Amorphous carbon coated silicon composite material and preparation method thereof

Abstract

The invention discloses an amorphous carbon coated silicon composite material and a preparation method thereof. The preparation method comprises the following steps: S1, lithium ion battery recovered carbon is placed in an acid solution for reaction and ball milling, and after filtration and drying, high-temperature activation is performed to obtain a solid A; s2, mixing the solid A in the S1 with a silicon-based core, transition metal chloride, an amorphous carbon source and deionized water to prepare mixed slurry, and carrying out spray drying granulation to obtain a precursor; s3, carrying out gradient carbonization on the precursor obtained in S2 under different atmosphere conditions; S4, putting the solid B obtained in S3 into an acid solution to react, washing with deionized water after the reaction is finished until the pH value of eluate is 7, and drying to obtain a final product. The lithium ion battery negative electrode material prepared from the amorphous carbon coated silicon composite material has the advantages of high first-circle coulombic efficiency, low expansion and long cycle.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion battery negative electrode materials, and particularly relates to an amorphous carbon-coated silicon composite material and a preparation method thereof. BACKGROUND

[0002] With the popularity of new energy vehicles and 3C digital products worldwide, a large number of lithium ion batteries that are scrapped and cannot be reused will be generated every year. The negative carbon material in the battery becomes unstable due to the repeated intercalation and deintercalation of lithium ions and the peeling effect of large solvent molecules, resulting in an increase in the interlayer spacing of graphite and an increase in the gap. After recovery, it is difficult to meet the performance requirements of negative electrode materials, and the recovery process is complex. It has not been paid attention to by researchers, and is often treated by burning, causing waste of resources and easy environmental pollution.

[0003] The theoretical specific capacity of the traditional graphite negative electrode of lithium ion batteries is only 372 mAh / g, which cannot meet the market demand. In recent years, silicon-based materials (theoretical specific capacity 4200 mAh / g) have become a research hotspot due to their high specific capacity. However, silicon undergoes a huge volume change during lithium extraction and insertion, which causes the active material to powder and fall off from the current collector, exposing new boundaries. Moreover, since silicon is a typical semiconductor material, its electrical conductivity is low, which makes its high-current density charge and discharge performance poor and cannot meet people's higher requirements for fast charging and discharging of batteries. Therefore, how to reduce the volume expansion effect of silicon-based materials and improve their electrical conductivity is of great significance for the application of silicon materials in lithium ion battery negative electrodes.

[0004] Graphene material has great application prospects in electrode materials such as lithium ion batteries and double-layer capacitors due to its large specific surface area, excellent electrical conductivity and good thermal conductivity. Currently, the preparation of graphene requires the use of potassium permanganate, concentrated sulfuric acid and other strong oxidizing agents in the oxidation-reduction process represented by the Hummers method to artificially expand the interlayer spacing of graphite and achieve graphite layer peeling. However, this method has the disadvantages of high operation energy consumption, waste acid pollution and difficult product quality control. Therefore, if the properties of recycled carbon from waste lithium ion batteries can be used to prepare graphene and applied to silicon-based materials, it will bring considerable economic benefits and realize the sustainable development of the power battery industry.

[0005] A graphene@egg yolk-eggshell silicon-carbon composite material is prepared by the following steps: step (1): obtaining a mixed colloid solution by dispersing silicon-based materials, oxidized graphite and acid; the silicon-based material is at least one of amorphous nano-silicon and amorphous silicon oxide SiO x x is 0.8-1.5; wherein the particle size of the amorphous nano-silicon is ~D50 10-400 nm; the particle size of the amorphous silicon oxide SiOx The particle size D50 of the particles is 100 nm to 1 um; the mass ratio of the silicon-based material to the graphite oxide is 5 to 10:1; step (2): adding a water-soluble salt of a transition metal and an alkali to the mixed colloidal solution, and performing a coprecipitation reaction, followed by solid-liquid separation, to obtain a solid A; the mass ratio of the silicon-based material to the water-soluble salt of the transition metal is 10 to 1:1; step (3): dispersing the solid A and an amorphous carbon source into a solvent, and performing a solvothermal reaction, and after the reaction, performing solid-liquid separation to obtain a solid B; the mass ratio of the solid A to the amorphous carbon source is 1:1 to 4; the temperature of the solvothermal reaction is 150 to 300 DEG C; step (4): after the solid B is treated with an acid solution and washed with water until the pH of the washing liquid is neutral, a precursor is obtained; step (5): the precursor is carbonized to obtain the graphene@yolk-egg shell silicon-carbon composite material. The scheme is only suitable for preparing the silicon-carbon composite material by using the graphite oxide, and cannot be applied to recycling the carbon from the waste lithium ion battery. SUMMARY

