Composite silicon-carbon negative electrode material, preparation method thereof, negative electrode sheet and lithium battery

Abstract

This invention discloses a composite silicon-carbon anode material, its preparation method, an anode sheet, and a lithium battery. The composite silicon-carbon anode material comprises nano-silicon powder, PAA, PEO, and carboxylated carbon nanotubes. The preparation method includes the following steps: mixing nano-silicon powder, PAA solution, and deionized water, stirring until homogeneous to obtain a first solution; adding the carboxylated carbon nanotubes to the first solution, stirring until homogeneous to obtain a second solution; adding PEO solution to the second solution to obtain a third solution; pouring the third solution into a drying container and drying to obtain a silicon-carbon thin film; thus obtaining the composite silicon-carbon anode material. This application improves the conductivity of the silicon anode by constructing a conductive network using carboxylated carbon nanotubes. Simultaneously, it can buffer the volume expansion of the silicon-based material, effectively improving the volume effect during charging and discharging of nano-silicon and slowing down the detachment of the active material from the conductive material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite silicon-carbon anode material and its preparation method, an anode sheet, and a lithium battery. Background Technology

[0002] Lithium-ion batteries are mainly composed of a positive electrode, a negative electrode, and an electrolyte, with the electrode materials playing the most crucial role in the battery's energy density. Silicon-based materials possess extremely high theoretical specific capacity (3587 mAh / g), nearly ten times that of graphite, currently used in commercial lithium-ion battery anodes. This allows them to avoid lithium dendrite formation, ensure a high operating voltage for the entire battery, and also offers advantages such as abundant reserves and environmental friendliness, making them an ideal anode material for lithium-ion batteries.

[0003] However, silicon anode materials still face the following problems in lithium battery applications: First, during the lithium insertion / extraction process, silicon undergoes significant volume expansion during lithiation and volume contraction during delithiation, generating substantial internal stress. This can lead to material pulverization and detachment from the current collector, damaging the electrode structure and affecting material performance. Second, due to the large volume effect of silicon, the SEI film formed on the material surface ruptures. Silicon particles are continuously exposed to the electrolyte, regenerating the SEI film. This continuous rupture and regeneration of the SEI film accelerates electrolyte consumption, but the amount of electrolyte in the battery is limited. Once the electrolyte is consumed, the battery will fail. Third, silicon anode batteries have low coulombic efficiency during the initial charge / discharge cycle. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a composite silicon-carbon anode material, its preparation method, an anode sheet, and a lithium battery.

[0005] The present invention discloses a composite silicon-carbon anode material, characterized in that it comprises nano-silicon powder, PAA, PEO and carboxylated carbon nanotubes.

[0006] According to one embodiment of the present invention, the mass ratio of PAA to PEO is 1:(0.2-1).

[0007] According to one embodiment of the present invention, the mass ratio of PAA, PEO, carboxylated carbon nanotubes, and nano-silicon powder is 3:(3-5):(2-4).

[0008] According to one embodiment of the present invention, the infrared spectrum of the composite silicon-carbon anode material measured is at 851 cm⁻¹. -1 -1100cm -1 It has a vibrational characteristic peak at 1715-1745 cm⁻¹. -1 It has a characteristic absorption peak.

[0009] According to one embodiment of the present invention, the thickness of the composite silicon-carbon anode material is 50-80 μm.

[0010] A method for preparing the above-mentioned composite silicon-carbon anode material includes the following steps:

[0011] Nano-silicon powder, PAA solution, and deionized water are mixed and stirred until homogeneous to obtain the first solution;

[0012] The carboxylated carbon nanotubes were added to the first solution and stirred until homogeneous to obtain the second solution.

[0013] PEO solution was added to the second solution to obtain the third solution;

[0014] The third solution was poured into a drying container and dried to obtain a silicon-carbon thin film;

[0015] A composite silicon-carbon anode material was obtained.

[0016] According to one embodiment of the present invention, the above-mentioned third solution is poured into a drying container and freeze-dried to obtain a silicon-carbon thin film, comprising the following sub-steps:

[0017] Pour the third solution into a dry container;

[0018] The above-mentioned dry container containing the third solution was placed in a freeze dryer and freeze-dried to obtain a dry container with a film.

[0019] The film was separated from the drying container to obtain a silicon-carbon film.

[0020] According to one embodiment of the present invention, the concentration of PAA solution is 10-25 mg / mL, and the concentration of PEO solution is 15-30 mg / mL.

