A low-expansion silver-doped silicon-carbon composite material and its preparation method and application

Abstract

The embodiment of the present invention discloses a low-expansion silver-doped silicon-carbon composite material, and the preparation method includes: first subjecting nano-silicon to acid etching treatment, then loading silver through silver-ammonia reaction, and finally mixing with a binder, a conductive liquid and a catalyst, then ball milling and carbonizing for secondary granulation. The present invention deposits silver element on the surface of porous nano-silicon that has been etched by silver mirror reaction. Compared with traditional solid-phase mixed doping, it has the characteristics of uniform deposition, controllable process, thin deposition thickness, etc., and has little effect on the energy density of the material. The deposited silver element is connected by chemical bonds and deposited on its surface, which reduces the interface impedance between the materials, improves power performance and reduces expansion. The secondary particle granulation process forms amorphous carbon after the binder is carbonized at high temperature. The added catalyst promotes the reaction progress of the granulation process and forms a small amount of pore structure during the carbonization process, reducing the expansion of the material.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery materials, and in particular relates to a low-expansion silver-doped silicon-carbon composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Silicon-carbon materials are used in high-energy-density lithium-ion batteries due to their high energy density and abundant resources. However, drawbacks such as large expansion when fully charged and poor power performance hinder their widespread application. Currently, the main approach to improving the expansion of silicon-carbon materials is to coat the surface with amorphous carbon. This, on the one hand, restricts the material's expansion during charge and discharge, and on the other hand, reduces the material's electronic impedance and improves power performance. Granulation technology has been applied to graphite composites to reduce their expansion, and secondary granulation of silicon materials can easily impart anisotropic properties to silicon-based materials, reducing their expansion. Metals, due to their high electronic conductivity, are often doped into composite materials to reduce the interfacial impedance between the core and shell and improve power performance. However, direct doping methods offer limited performance improvements. Summary of the Invention

[0003] To address the deficiencies of the prior art, the present invention provides a low-expansion silver-doped silicon-carbon composite material. The low-expansion, high-magnification silicon-carbon composite material is obtained by pre-treating nano-silicon, depositing metallic silver on the surface of the silicon-based material using a silver mirror reaction, and performing secondary granulation.

[0004] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0005] The technical purpose of the first aspect of the present invention is to provide a method for preparing a low-expansion silver-doped silicon-carbon composite material, comprising the following steps:

[0006] Silicon material pretreatment: contacting nano-silicon particles with acid vapor to perform surface etching treatment to obtain etched nano-silicon;

[0007] Silver doping: Mix a titanium-based silane coupling agent with an organic solvent, add etched nano-silicon dispersion, mix with silver nitrate solution, adjust the pH to 8-10 with ammonia water, add formaldehyde solution dropwise to carry out silver-ammonia reaction, then filter and dry to obtain nano-silicon / silver primary particles;

[0008] Secondary granulation: the nano silicon / silver primary particles, the binder, the conductive liquid and the catalyst are uniformly mixed, ball milled and carbonized to obtain the low expansion silver-doped silicon-carbon composite material.

[0009] Furthermore, the particle size of the nano-silicon particles is 50-500 nm.

[0010] Furthermore, the acid vapor is hydrofluoric acid vapor. The specific process of surface etching the nano-silicon particles is: contacting the nano-silicon with the acid vapor at a temperature of 50° C. to 100° C. and etching for 12 hours to 48 hours.

[0011] Furthermore, during the silver doping process, the mass ratio of the etched nano-silicon, titanium-based silane coupling agent and silver nitrate is 100:0.5-2:10-50.

[0012] Furthermore, during the silver doping process, the molar ratio of formaldehyde to silver nitrate is 1-3:1.

[0013] Furthermore, in the silver doping reaction, the organic solvent is selected from at least one of ethanol, methanol and isopropanol.

[0014] Furthermore, during the silver doping process, the titanium-based silane coupling agent is selected from at least one of diisopropyl titanate, isopropyl tris(dioctyl phosphate) titanate, isopropyl trioleate titanate, isopropyl tris(dodecylbenzenesulfonyl) titanate, isopropyl tris(dioctyl pyrophosphate) titanate, bis(dioctyl pyrophosphate) ethylene titanate and tetra-n-butyl titanate, and its mass concentration in the organic solvent is 1-10 wt%.

