Silicon-based negative electrode material and preparation method and application thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material and a preparation method and application thereof. The silicon-based negative electrode material comprises slurry and copper sheets, and the mass ratio of the slurry to the copper sheets is 0.5-1:8.4; the slurry comprises silicon powder, sodium alginate, a conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent; and the initiator is a polar solvent. The application realizes the structural stability of the silicon-based negative electrode material in the lithiumation / delithiation process by constructing a three-dimensional (3D) crosslinked network structure on the surface of silicon particles and optimizing the self-repairing SEI layer interface. The network structure can also effectively inhibit the volume expansion of the silicon negative electrode material, maintain the integrity of the silicon negative electrode morphology, and thus significantly improve the specific capacity and cycle performance of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] When used as a negative electrode of a lithium ion battery, although silicon material has the characteristics of high specific capacity, volume expansion occurs during battery cycling, which hinders its further application in lithium ion batteries. On the one hand, the huge volume change of silicon material during cycling can lead to serious particle pulverization and poor electrode contact. The volume change leads to unstable solid electrolyte interface (SEI), and the solid electrolyte interface film (SEI) on the electrode surface repeatedly breaks and regenerates, continuously consuming electrolyte and active lithium, which greatly reduces the cycle performance of the lithium ion battery. On the other hand, the low electrical conductivity of silicon and the thin oxide layer formed on the silicon particles can lead to poor electrochemical kinetics during alloying / dealloying, slow charge transfer, severe polarization, and limited rate performance. At the same time, the low kinetics can cause part of the lithium to not be completely removed during the first charge, resulting in low initial coulombic efficiency (ICE) and irreversible capacity loss. Therefore, in order to further improve the application of silicon material in lithium ion batteries, a silicon negative electrode material with low volume change rate during lithium ion battery cycling is urgently needed. SUMMARY

[0003] The purpose of the present application is to provide a silicon-based negative electrode material, which comprises a slurry and a copper sheet, and the mass ratio of the slurry to the copper sheet is 0.5-1:8.4.

[0004] The slurry comprises silicon powder, sodium alginate, a conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator, and a solvent.

[0005] The initiator is a polar solvent.

[0006] As a preferred, the mass volume ratio of the silicon powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator, and solvent is 7-8g:1-2g:1g:920-960μL:230-240μL:70-115mL.

[0007] As a preferred, the thickness of the copper sheet is 18-22mm, and the particle size of the silicon powder is 25-35nm.

[0008] As a preferred, the conductive agent is a carbon black conductive agent.

[0009] As a preferred, the polar solvent comprises one or more of ethanol, ethylene glycol, and isopropyl alcohol.

[0010] As a preferred, the solvent comprises water and / or ethanol.

[0011] The present invention also provides a method for preparing the silicon-based anode material, comprising the following steps:

[0012] (1) Mix silica powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent to obtain slurry;

[0013] (2) The slurry is coated on copper foil and dried to obtain the silicon-based anode material.

[0014] Preferably, the mixing temperature in step (1) is 24-26°C and the mixing time is 2-5 min.

[0015] Preferably, the drying temperature is 140-160℃ and the drying time is 2.5-3.5h.

[0016] The present invention also provides the application of the above-mentioned silicon-based anode material or the silicon-based anode material prepared by the above-mentioned method in lithium-ion batteries.

[0017] The present invention has the following beneficial effects:

[0018] This invention provides a silicon-based anode material, comprising a slurry and copper sheets, wherein the mass ratio of the slurry to the copper sheets is 0.5-1:8.4. The slurry comprises: silicon powder, sodium alginate, a conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator, and a solvent; the initiator is a polar solvent. This invention uses poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid (PEDOT:PSS) as a water-soluble conductive polymer, which is added to the slurry system. The sulfonic acid groups (-SO3H) in its molecular structure can be protonated to hydroxyl groups (-OH) in an acidic medium, and then interact with the silanol groups (Si-OH) on the surface of the silicon powder through hydrogen bonding to form a stable interfacial connection. This effectively buffers the volume deformation of the silicon anode material during the charging and discharging process of the lithium-ion battery, maintaining the integrity of the silicon-based anode structure.

