A method for preparing a silicon thin film electrode

Abstract

The application belongs to the technical field of electrode materials, and particularly relates to a preparation method of a silicon thin film electrode. The application provides a preparation method of a silicon thin film electrode, which comprises the following steps: growing a silicon thin film on the surface of a copper foil substrate by magnetron sputtering to obtain the silicon thin film electrode; and the conditions for growing the silicon thin film by magnetron sputtering comprise: a power density of 1.3-3.9 W / cm 2 , a reverse time of 4-10 mu s, a frequency of 1-10 kHz, and a working pressure of ≤0.5 Pa and not zero. The silicon thin film electrode provided by the application can effectively improve the cycle performance of a lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and specifically relates to a method for preparing a silicon thin film electrode. Background Technology

[0002] Silicon thin-film electrodes possess high theoretical specific capacity (4200 mAh / g, greater than the theoretical specific capacity of graphite anodes 372 mAh / g) and low reaction potential (<0.2V vs. Li). + With advantages such as Li, it is a promising new generation of high-energy-density anode material.

[0003] However, during charge-discharge cycles, silicon thin-film electrodes undergo alloying reactions accompanied by significant volume expansion and stress damage, ultimately leading to a decrease in the cycle performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a silicon thin film electrode, which can effectively improve the cycle performance of lithium-ion batteries.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a silicon thin-film electrode, comprising the following steps:

[0007] A silicon thin film is grown by magnetron sputtering on a copper foil substrate to obtain the silicon thin film electrode.

[0008] The conditions for growing the silicon thin film by magnetron sputtering include: a power density of 1.3–3.9 W / cm². 2 The reverse time is 4–10 μs, the frequency is 1–10 kHz, and the working pressure is ≤0.5 Pa and not zero.

[0009] Preferably, the method for growing the silicon thin film by magnetron sputtering is radio frequency magnetron sputtering.

[0010] Preferably, the thickness of the silicon thin film is 20 to 1000 nm.

[0011] Preferably, the copper foil substrate has a thickness of 30 μm and a purity of 99.3%.

[0012] Preferably, before magnetron sputtering the silicon thin film, a transition copper layer is further grown on the surface of the copper foil substrate by magnetron sputtering.

[0013] Preferably, the thickness of the transition copper layer is 10–500 nm.

[0014] Preferably, the conditions for growing the transition copper layer by magnetron sputtering include: power of 50-120W and working pressure of 0.3-3Pa.

[0015] Preferably, the method for growing the transition copper layer by magnetron sputtering is DC magnetron sputtering.

[0016] This invention provides a method for fabricating a silicon thin-film electrode, comprising the following steps: growing a silicon thin film on a copper foil substrate by magnetron sputtering to obtain the silicon thin-film electrode; the conditions for magnetron sputtering growth of the silicon thin film include: a power density of 1.3–3.9 W / cm². 2 The reverse time is 4–10 μs, the frequency is 1–10 kHz, and the working pressure is ≤0.5 Pa and not zero. This invention, by controlling the growth gas pressure during silicon thin-film electrode deposition, results in a denser thin-film structure deposited under low-pressure conditions. This structure is also under compressive stress, which helps alleviate the volumetric strain introduced by lithium-ion intercalation, improving the structural stability of the electrode. Ultimately, the silicon thin-film electrode provided by this invention can effectively improve the cycle performance and lifespan of lithium-ion batteries. Attached Figure Description

[0017] Figure 1 SEM images of the silicon thin films obtained in Example 1 and Comparative Examples 1-4;

[0018] Figure 2 The images show the surface roughness, crystal structure, and residual stress of the silicon thin films obtained in Example 1 and Comparative Examples 1-4, where... Figure 2 (a) represents roughness. Figure 2 (b) is the XRD pattern. Figure 2 (c) shows the results of the residual stress test;

[0019] Figure 3 The CV curves of the batteries assembled from the silicon thin films obtained in Example 1 and Comparative Examples 1-4 are shown.

