Preparation method of silicon-carbon negative electrode material of high-capacity lithium ion battery

Abstract

The invention discloses a preparation method of a high-capacity lithium ion battery silicon-carbon negative electrode material, which comprises the following steps: uniformly mixing starch, a cross-linking agent and nano silicon, and carrying out cross-linking reaction to obtain a silicon-carbon precursor A; uniformly mixing the silicon-carbon precursor A with a pore-forming agent solution; fully infiltrating and absorbing, drying to obtain a silicon-carbon precursor B, and carbonizing under the protection of inert atmosphere; then crushing and screening to obtain a silicon-carbon material; and carrying out carbon coating on the silicon-carbon material by using a chemical vapor deposition method, cooling to room temperature, and taking out to obtain the silicon-carbon negative electrode material. The starch is adopted as a carbon material precursor, the unique structure of the starch is utilized, and the conductivity and pore structure of the obtained porous carbon are optimized with the assistance of cross-linking doping and pore-forming processes, so that an accommodating space is provided for nano silicon particles. The lithium ion battery silicon-carbon negative electrode material prepared by the method has the advantages that the initial charging specific capacity is 1656.5 mAh / g, the initial coulombic efficiency is 89.2%, the capacity retention ratio is 85.8% after 1C circulation for 20 circles, and the lithium ion battery silicon-carbon negative electrode material has better performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery preparation, and particularly relates to a preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries. BACKGROUND

[0002] With the wide application of lithium ion batteries in new energy vehicles, portable electronic devices, large-scale energy storage and other fields, the market has increasingly high requirements for the performance of batteries. The theoretical specific capacity of traditional graphite negative electrode material is only 372 mAh / g, which has reached the limit of its theoretical specific capacity, and it is difficult to meet the performance requirements of high energy density batteries for high specific capacity negative electrode materials. Silicon-based materials have a theoretical specific capacity of up to 4200 mAh / g, which is more than ten times that of graphite negative electrode, and are inexpensive, environmentally friendly and abundant in earth's reserves, becoming the optimal choice for the next generation of high-capacity negative electrode materials. However, silicon will undergo severe volume expansion during charging and discharging, which can reach more than 300%, leading to material pulverization, collapse of the conductive network, continuous decomposition of the electrolyte to form unstable SEI films, and ultimately causing the battery capacity to drop sharply and the cycle life to be shortened dramatically, which seriously restricts the large-scale application of silicon-based materials.

[0003] Researchers have designed some solutions to address the defects of silicon. Silicon is nanoized to prepare nano-silicon particles to protect the silicon particles from pulverization. Or silicon is compounded with carbon, for example, carbon is coated on the surface of nano-silicon particles, which can effectively improve the cycle performance of silicon-carbon composite materials and adapt to the stress of volume expansion / contraction. However, the silicon-carbon composite technology still cannot well solve the problems of volume expansion of electrode materials, poor conductivity and insufficient cycle stability. In the current reports, pitch is generally used to coat silicon-carbon composite materials, which can improve the conductivity of the materials and effectively alleviate the problem of silicon volume expansion. However, after high-temperature carbonization, the pitch becomes graphite soft carbon. In high-power or high-current use scenarios, with the insertion of solvated lithium ions, the graphite layers are prone to exfoliation, causing material structure damage, battery thermal runaway, lithium precipitation and other phenomena, thereby affecting the battery life and causing safety problems. SUMMARY

[0004] To solve the above technical problems, the application provides a preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries.

[0005] The application is implemented through the following technical solutions.

[0006] The application provides a preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries, which comprises the following steps: 1) uniformly mixing starch, a crosslinking agent and nano-silicon and performing a crosslinking reaction to obtain a silicon-carbon precursor A; 2) uniformly mixing the silicon-carbon precursor A obtained in step 1) with a pore-forming agent solution; fully soaking and absorbing, and drying to obtain a silicon-carbon precursor B; 3) carbonizing the silicon-carbon precursor B under the protection of inert atmosphere; then crushing and screening to obtain a silicon-carbon material with a particle size range of 5-15 µm; 4) carbon-coating the silicon-carbon material obtained in step 3) using a chemical vapor deposition method, placing the silicon-carbon material in a CVD furnace, introducing an organic gas under an inert atmosphere, heating to 500-800℃ and holding for 2-3h, and taking out after cooling to room temperature to obtain a silicon-carbon negative electrode material.

[0007] Preferably, the mixing mode of the starch, crosslinking agent and nano-silicon in step 1) is spray drying mixing at 140-200℃, and the crosslinking reaction is carried out at a temperature of 100-180℃.

