Composite silicon-based negative electrode modified by piezoelectric effect and preparation method and application thereof

Abstract

The invention discloses a composite silicon-based negative electrode modified by a piezoelectric effect. The composite silicon-based negative electrode comprises a copper foil current collector, a negative electrode active layer blade-coated on the surface of the copper foil current collector and an inorganic piezoelectric coating sprayed on the surface of the negative electrode active layer, the inorganic piezoelectric coating is formed by uniformly spraying a piezoelectric solution on the surface of the negative electrode active layer under a high-temperature condition and drying; the piezoelectric solution is formed by mixing a piezoelectric ceramic material, a garnet type material, a second binder and a second organic solvent; and the negative active layer is formed by mixing a silicon-based active material, a conductive agent, a first binder and a first organic solvent. The composite silicon-based negative electrode with a double-layer piezoelectric-conductive negative electrode structure is formed by combining a piezoelectric material with a garnet type material, so that the defect of poor conductivity of the piezoelectric material is overcome, collaborative optimization of a piezoelectric effect and a conductive network is also realized, and the comprehensive performance of the battery is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and particularly relates to a composite silicon-based anode modified by the piezoelectric effect, a preparation method thereof, and an application thereof. Background Art

[0002] Facing the increasing demand for energy storage in portable electronic devices and electric vehicles, the industry is urgently calling for anode materials with higher energy density to drive the innovation of lithium-ion battery technology. Silicon-based materials have become the focus of attention because of their excellent theoretical specific capacity of up to 4200 mAh / g, far exceeding the standard of 372 mAh / g of graphite. This means that silicon-based materials can accommodate more lithium ions under the same weight condition, greatly improving the battery efficiency; in addition, due to their abundant reserves and affordable prices, they meet the vision of green and sustainable development. However, the practical application of silicon-based anodes also faces various challenges. During the charge and discharge cycle, the significant volume expansion phenomenon (up to 300% change) poses a severe test, resulting in the fragmentation and peeling of the active components, damage to the electrode structure, and seriously reducing the cycle stability and life of the battery. Along with the volume deformation, the SEI film frequently breaks and rebuilds, which also exacerbates the consumption of lithium ions.

[0003] To overcome these defects, various strategies have been proposed in the prior art. It has been reported that reducing the size of silicon-based materials to the nanoscale can effectively inhibit crack propagation. However, due to the large demand for binders and conductive agents and the significant volume expansion, it is challenging to improve the volume energy density by only using nanosilicon for commercial lithium-ion batteries. Another method is to mix silicon with carbon to improve conductivity, which is considered the best choice for practical lithium-ion batteries. In addition, designing a hollow or porous structure is an effective strategy to add internal voids to inhibit the volume expansion of silicon anodes and accelerate the transport of lithium ions.

[0004] However, even after various modifications, the volume expansion of silicon anodes still cannot be avoided. Therefore, "making the best use of the situation" has become a new idea, that is, trying to transform this inevitable phenomenon into a positive factor. Specifically, introducing piezoelectric materials into silicon-based anodes may become a feasible way out. On the one hand, piezoelectric materials can adapt to the volume change of silicon during lithiation through the piezoelectric effect. On the other hand, the piezoelectric potential generated by piezoelectric materials will change the mobility of lithium ions, and the applied electric field may greatly promote the diffusion of lithium ions. However, the modification method of directly mixing traditional piezoelectric materials with silicon-based anodes will improve the electric field of the anode, but there will still be excessive growth of the SEI layer. The excessive accumulation of SEI will lead to a decrease in ion transport and capacity of the anode. Summary of the Invention

[0005] To solve the above technical problems, the present invention combines a piezoelectric material with a garnet-type material to form a composite silicon-based negative electrode with a double-layer piezoelectric-conductive negative electrode structure, which not only makes up for the shortcoming of poor conductivity of the piezoelectric material, but also realizes the synergistic optimization of the piezoelectric effect and the conductive network, significantly improving the comprehensive performance of the battery.

