Composite silicon-based negative electrode material, preparation method thereof and lithium ion battery

Abstract

The application provides a composite silicon-based negative electrode material, a preparation method thereof and a lithium ion battery, and the composite silicon-based negative electrode material comprises a silicon-based material and a porous MOFs material after pore forming, the porous MOFs material has a porous structure; at least a part of the silicon-based material is embedded in the inside of the pore channel of the MOFs material; and the average pore diameter of the MOFs material after pore forming is 2-200nm. In the application, at least a part of the silicon-based material is embedded in the inside of the pore channel of the MOFs material after pore forming, the average pore diameter of which is 2-200nm, so that the volume expansion of silicon is inhibited, the average pore diameter of the MOFs material after pore forming is in the range of 2-200nm, the stability of the silicon negative electrode is improved, and the composite silicon-based negative electrode material with high specific energy can be obtained, the attenuation of the battery capacity is effectively inhibited, and the cycle performance and the rate performance are obviously improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a composite silicon-based anode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Since Sony commercialized lithium-ion batteries in the 1990s, the battery industry has experienced rapid development. Lithium-ion batteries, in particular, have become increasingly important in modern life due to their excellent cycle performance, lack of memory effect, high operating voltage, and environmental friendliness, making them an ideal energy source for electric vehicles and mobile devices.

[0003] Currently, graphite-based materials are used as anodes in commercial lithium-ion batteries, with a theoretical capacity of approximately 372 mAh / g. However, with technological advancements and increasing demands, graphite-based anode materials can no longer meet the requirements of next-generation high-energy-density lithium-ion batteries. Therefore, researchers urgently need to find alternative materials to graphite. Silicon (theoretical capacity approximately 4200 mAh / g) possesses a high theoretical capacity and suitable insertion / extraction of Li... + Potential has become the preferred anode material for next-generation lithium batteries. However, the huge volume expansion effect (approximately 300%) caused by the alloying of silicon and lithium results in rapid capacity decay, which has become a barrier to the commercialization of silicon.

[0004] To this end, researchers have made many improvements. For example, researchers have disclosed a new method for preparing silicon-carbon composite anode materials. The method for preparing composite anode materials includes the following steps: (1) dispersing nano-silicon powder in a solution containing a dispersant; (2) adding a metal salt to the solution obtained in step (1) and mixing evenly; (3) dissolving one of the organic ligands 2-methylimidazolium, ethylenediaminetetraacetic acid, aminocarboxylic acid ligand, ethylenediamine, glycine, lactic acid, and phenoxy ions in the same volume of solvent as in step (1), and adding it to the solution obtained in step (2) after complete dissolution. After the reaction, centrifuge and dry to form MOF-coated precursor material of nano-silicon powder; (4) adding a reducing metal to the MOF-coated precursor material of nano-silicon powder, and then performing thermal reduction in an inert gas, while simultaneously performing carbonization treatment; (5) washing and drying the material after the reaction in step (4) to obtain a new silicon-carbon composite anode material, which is a nitrogen-doped carbon-coated porous silicon composite material.

[0005] However, the composite materials prepared by the above-mentioned improvement methods are difficult to suppress the volume expansion of silicon because silicon is only formed on the surface of the MOF material. Furthermore, carbonization in a tube furnace filled with argon generally requires a temperature of over 800°C, which is costly. In addition, the use of reducing metals during the carbonization process causes the hydrogen, oxygen and other components in the MOF to volatilize, resulting in low atom utilization and waste of raw materials.

[0006] Therefore, how to reduce costs, suppress the volume expansion of silicon anodes, and improve the stability of silicon anodes are urgent technical problems that need to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a composite silicon-based anode material, its preparation method, and a lithium-ion battery. This invention embeds at least a portion of the silicon-based material into the pores of a MOF (Metal-Oxide-Factory) material with an average pore size of 2-200 nm after pore formation. This not only suppresses the volume expansion of silicon but also improves the stability of the silicon anode by maintaining the average pore size of the MOF material within the 2-200 nm range after pore formation. Based on this, a low-cost, high-energy-density composite silicon-based anode material can be obtained, effectively suppressing battery capacity decay and significantly improving cycle performance and rate performance. To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a composite silicon-based anode material, the composite silicon-based anode material comprising a silicon-based material and a porous MOFs material after pore formation, wherein the porous MOFs material has a porous structure.

[0009] At least a portion of the silicon-based material is embedded inside the pores of the MOFs material after pore formation;

[0010] The average pore size of the MOFs material after pore formation is 2-200nm, for example, it can be 2nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 100nm, 150nm or 200nm, etc., preferably 2-50nm.

[0011] In this invention, the average pore size of the MOFs material after pore formation is 2-200 nm, which can maximize the stability of the MOFs material framework and the overall structure. Because silicon particles repeatedly contract and expand during cycling, generating stress, if the average pore size of the MOFs material after pore formation is too large, the MOFs framework will be unstable, leading to insufficient stress resistance and premature failure. Conversely, if the average pore size is too small, it will hinder the embedding of silicon-based materials, preventing the framework from leveraging its advantages, resulting in insufficient silicon embedding and ineffective capacity improvement.