[0006] The purpose of the present application is to provide an amorphous carbon-coated silicon composite material and a preparation method thereof, which uses recycled carbon from waste lithium ion batteries as a graphene carbon source, realizes high-value utilization of graphite materials in recycled carbon, and improves the graphene content, reduces the silicon oxidation rate, and reduces the material interface impedance.

[0007] In order to achieve the above technical purpose, the present application adopts the following technical scheme:

[0008] A preparation method of an amorphous carbon-coated silicon composite material, comprising the following steps:

[0009] S1, reacting the recycled carbon from lithium ion batteries in an acid solution, ball milling, filtering, drying, and then high-temperature activation to obtain a solid A;

[0010] S2, mixing the solid A in S1 with a silicon-based core, a transition metal chloride, an amorphous carbon source, and deionized water to prepare a mixed slurry, and then sending the mixed slurry to a spray drying granulator to obtain a precursor;

[0011] S3, gradient carbonizing the precursor obtained in S2 under different atmospheres: in the first stage, keeping at 250 to 350 DEG C in an air atmosphere for 2 to 4 h; in the second stage, keeping at 600 to 700 DEG C in a nitrogen atmosphere for 2 to 4 h; in the third stage, keeping at 850 to 1050 DEG C in an argon atmosphere for 2 to 6 h, to finally obtain a solid B;

[0012] S4, reacting the solid B obtained in S3 in an acid solution, washing with deionized water until the pH of the washing liquid is 7, and then drying to obtain a final product.

[0013] The recovered carbon discussed in the present application refers to the valuable metal elements in the active material recovered from the solution by adopting the hydrometallurgy method after the positive and negative active materials and the current collector are separated from the waste lithium ion battery by disassembling, crushing and high-temperature heat treatment, and finally the carbon recovered from the solution is filtered.

[0014] The recovered carbon is subjected to impurity removal by acid immersion, ball milling and high-temperature activation to obtain a graphene precursor. Then, a silicon-based core coated with graphene and an organic compound is obtained by liquid phase in-situ coating and spray granulation to form a carbon-silicon composite precursor. After high-temperature carbonization, a silicon-carbon composite material with a silicon-based material as the core and good electrical conductivity is obtained. As a negative electrode material of a lithium ion battery, it has the advantages of high first-cycle coulomb efficiency, low swelling and long cycle.

[0015] In the low-temperature section (250-350℃), the amorphous carbon is oxidized and polymerized in an air atmosphere to form a porous carbon skeleton coated with a silicon core, avoiding direct contact at high temperature leading to oxidation; in the medium-temperature section (600-700℃), the recovered carbon graphite microcrystals are reorganized into few-layer graphene (3-8 layers) under transition metal catalysis in a nitrogen atmosphere, and the SiO2 on the surface of silicon is etched at the same time; in the high-temperature section (850-1050℃), the Si-O-C covalent bond is strengthened in an argon atmosphere, and the crystallinity of the carbon layer is improved.

[0016] In the second stage of gradient carbonization in S3, the amorphous carbon in the recovered carbon forms 3-8 layers of graphene under transition metal catalysis, the content of graphene accounts for 10-30% of the total weight of the amorphous carbon layer, and the coating thickness of the amorphous carbon is 5-20 nm.

[0017] In one preferred embodiment, the liquid-solid volume ratio of the lithium ion battery recovered carbon and the acid solution in S1 is 5-10:1, the reaction temperature is 30-100℃, and the stirring time is 6-12h; preferably, the liquid-solid volume ratio of the lithium ion battery recovered carbon and the acid solution in S1 is 8-10:1, the reaction temperature is 60-100℃, and the stirring time is 8-12h.