[0006] The first object of the present invention is to provide a composite silicon-based negative electrode modified by the piezoelectric effect. The composite silicon-based negative electrode includes: a copper foil current collector, a negative electrode active layer scraped on the surface of the copper foil current collector, and an inorganic piezoelectric coating sprayed on the surface of the negative electrode active layer; the inorganic piezoelectric coating is formed by uniformly spraying a piezoelectric solution on the surface of the negative electrode active layer and drying it under high temperature conditions; the piezoelectric solution is composed of a piezoelectric ceramic material, a garnet-type material, a second binder, and a second organic solvent; the negative electrode active layer is composed of a silicon-based active material, a conductive agent, a first binder, and a first organic solvent.

[0007] Specifically, the thickness of the inorganic piezoelectric coating is 2-5 μm.

[0008] Specifically, the piezoelectric ceramic material is any one or several of barium titanate, lithium tetraborate, lithium tantalate, sodium potassium niobate, and sodium bismuth titanate.

[0009] Specifically, the garnet-type material is one or several of lithium lanthanum zirconium oxide and tantalum-doped lithium lanthanum zirconium oxide.

[0010] Specifically, the silicon-based active material is any one of elemental silicon materials, silicon-carbon materials, and silicon-oxygen materials.

[0011] The second object of the present invention is also to provide a preparation method of the above composite silicon-based negative electrode, which includes the following steps:

[0012] S1 Dissolve the silicon-based active material, the conductive agent, and the first binder in the first organic solvent in sequence, and stir evenly to obtain a negative electrode slurry;

[0013] S2 Uniformly scrape the negative electrode slurry on the copper foil current collector, and put it into an oven for drying treatment to obtain a negative electrode active layer;

[0014] S3 Dissolve a certain content ratio of the piezoelectric ceramic material, the garnet-type material, and the second binder in the second organic solvent in sequence to prepare a piezoelectric solution;

[0015] S4 Uniformly spray the piezoelectric solution on the negative electrode active layer, put it into an oven for drying and perform rolling treatment to obtain an inorganic piezoelectric coating, forming a composite silicon-based negative electrode.

[0016] Specifically, in step S1, the mass ratio of the silicon-based active material, the conductive agent, and the first binder is 1:(0.2-5.8):(0.1-0.3).

[0017] Specifically, the mass ratio of the piezoelectric ceramic material, garnet-type material, and second binder described in step S3 is (7-8):(1.5-2.5):(0.05-0.5).

[0018] Specifically, the conductive agent described in step S1 is one or more of acetylene black, carbon nanotubes, graphene, and conductive carbon black; the first binder is one or more of lithium polyacrylate binder, polyvinylidene fluoride, sodium alginate, carboxymethyl cellulose, and styrene-butadiene rubber; the first organic solvent includes any one of water, N,N-dimethylformamide, and N-methylpyrrolidone.

[0019] Specifically, the second binder described in step S3 is one or more of polyvinylidene fluoride, sodium alginate, carboxymethyl cellulose, and styrene-butadiene rubber; the second organic solvent described in step S3 is one or more of styrene tetrahydrocarbon, N-methyl-2-pyrrolidone, and acetone.

[0020] The third object of the present invention also lies in providing an application of the composite silicon-based negative electrode as described above in a lithium-ion battery or a supercapacitor.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] (1) By introducing a piezoelectric ceramic material and a garnet-type material, the present invention utilizes the piezoelectric effect to absorb the expansion stress generated during lithium intercalation in the silicon-based negative electrode during charge and discharge, significantly alleviating the volume expansion of the silicon-based material, thereby effectively suppressing the destruction of the silicon-based negative electrode structure; the generated piezoelectric field during volume expansion alleviation promotes the transmission of lithium ions; at the same time, the ion transport network constructed by the garnet-type material further improves the conductivity of the negative electrode, so it exhibits low impedance and excellent charge and discharge capabilities, cycle stability, and lifespan;

[0023] (2) By combining a piezoelectric material with a garnet-type material to form a double-layer piezoelectric-conductive negative electrode structure, the present invention not only makes up for the shortcoming of poor conductivity of the piezoelectric material but also realizes the synergistic optimization of the piezoelectric effect and the conductive network. The piezoelectric potential generated by the piezoelectric ceramic material during charge and discharge can change the mobility of lithium ions, and the applied electric field greatly promotes the diffusion of lithium ions, thereby improving the transmission efficiency of lithium ions, reducing the internal resistance of the battery, and enhancing the charge and discharge performance of the battery; in addition, the ion transport network constructed by the garnet-type material and the conductive carbon network in the silicon-based negative electrode act synergistically to further improve the conductivity and ion transport efficiency of the silicon-based negative electrode, significantly enhancing the comprehensive performance of the battery;