[0012] This invention embeds at least a portion of the silicon-based material into the pores of MOFs material with an average pore size of 2-200 nm after pore formation. This not only suppresses the volume expansion of silicon, but also improves the stability of the silicon anode by ensuring that the average pore size of the MOFs material after pore formation is within the range of 2-200 nm. Based on this, a low-cost, high-energy-density composite silicon-based anode material can be obtained, which effectively suppresses the decay of battery capacity and significantly improves cycle performance and rate performance.

[0013] It should be noted that silicon-based materials can be partially embedded inside the pores of the pore-forming MOFs material, partially located on the surface of the pore-forming MOFs material, or completely embedded inside the pores of the pore-forming MOFs material.

[0014] As a preferred technical solution of the present invention, the silicon-based material includes any one or a combination of at least two of nano-silicon, silicon oxide, or silicon suboxide.

[0015] Preferably, the median particle size of the silicon-based material is 1-150 nm, for example, it can be 1 nm, 5 nm, 10 nm, 25 nm, 50 nm, 75 nm, 100 nm, 125 nm or 150 nm, etc.

[0016] In this invention, if the median particle size of the silicon-based material is too small, the cost will be too high; if the median particle size of the silicon-based material is too large, the structure of the composite silicon-based anode material will be unstable, and the MOFs material will not be able to effectively suppress the volume expansion of silicon during the charging and discharging process.

[0017] Preferably, the metal salt in the MOF material is selected from at least one of cobalt salt, nickel salt, copper salt, iron salt, and manganese salt.

[0018] Preferably, the organic ligand in the MOFs material is selected from at least one of 2-methylimidazole, 1-methylimidazole, 2-nitroimidazole, terephthalic acid, and trimesic acid.

[0019] Preferably, the MOFs material includes ZIF-67 and / or ZIF-8.

[0020] Preferably, the porosity of the MOFs material after pore formation is 20-60%, for example, it can be 20%, 30%, 40%, 50% or 60%, etc.

[0021] In this invention, the porosity of the MOFs material after pore formation is 20-60%, which can accommodate more silicon-based materials and is beneficial to improving the energy density of the battery.

[0022] Preferably, the mass ratio of the silicon-based material to the MOFs material after pore formation is (0.05-0.15):(0.2-0.6), wherein the silicon-based material selection range "0.05-0.15" can be, for example, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14 or 0.15, etc., and the ZIF-67 selection range "0.2-0.6" after pore formation can be, for example, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55 or 0.6, etc.

[0023] In this invention, if the mass ratio of silicon-based material to pore-forming MOFs material is too small, i.e., the amount of pore-forming MOFs material is too large, the framework structure formed by the MOFs material will be too thick, and its porous structure with silicon intercalation characteristics cannot be fully utilized, which is not conducive to the insertion or extraction of lithium ions during charging and discharging. If the mass ratio of silicon-based material to pore-forming MOFs material is too large, i.e., the amount of pore-forming MOFs material is too small, the volume expansion of silicon-based material during lithium storage cannot be suppressed, which will lead to lattice collapse.

[0024] As a preferred embodiment of the present invention, the outer surface of the composite silicon-based anode material is further coated with a carbon coating layer, and the carbon coating layer is partially embedded in the pores of the MOFs material after pore formation.

[0025] In this invention, the carbon coating layer provides a certain conductivity to the overall material, while some carbon is embedded in the pores of the MOFs material, which can suppress the volume expansion of silicon. Combined with the suppression of volume expansion of silicon-based materials by the MOFs material after pore formation, the two work together to make the silicon-based anode material have higher specific energy.

[0026] Preferably, the thickness of the carbon coating layer is 20-2000 nm, for example, it can be 40 nm, 400 nm or 1000 nm.

[0027] In this invention, the thickness of the carbon coating layer refers to the thickness from the interface between the carbon coating layer and the MOF material to the outermost layer of the composite silicon-based anode material.

[0028] In a second aspect, the present invention provides a method for preparing a composite silicon-based anode material as described in the first aspect, the method comprising the following steps:

[0029] The composite silicon-based anode material is obtained by mixing silicon-based materials and MOFs materials after pore formation.

[0030] The preparation method provided by this invention significantly reduces reaction energy consumption and optimizes operational convenience, thus possessing the potential for industrial-scale production.

[0031] As a preferred embodiment of the present invention, the preparation steps of the MOFs material include:

[0032] The MOF material is obtained by mixing metal salt, organic ligand, and solvent.

[0033] Preferably, the mass ratio of the metal salt to the organic ligand is (3-10):(3-10), wherein the range of the metal salt selection "3-10" can be, for example, 3, 4, 5, 6, 7, 8, 9 or 10, and the range of the organic ligand selection "3-10" can be, for example, 3, 4, 5, 6, 7, 8, 9 or 10.

[0034] As a preferred embodiment of the present invention, the pore-forming MOFs material is prepared by the following method, which includes the following steps:

[0035] The MOFs material is etched in a liquid environment using an etchant to obtain the MOFs material with pores formed.

[0036] Preferably, the etchant is an acidic etchant or an alkaline etchant;

[0037] Preferably, the acid etchant includes at least one selected from tannic acid, citric acid, oxalic acid, acetic acid, and hydrochloric acid.