[0008] Preferably, the crosslinking agent comprises one or more of citric acid, sodium pyrophosphate and ammonium dihydrogen phosphate.

[0009] Preferably, the mixing mass ratio of the hard carbon precursor and the crosslinking agent is 1-20:1; and the nano-silicon particle size D50 is <30-50 nm.

[0010] Preferably, in step 2), the silicon-carbon precursor A is mixed with an aqueous solution of the pore-forming agent, and the silicon-carbon precursor B is prepared by drying through thermal evaporation at 70-90℃ for 10-14h.

[0011] Preferably, the mixing mass ratio of the silicon-carbon precursor A and the pore-forming agent is 1:1-20.

[0012] Preferably, the pore-forming agent is one or more of potassium hydroxide, zinc chloride and phosphoric acid.

[0013] Preferably, in step 3), the carbonization temperature is 500-800℃, and the carbonization time is 0.5-10h.

[0014] Preferably, in step 4), the carbon-coating temperature is 600-800℃, the heating rate is 0.5-10℃ / min, and the holding time is 0.5-3h.

[0015] Preferably, in steps 3) and 4), the inert atmosphere is one or both of argon and nitrogen; and in step 4), the organic gas is acetylene gas.

[0016] The present application has the following beneficial effects: 1、The application adopts starch as a carbon material precursor, utilizes the unique structure of starch, and optimizes the conductivity and pore structure of the obtained porous carbon by cross-linking doping and pore forming process, so as to provide space for accommodating nano-silicon particles. In addition, the generated hard carbon has a larger interlayer spacing and specific surface area, which can accelerate the diffusion speed of lithium ions in amorphous carbon. In the composite material, the nano-silicon particles are embedded in the pore structure of the hard carbon skeleton, buffering the volume expansion of the silicon particles in the charging and discharging process. The conductivity of the hard carbon after doping of an alien element is enhanced, the overall conductivity of the silicon-carbon material is improved, and the rate performance of the negative electrode material is improved. Through CVD coating, a buffer layer is formed on the surface of the silicon-carbon composite negative electrode, reducing the battery polarization reaction and improving the stability of the electrode surface.

[0017] 2、The silicon-carbon negative electrode material prepared by the application has a first charge specific capacity of 1656.5 mAh / g, a first coulombic efficiency of 89.2%, and a capacity retention rate of 85.8% after 20 cycles of 1C, and has good performance.

[0018] 3、The porous biomass carbon material raw material and structure adopted by the application are controllable, low in cost, sustainable in regeneration, green and pollution-free, and easy to scale up. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is an SEM diagram of the silicon-carbon negative electrode material obtained by example 1 of the application; Figure 2 is an XRD diagram of the negative electrode material obtained by example 1 and comparative example 1 of the application; Figure 3 is an SEM diagram of the silicon-carbon negative electrode material obtained by comparative example 1 of the application; Figure 4 is an SEM diagram of the silicon-carbon negative electrode obtained by comparative example 5 of the application. DETAILED DESCRIPTION

[0020] The technical solutions of the application are further described below, but the scope of protection is not limited to the description.

[0021] Example 1: A preparation method of a high-capacity lithium ion battery silicon-carbon negative electrode material, comprising the following steps: 1) Mix starch and sodium dihydrogen phosphate (addition amount 5wt%) and nano-silicon (D50<30nm, 20wt%) in an aqueous solution, spray dry (160℃) to obtain a precursor A, and continue to dry in an oven at a temperature of 160℃ for 12h; 2) Mix the precursor A obtained in step 1) with 0.5mol / L zinc chloride solution (addition amount 5wt%) uniformly; and sufficiently immerse and absorb, and dry at 80℃ for 12h to obtain a silicon-carbon precursor B; 3): carbonization of the precursor B under the protection of inert atmosphere, at a heating rate of 5°C / min to 800°C, and holding for 2h; after cooling to room temperature, the silicon-carbon material with a particle size of 5-15µm is obtained by crushing and sieving; 4): carbon-coating of the silicon-carbon material obtained in step 3) by using chemical vapor deposition method, the sample is placed in a CVD furnace, acetylene gas is introduced under inert atmosphere, heated to 650°C and held for 2h, and then taken out after cooling to room temperature to obtain the silicon-carbon negative electrode material.