[0024] (3) The coating prepared by the spraying and rolling process of the present invention is thin and dense (with a thickness of 10-50um), which can effectively reduce the contact between the negative electrode and the electrolyte, reduce the loss of the electrolyte, and promote the formation of a stable SEI layer on the electrode surface; the preparation process is simple and controllable, the piezoelectric coating is uniform and dense, suitable for large-scale industrial production, and has high practicability and economy. Description of the Drawings

[0025] Figure 1 SEM image of the cross-section of the composite silicon-based negative electrode a prepared in Example 1 of the present invention;

[0026] Figure 2 SEM image of the cross-section of the composite silicon-based negative electrode b prepared in Example 2 of the present invention;

[0027] Figure 3 SEM image of the surface of the composite silicon-based negative electrode a prepared in Example 1 of the present invention;

[0028] Figure 4 SEM-EDS spectrum of the composite silicon-based negative electrode a prepared in Example 1 of the present invention;

[0029] Figure 5 Si element distribution map of the composite silicon-based negative electrode a prepared in Example 1 of the present invention;

[0030] Figure 6 C element distribution map of the composite silicon-based negative electrode a prepared in Example 1 of the present invention;

[0031] Figure 7 B element distribution map of the composite silicon-based negative electrode a prepared in Example 1 of the present invention;

[0032] Figure 8 (a) Voltage-specific capacity curve of the half-cell m-Si prepared in Comparative Example 1 of the present invention;

[0033] Figure 8 (b) Voltage-specific capacity curve of the half-cell m-Si-LBO prepared in Example 1 of the present invention;

[0034] Figure 8 (c) Comparison chart of the first-cycle CV curves of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0035] Figure 8 (d) Nyquist comparison chart of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0036] Figure 9 (a) Comparison chart of the cycling performance of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0037] Figure 9(b) is the comparison chart of the rate performance of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0038] Figure 10 (a) is the comparison chart of GITT tests during the discharge process of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0039] Figure 10 (b) is the comparison chart of GITT tests during the charging process of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention;

[0040] Figure 11 (a) is the SEM image of the silicon-based anode A prepared in Comparative Example 1 of the present invention after 50 cycles;

[0041] Figure 11 (b) is the SEM image of the silicon-based anode A prepared in Comparative Example 1 of the present invention after 50 cycles;

[0042] Figure 11 (c) is the SEM image of the composite silicon-based anode a prepared in Example 1 of the present invention after 50 cycles;

[0043] Figure 11 (d) is the SEM image of the composite silicon-based anode a prepared in Example 1 of the present invention after 50 cycles. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the content in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0045] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific implementation manners and are not used to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items. It should be understood that, unless otherwise specified, various raw materials in the present invention can be obtained commercially.

[0046] Example 1

[0047] S1 Take 90 mg of carbon-silicon material, 250 mg of carbon nanotubes (CNTs, aqueous system, concentration of 0.4%), 9 mg of conductive carbon black, and 30 mg of lithiated polyacrylic acid binder (PAA-Li, model LA132, concentration of 4%) and dissolve them in 0.3 mL of deionized water in sequence. Stir evenly at a speed of 1000 rpm for 30 min to obtain the negative electrode slurry a;

[0048] S2 Use a 100-μm doctor blade to evenly scrape the negative electrode slurry a onto the copper foil current collector, and put it into an oven. After drying at 80 °C for 12 h, obtain the negative electrode active layer a;

[0049] S3 In a glove box filled with argon, dissolve 0.8 g of lithium tetraborate (LBO), 0.25 g of tantalum-doped lithium lanthanum zirconium oxide (LLZTO), and 0.05 g of polyvinylidene fluoride (PVDF) in 20 ml of N-methyl-2-pyrrolidone (NMP) in sequence. After ultrasonic treatment for 1 h, stir evenly for 8 h to obtain the piezoelectric solution a;

[0050] S4 Use a sprayer to evenly spray the piezoelectric solution a onto the negative electrode active layer a at a speed of 3 mL / min, and put it into an oven for drying. After drying at 80 °C for 12 h; then use a roll press to perform a rolling treatment on it (adjust the rolling spacing of the roll press to 0.2 mm) to obtain the inorganic piezoelectric coating a with a thickness of 4.23 μm; finally obtain the composite silicon-based negative electrode a. Then cut the composite silicon-based negative electrode a into a circular battery negative electrode sheet a with a diameter of 10 mm.