[0015] Furthermore, during the silver doping process, the mass concentration of the silver nitrate solution is 2-5 wt %, and the mass concentration of the ammonia water is 5-30 wt %.

[0016] Furthermore, the temperature of the silver-ammonia reaction is 50-100° C., and the reaction time is 12-72 hours.

[0017] Furthermore, during the secondary granulation process, the mass ratio of the nano-silicon / silver primary particles, the binder, the conductive liquid and the catalyst is 100:1-5:0.5-2:0.5-2.

[0018] Furthermore, the binder is selected from petroleum asphalt and / or coal tar, and its softening point is 100-250°C; the conductive liquid is a carbon nanotube conductive liquid and / or a graphene conductive liquid, the mass concentration of the conductive liquid solid is 1-5wt%, and the solvent of the conductive liquid is N-methylpyrrolidone; the catalyst is selected from at least one of nano-iron, nano-cobalt and nano-nickel; and the particle size of the catalyst is 100-500nm.

[0019] Furthermore, during the secondary granulation process, the carbonization is carried out at 700-1000° C. for 3-12 hours.

[0020] The technical purpose of the second aspect of the present invention is to provide a low-expansion silver-doped silicon-carbon composite material prepared by the above method.

[0021] The technical purpose of the third aspect of the present invention is to provide the application of the low-expansion silver-doped silicon-carbon composite material as a battery negative electrode material.

[0022] The implementation of the present invention will have the following beneficial effects:

[0023] (1) The present invention deposits silver on the surface of the etched porous nano-silicon through the silver mirror reaction. Compared with the traditional solid-phase mixed doping, the present invention has the characteristics of uniform deposition, controllable process, thin deposition thickness, etc., and has little effect on the energy density of the material. At the same time, the porous nano-silicon obtained by acid treatment has a high specific surface area, which makes it more active and makes it easier for the deposited silver to be deposited on its surface, thereby reducing the interface impedance between the materials, improving the power performance and reducing expansion.

[0024] (2) The preparation process of the present invention includes a secondary particle granulation process. The amorphous carbon formed after the binder is carbonized at high temperature has the advantages of low impedance, etc., which improves power performance and reduces expansion. At the same time, a catalyst is added during the granulation process. On the one hand, it improves the reaction progress of the granulation process. On the other hand, it acts as a catalyst to form a small amount of pore structure during the carbonization process, thereby reducing material expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] in:

[0027] Figure 1 1000× SEM image of the low-expansion silver-doped silicon-carbon composite material prepared in Example 1;

[0028] Figure 2 This is a 10000× SEM image of the low-expansion silver-doped silicon-carbon composite material prepared in Example 1. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] In Examples 1-3, low expansion silver-doped silicon-carbon composite materials were prepared:

[0031] Example 1

[0032] S1, silicon material pretreatment: 100 g of nano-silicon (average particle size of 100 nm) was placed in a heating dish, heated to 80°C hydrofluoric acid vapor was introduced for surface etching for 24 h, washed with deionized water, and vacuum dried at 80°C for 24 h to obtain etched nano-silicon;

[0033] S2, silver doping: 100 g of the etched nano-silicon prepared in S1 was added to 20 mL of a 5 wt% ethanol solution of diisopropyl titanate and dispersed evenly. The mixture was then added to 500 mL of a 4 wt% (0.1176 mol) silver nitrate solution and 100 mL of a 10 wt% ammonia solution to adjust the pH to 9. After uniform dispersion, 7.06 mL (0.2352 mol) of formaldehyde solution was slowly added dropwise. The mixture was reacted at 80°C for 24 h to perform a silver-ammonia reaction. The mixture was filtered and dried in vacuo at 80°C for 24 h to obtain nano-silicon / silver primary particles.

[0034] S3, secondary granulation: 100g of nano-silicon / silver primary particles prepared in S2, 3g of petroleum asphalt (softening point 250°C), 100mL, 1wt% of carbon nanotube conductive liquid (the conductive liquid solvent is N-methylpyrrolidone), and 1g of nano-iron powder (average particle size of 500nm) are mixed evenly and ball-milled, and carbonized at 800°C for 6h to obtain the low-expansion silver-doped silicon-carbon composite material.