[0022] Example 2: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries, comprising the following steps: 1): mixing starch, 0.5mol / L citric acid solution (addition amount 10wt%), and nano-silicon (D50<30nm, 20wt%) in an aqueous solution, spray drying to obtain a precursor A, and then drying in an oven at a temperature of 120°C for 12h; 2): mixing the precursor A obtained in step 1) with 0.1mol / L potassium hydroxide solution (addition amount 10wt%) uniformly, and then fully soaking and absorbing, and drying at 80°C for 12h to obtain a silicon-carbon precursor B; 3): carbonization of the precursor B under the protection of inert atmosphere, at a heating rate of 5°C / min to 1000°C, and holding for 2h; after cooling to room temperature, the silicon-carbon material with a particle size of 5-15µm is obtained by crushing and sieving; 4): carbon-coating of the silicon-carbon material obtained in step 3) by using chemical vapor deposition method, the sample is placed in a CVD furnace, acetylene gas is introduced under inert atmosphere, heated to 700°C and held for 2h, and then taken out after cooling to room temperature to obtain the silicon-carbon negative electrode material.

[0023] Example 3: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries, comprising the following steps: 1): mixing starch, sodium trimetaphosphate (addition amount 5wt%), and nano-silicon (D50<30nm, 20wt%) by spray drying (160°C) to uniformly dry, and then drying at 160°C for 12h to obtain a precursor A; 2): mixing the precursor A obtained in step 1) with 0.2mol / L phosphoric acid (addition amount 10wt%) uniformly, and then fully soaking and absorbing, and drying at 80°C for 12h to obtain a silicon-carbon precursor B; 3): carbonization of the precursor B under the protection of inert atmosphere, at a heating rate of 5°C / min to 1000°C, and holding for 2h; after cooling to room temperature, the silicon-carbon material with a particle size of 5-15µm is obtained by crushing and sieving; 4): Carbon-coated silicon-carbon material obtained in step 3) is subjected to carbon coating using a chemical vapor deposition method, acetylene gas is introduced into a CVD furnace under an inert atmosphere, the temperature is raised to 700°C for 2h, and the silicon-carbon negative electrode material is obtained after cooling to room temperature.

[0024] Example 4: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries comprises the following steps: 1): Starch, sodium dihydrogen phosphate (added amount 5wt%), and nano-silicon (D50<200nm, 20wt%) are mixed in an aqueous solution, spray-dried to obtain a precursor A, and the precursor A is continuously dried in an oven at a temperature of 160°C for 12h; 2): The precursor A obtained in step 1) is mixed with a 0.5mol / L zinc chloride solution (added amount 5wt%) uniformly, and is fully soaked and absorbed, and is dried at 80°C for 12h to obtain a silicon-carbon precursor B; 3): The precursor B is carbonized under the protection of an inert atmosphere, the temperature is raised at a rate of 5°C / min to 800°C, and is kept for 2h; after being cooled to room temperature, the silicon-carbon material with a particle size in the range of 5-15µm is obtained by crushing and sieving; 4): The silicon-carbon material obtained in step 3) is subjected to carbon coating using a chemical vapor deposition method, acetylene gas is introduced into a CVD furnace under an inert atmosphere, the temperature is raised to 650°C for 2h, and the silicon-carbon negative electrode material is obtained after cooling to room temperature.

[0025] Comparative Example 1: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries is based on Example 1, wherein no crosslinking agent is added in step 1), and other conditions remain unchanged.

[0026] Comparative Example 2: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries is based on Example 1, wherein no pore-forming agent is added in step 2), and other conditions remain unchanged.

[0027] Comparative Example 3: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries is based on Example 1, wherein the silicon particles in step 1) have a D50<100nm, and other conditions remain unchanged.

[0028] Comparative Example 4: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries is based on Example 1, wherein the added amount of the silicon particles in step 1) is reduced to 10wt%, and other conditions remain unchanged.

[0029] Comparative Example 5: A preparation method of a high-capacity silicon-carbon negative electrode material for lithium ion batteries is based on Example 1, wherein the CVD coating in step 4) is cancelled, and other conditions remain unchanged.

[0030] Electrochemical performance test The silicon-carbon materials prepared in Examples 1-4 and Comparative Examples 1-5 above were assembled into lithium ion batteries and subjected to electrochemical performance tests. The silicon-carbon materials, a conductive agent (Super P), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 8:1:1, ground, coated on a copper foil current collector, and dried to obtain battery electrode sheets. A lithium metal sheet was used as a counter electrode to assemble a coin battery, and 1M LiPF6 (EC:DMC:EMC = 1:1:1 by volume) was used as an electrolyte.

[0031] The coin battery was assembled, and after standing for 12 hours, was tested at a voltage range of 0.01-3V using 20mA / g. The electrochemical performances of each example and comparative example are shown in the following table.