[0038] Preferably, the alkaline etching agent includes at least one selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, and barium hydroxide.

[0039] As a preferred embodiment of the present invention, the etchant is an acidic etchant, and the etching method includes:

[0040] The MOF material and acidic etchant are dispersed in a solvent and dried to obtain the pore-forming MOF material.

[0041] Preferably, the mass ratio of the MOFs material to the acidic etchant is (0.2-0.4):(1-2), wherein the MOFs material selection range "0.2-0.4" can be, for example, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38 or 0.4, and the acidic etchant selection range "1-2" can be, for example, 1, 1.2, 1.4, 1.6, 1.8 or 2, etc.

[0042] Preferably, the etchant is an alkaline etchant, and the etching method includes:

[0043] The MOF material is mixed with a solution containing an alkaline etchant and heated to obtain the MOF material after pore formation.

[0044] Preferably, the mass concentration of the solution containing the alkaline etching agent is 10-30%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30%, etc.

[0045] Preferably, the mass-to-volume ratio of the MOFs material and the alkaline etchant solution is (1-10)g:(1-20)mL, wherein the mass of the MOFs material is selected from the range of "(1-10)g", for example, 1g, 3g, 5g, 7g or 10g, and the volume of the alkaline etchant solution is selected from the range of "(1-20)mL", for example, 1mL, 5mL, 10mL, 15mL or 20mL.

[0046] In this invention, the mass-to-volume ratio of MOFs material and the solution containing alkaline etchant refers to the ratio of the mass of MOFs material to the volume of the solution containing alkaline etchant.

[0047] Preferably, the heating temperature is 30-50℃, for example, it can be 30℃, 32℃, 34℃, 36℃, 38℃, 40℃, 42℃, 44℃, 46℃, 48℃ or 50℃, etc.

[0048] In a preferred embodiment of the present invention, the etchant is an acidic etchant, and the preparation method further includes the steps of pre-electrochemically treating the silicon-based material and pre-electrochemically treating the MOFs material after hole formation.

[0049] The method for pre-electrochemically treating the silicon-based material includes: mixing the silicon-based material, a first electrochemical agent, and a solvent to obtain a charged silicon-based material;

[0050] The present invention does not specifically limit the solvent used in the electrochemical treatment process. For example, it may be water, ethanol, ethylene glycol or propanol.

[0051] The method for pre-electrochemical treatment of the pore-forming MOFs material includes: mixing the pore-forming MOFs material with a second electrical agent to obtain a charged MOFs material;

[0052] Among them, the charged silicon-based materials and the charged MOFs materials have opposite electrical properties.

[0053] In this invention, by performing an electrical treatment, the electrical properties of the silicon-based material and the MOFs material are reversed, which enables the silicon-based material and the MOFs material to be better assembled.

[0054] Preferably, the first electroactive agent is a cationic surfactant, and preferably includes at least one of hexadecyltrimethylammonium bromide, dodecyl dimethyl benzyl ammonium chloride, octadecyltrimethylammonium chloride, and methyl ditaurate ethyl-2-hydroxyethyl ammonium sulfate.

[0055] Preferably, the mass-to-volume ratio of the silicon-based material to the first electrical agent is (0.1-0.5)g:(1-3)mL, wherein the mass of the silicon-based material is selected from the range of (0.1-0.5)g, for example, 0.1g, 0.2g, 0.3g, 0.4g, or 0.5g, and the volume of the first electrical agent is selected from the range of (1-3)mL, for example, 1mL, 1.5mL, 2mL, 2.5mL, or 3mL, etc.

[0056] In this invention, the mass-to-volume ratio of silicon-based material to the first electrical agent refers to the ratio of the mass of the silicon-based material to the volume of the first electrical agent.

[0057] Preferably, the second electrical agent comprises at least one of sodium polystyrene sulfonate, sodium hexadecyl sulfate, sodium octadecyl sulfate, and sodium dioctyl succinate sulfonate.

[0058] Preferably, the mass-to-volume ratio of the pore-forming MOFs material to the second electrochemical agent is (50-100)g:(5-10)mL, wherein the mass of the pore-forming MOFs material is selected from the range of "(50-100)g", for example, 50g, 60g, 70g, 80g, 90g or 100g, and the volume of the second electrochemical agent is selected from the range of "(5-10)mL", for example, 5mL, 6mL, 7mL, 8mL, 9mL or 10mL, etc.

[0059] In this invention, the mass-to-volume ratio of the pore-forming MOFs material and the second electrical agent refers to the ratio of the mass of the pore-forming MOFs material to the volume of the second electrical agent.

[0060] As a preferred embodiment of the present invention, the preparation method further includes a step of carbon coating the mixture obtained after mixing the silicon-based material and the pore-forming MOF material, wherein the specific steps of the carbon coating include:

[0061] The mixture is combined with a carbon source and subjected to a hydrothermal reaction to obtain a carbon-coated composite silicon-based anode material.

[0062] Preferably, the carbon source includes at least one of citric acid, sugar carbon source, ester carbon source and biomass carbon source.