[0021] A negative electrode sheet comprising the aforementioned composite silicon-carbon negative electrode material.

[0022] A lithium battery comprising the aforementioned negative electrode.

[0023] The beneficial effects of this application are as follows: by constructing a conductive network through carboxylated carbon nanotubes, the conductivity of the silicon anode is improved. At the same time, it can also buffer the volume expansion of silicon-based materials, effectively improve the volume effect during the charging and discharging of nano-silicon, and slow down the separation of active material from conductive material. In addition, the PEO-PAA complex is in a gel state after the electrolyte is added. The PEO-PAA in gel state pre-lithiation treatment of the anode preferentially stores excess active lithium ions, providing sufficient lithium ions for the charging and discharging of the anode. It provides sufficient guarantee for the volume change of the active material nano-silicon during the charging and discharging process to consume lithium ions, and improves the coulombic efficiency and cycle stability of the first charge and discharge. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a flowchart illustrating the preparation method of the composite silicon-carbon anode material in the embodiments;

[0026] Figure 2 This is a schematic diagram of the preparation method of the composite silicon-carbon anode material in the embodiment;

[0027] Figure 3 The infrared spectrum of the composite silicon-carbon anode material in the embodiment is shown below.

[0028] Figure 4 The cycle capacity diagram shows the battery with different proportions of each component of the composite silicon-carbon anode material.

[0029] Figure 5 The cycling coulombic efficiency diagrams for the lithium batteries of Example 2 and the comparative example are shown.

[0030] Figure 6 The diagram shows the cycle capacity of the lithium batteries in Example 2 and the comparative example. Detailed Implementation

[0031] The following drawings disclose several embodiments of the present invention. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential. Furthermore, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0032] Furthermore, in this invention, the use of terms such as "first" and "second" is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the invention. They are merely used to distinguish components or operations described using the same technical terms, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but only if they are feasible for those skilled in the art. If a combination of technical solutions is contradictory or impossible to implement, such a combination should be considered nonexistent and not within the scope of protection claimed by this invention.

[0033] Example 1

[0034] Reference Figure 1 as well as Figure 2 , Figure 1 This is a flowchart illustrating the preparation method of the composite silicon-carbon anode material in the embodiments. Figure 2 This is a schematic diagram of the preparation method of the composite silicon-carbon anode material in this embodiment. The preparation method of the composite silicon-carbon anode material in this embodiment is characterized by including the following steps:

[0035] S1: Obtain PEO solution.

[0036] S2: Obtain PAA solution.

[0037] S3: Mix nano-silicon powder, PAA solution and deionized water, stir evenly to obtain the first solution.

[0038] S4: Add the carboxylated carbon nanotubes to the first solution and stir until homogeneous to obtain the second solution.

[0039] S5: Add PEO solution to the second solution to obtain the third solution.

[0040] S6: Pour the third solution into a drying container and dry to obtain a silicon-carbon film.

[0041] S7: Obtain composite silicon-carbon anode material.

[0042] Preferably, in step S1, the concentration of the PEO solution is 15-30 mg / mL. PEO, or polyethylene oxide, is a crystalline, thermoplastic polymer with a regular linear helical structure. The PEO solution can be prepared in-house or purchased commercially. Specifically, the concentration of the PEO solution can be 15 mg / mL, 20 mg / mL, 25 mg / mL, or 30 mg / mL. In this embodiment, 2 g of PEO is weighed and dissolved in deionized water to obtain a PEO solution with a concentration of 20 mg / mL.

[0043] Preferably, in step S2, the concentration of the PAA solution is 10-25 mg / mL. PAA, or acrylic acid homopolymer, contains abundant carboxyl functional groups and can act as an aqueous binder to form hydrogen bonds with the hydroxyl groups on the silicon anode surface. The PAA solution can be prepared in-house or purchased commercially. Specifically, the concentration of the PAA solution can be 10 mg / mL, 15 mg / mL, 20 mg / mL, or 25 mg / mL. In this embodiment, 2 g of PAA is weighed and dissolved in deionized water to obtain a PAA solution with a concentration of 20 mg / mL. Steps S1 and S2 can be performed simultaneously, and are not limited here.

[0044] Preferably, in step S3, the amount of nano-silicon powder added is 300 mg, the amount of deionized water added is 15 mL, the amount of PAA solution added is 2.5-7.5 mL, and the stirring time is 0.5-1.5 h.