[0020] Figure 4 EIS spectra of the batteries assembled from the silicon thin films obtained in Example 1 and Comparative Examples 1-4;

[0021] Figure 5 The cycling performance curves are for the batteries assembled from the silicon thin films obtained in Example 1 and Comparative Examples 1-4. Detailed Implementation

[0022] This invention provides a method for preparing a silicon thin-film electrode, comprising the following steps:

[0023] A silicon thin film is grown by magnetron sputtering on a copper foil substrate to obtain the silicon thin film electrode.

[0024] The conditions for growing the silicon thin film by magnetron sputtering include: a power density of 1.3–3.9 W / cm². 2 The reverse time is 4–10 μs, the frequency is 1–10 kHz, and the working pressure is ≤0.5 Pa and not zero.

[0025] Unless otherwise specified, all raw materials used in this invention are commercially available products well known to those skilled in the art.

[0026] In this invention, the thickness of the copper foil substrate is preferably 30 μm, and the purity is preferably 99.3%.

[0027] Before magnetron sputtering the growth of the silicon thin film, the present invention preferably includes magnetron sputtering the growth of a transition copper layer on the surface of the copper foil substrate.

[0028] In this invention, the preferred conditions for the magnetron sputtering growth of the transition copper layer include: a power of 50–120 W and an operating pressure of 0.3–3 Pa; more preferably, the conditions include: a power of 80 W and an operating pressure of 0.5 Pa. In this invention, the target material used for the magnetron sputtering growth of the transition copper layer is preferably a copper target with a purity of 99.6%. In this invention, the magnetron sputtering growth of the transition copper layer is preferably performed in a pure argon atmosphere. In this invention, the preferred method for the magnetron sputtering growth of the transition copper layer is direct current magnetron sputtering.

[0029] In this invention, the thickness of the transition copper layer is preferably 10-500 nm, and more preferably 300 nm.

[0030] In this invention, the conditions for growing the silicon thin film by magnetron sputtering include: a power density of 1.3–3.9 W / cm². 2 The reverse time is 4–10 μs, the frequency is 1–10 kHz, and the working pressure is ≤0.5 Pa and not zero; further preferred features include a power density of 2.6 W / cm³. 2 The reverse time is 4 μs, the frequency is 5 kHz, and the working pressure is 0.3 Pa. In this invention, the target material used for the magnetron sputtering growth of the silicon thin film is preferably a silicon target with a purity of 99.5%. In this invention, the magnetron sputtering growth of the silicon thin film is preferably carried out in a pure argon atmosphere. In this invention, the method of magnetron sputtering growth of the silicon thin film is preferably radio frequency magnetron sputtering. This invention does not impose any special limitations on the process of magnetron sputtering growth of the silicon thin film; any process well known to those skilled in the art can be used.

[0031] In this invention, the thickness of the silicon thin film is preferably 20-1000 nm, and more preferably 300 nm.

[0032] To further illustrate the present invention, a method for preparing a silicon thin film electrode provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1

[0034] A 300 nm thick transition copper layer was grown on the surface of a copper foil substrate (30 μm thick, 99.3% pure) using DC magnetron sputtering. The growth conditions for the transition copper layer were: 80 W power, 0.5 Pa working pressure, pure argon atmosphere, and a copper target with 99.6% purity.

[0035] Then, a silicon thin film with a thickness of 300 nm was grown on the surface of the transition copper layer using radio frequency magnetron sputtering to obtain the silicon thin film electrode. The growth conditions for the silicon thin film were: power density of 2.6 W / cm². 2 The reverse time is 4 μs, the frequency is 5 kHz, the working pressure is 0.5 Pa, and a silicon target with a purity of 99.5% (denoted as 0.5 Pa) is used in a pure argon atmosphere.