[0019] Using a polar solvent as an initiator, under thermal initiation conditions, the PEDOT segment in poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid can undergo intramolecular conformational recombination, changing from a benzene structure to a quinone structure, significantly improving its π-π conjugation degree, thereby enhancing the conductivity of the system.

[0020] Sodium alginate (SA) has a molecular structure rich in a high density of uniformly distributed carboxyl (-COOH) functional groups. Compared to carboxymethyl cellulose (CMC), it not only exhibits higher viscoelasticity and mechanical strength but also forms stronger chemical bonds with the silicon powder surface. The carboxyl groups in sodium alginate can undergo esterification with the hydroxyl groups (Si-OH) on the silicon powder surface to form stable ester bonds (-COO-Si-), thereby effectively suppressing the volume expansion effect of silicon anode materials during the charging and discharging process of lithium-ion batteries.

[0021] Sodium alginate, silicon powder, and poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid can interact through ester or hydrogen bonds to synergistically construct a three-dimensional (3D) cross-linked network structure. This network structure not only endows the silicon anode material with excellent mechanical stability but also increases the effective contact area between the active material, conductive agent, and current collector. During lithium-ion battery cycling, the integrity of the silicon anode material structure is maintained through a dynamic self-healing mechanism, suppressing problems such as active material stripping and excessive growth of the solid electrolyte interphase (SEI) film, and promoting the formation of a uniform and stable SEI film. This stable SEI significantly improves lithium-ion transport kinetics and reduces interfacial impedance, thereby effectively improving the cycle stability and rate performance of lithium-ion batteries.

[0022] This invention achieves structural stability of silicon-based anode materials during lithiation / delithiation processes by constructing a three-dimensional (3D) cross-linked network structure on the surface of silicon particles and optimizing the self-healing SEI layer interface. This network structure can also effectively suppress volume expansion of the silicon anode material and maintain the integrity of the silicon anode morphology, thereby significantly improving the specific capacity and cycle performance of lithium-ion batteries.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is a SEM image of the silicon-based anode material prepared in Example 1 of this invention;

[0025] Figure 2 Here is a SEM image of the silicon-based anode material prepared in Comparative Example 1 of this invention;

[0026] Figure 3 These are XRD comparison images of the silicon-based anode materials prepared in Example 1 and Comparative Example 1 of this invention;

[0027] Figure 4 This is a GCD curve of the lithium-ion battery assembled in Application Example 1 of the present invention;

[0028] Figure 5 This is the GCD curve of the lithium-ion battery assembled in Application Example 2 of this invention;

[0029] Figure 6 This is a comparison chart of the cycle performance tests of lithium-ion batteries assembled in Application Example 1 and Application Example 2 of this invention;

[0030] Figure 7 This is a rate performance test diagram of the lithium-ion battery prepared in Application Example 1 of this invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments. Unless otherwise defined, the technical or scientific terms used in this invention should be understood in their ordinary sense by those skilled in the art. The features mentioned above or in the specific examples mentioned in this invention can be combined arbitrarily, and these specific embodiments are only used to illustrate the invention and are not intended to limit the scope of the invention.

[0032] This invention provides a silicon-based anode material, comprising a paste and a copper sheet, wherein the mass ratio of the paste to the copper sheet is 0.5-1:8.4;

[0033] The slurry comprises: silica powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent;

[0034] The initiator is a polar solvent.

[0035] In some embodiments of the present invention, the mass-volume ratio of the silicon powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 7-8g:1-2g:1g:920-960μL:230-240μL:70-115mL.