[0018] In one preferred embodiment, the ball-to-material ratio of ball milling in S1 is 8-12:1, the rotation speed is 200-500rpm, and the ball milling time is 1-4 hours.

[0019] In one preferred embodiment, the high-temperature activation in S1 is placed in an inert atmosphere at 500-700℃ for 0.5-2 hours, preferably in N2 atmosphere at 600-700℃ for 1-2 hours.

[0020] In one preferred embodiment, the acid solution in S1 is at least one of HCl, H2SO4, HNO3, H3PO4, HPO3, HClO3, H2FeO4, HCOOH and CH3COOH, and the concentration of the acid solution is 3-10mol / L, preferably 4-6mol / L.

[0021] The above process parameters in S1 interact to consume residual Li and improve activation efficiency. Too large or too small will result in Li residue, which will passivate the transition metal in S2, thereby reducing the proportion of graphene in S2.

[0022] In one preferred embodiment, in the gradient carbonization process in S3, the air flow is 20-50 mL / min, the nitrogen flow is 30-100 mL / min, and the argon flow is 30-100 mL / min; preferably, the air flow is 25-40 mL / min, the nitrogen flow is 50-80 mL / min, and the argon flow is 60-100 mL / min.

[0023] The process parameter interval range can ensure that the prepared material has a suitable silicon surface oxide layer thickness, complete glucose carbonization, and a complete coating layer.

[0024] In one preferred embodiment, the silicon-based core in S2 is at least one of amorphous nanosilicon and amorphous silicon oxide SiOx (0.8≤x≤1.5); preferably, the particle size D50 of the amorphous nanosilicon is 10-350 nm, and the particle size D50 of the amorphous silicon oxide SiOx is 90-400 nm.

[0025] In one preferred embodiment, the granulation inlet temperature in S2 is 170-200°C, and the outlet temperature is 80-100°C, to obtain a precursor with a particle size D50 of 20-450 nm; preferably, the granulation inlet temperature is 190-200°C, and the outlet temperature is 80-90°C, to obtain a precursor with a particle size D50 of 20-200 nm.

[0026] In one preferred embodiment, the mass fraction of each substance in the mixed slurry in S2 is as follows: solid A accounts for 20-30%, silicon-based core accounts for 10-25%, transition metal chloride accounts for 3-10%, amorphous carbon source accounts for 20-30%, and deionized water accounts for 30-40%.

[0027] Preferably, the transition metal chloride in S2 is at least one of AlCl3, FeCl3, CuCl2, and CoCl2.

[0028] Preferably, the amorphous carbon source in S2 is at least one of glucose (C6H 12 O6), sucrose (C 12 H 22 O 11 ), cellulose (C6H 10 O5) n , and tannic acid (C 76 H 52 O 46vitamin C (C6H8O6), phenol-formaldehyde resin (PF), polyvinyl alcohol (PVA), tannic acid (PVA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), pitch (C n H 2n+2 ) at least one of vitamin C (C6H8O6), phenol-formaldehyde resin (PF), polyvinyl alcohol (PVA), tannic acid (PVA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), pitch (C

[0029] Preferably, the acid liquid in S4 is a 0.5-2 mol / L H2SO4 solution, the stirring reaction is 1-3 h, and the reaction temperature is 60-95℃.

[0030] The application further discloses an amorphous carbon-coated silicon composite material, which comprises an inner high-temperature activated recycled carbon layer and an outer amorphous carbon / silicon-based material layer, the inner high-temperature activated recycled carbon layer comprises 3-6 layers of graphene, and the ratio of the graphene to the total mass of the recycled carbon layer is greater than 18%, and the thickness of the outer amorphous carbon / silicon-based material layer is greater than or equal to 12 nm.

[0031] Or the amorphous carbon-coated silicon composite material prepared according to the preparation method.