[0051] Assemble the obtained circular battery negative electrode sheet a into a button-type half-cell and perform performance testing on it. The assembly of the half-cell is completed in a stainless-steel glove box filled with Ar. In this embodiment, a CR2025-type button-type half-cell is selected, a lithium sheet is used as the counter electrode, the separator is Celgard 2320, and the electrolyte is a mixed solution of 1 mol / L LiPF6 dissolved in a 1:1 volume ratio of ethylene carbonate (EC) and diethyl carbonate (DEC) to obtain the CR2025-type button-type half-cell a, denoted as m-Si-LBO.

[0052] Example 2

[0053] S1 Take 90 mg of silicon-carbon material (SiC), 11 mg of acetylene black, 9 mg of conductive carbon black, and 20 mg of sodium alginate (SA) and dissolve them in 0.5 mL of N,N-dimethylformamide in sequence. Stir evenly at a speed of 1000 rpm for 30 min to obtain the negative electrode slurry b;

[0054] S2 Use a 100-μm doctor blade to evenly scrape the negative electrode slurry b onto the copper foil current collector, and put it into an oven. After drying at 80 °C for 12 h, obtain the negative electrode active layer b;

[0055] In a glove box filled with argon, 0.7 g of lithium tantalate, 0.15 g of lithium lanthanum zirconium oxide (LLZO), and 0.01 g of SA were successively dissolved in 20 ml of styrene tetrahydrofuran (THF). After ultrasonic treatment for 1 h, it was uniformly stirred for 8 h to obtain piezoelectric solution b;

[0056] S4 Using a sprayer, piezoelectric solution b was uniformly sprayed on the negative electrode active layer b at a speed of 1 mL / min and then placed in an oven for drying. It was dried at 80 °C for 12 h; then it was roll-pressed using a roll press (adjusting the roll press spacing to 0.2 mm) to obtain an inorganic piezoelectric coating b with a thickness of 2.35 μm, and finally a composite silicon-based negative electrode b was obtained. The composite silicon-based negative electrode b was cut into a circular battery negative electrode sheet b with a diameter of 10 mm.

[0057] The obtained circular battery negative electrode sheet b was assembled into a button-type half-cell for performance testing. The half-cell assembly was completed in a stainless-steel glove box filled with Ar. In this example, a CR2025 type button-type half-cell was selected, with a lithium sheet as the counter electrode, a Celgard 2320 diaphragm, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 to obtain a CR2025 type button-type half-cell b.

[0058] Example 3

[0059] S1 90 mg of silicon oxide material (SiC), 9 mg of graphene, 250 mg of carbon nanotubes (CNTs, aqueous system, concentration of 0.04%), and 30 mg of carboxymethyl cellulose (CMC) were successively dissolved in 0.35 mL of N-methylpyrrolidone and uniformly stirred at a speed of 1000 rpm for 30 min to obtain negative electrode slurry c;

[0060] S2 Using a 100-μm doctor blade, negative electrode slurry c was uniformly blade-coated on a copper foil current collector and placed in an oven. After drying at 80 °C for 12 h, a negative electrode active layer c was obtained;

[0061] S3 In a glove box filled with argon, 0.75 g of potassium sodium niobate (KNN), 0.2 g of LLZTO, and 0.005 g of CMC were successively dissolved in 20 ml of styrene tetrahydrofuran (THF). After ultrasonic treatment for 1 h, it was uniformly stirred for 8 h to obtain piezoelectric solution c;

[0062] S4 Using a sprayer, piezoelectric solution c was uniformly sprayed on the negative electrode active layer c at a speed of 5 mL / min and then placed in an oven for drying. It was dried at 80 °C for 12 h; then it was roll-pressed using a roll press (adjusting the roll press spacing to 0.2 mm) to obtain an inorganic piezoelectric coating c with a thickness of 4.79 μm, and finally a composite silicon-based negative electrode c was obtained. The composite silicon-based negative electrode c was cut into a circular battery negative electrode sheet c with a diameter of 10 mm.