[0036] Comparative Example 1

[0037] A silicon thin film electrode was prepared according to the method of Example 1, except that the growth pressure of the silicon thin film was 1.5 Pa (denoted as 1.5 Pa).

[0038] Comparative Example 2

[0039] A silicon thin film electrode was prepared according to the method of Example 1, except that the growth pressure of the silicon thin film was 3.0 Pa (denoted as 3.0 Pa).

[0040] Comparative Example 3

[0041] The silicon thin film electrode was prepared according to the method of Example 1, except that the growth working pressure of the silicon thin film was designed to be an increasing gas pressure, specifically, deposition and growth at 0.5 Pa for 10 min, deposition and growth at 1.0 Pa for 10 min, and deposition and growth at 3.0 Pa for 10 min (denoted as 0.5-1.0-3.0 Pa).

[0042] Comparative Example 4

[0043] The silicon thin film electrode was prepared according to the method of Example 1, except that the growth pressure of the silicon thin film was designed to be a decreasing pressure, specifically, deposition and growth at 3.0 Pa for 10 min, deposition and growth at 1.0 Pa for 10 min, and deposition and growth at 0.5 Pa for 10 min (denoted as 3.0-1.5-0.5 Pa).

[0044] Performance testing

[0045] Test Example 1

[0046] The silicon thin film electrodes obtained in Example 1 and Comparative Examples 1-4 were subjected to scanning electron microscopy (SEM) tests, and the test results are as follows: Figure 1 As shown, the left side consists of surface SEM images, and the right side consists of cross-sectional SEM images; from Figure 1 It can be seen that the silicon films deposited under different gas pressures have similar morphologies, with relatively smooth and continuous surfaces, free from obvious defects such as cracks and pores. However, some areas exhibit a granular morphology, which may be related to the amorphous structure of the films. In addition, by observing the cross-section of the same sample, the interface between the transition copper layer and the silicon film can be clearly distinguished, and it can be determined that the thicknesses of the two are approximately equal. Based on the overall thickness of 600 nm marked in the figure, it can be determined that the thickness of the silicon films deposited under different gas pressures is 300 nm.

[0047] Test Example 2

[0048] The surface roughness, crystal structure, and residual stress of the silicon thin film electrodes obtained in Example 1 and Comparative Examples 1-4 were tested.

[0049] AFM was used to characterize the roughness information of the silicon thin film, and the results are as follows: Figure 2 As shown in (a), it can be seen that the film roughness hardly changes with the working pressure, and the average roughness is close to (0.72±0.15) nm, which is consistent with... Figure 1 The surface morphology shown is consistent;

[0050] Figure 2 (b) shows the XRD pattern of the silicon thin film. The diffraction peaks at 2θ = 43.37°, 50.67°, and 74.68° correspond to Cu(111), Cu(200), and CuO(220), respectively, all originating from the transition copper layer. Furthermore, characteristic peaks appear in the diffraction angle range of 10°–30°, indicating that the silicon thin films deposited at room temperature are all in an amorphous state.

[0051] The residual stress of the silicon thin film was characterized using a profiler (P-7, KLATenco Inc.). The test method was as follows: during a single measurement, the scanning length was set to 32 mm, the scanning rate to 400 μm / s, the sampling frequency to 200 Hz, and the normal load to 2 mg. The residual stress was obtained by substituting the curvature information before and after coating into the Stoney formula (1).

[0052]

[0053] In the formula, σ is the film stress; E and v are the Young's modulus and Poisson's ratio of the substrate; h s h fThese represent the thicknesses of the substrate and the thin film, respectively; R0 and R correspond to the radii of curvature before and after coating, respectively.

[0054] The calculated stress results are as follows Figure 2 (c) and Table 1 are shown;

[0055] Table 1. Residual stress of silicon thin film electrodes obtained in Example 1 and Comparative Examples 1-4.