[0063] The present invention does not limit the type of carbohydrate carbon source; for example, it may be sucrose. The present invention also does not limit the type of ester carbon source; for example, it may be phenolic resin.

[0064] Preferably, the mass ratio of the mixture to the carbon source is (1-100):(1-100), wherein the range of the mixture "1-100" can be, for example, 1, 5, 10, 25, 50, 75 or 100, and the range of the carbon source "1-100" can be, for example, 1, 5, 10, 25, 50, 75 or 100.

[0065] Preferably, the temperature of the hydrothermal reaction is 200-300℃, for example, it can be 200℃, 220℃, 240℃, 260℃, 280℃ or 300℃.

[0066] Preferably, the hydrothermal reaction time is 8-12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0067] Preferably, the silicon-based material and the pore-forming MOFs material are mixed by ball milling.

[0068] Preferably, the ball-to-material ratio during ball milling is (1-10):1, for example, it can be 1:1, 3:1, 5:1, 7:1 or 10:1, etc.

[0069] In this invention, the ball-to-material ratio refers to the ratio of the amount of grinding media to the amount of material.

[0070] Preferably, the rotational speed of the ball mill is 100-500 rpm, for example, it can be 100 rpm, 200 rpm, 300 rpm, 400 rpm or 500 rpm.

[0071] Preferably, the ball milling time is 1-6 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.

[0072] As a preferred technical solution, the preparation method includes the following steps:

[0073] (Ⅰ) The silicon-based material and the first electrical agent were mixed with the solvent at a mass-volume ratio of (0.1-0.5)g:(1-3)mL to obtain the charged silicon-based material;

[0074] (II) At room temperature, MOFs material and acidic etchant are stirred and dispersed in solvent for 10-30 min at a mass ratio of (0.2-0.4):(1-2), and then vacuum dried at 40-80℃ for 2-4 h to obtain MOFs material after pore formation.

[0075] (III) The MOFs material after pore formation is mixed with the second electrical agent so that the electrical properties of the MOFs material obtained after treatment are opposite to those of the charged silicon-based material, thereby obtaining a charged MOFs material.

[0076] The mass-to-volume ratio of the pore-forming MOFs material and the second electrical agent is (50-100) g:(5-10) mL.

[0077] (IV) The charged silicon-based material and the charged MOFs material are ball-milled at a speed of 100-500 rpm for 1-6 hours, with a ball-to-material ratio of (1-10):1, to obtain a mixture;

[0078] The mass ratio of the charged silicon-based material to the charged MOF material is (0.05-0.15):(0.2-0.6).

[0079] (V) The mixture and carbon source are mixed in water and subjected to a hydrothermal reaction at 200-300°C for 8-12 hours to obtain the composite silicon-based anode material.

[0080] Thirdly, the present invention provides a sodium-ion battery, wherein the negative electrode of the sodium-ion battery comprises a composite silicon-based negative electrode material as described in the first aspect.

[0081] The composite silicon-based anode material provided by this invention can form a more stable SEI film, reduce the repeated formation of the SEI film, thereby reducing electrolyte consumption and effectively improving the coulombic efficiency of the battery.

[0082] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0083] Compared with the prior art, the present invention has the following beneficial effects:

[0084] (1) By embedding at least a portion of the silicon-based material into the pores of MOFs material with an average pore size of 2-200 nm after pore formation, the present invention not only suppresses the volume expansion of silicon, but also improves the stability of silicon anode by ensuring that the average pore size of MOFs material after pore formation is in the range of 2-200 nm. Based on this, a low-cost, high-energy-density composite silicon-based anode material can be obtained, and the capacity decay of the battery is effectively suppressed, and the cycle performance and rate performance are significantly improved.

[0085] (2) The composite silicon-based anode material provided by the present invention can form a more stable SEI film as an anode material, reduce the repeated generation of SEI film, thereby reduce the consumption of electrolyte and effectively improve the coulombic efficiency of the battery. Attached Figure Description

[0086] Figure 1 This is a TEM image of the composite silicon-based anode material provided in Embodiment 1 of the present invention. Detailed Implementation

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0088] In the following examples, room temperature refers to 25°C.

[0089] Example 1

[0090] This embodiment provides a composite silicon-based anode material, which includes a silicon-based material and a ZIF-67 after pore formation, and a carbon coating layer covering the surface of the silicon-based material and the ZIF-67 after pore formation. At least a portion of the silicon-based material is embedded inside the pores of the ZIF-67, and a portion of the carbon coating layer covers the surface of the silicon-based material and the ZIF-67 after pore formation, while another portion is embedded inside the pores of the ZIF-67 after pore formation.

[0091] The median particle size of the silicon-based material is 150 nm, and the ZIF-67 after pore formation has a porous structure with an average pore size of 200 nm and a porosity of 26.68%. The mass ratio of the silicon-based material to the ZIF-67 after pore formation is 0.1:0.4. The thickness of the carbon coating layer is 1000 nm.