[0063] The obtained circular battery negative electrode sheet c was assembled into a button-type half-cell for performance testing. The assembly of the half-cell was completed in a stainless-steel glove box filled with Ar. In this example, a CR2025 type button-type half-cell was selected, with a lithium sheet as the counter electrode, a Celgard 2320 diaphragm, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solution of EC and DEC with a volume ratio of 1:1, to obtain the CR2025 type button-type half-cell c.

[0064] Example 4

[0065] S1: 90 mg of elemental silicon material (SiC), 500 mg of carbon nanotubes (CNTs, aqueous system, concentration of 0.04%), 18 mg of conductive carbon black, and 20 mg of styrene-butadiene rubber (SBR) were successively dissolved in 0.25 mL of deionized water and uniformly stirred at a speed of 1000 rpm for 30 min to obtain the negative electrode slurry d;

[0066] S2: The negative electrode slurry d was uniformly coated on the copper foil current collector using a 100-μm doctor blade, placed in an oven, and dried at 80 °C for 12 h to obtain the negative electrode active layer d;

[0067] S3: 0.78 g of barium titanate nanowires, 0.23 g of lithium lanthanum zirconium oxide (LLZO), and 0.03 g of SBR were successively dissolved in 20 mL of acetone in a glove box filled with argon, ultrasonically treated for 1 h, and then uniformly stirred for 8 h to obtain the piezoelectric solution d;

[0068] S4: The piezoelectric solution d was uniformly sprayed on the negative electrode active layer d at a speed of 2 mL / min using a sprayer and placed in an oven for drying, and dried at 80 °C for 12 h; then it was roll-pressed (adjusting the roll-pressing spacing of the roll press to 0.2 mm) to obtain the inorganic piezoelectric coating d with a thickness of 3.68 μm, and finally the composite silicon-based negative electrode d was obtained. The composite silicon-based negative electrode d was cut into a circular battery negative electrode sheet d with a diameter of 10 mm.

[0069] The obtained circular battery negative electrode sheet d was assembled into a button-type half-cell for performance testing. The assembly of the half-cell was completed in a stainless-steel glove box filled with Ar. In this example, a CR2025 type button-type half-cell was selected, with a lithium sheet as the counter electrode, a Celgard 2320 diaphragm, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solution of EC and DEC with a volume ratio of 1:1, to obtain the CR2025 type button-type half-cell d.

[0070] Example 5

[0071] S1 Take 90 mg of elemental silicon material (SiC), 250 mg of carbon nanotubes (CNTs, oil-based, concentration of 0.04%), 19 mg of conductive carbon black, and 10 mg of PVDF and dissolve them in 0.25 mL of N-methylpyrrolidone in sequence, and stir evenly at a speed of 1000 rpm for 30 min to obtain the negative electrode slurry e;

[0072] S2 Use a 100-μm doctor blade to evenly scrape the negative electrode slurry d onto the copper foil current collector, put it into an oven, and dry it at 80 °C for 12 h to obtain the negative electrode active layer e;

[0073] S3 In a glove box filled with argon, take 0.7 g of sodium bismuth titanate (BNT), 0.15 g of tantalum-doped lithium lanthanum zirconium oxide (LLZTO), and 0.005 g of PVDF and dissolve them in 20 ml of acetone in sequence. After ultrasonic treatment for 1 h, stir evenly for 8 h to obtain the piezoelectric solution e;

[0074] S4 Use a sprayer to evenly spray the piezoelectric solution e onto the negative electrode active layer d at a speed of 5 mL / min, put it into an oven for drying, and dry it at 80 °C for 12 h; then use a roll press to perform roll pressing treatment on it (adjust the roll pressing distance of the roll press to 0.5 mm) to obtain the inorganic piezoelectric coating e with a thickness of 5.03 μm, and finally obtain the composite silicon-based negative electrode e. Then cut the composite silicon-based negative electrode e into a circular battery negative electrode sheet e with a diameter of 10 mm.