[0032] As can be seen from the above table, the silicon-containing biomass hard carbon negative electrode material prepared by the present application has a high reversible capacity. The silicon-carbon material obtained in Example 1 has a smooth spherical particle morphology ( Figure 1 ). In Comparative Example 1, the precursor was not subjected to a crosslinking reaction, and the XRD structure of the material did not change significantly ( Figure 2 ). As can be seen from the SEM results, the structure of the obtained sample is relatively loose ( Figure 3 ), and the capacity and initial efficiency of the test decrease. In Comparative Example 2, the pore-forming process was cancelled, and the reversible capacity and cycle stability of the prepared silicon-carbon negative electrode material decreased. This is because the activation and pore-forming of the silicon-containing biomass can improve the infiltration of the electrolyte into the electrode, and effectively alleviate the volume expansion of the electrode during the charging and discharging process. In Comparative Example 3, the particle size of the silicon particles increased to 100nm, and both the capacity and cycle stability decreased. This indicates that the pore structure is beneficial to the uniform distribution of smaller silicon nanoparticles in the carbon skeleton, and is beneficial to improving the capacity and stability of the electrode. In Comparative Example 4, different silicon addition amounts were compared. When the silicon content decreased, the capacity of the silicon-carbon negative electrode decreased, but the initial efficiency and cycle performance improved. This is because the volume expansion is alleviated when the silicon content decreases, and the conductivity of the electrode material is improved, resulting in improved stability. In Comparative Example 5, it can be seen that the silicon-carbon material without carbon coating has a rough surface ( Figure 4 ), with numerous obvious particles, and the performance test has a significantly reduced initial efficiency. This is because the hard carbon negative electrode material has many defects, and some lithium is lost due to side reactions during the first charging and discharging process. In addition, the silicon particles exposed to the outside react with the electrolyte, and the initial efficiency is improved after surface CVD coating.

[0033] The application adopts starch as a carbon material precursor, utilizes the unique structure of starch, and optimizes the pore structure of the porous carbon by means of a pore forming process to provide accommodation space for nano-silicon particles. In addition, the generated hard carbon has a larger interlayer spacing and specific surface area, which can accelerate the diffusion speed of lithium ions in amorphous carbon. In the composite material, the nano-silicon particles are embedded in the pore structure of the hard carbon skeleton, buffering the volume expansion of the silicon particles in the charging and discharging process. The conductivity of the hard carbon after hetero-element doping is enhanced, the overall conductivity of the silicon-carbon material is improved, and the rate performance of the negative electrode material is improved. Through CVD coating, a buffer layer is formed on the surface of the silicon-carbon composite negative electrode, reducing the battery polarization reaction and improving the stability of the electrode surface.

Claims

1. A method for preparing a high-capacity lithium-ion battery silicon-carbon anode material, characterized in that, Includes the following steps: 1): Starch, crosslinking agent and nano-silicon are mixed evenly and crosslinked to obtain silicon-carbon precursor A; 2): Mix the silicon-carbon precursor A obtained in step 1) with the pore-forming agent solution until homogeneous; allow it to fully absorb and dry to obtain silicon-carbon precursor B; 3): The silicon-carbon precursor B is carbonized under an inert atmosphere; then it is crushed and sieved to obtain silicon-carbon materials with a particle size range of 5-15µm. 4): Carbon coating is performed on the silicon-carbon material obtained in step 3) using chemical vapor deposition. The silicon-carbon material is passed through an organic gas in an inert atmosphere, heated to 500-800℃ and held for 2-3 hours, and then cooled to room temperature to obtain the silicon-carbon anode material.

2. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: In step 1), the starch, crosslinking agent and nano-silicon are mixed by spray drying at 140-200℃, and then crosslinking reaction is carried out at 100-180℃.

3. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: The crosslinking agent includes one or more of citric acid, sodium pyrophosphate, and ammonium dihydrogen phosphate.

4. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: The mass ratio of starch to crosslinking agent is 1 to 20:1; the size of the nano-silicon particles is D50 < 50 nm.

5. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: In step 2), silicon-carbon precursor A is mixed with an aqueous solution of pore-forming agent, and silicon-carbon precursor B is obtained by thermal evaporation at 70-90℃ for 10-14 hours and then dried.

6. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: The mass ratio of silicon-carbon precursor A to pore-forming agent is 1:1 to 20.

7. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: The pore-forming agent is one or more of potassium hydroxide, zinc chloride, and phosphoric acid.

8. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: In step 3), the carbonization temperature is 500–800℃ and the carbonization time is 0.5–10h.

9. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: In step 4), the carbon coating temperature is 600–800℃, the heating rate is 0.5–10℃ / min, and the holding time is 0.5–3h.

10. The method for preparing a high-capacity lithium-ion battery silicon-carbon anode material as described in claim 1, characterized in that: In steps 3) and 4), the inert atmosphere is one or both of argon and nitrogen, and in step 4), the organic gas is acetylene.

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