Silicon-based negative electrode binder as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode binder as well as a preparation method and application thereof. The silicon-based negative electrode binder comprises sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrolsulfon acid, an initiator and a solvent. On the basis of double design of a 3D cross-linked network formed by sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrolsulfon acid and a silicon material and a self-healing SEI layer interface, volume expansion of a silicon-based negative electrode in a lithiation / lithium removal process is inhibited, so that the capacity of the silicon-based negative electrode material is improved, and the cycle performance of a lithium ion battery is improved.

Description

Technical Field

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

[0002] With the widespread application of lithium-ion batteries in electric vehicles and energy storage, the requirements for their energy density are becoming increasingly higher. Using materials with high specific capacity is an effective means to improve battery energy density. Although silicon-based negative electrode materials have a high specific capacity, unlike the intercalation mechanism of lithium embedded in traditional negative electrode graphite materials of lithium-ion batteries, silicon changes significantly in volume (-400%) during lithiation and delithiation. Repeated expansion and contraction will generate adverse stress, causing silicon particles to break and pulverize and separate from the current collector, resulting in the complete loss of electrochemical activity of some active substances, causing rapid decay of battery capacity.

[0003] To address the volume change issue, binders are often used to maintain the mechanical integrity of silicon-based anode materials. However, traditional polymer binders, such as carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR), polyacrylic acid (PAA), and guar gum (GG), while exhibiting strong adhesion and chemical stability, struggle to suppress the volume expansion of silicon-based anode materials during cycling. Summary of the Invention

[0004] The object of the present invention is to provide a silicon-based negative electrode binder comprising the following raw materials:

[0005] Sodium alginate, poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent.

[0006] Preferably, the mass volume ratio of the sodium alginate, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 0.0375-0.0400 g:40-50 μL:10-20 μL:1-2 g.

[0007] Preferably, the mass volume ratio of the sodium alginate, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 0.0375-0.038 g:42-48 μL:12-18 μL:1.2-1.8 g.

[0008] Preferably, the initiator comprises one or more of ethanol, ethylene glycol and isopropanol.

[0009] Preferably, the solvent is a polar solvent.

[0010] Preferably, the polar solvent comprises water and / or ethanol.

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

[0012] Sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent are mixed and subjected to hydrothermal reaction to obtain the silicon-based negative electrode binder.

[0013] Preferably, the mixing temperature is 25-30° C., and the mixing time is 40-90 min.

[0014] Preferably, the temperature of the hydrothermal reaction is 140-160° C., and the time of the hydrothermal reaction is 2.5-3.5 hours.

[0015] The present invention also provides the use of the above-mentioned silicon-based negative electrode binder or the silicon-based negative electrode binder prepared by the above-mentioned method for preparing the silicon-based negative electrode binder in a lithium-ion battery.

[0016] The present invention has the following beneficial effects:

[0017] The present invention provides a silicon-based negative electrode binder, comprising the following raw materials: sodium alginate, poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent.

[0018] The present invention uses poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid (PEDOT:PSS) as raw materials to increase the contact area between the binder and silicon particles. At the same time, it can cross-link with the hydroxyl groups on the surface of the silicon particles in the form of hydrogen bonds, thereby improving the bonding strength. During the charge and discharge process, the hydrogen bonds can be quickly reorganized after breaking to repair the microcracks caused by the volume expansion of silicon. That is, the dynamic reversibility of the hydrogen bonds (breaking and reorganization) can dissipate stress during volume changes and maintain the integrity of the electrode; in addition, the dynamic covalent bonds spontaneously reorganize after breaking under specific conditions (such as pH and temperature) to repair damage. Therefore, the dynamic reversible chemical bonding mechanism of hydrogen bonds gives the material self-healing properties, thereby ensuring the integrity of the silicon-based negative electrode during the battery cycle, solving the problems of failure of the active components of the silicon-based negative electrode and excessive decay of the battery capacity.

[0019] The carboxyl functional groups on the surface of sodium alginate (SA) can chemically bond with the hydroxyl groups on the surface of silicon particles to form ester groups, effectively inhibiting the volume expansion of silicon particles during the cycle.

[0020] Sodium alginate and poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid are used in combination. The two can interact through ester groups or hydrogen bonds to form a relatively stable 3D cross-linked mechanical network structure. During the cycle, they form a more stable solid electrolyte interface film (SEI film) through self-healing function, thereby further improving the lithium ion transmission efficiency and achieving improved cycle performance of silicon-based negative electrodes.