[0032] Compared with the prior art, the application has the following beneficial effects:

[0033] 1) The traditional method of recycling lithium ion batteries piles up the negative carbon material as waste slag, and the method of the application innovatively applies catalytic recombination of lithium battery recycled carbon negative electrodes, converts residual graphite crystallites into few-layer graphene (3-8 layers, 10-30% of the proportion) under the action of transition metal chloride in the medium temperature section (600-700℃), realizes in-situ preparation of graphene at low cost, and forms a dense amorphous carbon layer by using glucose low-temperature carbonization, and constructs a double-functional coating structure of "graphene conductive network + amorphous carbon buffer layer".

[0034] 2) The application precisely controls the reaction path through three-stage gradient carbonization, thereby improving the content of graphene, reducing the oxidation rate of silicon, and reducing the interface impedance of the material.

[0035] 3) The Cl free radicals generated by the decomposition of transition metal chloride etch the silicon surface oxide layer, promote the formation of Si-O-C covalent bonds, and reduce the interface impedance. The embedded graphene network restrains the expansion of silicon particles through the crack blocking mechanism, and cooperates with the mechanical buffering effect of amorphous carbon to reduce the volume expansion of the silicon negative electrode during charging and discharging. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The transmission electron microscope photo of the material prepared in Example 1 shows that 3-5 layers of graphene are embedded in the amorphous carbon layer.

[0037] Figure 2 The transmission electron microscope photo of the material prepared in Example 2 shows that 4-6 layers of graphene are embedded in the amorphous carbon layer.

[0038] Figure 3 The transmission electron microscope photograph of the material prepared for Comparative Example 1 only has amorphous carbon generated, without a core-shell structure.

[0039] Figure 4 The transmission electron microscope photograph of the material prepared for Comparative Example 2 has no graphene generated in the amorphous carbon layer. DETAILED DESCRIPTION

[0040] The application will be further described below in conjunction with specific examples. It should be noted that these examples are only used to illustrate the application, and are not used to limit the protection scope of the application. Improvements and adjustments made by the skilled person according to the application in practical applications still belong to the protection scope of the application.

[0041] Example 1

[0042] (1) 100 g of recycled carbon negative electrode was weighed and placed in 800 mL of 5 mol / L HCl solution (liquid to solid volume ratio 8:1), and stirred at 70°C for 10 h. Then the solution was transferred to a ball mill, the ball to material ratio was controlled to be 10:1, the rotation speed was 200 rpm, and the ball milling was performed for 4 hours. After filtration, the filter residue was dried, and then heated at 600°C for 1 h in a N2 atmosphere to obtain solid A.

[0043] (2) 20 g of D50=50 nm amorphous nano-silicon was weighed and mixed with 25 g of solid A, 6 g of FeCl3, 30 g of glucose, and 40 g of deionized water, and then ball-milled for 2 h to prepare a slurry (solid content 42%).

[0044] (3) The slurry was spray dried (inlet temperature 190°C, outlet temperature 90°C) to obtain a precursor with D50=150 nm.

[0045] (4) Precursor gradient carbonization:

[0046] First stage: 300°C air (flow rate 30 mL / min) for 3 h.

[0047] Second stage: 650°C N2 (flow rate 50 mL / min) for 3 h.

[0048] Third stage: 950°C Ar (flow rate 60 mL / min) for 4 h→solid B.

[0049] (5) Solid B was stirred with 1M H2SO4 at 80°C for 2 h, washed with water to pH=7, and dried to obtain the final product.

[0050] The amorphous carbon-coated silicon composite material prepared in this embodiment has a core-shell structure, the silicon core is coated with amorphous carbon (thickness 12 nm), and 3-5 layers of graphene (accounting for 22.5%) are embedded in the carbon layer. As a negative electrode material for lithium ion batteries, the first cycle coulomb efficiency is 89.7%, and the interface impedance is 42 Ω·cm 2 , the SiO2 content is 4wt%, the capacity retention rate after 100 cycles at 1C is 93.1%, and the electrode expansion rate is 18.2%.

[0051] Example 2

[0052] (1) Take 100g of recycled carbon negative electrode and put it in 800mL of 6mol / L H2SO4 (liquid-solid volume ratio 8:1), stir at 65℃ for 8h. The subsequent treatment is the same as in Example 1 to obtain solid A.

[0053] (2) Take 20g SiOx (x=1.2, D50=200nm) and mix with 25g of solid A, add 8g of CoCl2, 25g of phenolic resin, 45g of water, and ball mill for 2h to prepare a slurry.