[0056] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Residual stress / MPa -157.2±1.2 118.6±3.4 110.7±2.7 93.6±1.2 -0.9±5.1

[0057] The results show that the silicon film deposited under low pressure (0.5 Pa) in Example 1 is under compressive stress, while the silicon films in Comparative Examples 1 to 3 are all under tensile stress. The silicon film deposited under decreasing pressure in Comparative Example 4 is under less stress and can be considered to be under stress-free conditions.

[0058] Test Example 3

[0059] The silicon thin film electrodes obtained in Example 1 and Comparative Examples 1-4 were assembled into "H"-type half-cells, and their electrochemical performance was tested.

[0060] Assembly process: A Ni mesh tightly wraps a Li metal sheet as the counter electrode and reference electrode, and a silicon thin film is used as the working electrode. Both electrodes are led out with Ni wire and sealed with rubber stoppers. Then, approximately 10 mL of electrolyte, a 1 mol / L LiClO4 mixed solution, is added to an "H"-shaped test tube. The electrolyte is a 1 mol / L LiClO4 mixed solution, with a 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) as the solvent. Battery assembly and testing are all conducted in a low-oxygen (<1 ppm) glove box.

[0061] Cyclic voltammetry (CV) curves were measured using an electrochemical workstation (650e, CHI). The scan range was selected as (0.001–2.0) V, and the scan rate was 0.1 mV / s. Then, the perturbation amplitude was set to 5 mV, and the frequency range was (10 Hz, ... -2 ~10 6 Electrochemical impedance spectroscopy (EIS) of the thin-film electrode before and after cycling was analyzed at 20 μA / cm². Constant current charge / discharge testing (CC; CT2001A, LAND) was performed. 2 The constant current density was maintained within the range of (0.01–1.5) V.

[0062] Figure 3 The CV curves are for the silicon thin film. To eliminate interference from the copper foil substrate and transition copper layer, samples without deposited silicon thin films were tested under the same conditions, such as... Figure 3As shown in (a), no reduction / oxidation peak signal was observed; the silicon thin film obtained in Example 1 has a significantly different CV curve shape compared to the film deposited under high pressure. The high-pressure deposited film only shows a pair of reduction / oxidation peaks at ~1.1V / 1.0V, while the sample of Example 1 shows... Figure 3 As shown in (d), during the initial discharge (alloying) process, the silicon thin film exhibits reduction peaks at three positions: 1.3V, 0.9V, and (0.3–0)V. The reduction peaks at 1.3V and 0.9V correspond to electrolyte decomposition and the formation of the SEI passivation layer, while the reduction peaks in the (0.3–0)V range correspond to the formation of lithium-poor phases LiSi and Li. 12 Si7 and reversible Li7Si3, Li 13 Si4 and Li 22 The Si5 alloy phase corresponds to the coexistence of two phases, resulting in a silicon film volume expansion of approximately 3–4 times. During the initial charge (dealloying) process, oxidation peaks appear sequentially at 0.46V, 0.31V, and 1.0V, corresponding to the dealloying reaction. Due to the low formation energy of the reversible alloy phase (approximately 1 eV), it readily undergoes dealloying to form amorphous Si, while LiSi and Li... 12 Si7 exhibits high formation energies (54.3 eV and 58.8 eV), making it difficult to decompose once formed. Subsequently, with increasing cycle count, the reduction peaks at 1.3 V and 0.9 V disappear, and the area enclosed by the curves decreases significantly, corresponding to a large irreversible capacity loss. Meanwhile, the reduction peak signal intensity in the (0.3–0) V range shows a decaying trend, corresponding to the formation of only reversible Li7Si3. 13 Si4 and Li 22 In the Si5 alloy phase, the oxidation peak at a high potential of 0.46V shifts to a low potential of 0.31V, indicating an increase in the thin film electrode impedance after the first cycle, but the oxidation peak at 1.0V remains almost unchanged.