[0092] This embodiment also provides a method for preparing a composite silicon-based anode material, the method comprising the following steps:

[0093] (1) Mix the silicon-based material, the first electrochemical agent and 50 mL of solvent, and centrifuge to obtain the positively charged silicon-based material;

[0094] The silicon-based material is nano-silicon, the first electronic agent is hexadecyltrimethylammonium bromide, the solvent is ethanol, and the mass-volume ratio of the silicon-based material to the first electronic agent is 0.1g:1mL.

[0095] (2) Mix the metal salt, organic ligand and 40 mL of ethanol, centrifuge and dry to obtain ZIF-67; Pore formation treatment: At room temperature, stir and disperse the ZIF-67 and tannic acid in 300 mL of water for 20 min, centrifuge and wash three times with water and ethanol respectively, and then vacuum dry at 60 °C for 3 h to obtain ZIF-67 with pores; Then mix the ZIF-67 with 7 mL of the second charge agent to obtain negatively charged ZIF-67;

[0096] The metal salt is cobalt acetate, the organic ligand is 2-methylimidazole, the mass ratio of the metal salt to the organic ligand is 5:5, the mass ratio of ZIF-67 to tannic acid is 0.3:1.5, the second electrochemical agent is sodium polystyrene sulfonate, and the mass-volume ratio of ZIF-67 and the second electrochemical agent after pore formation is 0.1g:7mL.

[0097] (3) The positively charged silicon-based material and the negatively charged ZIF-67 were ball-milled at 300 rpm for 3 hours with a ball-to-material ratio of 10:1. After standing and separating, the mixture was obtained.

[0098] (4) The mixture with a mass ratio of 1:1 and 3.5g of citric acid are mixed in water and subjected to a hydrothermal reaction at 200°C for 12 hours to obtain the composite silicon-based anode material.

[0099] Figure 1 The TEM image of the composite silicon-based anode material provided in this embodiment is shown. As can be seen from the figure, the thickness of the coating layer is about 150 nm. The coated carbon layer can provide a certain conductivity to the interior and also isolates the electrolyte from direct contact with the silicon particles, thus preventing the formation of an unstable SEI film (repeated changes in silicon volume will cause the SEI to be unstable, and if it is damaged, it will continuously consume the electrolyte to form a new SEI).

[0100] Example 2

[0101] This embodiment provides a composite silicon-based anode material, which includes a silicon-based material and a ZIF-67 after pore formation, and a carbon coating layer covering the surface of the silicon-based material and the ZIF-67 after pore formation. At least a portion of the silicon-based material is embedded inside the pores of the ZIF-67, and a portion of the carbon coating layer covers the surface of the silicon-based material and the ZIF-67 after pore formation, while another portion is embedded inside the pores of the ZIF-67 after pore formation.

[0102] The median particle size of the silicon-based material is about 60 nm, and the ZIF-67 after pore formation has a porous structure with an average pore size of about 100 nm and a porosity of 38.71%. The mass ratio of the silicon-based material to the ZIF-67 after pore formation is 1:1. The thickness of the carbon coating layer is about 100 nm.

[0103] This embodiment also provides a method for preparing a composite silicon-based anode material, the method comprising the following steps:

[0104] (1) Mix the silicon-based material, the first electrochemical agent and 50 mL of solvent, and centrifuge to obtain the positively charged silicon-based material;

[0105] The silicon-based material is silicon oxide, the first electronic agent is hexadecyltrimethylammonium bromide, the solvent is water, and the mass-volume ratio of the silicon-based material to the first electronic agent is 3g:100mL.

[0106] (2) Mix the metal salt, organic ligand and 40 mL of ethanol, centrifuge and dry to obtain ZIF-67; Pore formation treatment: At room temperature, stir and disperse the ZIF-67 and tannic acid in 300 mL of water for 10 min, centrifuge and wash three times with water and ethanol respectively, and then vacuum dry at 40 °C for 4 h to obtain ZIF-67 with pores; then mix the ZIF-67 with 5 mL of the second charge agent to obtain negatively charged ZIF-67;

[0107] Among them, the metal salt is nickel acetate, the organic ligand is 1-methylimidazole, the mass ratio of metal salt to organic ligand is 3:10, the mass ratio of ZIF-67 to tannic acid is 0.4:1, the second electronic agent is sodium polystyrene sulfonate, and the mass-volume ratio of ZIF-67 and the second electronic agent after pore formation is 3g:20mL.

[0108] (3) The positively charged silicon-based material and the negatively charged ZIF-67 were ball-milled at 100 rpm for 6 hours with a ball-to-material ratio of 10:1. After standing and separating, the mixture was obtained.

[0109] (4) The mixture with a mass ratio of 1:4 and citric acid are mixed in water and subjected to a hydrothermal reaction at 250°C for 10 hours to obtain the composite silicon-based anode material.

[0110] Example 3

[0111] This embodiment provides a composite silicon-based anode material, which includes a silicon-based material and a ZIF-67 after pore formation, and a carbon coating layer covering the surface of the silicon-based material and the ZIF-67 after pore formation. At least a portion of the silicon-based material is embedded inside the pores of the ZIF-67, and a portion of the carbon coating layer covers the surface of the silicon-based material and the ZIF-67 after pore formation, while another portion is embedded inside the pores of the ZIF-67 after pore formation.