[0021] The present invention is based on the dual design of a 3D cross-linked network formed by sodium alginate and poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid with silicon material and a self-healing SEI layer interface, which inhibits the volume expansion of the silicon-based negative electrode during the lithiation / delithiation process, thereby increasing the capacity of the silicon-based negative electrode material and improving the cycle performance of the lithium battery.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the silicon-based negative electrode sheet prepared in Application Example 1 of the present invention;

[0024] Figure 2 This is a SEM image of the silicon-based negative electrode sheet prepared in Application Example 2 of the present invention;

[0025] Figure 3 1 is a comparison chart of X-ray diffraction of silicon-based negative electrode sheets prepared in Application Example 1 and Application Example 2 of the present invention;

[0026] Figure 4 is a GCD curve diagram of the lithium ion battery prepared in Application Example 3 of the present invention;

[0027] Figure 5 is a GCD curve diagram of the lithium ion battery prepared in Application Example 4 of the present invention;

[0028] Figure 6 1 is a comparison chart of the cycle performance of lithium-ion batteries prepared in Application Example 3 and Application Example 4 of the present invention;

[0029] Figure 7 This is a rate performance test chart of the lithium-ion battery prepared in Application Example 3 of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described below with reference to the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0031] The present invention provides a silicon-based negative electrode binder, comprising the following raw materials: sodium alginate, poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent.

[0032] In some embodiments of the present invention, the mass volume ratio of the sodium alginate, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 0.0375-0.0400 g: 40-50 μL: 10-20 μL: 1-2 g.

[0033] In some embodiments of the present invention, the mass volume ratio of the sodium alginate, poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 0.0375-0.038 g:42-48 μL:12-18 μL:1.2-1.8 g.

[0034] In some embodiments of the present invention, the initiator comprises one or more of ethanol, ethylene glycol, and isopropanol.

[0035] The present invention uses ethanol, ethylene glycol and isopropanol as initiators. The highly polar initiators can weaken the electrostatic interaction between PEDOT and PSS, reduce the wrapping of PSS on PEDOT, and promote the gradual extension of the PEDOT chain from the curled state to form a longer conjugated structure, thereby improving the conductivity.

[0036] In some embodiments of the present invention, the solvent is a polar solvent.

[0037] In some embodiments of the present invention, the polar solvent comprises water and / or ethanol.

[0038] The present invention also provides a method for preparing the above-mentioned silicon-based negative electrode binder, comprising the following steps:

[0039] Sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent are mixed and subjected to hydrothermal reaction to obtain the silicon-based negative electrode binder.

[0040] In some embodiments of the present invention, the mixing temperature is 25-30° C., and the mixing time is 40-90 min.

[0041] In some embodiments of the present invention, the mixing process includes stirring and ultrasonication performed sequentially. The stirring time is 30-60 minutes, and the ultrasonication time is 10-30 minutes.

[0042] In some embodiments of the present invention, the temperature of the hydrothermal reaction is 140-160° C., and the time of the hydrothermal reaction is 2.5-3.5 hours.

[0043] The present invention adopts hydrothermal reaction to prepare silicon-based negative electrode binder. Under the hydrothermal reaction temperature, it can promote the molecular chain movement of poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid (PEDOT:PSS), further break the insulation barrier of PSS and increase conductivity.

[0044] The present invention also provides the use of the above-mentioned silicon-based negative electrode binder or the silicon-based negative electrode binder prepared by the above-mentioned method for preparing the silicon-based negative electrode binder in a lithium-ion battery.

[0045] Example 1

[0046] Mix 0.375g of sodium alginate, 40μL of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, 10μL of isopropyl alcohol, and 1.65g of water. Stir at 25°C for 30 minutes, then sonicate for 10 minutes. The resulting mixture is transferred to a polytetrafluoroethylene-lined container and hydrothermally reacted at 150°C for 3 hours to produce a silicon-based anode binder.

[0047] Example 2

[0048] Mix 0.375g of sodium alginate, 50μL of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, 15μL of ethanol, and 1g of water. Stir at 25°C for 60 minutes, then sonicate for 25 minutes. The resulting mixture is transferred to a polytetrafluoroethylene-lined container and hydrothermally reacted at 145°C for 3.5 hours to produce a silicon-based anode binder.

[0049] Example 3

[0050] Mix 0.4 g of sodium alginate, 45 μL of poly(3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, 20 μL of ethylene glycol, and 2 g of ethanol. Stir at 30°C for 45 minutes, then sonicate for 30 minutes. The resulting mixture is transferred to a polytetrafluoroethylene-lined container and hydrothermally reacted at 160°C for 2.5 hours to produce a silicon-based anode binder.