[0063] Figure 4 The EIS spectra of silicon thin-film electrodes before and after four cycles are shown. The obtained curves consist of arcs in the high-frequency region and oblique lines in the low-frequency region. The arcs in the high-frequency region represent the interface transfer resistance, and the oblique lines in the low-frequency region represent the ion diffusion capability. It was found that for all Si thin films deposited under different pressures, the impedance spectra before cycling did not show arcs in the high-frequency region; however, after cycling, obvious arcs appeared in the high-frequency region. This indicates that the Si thin film structure is significantly damaged after the first cycle, with cracking and the formation of an SEI film at the interface. Consequently, the electrical contact of the electrode material decreases, and the impedance increases.

[0064] The test results are shown in Figure 2;

[0065] Table 2 shows the interface transfer impedance of the silicon thin film electrodes obtained in Example 1 and Comparative Examples 1-4.

[0066] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Interface transfer impedance / Ω 120 120 90 100 90

[0067] It can be seen that the low-pressure grown film has a larger internal resistance, possibly because the silicon film deposited at low pressure is more dense and has a larger ion transport impedance.

[0068] Figure 5 The constant current charge-discharge curves of the silicon thin-film electrode show that the silicon thin-film electrode obtained in Example 1 exhibits a distinct voltage plateau in its charge-discharge curve. This is significantly different from the linear decay curve corresponding to high-pressure deposited thin films, and is consistent with the variation pattern of the CV curves mentioned above. Figure 5 As shown in (d) and 5(e), the initial discharge curve linearly decreases from 1.3V to 0.3V. This process includes electrolyte decomposition and SEI film formation, inevitably consuming a large amount of Li. + This is one of the reasons for the initial irreversible capacity loss. Simultaneously, the initial discharge also forms lithium-depleted phases LiSi and Li. 12 Components such as Si7, due to their high formation energy (~50 eV), are difficult to decompose once formed, thus contributing to capacity loss. Subsequently, a near-horizontal discharge plateau appears in the (0.3–0) V range, corresponding to a series of alloying reactions; a longer plateau indicates stronger lithium storage capacity. Furthermore, during the initial discharge, the Si electrode contains two phases, namely amorphous Li... x Si alloys, and Li x Li forms abruptly from Si at the 0.5mV position. 15 In the Si4 crystalline phase, the alloy components have a larger unit volume, so the film volume expands and compressive stress is generated, causing irreversible damage to the film structure and resulting in poor electrical contact.

[0069] The test results are shown in Table 3.

[0070] Table 3. Electrochemical cycling performance of the silicon thin film electrodes obtained in Example 1 and Comparative Examples 1-4

[0071]

[0072] Therefore, the silicon thin film electrode obtained in Example 1 has excellent cycle performance.

[0073] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a silicon thin film electrode, characterized by, The steps are: A silicon thin film electrode is obtained by magnetron sputtering growth of a silicon thin film on the surface of a copper foil substrate; Before the magnetron sputtering growth of the silicon thin film, a transition copper layer is further grown on the surface of the copper foil substrate by magnetron sputtering; the thickness of the transition copper layer is 300 nm; The conditions for growing the silicon thin film by magnetron sputtering include: power density 2.6 W / cm 2 , reverse time 4 μs, frequency 5 kHz, and working pressure 0.5 Pa; The thickness of the silicon thin film is 300 nm.

2. The production method according to claim 1, characterized by, The method for magnetron sputtering growth of the silicon thin film is radio frequency magnetron sputtering.

3. The preparation method according to claim 1, characterized in that, The thickness of the copper foil substrate is 30 μm, and the purity is 99.3%.

4. The method of claim 1, wherein, The conditions for magnetron sputtering growth of the transition copper layer include a power of 50-120 W and a working pressure of 0.3-3 Pa.

5. The preparation method according to claim 4, characterized in that, The method for magnetron sputtering growth of the transition copper layer is direct current magnetron sputtering.

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