[0035] Example 2

[0036] S1, silicon material pretreatment: 100 g of nano-silicon (average particle size of 50 nm) was placed in a heating dish, heated to 50°C hydrofluoric acid vapor for surface etching for 48 h, washed with deionized water, and vacuum-dried at 80°C for 24 h to obtain etched nano-silicon;

[0037] S2, silver doping: 100 g of the etched nano-silicon prepared in S1 was added to a 50 mL, 1 wt% methanol solution of isopropyl tri(dioctylphosphoyloxy) titanate and dispersed uniformly. The mixture was then added to a 1000 mL, 1 wt% (0.058 mol) silver nitrate solution and 1000 mL, 50 wt% ammonia water was added to adjust the pH to 10. After uniform dispersion, 1.76 g (0.058 mol) of formaldehyde solution was slowly added dropwise. The mixture was reacted at 50° C. for 72 h to perform a silver-ammonia reaction. The mixture was filtered and dried in vacuo at 80° C. for 24 h to obtain nano-silicon / silver primary particles.

[0038] S3, secondary granulation: 100g of nano-silicon / silver primary particles prepared in S2, 1g of petroleum asphalt (softening point 250°C), 50mL, 1wt% of graphene conductive liquid (the conductive liquid solvent is N-methylpyrrolidone), and 0.5g of nano-cobalt (average particle size 100nm) are mixed evenly and ball milled, and carbonized at 700°C for 12h to obtain the low-expansion silver-doped silicon-carbon composite material.

[0039] Example 3

[0040] S1, silicon material pretreatment: 100 g of nano-silicon (average particle size of 500 nm) was placed in a heating dish, heated hydrofluoric acid vapor at 100°C was introduced for surface etching for 12 h, washed with deionized water, and vacuum dried at 80°C for 24 h to obtain etched nano-silicon;

[0041] S2, silver doping: 100 g of the etched nano-silicon prepared in S1 was added to 20 mL of a 10 wt% isopropanol solution of tetra-n-butyl titanate and dispersed uniformly. The mixture was then added to 1000 mL of a 5 wt% (0.29 mol) silver nitrate solution and 100 mL of a 30 wt% ammonia solution to adjust the pH to 8. After uniform dispersion, 26.1 mL (0.87 mol) of formaldehyde solution was slowly added dropwise. The mixture was reacted at 100° C. for 12 h to perform a silver-ammonia reaction. The mixture was filtered and dried in vacuo at 80° C. for 24 h to obtain nano-silicon / silver primary particles.

[0042] S3, secondary granulation: 100g of nano-silicon / silver primary particles prepared in S2, 5g of petroleum asphalt (softening point 100°C), 40mL, 5wt% of carbon nanotube conductive liquid (the conductive liquid solvent is N-methylpyrrolidone), and 2g of nano-nickel (average particle size 50nm) are mixed evenly and ball-milled, and carbonized at 1000°C for 3h to obtain the low-expansion silver-doped silicon-carbon composite material.

[0043] Comparative Example 1

[0044] (1) The same as step S1 of Example 1, to obtain an etched nano-silicon material;

[0045] (2) 100 g of etched nano-silicon material, 3 g of petroleum asphalt (softening point 250 ° C), 100 mL, 1 wt% carbon nanotube conductive liquid (the conductive liquid solvent is N-methylpyrrolidone), and 1 g of nano-iron powder (average particle size of 100 nm) were mixed evenly and ball-milled, and carbonized at 800 ° C for 6 h to obtain a silicon-carbon composite material.

[0046] Comparative Example 2

[0047] 100 g of nano-silicon (average particle size of 100 nm), 3 g of petroleum asphalt (softening point 250°C), and 100 mL of 1 wt% carbon nanotube conductive liquid (the conductive liquid solvent is N-methylpyrrolidone) are mixed evenly and ball-milled, and then carbonized at 800°C for 6 h to obtain a silicon-carbon composite material.

[0048] Comparative Example 3

[0049] Except that 1 g of nano iron powder catalyst is not added in step S3, other raw materials and steps are the same as those in Example 1.

[0050] Comparative Example 4

[0051] S1, same as step S1 of Example 1;

[0052] S2, add 100g of the etched nano-silicon prepared in S1 and 12.58g of nano-silver (particle size of 500nm) to 500g of ethanol and transfer to a ball mill for mixing and milling for 24h to load the silver onto the etched nano-silicon;

[0053] S3, the same as step S3 in Example 1, to obtain a silicon-carbon composite material.

[0054] Comparative Example 5

[0055] S1, same as step S1 of Example 1;

[0056] S2, same as step S2 of Example 1;

[0057] Without performing step S3, a nano-silicon / silver composite material is obtained.