[0112] The median particle size of the silicon-based material is about 60 nm, and the ZIF-67 after pore formation has a porous structure with an average pore size of about 80 nm and a porosity of 30.51%. The mass ratio of the silicon-based material to the ZIF-67 after pore formation is 2:3. The thickness of the carbon coating layer is about 200 nm.

[0113] This embodiment also provides a method for preparing a composite silicon-based anode material, the method comprising the following steps:

[0114] (1) Mix the silicon-based material, the first electrochemical agent and 50 mL of solvent, and centrifuge to obtain the positively charged silicon-based material;

[0115] The silicon-based material is silicon suboxide, the first electronic agent is hexadecyltrimethylammonium bromide, the solvent is propanol, and the mass-volume ratio of the silicon-based material to the first electronic agent is 0.5g:10mL.

[0116] (2) Mix the metal salt, organic ligand and 40 mL of ethanol, centrifuge and dry to obtain ZIF-67; Pore formation treatment: At room temperature, stir and disperse the ZIF-67 and tannic acid in 300 mL of water for 30 min, centrifuge and wash three times with water and ethanol respectively, and then vacuum dry at 80 °C for 2 h to obtain ZIF-67 with pores; then mix the ZIF-67 with 10 mL of the second charge agent to obtain negatively charged ZIF-67;

[0117] The metal salt is copper chloride, the organic ligand is 2-nitroimidazole, the mass ratio of the metal salt to the organic ligand is 10:3, the mass ratio of ZIF-67 to tannic acid is 0.2g:2, the second electronic agent is sodium polystyrene sulfonate, and the mass-volume ratio of ZIF-67 and the second electronic agent after pore formation is 1g:10mL.

[0118] (3) The positively charged silicon-based material and the negatively charged ZIF-67 were ball-milled at 500 rpm for 1 h with a ball-to-material ratio of 10:1. After standing and separating, the mixture was obtained.

[0119] (4) The mixture with a mass ratio of 1:3 and citric acid are mixed in water and subjected to a hydrothermal reaction at 300°C for 8 hours to obtain the composite silicon-based anode material.

[0120] Example 4

[0121] This embodiment provides a composite silicon-based anode material, which includes a silicon-based material and a pore-formed ZIF-8, as well as a carbon coating layer covering the surface of the silicon-based material and the pore-formed ZIF-8. At least a portion of the silicon-based material is embedded inside the pores of the ZIF-8, and a portion of the carbon coating layer covers the surface of the silicon-based material and the pore-formed ZIF-8, while another portion is embedded inside the pores of the pore-formed ZIF-8.

[0122] The median particle size of the silicon-based material is about 30 nm, and the ZIF-67 after pore formation has a porous structure with an average pore size of about 50 nm and a porosity of 32.23%. The mass ratio of the silicon-based material to the ZIF-67 after pore formation is 1:1. The thickness of the carbon coating layer is about 150 nm.

[0123] This embodiment also provides a method for preparing a composite silicon-based anode material, the method comprising the following steps:

[0124] (1) Dissolve 5g of metal salt and 5g of organic ligand in 40mL of ethanol, and place in a water bath at 50℃ to stir and evaporate the solvent. Then filter, separate and dry to obtain ZIF-8; Pore forming treatment: stir the ZIF-8 and 50mL of sodium hydroxide solution (mass concentration of 20%) for 1h, then filter, separate and dry to obtain ZIF-8 after pore forming.

[0125] The metal salt is zinc acetate, the organic ligand is 2-methylimidazole, the mass ratio of the metal salt to the organic ligand is 5:5, and the mass-volume ratio of ZIF-8 to sodium hydroxide solution is 2g:50mL.

[0126] (2) 0.5g of silicon-based material and 1g of the pore-forming ZIF-8 were ball-milled at 300rpm for 3h with a ball-to-material ratio of 10:1. After standing and separating, the mixture was obtained.

[0127] Among them, the silicon-based material is nano-silicon;

[0128] (3) The mixture with a mass ratio of 1:2 and 3.5g of citric acid are mixed in water and subjected to a hydrothermal reaction at 200°C for 12 hours to obtain the composite silicon-based anode material.

[0129] Comparative Example 1

[0130] The difference between this comparative example and Example 1 is that ZIF-67 is not subjected to pore-forming treatment, that is, the pore-forming treatment in step (2) is not performed, but ZIF-67 is directly mixed with the second electrical agent.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Comparative Example 2

[0133] This comparative example uses unmodified nano-silicon as the silicon-based anode material.

[0134] Comparative Example 3

[0135] This comparative example uses graphite as the negative electrode material.

[0136] Performance testing

[0137] The negative electrode materials prepared in Examples 1-4 and Comparative Examples 1-2 were mixed with conductive carbon black and polyacrylic acid in a mass ratio of 90:5:5 in deionized water. The mixture was then mechanically stirred on a magnetic stirrer for 12 hours. After stirring, the resulting slurry was slowly and evenly coated onto copper foil to obtain a negative electrode sheet. The negative electrode sheet was placed in a vacuum drying oven and dried at 80°C for 12 hours. The next day, the sheet was removed and cut into 12mm round pieces using a Shenzhen Kejing cutting machine for later use.