[0075] Assemble the obtained circular battery negative electrode sheet e into a button-type half-cell and perform performance testing on it. The assembly of the half-cell is completed in a stainless-steel glove box filled with Ar. In this example, a CR2025 type button-type half-cell is selected, a lithium sheet is used as the counter electrode, the separator is Celgard 2320, and the electrolyte is a mixed solution of 1 mol / L LiPF6 dissolved in a 1:1 volume ratio of EC and DEC to obtain the CR2025 type button-type half-cell e, denoted as m-Si.

[0076] Comparative Example 1

[0077] S1 Take 90 mg of elemental silicon material, 250 mg of carbon nanotubes (CNTs, water-based, concentration of 0.4%), 9 mg of conductive carbon black, and 300 mg of lithiated polyacrylic acid binder (PAA-Li, model LA132, concentration of 4%) and dissolve them in 0.3 mL of deionized water in sequence, and stir evenly at a speed of 1000 rpm for 30 min to obtain the negative electrode slurry A;

[0078] S2 Use a 100-μm doctor blade to evenly scrape the negative electrode slurry A onto the copper foil current collector, put it into an oven, and dry it at 80 °C for 12 h to obtain the negative electrode active layer A, and finally obtain the silicon-based negative electrode A. Then cut the silicon-based negative electrode A into a circular battery negative electrode sheet A with a diameter of 10 mm.

[0079] The obtained circular battery negative electrode sheet A was assembled into a button-type half-cell for performance testing, and the assembly of the half-cell was completed in a stainless-steel glove box filled with Ar. In this comparative example, a CR2025-type button-type half-cell was selected, with a lithium sheet as the counter electrode, a Celgard 2320 diaphragm, and an electrolyte of 1 mol / L LiPF6 dissolved in a mixed solution of EC and DEC with a volume ratio of 1:1, obtaining a CR2025-type button-type half-cell A, denoted as m-Si.

[0080] Performance testing

[0081] Test and analysis methods used in the examples: SEM and mapping analysis: The morphology of the samples was observed using a FEI Quanta 450 FEG field emission scanning electron microscope from FEI Company, USA, and mapping analysis was performed on the morphology images. The acceleration voltage of the scanning electron microscope was 15 kV. The sample powder dispersed in ethanol was dropped on a copper foil, dried, and fixed on a sample stage with conductive glue, and gold spraying treatment was carried out before testing. Charge-discharge testing: The charge-discharge curves of the samples were measured using a BTS51800 battery testing system (model CT-3008W) from Shenzhen Neware Electronic Co., Ltd., with a charge-discharge voltage range of 0.01 - 1.5 V and a current density of 0.2 A / g -1 . Cycling performance testing: The charge-discharge performance of the samples was tested using a BTS-type battery tester from Shenzhen Neware Company. CV curve analysis: The chemical behavior of the samples was detected using a CHI660 tester from Shanghai Chenhua, with a voltage range of 0.01 - 3.0 V.

[0082] Rate performance testing: With 10 cycles as a cycle period, the rate performance of the samples was tested at different current densities (2, 4, 6, 8, 8, 10, 12 A / g). EIS analysis: The samples were subjected to EIS testing using a CHI660 tester from Shanghai Chenhua, with the open-circuit voltage of the battery and a frequency range of 0.01 HZ - 100 kHz.

[0083] 1. Scanning electron microscope and energy-dispersive X-ray spectroscopy testing

[0084] In the present invention, a scanning electron microscope (SEM) was used to characterize the morphological changes of the composite silicon-based negative electrode a prepared in Example 1 of different electrodes before and after cycling and the silicon-based negative electrode A prepared in Comparative Example 1. Figure 1 This is the SEM image of the cross-section of the composite silicon-based negative electrode a prepared in Example 1 of the present invention; Figure 2 This is the SEM image of the cross-section of the composite silicon-based negative electrode b prepared in Example 2 of the present invention;

[0085] Figure 3SEM image of the surface of composite silicon-based anode a prepared in Example 1 of the present invention; it can be seen from the cross-sectional SEM image and the surface SEM image that an inorganic piezoelectric coating is uniformly formed on the composite silicon-based anodes prepared in Examples 1-2, and the piezoelectric coating is uniform and dense.