[0058] Performance tests of the materials prepared in the above examples and comparative examples:

[0059] (1) SEM test

[0060] The silicon-carbon composite material prepared in Example 1 was subjected to SEM testing, and the test results are as follows: Figure 1 and Figure 2 As shown. Figure 1 It can be seen that the material presents a granular structure with a slight granulation structure, and the particle size distribution of the material is uniform and reasonable, with the particle size ranging from 2-6μm; Figure 2 It can be seen that the composite material contains a small amount of carbon nanotubes wrapped around the surface of silicon.

[0061] (2) Physical and chemical properties and button battery testing

[0062] The composite materials prepared in Examples 1-3 and Comparative Examples 1-5 were tested for tap density, specific surface area, and powder conductivity. These tests were conducted according to the national standard GBT-24533-2019, "Graphite-based Anode Materials for Lithium-ion Batteries." The test results are shown in Table 1.

[0063] Table 1

[0064]

[0065] (3) Button battery test

[0066] The composite materials from Examples 1-3 and Comparative Examples 1-5 were used as negative electrode materials for lithium-ion batteries and assembled into button cells. The negative electrode material preparation method involved adding a binder, a conductive agent, and a solvent to the composite material, stirring to form a slurry, coating the mixture on copper foil, and then drying and rolling the resulting material. The binder used was PVDF, the conductive agent was SP, and the solvent was NMP. A negative electrode sheet was prepared using a composite material composition of SP:PVDF:NMP = 95g:1g:4g:220mL. A metallic lithium sheet served as the counter electrode. The electrolyte used was LiPF6 / EC+DEC, with LiPF6 as the electrolyte and a 1:1 volume ratio of EC and DEC as the solvent. The electrolyte concentration was 1.3 mol / L. Polypropylene (PP) film was used as the separator. The button cells were assembled in an argon-filled glove box. The electrochemical performance was tested on a Wuhan Blue Power CT2001A battery tester with a charge and discharge voltage range of 0.005 V to 2.0 V and a charge and discharge rate of 0.1 C. The first discharge capacity and first efficiency of the button cell were tested. The test results are shown in Table 2.

[0067] Table 2

[0068]

[0069]

[0070] As can be seen from Tables 1 and 2, the specific capacity and initial efficiency of the composite materials prepared in the examples of the present invention are significantly better than those in the comparative examples. This may be because the silver-ammonia reaction deposits silver with high electronic conductivity on the surface of the nano-silicon, improving the material's conductivity and tap density. At the same time, the silver reacts less with the electrolyte, improving the initial efficiency. Furthermore, the addition of a catalyst in the example reaction has a pore-forming catalytic effect, increasing the material's specific surface area.

[0071] (3) Soft pack battery test:

[0072] The composite materials in Examples 1-3 and Comparative Examples 1-5 were respectively mixed with 90% artificial graphite as negative electrode materials to prepare negative electrode sheets, and NCM532 was used as the positive electrode material; LiPF6 was used as the electrolyte in the electrolyte, and a mixture of EC and DEC with a volume ratio of 1:1 was used as the solvent; Celgard 2400 membrane was used as the separator to prepare 5Ah soft-pack batteries.

[0073] a. Liquid absorption capacity test

[0074] Using a 1mL burette, draw up VmL of electrolyte and drip one drop onto the electrode surface. The time is measured until the electrolyte is completely absorbed. The time t is recorded and the electrode absorption rate (V / t) is calculated. The test results are shown in Table 3.

[0075] b. Liquid retention rate test

[0076] The theoretical liquid absorption of the electrode, m1, was calculated based on the electrode parameters. The electrode weight, m2, was then weighed. The electrode was then placed in the electrolyte and soaked for 24 hours. The electrode weight was then weighed, m3, and the electrode absorption was calculated as m3-m2. The liquid retention rate was then calculated using the following formula: Liquid retention rate = (m3-m2)*100% / m1. The test results are shown in Table 3.

[0077] Table 3

[0078]

[0079]

[0080] As can be seen in Table 3, the composite materials obtained in Examples 1-3 exhibit significantly higher liquid absorption and retention capacities than the comparative examples. These experimental results demonstrate that the composite materials of the present invention possess high liquid absorption and retention capacities. This may be due to the larger specific surface area of ​​the composite materials in the examples, which enhances their liquid absorption and retention capacities.