[0051] Application Example 1

[0052] The silicon-based negative electrode binder prepared in Example 1 was applied to prepare a silicon-based negative electrode sheet. The specific process included:

[0053] 0.3 g of silicon powder was ground for 20 min, mixed with 0.0375 g of Super P (conductive agent carbon black), and ground for another 10 min. Then, the silicon-based negative electrode binder prepared in Example 1, 10 μL of isopropyl alcohol, and 2 mL of water were mixed and ground at 25° C. for 2 min to obtain a slurry.

[0054] The slurry was evenly applied on the copper foil, and then placed in an oven at 150°C for 3 hours to obtain a silicon-based negative electrode sheet.

[0055] Application Example 2

[0056] After grinding 0.3 g of silicon powder for 20 min, 0.0375 g of polyacrylic acid (PAA) was added and the mixture was further ground for 5 min. Subsequently, 0.0375 g of SuperP (conductive agent carbon black) was added and the mixture was mixed and the mixture was further ground for 10 min. The mixture was then ground at 25°C for 2 min to obtain a slurry.

[0057] The slurry was evenly applied on the copper foil, and then placed in an oven at 150°C for 3 hours to obtain a silicon-based negative electrode sheet.

[0058] Characterization testing

[0059] Scanning electron microscope was used to characterize the silicon-based negative electrode sheets prepared in Example 1 and Example 2. Figure 1 and Figure 2 As shown. Figure 1 It can be seen that the silicon active material is in the form of nanospheres with uniform particle size distribution (30-60nm), which are well dispersed in the electrode; the silicon-based negative electrode binder formed by hydrothermal reaction forms a continuous coating layer on the surface of the silicon particles.

[0060] according to Figure 2 It can be seen that in the silicon-based negative electrode prepared in Application Example 2, the conductive agent Super P exhibits significant agglomeration, and some silicon powder particles are not effectively coated by the binder polyacrylic acid and the conductive agent. This microstructural defect leads to a discontinuous electron conduction network, reduced active material utilization, and deteriorated interface stability.

[0061] X-ray diffraction analysis was performed on Example 1 and Example 2. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the silicon-based negative electrode sheet prepared in Application Example 1 has three prominent main diffraction peaks and four weaker secondary diffraction peaks. Comparison with a standard PDF card confirms that the positions of the three main diffraction peaks are completely consistent with the characteristic peaks of metallic copper (Cu PDF#04-0836), while the four secondary diffraction peaks correspond to the diffraction of the four crystal planes of single-crystalline silicon (SiPDF#03-0517). Compared with Application Example 1, the silicon-based negative electrode sheet prepared in Application Example 2 shows no significant shift in diffraction peak positions or the appearance of new diffraction peaks.

[0062] Application Example 3

[0063] The silicon-based negative electrode sheet prepared in Application Example 1 is assembled into a lithium-ion battery. The preparation process includes:

[0064] The silicon-based negative electrode sheet prepared in Application Example 1 was used as the negative electrode, the lithium sheet was used as the positive electrode, a mixed solution of ethylene carbonate, dimethyl carbonate and diethyl carbonate (volume ratio of 1:1:1) was used as the electrolyte, and lithium hexafluorophosphate and ethylene carbonate were added to the electrolyte (the molar concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / L, and the mass concentration of ethylene carbonate was 5%). The electrolyte dosage of a single battery was 90 μL, a porous polypropylene film (diameter of 19 mm) was used as a separator, and a model CR2032 button cell was used to assemble the battery in an argon-protected (water and oxygen <0.01 ppm) glove box to obtain a lithium-ion battery.

[0065] Application Example 4

[0066] The silicon-based negative electrode sheet prepared in Application Example 2 was assembled into a lithium-ion battery, and the assembly process was the same as that in Application Example 3.

[0067] Electrochemical performance test

[0068] The lithium ion batteries prepared in Application Examples 3 and 4 were subjected to constant current charge and discharge tests at a current density of 0.2 A / g. The obtained GCD curves are shown in FIG. Figure 4 and Figure 5 As shown. Figure 4 It can be seen that the first coulombic efficiency of the lithium-ion battery prepared in Application Example 3 reaches 91.42%, and the first discharge specific capacity reaches 4303.04 mAh / g, which proves that the silicon-based negative electrode binder provided by the present invention can form a stable SEI interface and a three-dimensional conductive network after being applied to lithium-ion batteries, effectively inhibiting interface side reactions. Figure 5 It can be seen that the initial coulombic efficiency of the lithium ion battery prepared in Application Example 4 is 82.47%, which is 9.79% lower than that of the present invention; the specific capacity is 3495.9 mAh / g, which is 83.24% of the theoretical value.