[0054] (3) Spray drying of the slurry (inlet 190℃, outlet 90℃), obtain D50=180nm precursor.

[0055] (4) Gradient carbonization:

[0056] 300℃ air (flow rate 40mL / min) for 2.5h.

[0057] 680℃ N2 (flow rate 60mL / min) for 3.5h.

[0058] 1000℃ Ar (flow rate 70mL / min) for 5h→solid B.

[0059] (5) The same as Example 1 acid washing and drying.

[0060] The amorphous carbon-coated silicon composite material prepared in this embodiment has a core-shell structure, the silicon core is coated with amorphous carbon (thickness 12 nm), and 3-5 layers of graphene (accounting for 22.5%) are embedded in the carbon layer. As a negative electrode material for lithium ion batteries, the first cycle coulomb efficiency is 89.7%, and the interface impedance is 42 Ω·cm 2 , 3C rate capacity 1560mAh / g, electrode thickness expansion 16.8% after 100 cycles.

[0061] Example 3

[0062] (1) Take 100g of recycled carbon negative electrode and put it in 600mL of 4mol / L HCl+200mL of 2mol / L H3PO4 mixed acid (liquid-solid volume ratio 8:1), stir at 75℃ for 9h. The subsequent treatment is the same as in Example 1 to obtain solid A.

[0063] (2) Take 25 g SiOx(x = 0.9, D50 = 150 nm) and mix with 30 g solid A, add 3 g AlCl3+ 4 g FeCl3, 28 g pitch, 35 g water, pulp and spray to get the precursor (D50 = 220 nm).

[0064] (3) Gradient carbonization:

[0065] 350°C air (flow rate 25 mL / min) for 4 h.

[0066] 700°C N2(flow rate 80 mL / min) for 2 h.

[0067] 850°C Ar (flow rate 100 mL / min) for 6 h → solid B.

[0068] (4) The same as Example 1 acid washing and drying.

[0069] The amorphous carbon-coated silicon composite material prepared in this example has a core-shell structure, the carbon coating layer is 18 nm thick, and the graphene is distributed in a network. As a lithium ion battery negative electrode material, the first cycle coulombic efficiency is 87.6%, and the interface impedance is 44 Ω·cm 2 , the capacity retention rate at -20°C / 0.2C is 81%.

[0070] Comparative Example 1

[0071] (1) Recovered carbon directly ball milled and dried without acid leaching and activation → solid A.

[0072] (2) The same as steps (2)-(5) in Example 1.

[0073] The amorphous carbon-coated silicon composite material prepared in this example has no core-shell structure, residual Li consumes active lithium, the first cycle coulombic efficiency drops to 72.3%; transition metals are passivated by Li, and the proportion of graphene is only 3.2%; as a lithium ion battery negative electrode material, the capacity retention rate after 100 cycles is 61.0%, and the expansion rate is 35.8%.

[0074] Comparative Example 2

[0075] (1) The same as step (1) in Example 1 to obtain solid A.

[0076] (2) Remove transition metal chlorides from the formula in step (2), and the other steps are the same as Example 1.

[0077] The material prepared in this example has no graphene generated; the interface impedance is 98 Ω·cm 2 (42 Ω·cm 2 in Example 1); as a lithium ion battery negative electrode material, the silicon particles are broken after 100 cycles, and the expansion rate is 261%.

[0078] Comparative Example 3

[0079] Step (3) is directly 950°C Ar for 4h (cancel the gradient procedure), and other steps are the same as Example 1.

[0080] The material prepared in this example has thickened silicon surface oxide layer (SiO2 content 18wt%); glucose carbonization is incomplete, and the coating layer is cracked; as a negative material for lithium ion battery, the first cycle coulombic efficiency is 81.4%, and the capacity retention rate is 69.3% after 100 cycles.

[0081] Comparative Example 4

[0082] (1)-(3) are the same as Example 1.

[0083] (4) is directly used after carbonization without pickling.

