SEM) images of (a) the original sample and (b) the modified sample.

[0030] Figure 4 High-resolution transmission electron microscopy (HR-TEM) images of (a) the original sample and (b) the modified sample.

[0031] Figure 5 (a) Cycle performance and (b) Rate performance of lithium-ion batteries assembled for the original sample and the modified sample. Detailed Implementation

[0032] To more clearly illustrate the present invention, the magnesium fluoride interface-modified SiOC composite anode material provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Any similar products obtained by combining the present invention with other prior art features based on the teachings of the present invention should fall within the scope of protection of the present invention.

[0033] The operating and testing methods used in this invention are all conventional techniques in the field. Unless otherwise specified, they are all performed according to the conventional experimental conditions described in the literature in this field. All reagents used are commercially available conventional products.

[0034] All embodiments of the present invention use a commercial infrared tablet press for precursor tableting. The shape and size of the mold can be adjusted according to requirements. The following embodiments all use a cylindrical mold with a diameter of 15.4 mm.

[0035] Comparative Example 1

[0036] This embodiment provides an integrated carbon honeycomb structure SiOC composite anode material (original sample) as a comparison basis. The preparation steps are as follows: (1) Dissolve nickel nitrate and citric acid in deionized water, wherein the concentration of citric acid is 1 mol / L and the concentration of nickel nitrate is 2 mol / L; (2) Immerse the irregular block-shaped PMMA microsphere template in the above impregnation solution, impregnate at room temperature for 12 h, filter and dry at 80℃ for 12 h to obtain the initial precursor; (3) Weigh 120 mg of the initial precursor, place it in a cylindrical mold with an inner diameter of 15.4 mm, press it with a pressure of 6 MPa for 30 s, and demold to obtain a disc-shaped precursor blank; (4) Place the disc-shaped precursor blank in the high temperature zone of a dual-temperature zone tube furnace (20 cm away from the low temperature zone), weigh twice the mass of the blank and place it in the low temperature zone; (5) Introduce a flow rate of 5 A hydrogen-argon mixture in sccm was heated to 600℃ in the high-temperature zone at a rate of 10℃ / min, and simultaneously heated to 350℃ in the low-temperature zone. After holding at this temperature for 30 min, heating was stopped, and the sample was allowed to cool naturally to room temperature under continuous ventilation to obtain a circular original sample. Figure 1 ).like Figure 1 and Figure 3 As shown, the disc has a geometric diameter of approximately 13.0 mm and a uniform thickness of approximately 240 μm; Figure 2 and Figure 4 As shown, the main components of the material are SiOC, metallic nickel, and low-graphitization graphene-like carbon, with CNF conductive agent grown in situ on the pore walls.

[0037] Example 1

[0038] This embodiment provides an integrated carbon honeycomb structure SiOC composite anode material modified with MgF2 (modified sample). The preparation steps are as follows: (1) Take the original sample disc prepared according to the same method as in Example 1; (2) Dissolve 30 mg MgSiF6·6H2O in 10 mL of anhydrous ethanol / deionized water mixed solvent (volume ratio 9:1), stir magnetically until completely dissolved, and obtain a clear solution; (3) Use a microsyringe to uniformly drop the precursor solution (about 1 mL / disc) onto the surface of the original sample. The solution rapidly wets the interior of the three-dimensional porous structure by capillary action; (4) Place the sample loaded with solution in a vacuum drying oven and dry at 80℃ for 8 h to completely remove the solvent; (5) Transfer the dried sample to a tube furnace and heat it to 400℃ at 5℃ / min under an argon atmosphere (flow rate 50 sccm) and keep it at that temperature for 2 h; (6) Cool naturally to room temperature in an argon flow to obtain a disc-shaped modified sample ( Figure 1 ).like Figure 1 and Figure 3 As shown, the disc has a geometric diameter of approximately 13.0 mm and a uniform thickness of approximately 240 μm; Figure 2 and Figure 4As shown, the main components of the material are SiOC, NiO and low-graphitization graphene-like carbon. CNF conductive agent is grown in situ on the pore walls, and the surface is uniformly coated with a MgF2 nano-coating with a thickness of about 5 nm.

[0039] Example 2

[0040] 2032-type button cells were assembled in an argon-protected glove box (H₂O < 0.5 ppm, O₂ < 0.5 ppm). Comparative Example 1 (original sample) and Example 1 (modified sample) were used directly as integrated electrodes (without copper current collectors), with lithium foil as the counter electrode, Whatman glass fiber as the separator, and 1 mol / L LiPF₆ solution as the electrolyte (solvent: EC / DEC / DMC, volume ratio 1:1:1). Electrochemical performance was tested. Tests were conducted at room temperature, with a voltage range of 3.0–0.01 V. Figure 5 The test results show that the MgF2-coated modified sample exhibits significantly better high-rate cycling stability and rate performance than the original sample: when the current density increases from 0.25 mA / cm², the modified sample demonstrates significantly better performance. 2 Gradually increased to 4.0 mA / cm 2 At that time, the reversible areal capacities of the modified samples were 5.3, 4.8, 4.5, 4.2, 3.9, and 2.6 mAh / cm³, respectively. 2 It outperformed the original sample at all current densities. At 4.0 mA / cm², it was superior to the original sample. 2 After 100 cycles at high current density, the reversible areal capacity of the modified sample is 3.8 mA / cm². 2 It is 1.9 times that of the original sample; when the current density recovers to 0.25 mA / cm² 2 At that time, its capacity can be fully restored to 5.4 mAh / cm³. 2 Furthermore, it exhibits excellent long-term cycling stability. This fully demonstrates the protective effect of the mechanically adaptive SEI interface layer formed by the in-situ transformation of MgF2 on the electrode structure and its own stability during long-term cycling.