[0045] Preferably, in step S4, the amount of carboxylated carbon nanotubes added is 400 mg, and the stirring time is 0.2-0.7 h. The carboxylated carbon nanotubes construct a conductive network in the composite silicon-carbon anode material, improving the conductivity of the silicon anode. Simultaneously, they can buffer the volume expansion of the silicon-based material, effectively mitigating the volume effect during charge and discharge of nano-silicon and slowing down the detachment of the active material from the conductive material.

[0046] Reference Figure 3 , Figure 3 The image shows the infrared spectrum of the composite silicon-carbon anode material in the embodiment. Preferably, in step S5, the amount of PAA solution added is 7.5-12.5 mL, and the mass ratio of PAA to PEO in the third solution is 1:(0.2-1); the mass ratio of PAA to PEO, carboxylated carbon nanotubes, and nano-silicon powder is 3:4:3. The hydroxyl groups in PEO and the carboxyl groups in PAA complex to form a PEO-PAA complex. Simultaneously, the hydroxyl groups in PEO also complex with the carboxyl groups in the carboxylated carbon nanotubes. The complex contains hydrogen bonds, making it difficult to dissolve in the electrolyte and effectively storing abundant lithium ions. This provides sufficient lithium ions for the pre-lithiation of the silicon anode and adequately guarantees the lithium ion consumption due to volume changes during the charge-discharge process of the active material nano-silicon, improving the coulombic efficiency and cycle stability of the first charge-discharge cycle. Figure 3 It can be seen that 851 cm⁻¹ in the infrared spectrum -1 -1100cm -1 The characteristic peak at 1730 cm⁻¹ is mainly due to CH bond vibration. -1 There is a strong characteristic absorption peak at this location, which is the characteristic absorption peak of the ester group. This indicates that strong hydrogen bonds have been formed in the composite silicon-carbon anode material. It also indicates that the hydroxyl groups in PAA and the carboxyl groups in PEO and carboxylated carbon nanotubes have reacted to generate ester groups.

[0047] Specifically, step S6 also includes the following sub-steps:

[0048] S61: Pour the third solution into a dry container.

[0049] S62: Place the above-mentioned dry container containing the third solution into a freeze dryer, and after freeze drying, obtain a dry container with a film.

[0050] S63: Separate the film from the drying container to obtain a silicon-carbon film.

[0051] Preferably, in step S61, the diameter of the drying container is 18-22 mm, and the drying container is a petri dish. In step S62, the freeze-drying time is 44-52 hours. Since freeze-drying first freezes the third solution into a solid and then sublimates the solution, a thin film with abundant pores and strong toughness is prepared. This results in a thin film with large through-pores, which effectively suppresses the volume expansion of the composite silicon-carbon anode material during charge-discharge cycles. At the same time, the through-pores enable the composite silicon-carbon anode material to form a network structure, providing more channels for electron migration, reducing the internal resistance of the battery, and improving the electrical performance of the battery.

[0052] Specifically, step S7 also includes the following sub-steps:

[0053] S71: Roll-pressed film.

[0054] S72: A composite silicon-carbon anode material was obtained.

[0055] Preferably, in step S7, after rolling, the thickness of the composite silicon-carbon anode material is 50-80 μm.

[0056] The method for preparing the composite silicon-carbon anode material in this embodiment improves the conductivity of the silicon anode by constructing a conductive network using carboxylated carbon nanotubes. Simultaneously, it buffers the volume expansion of the silicon-based material, effectively mitigating the volume effect during charge and discharge of the nano-silicon and slowing the separation of the active material from the conductive material. Furthermore, the PEO-PAA complex forms a gel state after the electrolyte is added. This gel-structured PEO-PAA pre-lithiates the anode, preferentially storing excess active lithium ions to provide sufficient lithium ions for charge and discharge. This ensures adequate lithium ion consumption during the volume change of the active nano-silicon during charge and discharge, improving the coulombic efficiency and cycle stability of the first charge and discharge cycle.