[0138] The prepared negative electrode sheet was transferred to a glove box to assemble a full cell. Using a 2032 battery case, a polypropylene separator, and commercial LB315 electrolyte, a half cell was assembled with the prepared negative electrode sheet as the negative electrode and a lithium sheet as the counter electrode. The assembled battery needed to stand for 12 hours before electrochemical testing was performed.

[0139] Various technical tests were conducted using the Newway button cell tester, including charge / discharge cycle and rate performance tests.

[0140] The test conditions were: constant temperature and humidity at 25℃, voltage range of 0.01-1.5V; the rate performance test consisted of 5 cycles at each current density, i.e., at 0.1A g. -1 2A g -1 0.1A g -1 The test was conducted at the current density. The test results are shown in Table 1.

[0141] Table 1

[0142]

[0143]

[0144] It should be noted that "plummeting" in the table refers to a sudden drop in battery capacity, reaching a stage where it is basically impossible to charge or discharge.

[0145] analyze:

[0146] As shown in the table above, this invention effectively suppresses the volume expansion of silicon by embedding at least a portion of the silicon-based material into the pores of the pore-formed MOF material. Based on this, a high-energy-density composite silicon-based anode material can be obtained, and the capacity decay of the battery is effectively suppressed. Furthermore, the composite silicon-based anode material provided by this invention, as an anode material, can form a more stable SEI film, reducing the repeated formation of the SEI film, thereby reducing electrolyte consumption and effectively improving the electrochemical performance of the battery.

[0147] The data from Examples 1-4 and Comparative Example 1 show that the capacity in the second cycle of acid-base etching with pores was not significantly different from that without pores. This is presumably because the amount of nano-silicon added remained constant, resulting in minimal capacity difference in the early stages. However, after 100 cycles, the capacity of Comparative Example 1 without pores decayed very rapidly, to 0.1 A g.-1 The capacity retention rate is only 31.85%, which cannot meet the requirements of lithium-ion batteries.

[0148] The data from Examples 1-4 and Comparative Examples 2-3 show that the pure nano-silicon anode failed to cycle for 100 cycles. Although the initial capacity was high, it could not meet the cycling requirements. Graphite had a lower initial capacity and a higher cycle retention rate. Although the material had stable electrochemical performance, its low specific capacity limited its upper limit.

[0149] Therefore, in summary, the composite silicon anode material prepared in this invention combines both good cycle stability and high specific capacity, making it a promising anode material. Furthermore, this invention provides a simple and feasible industrial-scale solution, offering valuable reference for future researchers.

[0150] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite silicon-based anode material, characterized in that, The composite silicon-based anode material includes a silicon-based material and a porous MOFs material after pore formation, wherein the porous MOFs material has a porous structure. At least a portion of the silicon-based material is embedded inside the pores of the MOFs material after pore formation; The average pore size of the MOFs material after pore formation is 40-200 nm. The mass ratio of the silicon-based material to the pore-forming MOFs material is (0.05-0.15):(0.2-0.6); The outer surface of the composite silicon-based anode material is also covered with a carbon coating layer. Part of the carbon coating layer is embedded in the pores of the pore-forming MOFs material, and another part covers the surface of the silicon-based material and the pore-forming MOFs material.

2. The composite silicon-based anode material according to claim 1, characterized in that, The silicon-based material includes any one or a combination of at least two of nano-silicon, silicon oxide, or silicon suboxide.

3. The composite silicon-based anode material according to claim 1, characterized in that, The median particle size of the silicon-based material is 1-150 nm.

4. The composite silicon-based anode material according to claim 1, characterized in that, The metal salt in the MOFs material is selected from at least one of cobalt salt, nickel salt, copper salt, iron salt, and manganese salt; the organic ligand in the MOFs material is selected from at least one of 2-methylimidazole, 1-methylimidazole, 2-nitroimidazole, terephthalic acid, and trimesic acid.

5. The composite silicon-based anode material according to claim 1, characterized in that, The MOFs materials include ZIF-67 and / or ZIF-8.

6. The composite silicon-based anode material according to claim 1, characterized in that, The porosity of the MOFs material after pore formation is 20-60%.

7. The composite silicon-based anode material according to claim 1, characterized in that, The thickness of the carbon coating layer is 20-2000 nm.

8. A method for preparing a composite silicon-based anode material as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: The composite silicon-based anode material is obtained by mixing silicon-based materials and MOFs materials after pore formation.

9. The preparation method according to claim 8, characterized in that, The pore-forming MOFs material is prepared by the following method, which includes the following steps: The MOFs material is etched in a liquid environment using an etchant to obtain the MOFs material with pores.

10. The preparation method according to claim 9, characterized in that, The etching agent is an acidic etching agent or an alkaline etching agent.

11. The preparation method according to claim 10, characterized in that, The acidic etchant includes at least one of tannic acid, citric acid, oxalic acid, acetic acid, and hydrochloric acid.

12. The preparation method according to claim 10, characterized in that, The alkaline etching agent includes at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, and barium hydroxide.

13. The preparation method according to claim 10, characterized in that, The etching agent is an acidic etching agent, and the etching method includes: The MOF material and acidic etchant are dispersed in a solvent and dried to obtain the pore-forming MOF material.