[0084] The material prepared in this example has residual Fe particles catalyzing electrolyte decomposition (SEI film thickness > 80nm) when used as a negative material for lithium ion battery; the self-discharge rate is 8.3% / day (1.5% / day for Example 1); and the battery is short-circuited after 50 cycles.

Claims

1. A method for producing an amorphous carbon-coated silicon composite material, characterized by, Includes the following steps: S1. The carbon recovered from lithium-ion batteries is reacted in acid, ball-milled, filtered, dried, and then activated at high temperature to obtain solid A. S2. The solid A in S1 is mixed with silicon-based core, transition metal chloride, amorphous carbon source and deionized water to form a mixed slurry, which is then spray-dried and granulated to obtain the precursor. S3. The precursor obtained in S2 is subjected to gradient carbonization under different atmospheres: in the first stage, it is kept at 250-350℃ in an air atmosphere for 2-4 hours; in the second stage, it is kept at 600-700℃ in a nitrogen atmosphere for 2-4 hours; in the third stage, it is kept at 850-1050℃ in an argon atmosphere for 2-6 hours, finally obtaining solid B. S4. The solid B obtained in S3 is placed in an acid solution for reaction. After the reaction is completed, it is washed with deionized water until the pH of the washing solution is 7. After drying, the final product is obtained.

2. The method for producing an amorphous carbon-coated silicon composite material according to claim 1, characterized by: In S1, the liquid-to-solid volume ratio of the recovered carbon and acid in the lithium-ion battery is 5–10:1, the reaction temperature is 30–100°C, and the stirring time is 6–12 h; preferably, the liquid-to-solid volume ratio of the recovered carbon and acid in S1 is 8–10:1, the reaction temperature is 60–100°C, and the stirring time is 8–12 h.

3. The method of claim 1, wherein: In S1, the ball-to-material ratio of the ball mill is 8-12:1, the rotation speed is 200-500 rpm, and the milling time is 1-4 hours.

4. The method of claim 1, wherein: S1 is activated at high temperature by placing it in an inert atmosphere at 500-700℃ for 0.5-2 hours, preferably in an N□ atmosphere at 600-700℃ for 1-2 hours.

5. The method of claim 1, wherein: The acid in S1 is at least one of HCl, H2SO4, HNO3, H3PO4, HPO3, HClO3, H2FeO4, HCOOH, and CH3COOH, and the concentration of the acid is 3 to 10 mol / L, preferably 4 to 6 mol / L.

6. The method of claim 1, wherein: During the gradient carbonization process in S3, the air flow rate is 20–50 mL / min, the nitrogen flow rate is 30–100 mL / min, and the argon flow rate is 30–100 mL / min; preferably, the air flow rate is 25–40 mL / min, the nitrogen flow rate is 50–80 mL / min, and the argon flow rate is 60–100 mL / min.

7. The method of claim 1-6, wherein: The silicon-based core mentioned in S2 is at least one of amorphous nano-silicon and amorphous silicon oxide SiOx (0.8≤x≤1.5); preferably, the particle size D50 of the amorphous nano-silicon particles is 10~350nm, and the particle size D50 of the amorphous silicon oxide SiOx particles is 90nm~400nm.

8. The method of claim 1-6, wherein: In S2, the granulation inlet temperature is 170-200℃ and the outlet temperature is 80-100℃, resulting in a precursor particle size D50 of 20-450nm. Preferably, the granulation inlet temperature is 190-200℃ and the outlet temperature is 80-90℃, resulting in a precursor particle size D50 of 20-200nm.

9. The method of claim 1-6, wherein: The mass fractions of each substance in the S2 mixture slurry are as follows: solid A accounts for 20-30%, silicon-based core accounts for 10-25%, transition metal chloride accounts for 3-10%, amorphous carbon source accounts for 20-30%, and deionized water accounts for 30-40%.

10. An amorphous carbon-coated silicon composite material, characterized by: A high temperature activated recycled carbon layer comprising 3-6 layers of graphene, the graphene being present in a ratio greater than 18% of the total mass of the recycled carbon layer, an amorphous carbon / silicon-based material layer, the amorphous carbon / silicon-based material layer having a thickness greater than or equal to 12 nm; Or an amorphous carbon-coated silicon composite material produced according to the production process of any one of claims 1-9.

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