[0057] Example 2

[0058] The composite silicon-carbon anode material in this embodiment was prepared using the method described in Example 1. The composite silicon-carbon anode material comprises nano-silicon powder, PAA, PEO, and carboxylated carbon nanotubes, with a thickness of 50-80 μm. In the composite silicon-carbon anode material, the mass ratio of PAA to PEO is 1:(0.2-1), and the mass ratio of PAA to PEO, carboxylated carbon nanotubes, and nano-silicon powder is 3:(3-5):(2-4). The infrared spectrum of the composite silicon-carbon anode material was measured at 851 cm⁻¹. -1 -1100cm -1 It has a vibrational characteristic peak at 1715-1745 cm⁻¹. -1 The composite silicon-carbon anode material in this embodiment exhibits a characteristic absorption peak at 1730 cm⁻¹. -1A strong characteristic absorption peak exists at this location, which is the characteristic absorption peak of the ester group. The composite silicon-carbon anode material is a porous thin film with abundant pores.

[0059] Example 3

[0060] A negative electrode sheet includes the composite silicon-carbon negative electrode material of Example 2. The composite silicon-carbon negative electrode material is cut into circular pieces with a diameter of 16 mm and assembled into a negative electrode sheet according to existing methods.

[0061] Example 4

[0062] A lithium battery includes the negative electrode sheet as described in Example 3. The negative electrode sheet is assembled into a lithium-ion button cell using existing methods.

[0063] To further understand the invention's content, features, and effects, the following embodiments are provided, along with detailed descriptions in conjunction with the accompanying drawings:

[0064] Example 1

[0065] 2g of PEO was weighed and added to deionized water to prepare a 20mg / mL PEO solution. 2g of PAA was weighed and added to deionized water to prepare a 20mg / mL PAA solution. 300mg of nano-silicon powder was weighed and placed in a beaker, 15mL of deionized water was added, followed by 2.5mL of PAA solution. A stir bar was added, and the mixture was stirred thoroughly for 1 hour to obtain the first solution. 400mg of XFM09 carboxylated carbon nanotubes from Xianfeng Nano was weighed and added to the first solution, and the mixture was stirred for 0.5 hours to obtain the second solution. 12.5mL of PEO solution was added to the second solution to obtain the third solution. The third solution was poured into a 20mm diameter drying container and placed in a freeze dryer for 48 hours. The film was then separated from the drying container to obtain a silicon-carbon film. The silicon-carbon film was rolled using a roller press to prepare a composite silicon-carbon anode material. The composite silicon-carbon anode material is cut into 16mm diameter discs using a slicer and then assembled into lithium-ion button batteries using existing methods.

[0066] Example 2

[0067] The amount of PAA solution added was 5 mL, the amount of PEO solution added was 10 mL, and all other conditions were the same as in Example 1. The lithium-ion button battery was assembled according to the existing method.

[0068] Example 3

[0069] The amount of PAA solution added was 7.5 mL, the amount of PEO solution added was 7.5 mL, and all other conditions were the same as in Example 1. The lithium-ion button battery was assembled according to the existing method.

[0070] The liquid absorption rate of the above-mentioned composite silicon-carbon anode material was tested, and the test results are shown in Table 1.

[0071] Table 1. Liquid absorption rate of composite silicon-carbon anode material after immersion in electrolyte for 1 hour.

[0072]

[0073]

[0074] Referring to Table 1, which shows the liquid absorption rate of the composite silicon-carbon anode material after immersion in electrolyte for 1 hour, the data in the table shows that as the proportion of PAA solution increases, the liquid absorption rate of the composite silicon-carbon anode material gradually decreases, but the structural stability of the composite silicon-carbon anode material gradually improves. When the mass ratio of PEO to PAA is 1:0.5, the prepared composite silicon-carbon anode material is not only structurally stable, but also has high liquid absorption.

[0075] Example 4

[0076] The amount of nano-silicon powder added was 200 mg, the amount of Xianfeng Nano XFM09 carboxylated carbon nanotubes added was 500 mg, and the other conditions were the same as in Example 2. The lithium-ion button battery was assembled according to the existing method.

[0077] Example 5

[0078] The amount of nano-silicon powder added was 400 mg, the amount of Xianfeng Nano XFM09 carboxylated carbon nanotubes added was 300 mg, and the other conditions were the same as in Example 2. The lithium-ion button battery was assembled according to the existing method.