[0036] In some embodiments of the present invention, the thickness of the copper sheet is 18-22 mm, and the particle size of the silicon powder is 25-35 nm.

[0037] In some embodiments of the present invention, the conductive agent is carbon black conductive agent.

[0038] In some embodiments of the present invention, the carbon black conductive agent includes one or more of Super P, Ketjen black, and acetylene black.

[0039] In some embodiments of the present invention, the solid content of the poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid is 1.3-1.7 wt%.

[0040] In some embodiments of the present invention, the polar solvent includes one or more of ethanol, ethylene glycol, and isopropanol.

[0041] In some embodiments of the present invention, the solvent includes water and / or ethanol.

[0042] The present invention also provides a method for preparing the silicon-based anode material, comprising the following steps:

[0043] (1) Mix silica powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent to obtain slurry;

[0044] (2) The slurry is coated on copper foil and dried to obtain the silicon-based anode material.

[0045] In some embodiments of the present invention, the specific process of mixing in step (1) includes: grinding silicon powder, adding sodium alginate, continuing to grind, then adding a conductive agent, continuing to grind, obtaining a ground material, adding poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent to the ground material, and mixing.

[0046] In some embodiments of the present invention, the mixing temperature in step (1) is 24-26°C and the mixing time is 2-5 min.

[0047] In some embodiments of the present invention, the drying temperature is 140-160°C and the drying time is 2.5-3.5 hours.

[0048] The present invention also provides the application of the above-mentioned silicon-based anode material or the silicon-based anode material prepared by the above-mentioned method in lithium-ion batteries.

[0049] Example 1

[0050] (1) Grind 0.15g of silicon powder with a particle size of 30nm for 20min, add 0.0188g of sodium alginate and continue grinding for 10min, then add 0.0188g of SuperP (conductive agent) and continue grinding for 10min to obtain the ground material. Add 20μL of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid with a solid content of 1.5wt%, 5μL of isopropanol (initiator) and 2mL of water (solvent) to the ground material and mix at 25℃ for 2min to obtain the slurry.

[0051] (2) Take 0.6g of the above slurry and coat it evenly on a copper foil with a thickness of 20mm and a mass of 8.4g. Then dry it in an oven at 150℃ for 3h to obtain silicon-based anode material.

[0052] Example 2

[0053] (1) Grind 0.15g of silicon powder with a particle size of 25nm for 18min, add 0.0188g of sodium alginate and continue grinding for 8min, then add 0.0188g of Ketjen black (conductive agent) and continue grinding for 12min to obtain the ground material. Add 20μL of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid with a solid content of 1.3wt%, 5μL of ethanol (initiator) and 2mL of water (solvent) to the ground material and mix at 24℃ for 4min to obtain the slurry.

[0054] (2) Take 1g of the above slurry and coat it evenly on a copper foil with a thickness of 20mm and a mass of 8.4g. Then dry it in an oven at 160℃ for 2.5h to obtain silicon-based anode material.

[0055] Example 3

[0056] (1) Grind 0.15g of silicon powder with a particle size of 35nm for 22min, add 0.0188g of sodium alginate and continue grinding for 12min, then add 0.0188g of acetylene black (conductive agent) and continue grinding for 12min to obtain the ground material. Add 20μL of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid with a solid content of 1.7wt%, 5μL of ethylene glycol (initiator) and 2mL of ethanol (solvent) to the ground material and mix at 26℃ for 5min to obtain the slurry.

[0057] (2) Take 0.5g of the above slurry and coat it evenly on a copper foil with a thickness of 20mm and a mass of 8.4g. Then dry it in an oven at 140℃ for 3.5h to obtain silicon-based anode material.

[0058] Comparative Example 1

[0059] Grind 0.15g of silicon powder with a particle size of 30nm for 20min, then add 0.0188g of polyacrylic acid (PAA) and continue grinding for 10min. Then add 0.0188g of SuperP (conductive agent) and continue grinding for 10min to obtain the ground material.