[0086] Figure 11 (a) SEM image of silicon-based anode A prepared in Comparative Example 1 of the present invention after 50 cycles; Figure 11 (b) SEM image of silicon-based anode A prepared in Comparative Example 1 of the present invention after 50 cycles; Figure 11 (c) SEM image of composite silicon-based anode a prepared in Example 1 of the present invention after 50 cycles; Figure 11 (d) SEM image of composite silicon-based anode a prepared in Example 1 of the present invention after 50 cycles. After 50 cycles, a large number of cracks and serious structural collapse appear on the surface of silicon-based anode A prepared in Comparative Example 1, and the swelling is obvious. However, after 50 cycles of lithium insertion and extraction using composite silicon-based anode a prepared in Example 1, the electrode can still maintain a dense and complete structure, form a thin and stable SEI layer, maintain the conductive network and mechanical network, keep the composite silicon-based electrode intact during deep charge-discharge cycles, significantly relieve the volume expansion of the silicon-based material, and thus effectively inhibit the damage of the silicon-based anode structure. It shows that the addition of inorganic piezoelectric ceramic material LBO can relieve the cracking and pulverization of the electrode sheet, effectively relieve the stress of micron silicon expansion, improve the stability of the electrode structure, and ensure the cycle stability of the electrode.

[0087] Figure 4 SEM-EDS spectrum of composite silicon-based anode a prepared in Example 1 of the present invention; Figure 5 Si element distribution map of composite silicon-based anode a prepared in Example 1 of the present invention; Figure 6 C element distribution map of composite silicon-based anode a prepared in Example 1 of the present invention; Figure 7 B element distribution map of composite silicon-based anode a prepared in Example 1 of the present invention. Through SEM-EDS analysis, it can be obtained that the inorganic piezoelectric layer is uniformly distributed with B, C, and Si elements, indicating that the inorganic piezoelectric material lithium tetraborate LBO is uniformly coated on the surface of the silicon-based anode.

[0088] 2. Electrochemical performance test

[0089] Figure 8 (a) Voltage-specific capacity curve of half-cell m-Si prepared in Comparative Example 1 of the present invention; Figure 8 (b) Voltage-specific capacity curve of half-cell m-Si-LBO prepared in Example 1 of the present invention; Figure 8 (c) Comparative diagram of the first-cycle CV curves of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention; Figure 8(d) is the Nyquist comparison diagram of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention. From Figure 8 (a) and Figure 8 (b) show that the lithium insertion potentials of the two groups of half-cell samples are similar. Figure 8 (c) shows that the introduction of the LBO coating on the electrode surface does not affect the lithium insertion process of the electrode. There is a small reduction peak at 0.45 V for the m-Si half-cell sample in Comparative Example 1, which is the reduction reaction for SEI formation. No obvious reduction peak was observed in the m-Si-LBO half-cell sample prepared in Example 1, indicating that the LBO coating avoided direct contact between the electrode and the electrolyte and reduced the formation of SEI. Figure 8 (d) shows that the half-cell prepared in Example 1 contains two high-frequency regions. The first intermediate-frequency region generates impedance Rct due to charge exchange, and the other high-frequency region generates R due to inorganic piezoelectric protrusions on the surface of the silicon-based negative electrode. SEI That is, the half-cell obtained in Example 1 has a smaller resistance, that is, the inorganic piezoelectric coating reduces the battery impedance and improves the lithium-ion transport efficiency.

[0090] Figure 9 (a) is the comparison diagram of the cycling performance of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention. It can be seen that the m-Si-LBO obtained in Example 1 can be stably cycled 100 times at a current density of 6 A / g. -1 The capacity retention rate is as high as 98%. Figure 9 (b) is the comparison diagram of the rate performance of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention. It can be seen that when the current density is 1, 2, 4, 6, 8, 8, 10, 12 A / g, the discharge capacities of Example 1 are 2815, 2370, 1970, 1615, 1459, 1364, and 1270 mAh / g respectively. When the current density returns to 1 A / g, the capacity of Example 1 recovers to 2605 mAh / g, that is, the capacity recovery rate of the m-Si-LBO obtained in Example 1 is as high as 92.5%. After the material is coated with LBO, its cycling stability and rate performance are significantly improved. The introduction of LBO can provide additional lithium-ion transport channels, and the volume expansion of silicon particles can be effectively alleviated through the piezoelectric effect. At the same time, the piezoelectric field generated by the piezoelectric effect can improve ion transport and the rate performance of the battery.