[0079] The cycle performance of the lithium batteries in Examples 2, 4, and 5 was tested, and the test results are referred to [reference needed]. Figure 4 , Figure 4 The graph shows the cycle capacity of batteries with different proportions of components in the composite silicon-carbon anode material. As can be seen from the graph, the discharge specific capacity of the composite silicon-carbon anode material increases with the increase in the amount of XFM09 carboxylated carbon nanotubes used by Xianfeng Nano. In the silicon-carbon anode, carboxylated carbon nanotubes act as a conductive agent, and nano-silicon is the active material. The lower the proportion of active material and the more conductive agent, the greater the discharge specific capacity, but the energy density is relatively lower. A higher proportion of active material and a lower proportion of conductive agent results in faster capacity decay. This is because with increasing cycle count, the continuous charge-discharge expansion of nano-silicon can cause the conductive material to peel off, leading to capacity decay. Therefore, considering both energy density and capacity stability, the optimal mass ratio of PEO-PAA: carboxylated carbon nanotubes: nano-silicon powder is 3:4:3.

[0080] Comparative Example

[0081] A conventional silicon-carbon battery was used as a comparison. The conventional silicon-carbon battery is a button cell with a positive electrode made of a mixture of PVDF, carbon nanotubes and silicon in a mass ratio of 1:6:3, a negative electrode made of lithium metal and a separator made of PP.

[0082] The cyclic coulombic efficiency and cyclic capacity of Example 2 and the comparative example were tested, and the test results are as follows: Figure 5 and Figure 6 As shown, Figure 5 The diagram shows the cycle coulombic efficiency of the lithium batteries in Example 2 and the comparative example. Figure 6 The graph shows the cycle capacity of the lithium batteries in Example 2 and the comparative example. As can be seen from the graph, compared with conventional silicon-carbon batteries, the lithium battery provided in this application has higher cycle coulombic efficiency and cycle capacity.

[0083] In summary, the composite silicon-carbon anode material in this application improves the conductivity of the silicon anode by constructing a conductive network through carboxylated carbon nanotubes. Simultaneously, it buffers the volume expansion of the silicon-based material, effectively mitigating the volume effect during charge and discharge of the nano-silicon and slowing down the separation of the active material from the conductive material. Furthermore, the PEO-PAA complex forms a gel state after the electrolyte is added. The PEO-PAA gel structure pre-lithiated the anode, preferentially storing excess active lithium ions to provide sufficient lithium ions for charge and discharge. This provides ample assurance for the volume change of the active nano-silicon during charge and discharge, improving the coulombic efficiency and cycle stability during the first charge and discharge cycle.

[0084] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A composite silicon-carbon anode material, characterized in that, Including nano-silicon powder, acrylic homopolymer, polyethylene oxide, and carboxylated carbon nanotubes; The mass ratio of the acrylic homopolymer to the polyethylene oxide is 1:(0.2-1). The mass ratio of the acrylic homopolymer to the polyethylene oxide, the carboxylated carbon nanotubes, and the nano-silicon powder is 3:(3-5):(2-4). Its measured infrared spectrum is at 851 cm⁻¹ -1 -1100cm -1 It has a vibrational characteristic peak at 1715-1745 cm⁻¹. -1 It has a characteristic absorption peak.

2. A method for preparing the composite silicon-carbon anode material according to claim 1, characterized in that, Includes the following steps: Nano-silicon powder, acrylic homopolymer solution, and deionized water are mixed and stirred until homogeneous to obtain the first solution; Carboxylated carbon nanotubes were added to the first solution and stirred until homogeneous to obtain the second solution; Adding a polyethylene oxide solution to the second solution yields a third solution; The third solution is poured into a drying container and dried to obtain a silicon-carbon thin film; A composite silicon-carbon anode material was obtained.

3. The method for preparing the composite silicon-carbon anode material according to claim 2, characterized in that, The third solution is poured into a drying container and dried to obtain a silicon-carbon thin film, comprising the following sub-steps: The third solution is poured into a drying container; The dry container containing the third solution is placed in a freeze dryer and freeze-dried to obtain a dry container with a film. The film was separated from the drying container to obtain a silicon-carbon film.

4. The method for preparing the composite silicon-carbon anode material according to claim 2, characterized in that, The thickness of the composite silicon-carbon anode material is 50-80 μm.

5. The method for preparing the composite silicon-carbon anode material according to claim 2, characterized in that, The concentration of the acrylic homopolymer solution is 10-25 mg / mL, and the concentration of the polyethylene oxide solution is 15-30 mg / mL.

6. A negative electrode sheet, characterized in that, This includes composite silicon-carbon anode materials obtained using the preparation method described in claim 5.

7. A lithium battery, characterized in that, Includes the negative electrode sheet as described in claim 6.

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