[0060] Take 0.6g of the above-mentioned grinding material and coat it evenly on a copper foil with a thickness of 20mm and a mass of 8.4g. Then dry it in an oven at a temperature of 150℃ for 3 hours to obtain a silicon-based anode material.

[0061] Characterization detection

[0062] The silicon-based anode materials prepared in Example 1 and Comparative Example 1 were observed using a scanning electron microscope, such as... Figure 1 and Figure 2 As shown. According to Figure 1As can be seen, the silicon-based anode material prepared in Example 1 has uniformly distributed silicon powder, and a uniform composite coating of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid and sodium alginate forms on the surface of the silicon powder particles. The carboxyl groups on the sodium alginate molecular chain form ester groups with the hydroxyl groups of the silicon surface oxide layer, achieving complete coating. The composite coating synergistically constructed by the two can provide mechanical buffering for the silicon powder, while also forming a continuous conductive path on the surface of the silicon anode. This structure effectively suppresses the problem of volume expansion of the silicon-based anode during lithium-ion battery cycling, while ensuring excellent charge transport performance. Figure 2 It can be seen that SuperP (conductive agent) is significantly aggregated around the silicon powder, and some silicon powder is directly exposed outside the polyacrylic acid (binder) and conductive agent.

[0063] X-ray diffraction analysis was performed on the silicon-based anode materials prepared in Example 1 and Comparative Example 1, and the results are as follows: Figure 3 As shown. According to Figure 3 It can be seen that the silicon-based anode material prepared in Example 1 has 3 obvious peaks and 4 weak low peaks. The 3 peaks correspond to Cu PDF#04-0836 card; the 4 weak low peaks correspond to Si PDF#03-0517 card, which correspond to 4 different crystal planes of silicon respectively; compared with Example 1, the silicon-based anode material prepared in Comparative Example 1 did not show obvious diffraction peak position shifts or the appearance of new diffraction peaks.

[0064] Application Example 1

[0065] The silicon-based anode material prepared in Example 1 was used as the anode of the lithium-ion battery, and high-purity lithium sheets were used as the cathode. A mixed system of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (volume ratio of 1:1:1) was used as the electrolyte. Lithium hexafluorophosphate and fluoroethylene carbonate (concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L, and mass concentration of fluoroethylene carbonate in the electrolyte was 5%) were added to the electrolyte. The electrolyte dosage for a single battery was 90 μL. The battery was assembled in an argon-protected glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), with a 19 mm diameter polypropylene separator (Celgard 2400) placed in it, and a CR2032 type lithium-ion battery was assembled.

[0066] Application Example 2

[0067] The assembly steps are the same as those for the lithium-ion battery in Application Example 1, except that the silicon-based anode material prepared in Comparative Example 1 is used as the anode of the lithium-ion battery.

[0068] Electrochemical performance testing

[0069] The lithium-ion battery prepared in Application Example 1 was subjected to constant current charge-discharge testing at a current density of 0.2 A / g, and the resulting GCD curve is shown below.Figure 4 As shown. According to Figure 4 It can be seen that when the silicon-based anode sheet prepared in Example 1 of this invention is used as the anode material of a lithium-ion battery, the initial coulombic efficiency of the lithium-ion battery reaches 91.76%, and the initial discharge specific capacity is as high as 3256.65 mAh / g, indicating that the interfacial side reactions are effectively suppressed and a relatively stable interface and conductive network structure is formed.

[0070] The lithium-ion battery prepared in Application Example 2 was subjected to constant current charge-discharge testing at a current density of 0.2 A / g, and its GCD curve is shown below. Figure 5 As shown. From Figure 5 It can be seen that when the silicon-based anode sheet prepared by Comparative Example 1 is used as the anode material of a lithium-ion battery, the initial coulombic efficiency of the lithium-ion battery is only 82.4%, which is much lower than that of Application Example 1 of this invention (91.76%), and the initial discharge specific capacity is 3495.9 mAh / g. This indicates that using polyacrylic acid alone as a binder makes it difficult to construct a stable solid electrolyte interface (SEI) film, cannot effectively alleviate the volume change of the silicon anode material during lithium insertion / extraction, and has insufficient ability to maintain the structural integrity of the silicon anode material, leading to contact failure between the active material and the current collector.