Claims

1. A magnesium fluoride interfacial modified SiOC composite anode material based on integrated integrated carbonaceous honeycomb architecture, characterized in that, The composite material has an overall interconnected three-dimensional porous honeycomb structure, which includes, from the inside out: a graphene carbon matrix constituting a three-dimensional ordered macroporous (3DOM) structure; Ni / NiO nanoparticles embedded in the pore walls of the graphene carbon matrix; a carbon nanofiber (CNF) conductive network that is interspersed and distributed in the pores and grown in situ; an amorphous SiOC ceramic phase active material that is uniformly coated on the surface of the pore walls and the overall honeycomb structure and forms a three-dimensional interconnected porous structure; and a magnesium fluoride (MgF2) nanoprotective layer that is generated in situ and coated on the outermost surface of the composite material.

2. The material according to claim 1, characterized in that, The thickness of the MgF2 nanocoating is 2-10 nm, preferably 5 nm.

3. The method for preparing the material according to claim 1 or 2, characterized in that, Includes the following steps: (1) Prepare a precursor impregnation solution by mixing the complexing agent and the metal salt in a certain proportion; (2) The random-shaped organic colloidal microsphere template is fully impregnated in the solution of step (1), filtered and dried to obtain the primary precursor; (3) The primary precursor is placed in a mold and pressed into a sheet to obtain a block precursor; (4) The block precursor is placed in the high temperature zone of a dual-temperature zone tube furnace, and the silane coupling agent is placed in the low temperature zone. The mixture is then calcined in an inert atmosphere. The low temperature zone is 350°C and the high temperature zone is 600°C. The temperature is maintained for 0.5-5 h to obtain an integrated carbon honeycomb structure and a composite matrix of SiOC. The matrix has a 3DOM structure. The pore walls are made of graphene carbon matrix inlaid with metallic nickel and coated with SiOC. Dense CNFs are grown in situ on the pore walls. (5) Dissolve the soluble magnesium fluoride complex in anhydrous ethanol / water mixed solvent to prepare a homogeneous and transparent precursor solution; (6) The solution from step (5) is fully permeated into the three-dimensional porous structure of the composite matrix from step (4) by dripping. (7) The composite matrix loaded with magnesium fluorine complex obtained in step (6) is vacuum dried to obtain an intermediate product loaded with MgSiF6 precursor. (8) The above intermediate product is heat-treated in an inert atmosphere at a temperature of 300-500℃ for 0.5-5 h; then cooled in the furnace.

4. The method according to claim 3, characterized in that, In step (1), the complexing agent is selected from citric acid, and the metal salt is selected from nickel nitrate; wherein, the concentration of citric acid is 0.5-2 mol / L (preferably 1 mol / L), and the concentration of metal salt is 1-3 mol / L (preferably 2 mol / L). Step (2) The irregularly shaped organic gel crystals are impregnated with polymethyl methacrylate (PMMA) for 3-16 hours at room temperature, preferably 12 hours. In step (3), the pressure during tableting is 6-15 MPa (preferably 10 MPa), and the pressure is held for 10-60 s (preferably 30 s); a block precursor with a diameter of centimeters and uniform thickness is obtained, with a thickness of several hundred nanometers to millimeters (preferably 100-1000 micrometers). Step (4) The silane coupling agent is KH-560, and its mass is 0.1-10 times that of the precursor, preferably 2 times; the inert atmosphere is nitrogen, argon or hydrogen-argon mixture, preferably hydrogen-argon mixture; the heating rate of the low temperature zone and the high temperature zone is 1-30 ℃ / min, preferably 10 ℃ / min in the high temperature zone, while ensuring that the holding time of the low temperature zone and the high temperature zone is synchronized. Step (5) The soluble magnesium fluoride complex is selected from magnesium hexafluorosilicate MgSiF6·6H2O, with a concentration of 1-5 mg / mL, preferably 3 mg / mL, and an anhydrous ethanol / water volume ratio of 5-10:1, preferably 9:1; When using the dropwise addition method in step (6), the permeation volume of a single disc is 0.5-2 mL, preferably 1 mL; Step (7) The composite matrix containing magnesium fluorine complex obtained in step (6) is vacuum dried at a temperature of 40-100℃ for 6-12 h. Step (8) The inert atmosphere is nitrogen, argon or a hydrogen-argon mixture, preferably argon; the gas flow rate is 1-500 sccm, preferably 50 sccm, and the heating rate is 1-30℃ / min, preferably 10℃ / min.

5. The method according to claim 3, characterized in that, Step (8) The temperature is 400℃, and the temperature is maintained for 2 hours.

6. The method according to claim 3, characterized in that, During the heat treatment process in step (8), the metallic Ni in the composite matrix is ​​converted into NiO.

7. The application of the material described in claim 1 or 2, as an integrated electrode for direct assembly of lithium batteries, without the need for copper current collectors.

8. A lithium-ion battery, wherein the material described in claim 1 or 2 does not require the use of a traditional copper current collector and can be directly used as an integrated electrode in battery assembly, wherein: The assembled half-cell uses lithium foil as the counter electrode, Whatman glass fiber as the battery separator, and LiPF6 solution (concentration of 1 mol / L) dissolved in a mixture of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1.

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