14. The preparation method according to claim 13, characterized in that, The mass ratio of the MOF material to the acidic etchant is (0.2-0.4):(1-2).

15. The preparation method according to claim 10, characterized in that, The etching agent is an alkaline etching agent, and the etching method includes: The MOF material is mixed with a solution containing an alkaline etchant and heated to obtain the MOF material after pore formation.

16. The preparation method according to claim 15, characterized in that, The mass concentration of the solution containing the alkaline etching agent is 10-30%.

17. The preparation method according to claim 15, characterized in that, The mass-to-volume ratio of the MOF material and the solution containing the alkaline etchant is (1-10) g:(1-20) mL.

18. The preparation method according to claim 15, characterized in that, The heating temperature is 30-50℃.

19. The preparation method according to claim 10, characterized in that, The etchant is an acidic etchant, and the preparation method further includes the steps of pre-electrochemically treating the silicon-based material and pre-electrochemically treating the MOFs material after pore formation.

20. The preparation method according to claim 19, characterized in that, The method for pre-electrifying the silicon-based material includes mixing the silicon-based material, a first electrochemical agent, and a solvent to obtain a charged silicon-based material.

21. The preparation method according to claim 20, characterized in that, The method for pre-electrochemical treatment of the pore-forming MOFs material includes: mixing the pore-forming MOFs material with a second electrical agent to obtain a charged MOFs material; Among them, the charged silicon-based materials and the charged MOFs materials have opposite electrical properties.

22. The preparation method according to claim 20, characterized in that, The first electrochemical agent is a cationic surfactant.

23. The preparation method according to claim 22, characterized in that, The cationic surfactant includes at least one of hexadecyltrimethylammonium bromide, dodecyl dimethyl benzyl ammonium chloride, octadecyltrimethylammonium chloride, and methyl ditaurate ethyl-2-hydroxyethyl ammonium sulfate.

24. The preparation method according to claim 20, characterized in that, The mass-to-volume ratio of the silicon-based material to the first electrochemical agent is (0.1-0.5) g:(1-3) mL.

25. The preparation method according to claim 21, characterized in that, The second electrical agent includes at least one of sodium polystyrene sulfonate, sodium hexadecyl sulfate, sodium octadecyl sulfate, and sodium dioctyl succinate sulfonate.

26. The preparation method according to claim 21, characterized in that, The mass-to-volume ratio of the pore-forming MOFs material to the second electrochemical agent is (50-100) g:(5-10) mL.

27. The preparation method according to claim 8, characterized in that, The preparation method further includes a step of carbon coating the mixture obtained after mixing the silicon-based material and the pore-forming MOF material, wherein the specific steps of the carbon coating include: The mixture is combined with a carbon source and subjected to a hydrothermal reaction to obtain a carbon-coated composite silicon-based anode material.

28. The preparation method according to claim 27, characterized in that, The carbon source includes at least one of citric acid, sugar carbon source, ester carbon source and biomass carbon source.

29. The preparation method according to claim 27, characterized in that, The mass ratio of the mixture to the carbon source is (1-100):(1-100).

30. The preparation method according to claim 27, characterized in that, The temperature of the hydrothermal reaction is 200-300℃.

31. The preparation method according to claim 27, characterized in that, The hydrothermal reaction takes 8-12 hours.

32. The preparation method according to claim 27, characterized in that, The method of mixing the silicon-based material and the pore-forming MOFs material includes ball milling.

33. The preparation method according to claim 32, characterized in that, The ball-to-material ratio during ball milling is (1-10):

1.

34. The preparation method according to claim 32, characterized in that, The ball mill rotates at a speed of 100-500 rpm.

35. The preparation method according to claim 32, characterized in that, The ball milling time is 1-6 hours.

36. The preparation method according to claim 8, characterized in that, The preparation method includes the following steps: (I) The silicon-based material and the first electrical agent are mixed with the solvent at a mass-volume ratio of (0.1-0.5)g:(1-3)mL to obtain the charged silicon-based material; (II) At room temperature, MOFs material and acidic etchant are stirred and dispersed in solvent for 10-30 min at a mass ratio of (0.2-0.4):(1-2), and then vacuum dried at 40-80℃ for 2-4 h to obtain MOFs material after pore formation. (III) The MOFs material after pore formation is mixed with the second electrical agent so that the electrical properties of the MOFs material obtained after treatment are opposite to those of the charged silicon-based material, thereby obtaining a charged MOFs material; The mass-to-volume ratio of the pore-forming MOFs material and the second electrical agent is (50-100) g:(5-10) mL. (IV) The charged silicon-based material and the charged MOFs material are ball-milled at a speed of 100-500 rpm for 1-6 hours, with a ball-to-material ratio of (1-10):1, to obtain a mixture; The mass ratio of the charged silicon-based material to the charged MOF material is (0.05-0.15):(0.2-0.6). (V) The mixture and carbon source are mixed in water and subjected to a hydrothermal reaction at 200-300°C for 8-12 hours to obtain the composite silicon-based anode material.

37. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the composite silicon-based negative electrode material as described in any one of claims 1-7.

Images