[0071] The lithium-ion batteries prepared in Application Examples 1 and 2 were subjected to cycle performance tests at a current density of 1 A / g, and the results are as follows: Figure 6 As shown. From Figure 6 It can be seen that when the lithium-ion battery prepared in Example 1 reaches 70 cycles, the capacity retention rate is 76.02%, and the average coulombic efficiency is as high as 99.2%, which fully demonstrates that the silicon-based anode material prepared in Example 1 of this invention has excellent structural stability. In contrast, the lithium-ion battery prepared in Example 2 has a cycle life of less than 40 cycles under the same test conditions, showing a rapid decay trend and a significantly reduced capacity retention rate. This indicates that the silicon-based anode material prepared in Example 1 of this invention has a stable cross-linked structure, alleviating the problems of electrode pulverization and capacity decay caused by volume changes in traditional silicon-based anode materials.

[0072] The rate performance of the lithium-ion battery prepared using Example 1 was tested, and the results are as follows: Figure 7 As shown. From Figure 7 It can be seen that under high-rate conditions of 1C (1C = 4A / g), the electrode material can still maintain a reversible capacity of 1255 mAh / g; when the rate returns to 0.05C, the specific capacity can be recovered to 3000 mAh / g, with a capacity recovery rate of 81.54%. This indicates that the silicon anode material provided by this invention has a stable electrode structure, and the synergistic effect of Si-OC covalent bonds and hydrogen bonds ensures the structural integrity of the material during the lithium-ion insertion / extraction process.

[0073] Therefore, this invention provides a silicon-based anode material that effectively solves the volume change problem of silicon-based anode materials during lithium battery cycling through multiple interactions such as hydrogen bonding, chemical bonding, and physical crosslinking between poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid (PEDOT:PSS), sodium alginate (SA), and silicon powder. Experiments show that when this silicon-based anode material is applied to the anode of a lithium-ion battery, the lithium-ion battery exhibits an initial coulombic efficiency of 91.76%, a plateau capacity of 2200 mAh / g at a current density of 1.0 A / g, and retains 76.02% capacity after 70 stable cycles.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A silicon-based anode material, characterized in that, It includes a paste and copper sheets, wherein the mass ratio of the paste to the copper sheets is 0.5-1:8.4; The slurry comprises: silica powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent; The initiator is a polar solvent; The mass-volume ratio of the silicon powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 7-8g:1-2g:1g:920-960μL:230-240μL:70-115mL. The conductive agent is carbon black conductive agent; The polar solvent includes one or more of ethanol and isopropanol.

2. The silicon-based anode material according to claim 1, characterized in that, The copper sheet has a thickness of 18-22 mm, and the silicon powder has a particle size of 25-35 nm.

3. The silicon-based anode material according to claim 1, characterized in that, The solvent includes water and / or ethanol.

4. A method for preparing the silicon-based anode material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix silica powder, sodium alginate, conductive agent, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent to obtain slurry; (2) The slurry is coated on copper foil and dried to obtain the silicon-based anode material.

5. The method for preparing the silicon-based anode material according to claim 4, characterized in that, The mixing temperature in step (1) is 24-26℃, and the mixing time is 2-5 min.

6. The method for preparing the silicon-based anode material according to claim 5, characterized in that, The drying temperature is 140-160℃, and the drying time is 2.5-3.5h.

7. The application of the silicon-based anode material according to any one of claims 1-3 or the silicon-based anode material prepared by the preparation method according to any one of claims 4-6 in lithium-ion batteries.

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