[0069] The lithium ion batteries prepared in Application Example 3 and Application Example 4 were subjected to cycle performance tests. The results are as follows: Figure 6 .according to Figure 6 It can be seen that the lithium-ion battery prepared in Application Example 3 has a capacity of 2978.47 mAh / g after 56 cycles at 1 A / g, and a capacity retention rate of 81.06%, which is significantly better than that of Application Example 4. This shows that the stable cross-linked network formed by the silicon-based negative electrode binder provided by the present invention can effectively suppress the electrode structure degradation caused by volume expansion of the silicon negative electrode during cycling, and the dynamic bonding effect maintains the structural integrity of the silicon negative electrode during cycling.

[0070] The rate performance of the lithium-ion battery prepared in Application Example 3 was tested, and the results were as follows: Figure 7 As shown. Figure 7 It can be seen that under the high rate condition of 1C (4A / g), the reversible specific capacity of the battery still maintains 1550mAh / g; when the rate is restored to 0.05C (0.2A / g), the reversible specific capacity is restored to 3250mAh / g, and the capacity recovery rate reaches 81.49%, which has excellent electrochemical dynamic characteristics. This is because the silicon negative electrode binder of the present invention and the silicon powder synergistically form a three-dimensional interpenetrating network structure through covalent crosslinking (Si-OC) and hydrogen bonding, which effectively maintains the structural integrity of the silicon negative electrode during the rapid lithium ion insertion and extraction process; at the same time, the dynamic reversible chemical bonding mechanism of the silicon negative electrode binder gives the material self-healing properties, ensuring structural stability in long-term cycles.

[0071] Therefore, the three-dimensional interpenetrating network structure formed by the silicon-based negative electrode binder provided by the present invention after combining with silicon powder can effectively alleviate the volume change of the silicon-based negative electrode during the charge and discharge process; the unique dynamic bonding mechanism gives the silicon-based negative electrode self-healing properties, ensuring the stability of the electrode structure. Electrochemical tests show that after applying the silicon negative electrode binder provided by the present invention to lithium-ion batteries, the lithium-ion battery's initial coulombic efficiency reaches 91.42%, and it can provide a reversible capacity of 3000mAh / g at a current density of 1.0A / g. After 56 cycles, the capacity retention rate reaches 81.06%, which is significantly better than lithium-ion batteries with traditional silicon-based negative electrode materials, providing an effective solution for the development of high-energy-density lithium-ion batteries.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements 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 negative electrode binder, characterized in that: Including the following raw materials: Sodium alginate, poly (3,4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent.

2. The silicon-based negative electrode binder according to claim 1, characterized in that The mass volume ratio of the sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 0.0375-0.0400 g: 40-50 μL: 10-20 μL: 1-2 g.

3. The silicon-based negative electrode binder according to claim 2, characterized in that The mass volume ratio of the sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrene sulfonic acid, initiator and solvent is 0.0375-0.038 g: 42-48 μL: 12-18 μL: 1.2-1.8 g.

4. The silicon-based negative electrode binder according to claim 1, characterized in that The initiator includes one or more of ethanol, ethylene glycol and isopropyl alcohol.

5. The silicon-based negative electrode binder according to claim 1, characterized in that The solvent is a polar solvent.

6. The silicon-based negative electrode binder according to claim 5, characterized in that The polar solvent includes water and / or ethanol.

7. A method for preparing the silicon-based negative electrode binder according to any one of claims 1 to 6, characterized in that: The following steps are involved: Sodium alginate, poly (3, 4-ethylenedioxythiophene) / polystyrene sulfonic acid, an initiator and a solvent are mixed and subjected to hydrothermal reaction to obtain the silicon-based negative electrode binder.

8. The method for preparing a silicon-based negative electrode binder according to claim 7, wherein: The mixing temperature is 25-30° C., and the mixing time is 40-90 min.

9. The method for preparing a silicon-based negative electrode binder according to claim 7, wherein: The temperature of the hydrothermal reaction is 140-160° C., and the time of the hydrothermal reaction is 2.5-3.5 hours.

10. Use of the silicon-based negative electrode binder according to any one of claims 1 to 6 or the silicon-based negative electrode binder prepared by the method for preparing the silicon-based negative electrode binder according to any one of claims 7 to 9 in a lithium-ion battery.

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