[0081] c. Electrode rebound rate test

[0082] First, the average thickness of the electrode was measured using a thickness gauge, which was D1. The electrode was then dried in a vacuum drying oven at 80 degrees for 48 hours, and the measured thickness was D2. After the soft-pack battery was fully charged, its thickness was dissected and measured, which was D3. The thickness was calculated using the following formula: Electrode rebound rate = (D2-D1)*100% / D1, and electrode full-charge rebound rate = (D3-D1)*100% / D1. The test results are shown in Table 4.

[0083] d. Electrode resistivity test

[0084] The resistivity of the electrode was tested using a resistivity tester, and the test results are shown in Table 4.

[0085] Table 4

[0086]

[0087]

[0088] The data in Table 4 show that the rebound rate of the negative electrode sheet produced using the composite material prepared using the embodiment of the present invention is significantly lower than that of the comparative example. This means that the negative electrode sheet produced using the composite material of the present invention has a lower rebound rate. This may be due to the fact that the silver deposited on the surface of the nano-silicon reduces the material's impedance and the resistivity of the electrode sheet, while the high electronic conductivity of the carbon nanotubes in this embodiment reduces its impedance and restrains the material's expansion.

[0089] e. Cyclic performance test

[0090] The battery's cycling performance was tested at a charge / discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, and a temperature of 25±3°C. The test results are shown in Table 5.

[0091] Table 5

[0092]

[0093] As can be seen from Table 5, the cycle performance of the battery made of the composite material prepared in the embodiment of the present invention is significantly better than that of the comparative example. The reason may be that the electrode made of the composite material of the present invention has a lower expansion rate, and the structure of the electrode is more stable during the charge and discharge process, thereby improving its cycle performance. In addition, the composite material contains a porous structure left by the conductive agent and the catalyst, which improves the liquid absorption and retention performance of the material and reduces the impedance, thereby improving the cycle performance.

[0094] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a low-expansion silver-doped silicon-carbon composite material, comprising the following steps: Silicon material pretreatment: contacting nano-silicon with hydrofluoric acid vapor at a temperature of 50°C-100°C, etching for 12-48 hours to obtain etched nano-silicon; Silver doping: Mix a titanium-based silane coupling agent with an organic solvent, add etched nano-silicon dispersion, mix with silver nitrate solution, adjust the pH to 8-10 with ammonia water, add formaldehyde solution dropwise to carry out silver-ammonia reaction, then filter and dry to obtain nano-silicon / silver primary particles; Secondary granulation: mixing the nano silicon / silver primary particles, the binder, the conductive liquid and the catalyst uniformly, ball milling and carbonizing to obtain the low expansion silver-doped silicon-carbon composite material; Wherein, the conductive liquid is a carbon nanotube conductive liquid and / or a graphene conductive liquid, and the catalyst is selected from at least one of nano-iron, nano-cobalt and nano-nickel.

2. The preparation method according to claim 1, characterized in that During the silver doping process, the mass ratio of the etched nano-silicon, the titanium-based silane coupling agent and the silver nitrate is 100:0.5-2:10-50.

3. The preparation method according to claim 1, characterized in that During the silver doping process, the molar ratio of formaldehyde to silver nitrate is 1-3:

1.

4. The preparation method according to claim 1, characterized in that During the silver doping process, the titanium-based silane coupling agent is selected from at least one of diisopropyl titanate, isopropyl tris(dioctyl phosphate) titanate, isopropyl trioleate titanate, isopropyl tris(dodecylbenzenesulfonyl) titanate, isopropyl tris(dioctyl pyrophosphate) titanate, bis(dioctyl pyrophosphate) ethylene titanate and tetra-n-butyl titanate.

5. The preparation method according to claim 1, characterized in that The temperature of the silver-ammonia reaction is 50-100° C., and the reaction time is 12-72 hours.

6. The preparation method according to claim 1, characterized in that During the secondary granulation process, the mass ratio of the nano-silicon / silver primary particles, the binder, the conductive liquid and the catalyst is 100:1-5:0.5-2:0.5-2.

7. The preparation method according to claim 1, characterized in that The solvent of the conductive liquid is N-methylpyrrolidone.

8. A low-expansion silver-doped silicon-carbon composite material prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the low-expansion silver-doped silicon-carbon composite material according to claim 8 as a negative electrode material for a battery.

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