[0091] Figure 10 (a) is the GITT test comparison diagram during the discharge process of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention; Figure 10 (b) is the GITT test comparison diagram during the charging process of the half-cells prepared in Example 1 and Comparative Example 1 of the present invention. Through the GITT test, it can be seen that for the half-cell with an inorganic piezoelectric coating containing LBO, the lithium-ion diffusion rate is significantly increased.

Claims

1. A composite silicon-based anode modified by the piezoelectric effect, characterized in that, The composite silicon-based anode includes a copper foil current collector, a negative electrode active layer scraped on the surface of the copper foil current collector, and an inorganic piezoelectric coating sprayed on the surface of the negative electrode active layer; the inorganic piezoelectric coating is formed by uniformly spraying a piezoelectric solution on the surface of the negative electrode active layer and drying it under high temperature conditions; the piezoelectric solution is composed of a piezoelectric ceramic material, a garnet-type material, a second binder, and a second organic solvent; the negative electrode active layer is composed of a silicon-based active material, a conductive agent, a first binder, and a first organic solvent.

2. The composite silicon-based negative electrode according to claim 1, wherein The piezoelectric ceramic material is any one or several of barium titanate, lithium tetraborate, lithium tantalate, sodium potassium niobate, and sodium bismuth titanate.

3. The silicon-based negative electrode according to claim 1, characterized in that, The garnet-type material is one or several of lithium lanthanum zirconium oxide and tantalum-doped lithium lanthanum zirconium oxide.

4. The composite silicon-based negative electrode according to claim 1, characterized in that, The silicon-based active material is any one of elemental silicon material, silicon-carbon material, and silicon-oxygen material.

5. A method for preparing a composite silicon-based anode according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1: Dissolve the silicon-based active material, the conductive agent, and the first binder in the first organic solvent in sequence, and stir evenly to obtain a negative electrode slurry. S2: Uniformly scrape the negative electrode slurry on the copper foil current collector, and put it into an oven for drying treatment to obtain a negative electrode active layer. S3: Dissolve a certain content ratio of the piezoelectric ceramic material, the garnet-type material, and the second binder in the second organic solvent in sequence to prepare a piezoelectric solution. S4: Uniformly spray the piezoelectric solution on the negative electrode active layer, put it into an oven for drying and perform rolling treatment to obtain an inorganic piezoelectric coating, thereby forming a composite silicon-based anode.

6. The preparation method of the composite silicon-based negative electrode according to claim 5, characterized in that, In step S1, the mass ratio of the silicon-based active material, the conductive agent, and the first binder is 1:(0.2 - 5.8):(0.1 - 0.3).

7. The preparation method of the composite silicon-based negative electrode according to claim 5, characterized in that, In step S3, the mass ratio of the piezoelectric ceramic material, the garnet-type material, and the second binder is (7 - 8):(1.5 - 2.5):(0.05 - 0.5).

8. The preparation method of the composite silicon-based negative electrode according to claim 5, characterized in that, In step S1, the conductive agent is any one or several of acetylene black, carbon nanotubes, graphene, and conductive carbon black; the first binder is any one or several of a lithiated polyacrylic acid binder, polyvinylidene fluoride, sodium alginate, carboxymethyl cellulose, and styrene-butadiene rubber; the first organic solvent includes any one of water, N,N-dimethylformamide, and N-methylpyrrolidone.

9. The preparation method of the composite silicon-based negative electrode according to claim 5, characterized in that, In step S3, the second binder is any one or several of polyvinylidene fluoride, sodium alginate, carboxymethyl cellulose, and styrene-butadiene rubber; in step S3, the second organic solvent is any one of styrene tetrahydrocarbon, N-methyl-2-pyrrolidone, and acetone.

10. Application of a composite silicon-based anode as described in any one of claims 1 - 4 in a lithium-ion battery or a supercapacitor.

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