Method for in-situ regulation of preparation of silicon negative electrode composite SEI film based on electrochemical impedance spectroscopy

Abstract

This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy. The method includes the following steps: S1. Constructing a battery system by adding an electrochemically active organic precursor and film-forming additives to the electrolyte; S2. In-situ monitoring by performing in-situ electrochemical impedance spectroscopy (EIS) scanning on the battery to capture the SEI film growth dynamics in real time; S3. Feature identification by analyzing the EIS spectrum in real time to obtain the Ri... SEI Growth rate | ΔR SEI The inflection point or the point of stabilization at / △t| is the induction trigger point; S4. Dynamic induction: Apply a constant potential + high-frequency pulse electrochemical induction signal to perform dynamic induction; S5. Complete the first cycle of formation to obtain the composite SEI film. This application constructs a composite SEI film of an inorganic base layer and an organic flexible layer by combining real-time EIS monitoring and dynamic induction, effectively alleviating the problem of SEI film rupture, realizing the intelligent and controllable preparation of the composite SEI film, and improving the cycle life and consistency of silicon anode cells.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for preparing a silicon anode composite SEI film based on in-situ regulation of electrochemical impedance spectroscopy. Background Technology

[0002] Silicon-based anodes are considered a core material for next-generation lithium batteries due to their high specific capacity. However, the dramatic volume expansion (>300%) of silicon during cycling can cause repeated rupture of the SEI film. To address this issue, the industry often uses film-forming additives in the electrolyte, such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), or polymerizable monomers, in an attempt to construct a composite SEI film that combines rigidity and flexibility in situ.

[0003] However, existing battery formation processes suffer from serious "blindness":

[0004] 1. Lack of process awareness: Traditional formation processes are usually carried out according to a fixed "constant current-constant voltage" procedure, which makes it impossible to perceive the film formation state of the micro-interface inside the battery.

[0005] 2. Uncontrolled film formation timing: The reduction potentials of inorganic and organic components are different. If not properly controlled, organic monomers may polymerize before the inorganic layer forms, resulting in direct coverage of the silicon surface and hindering lithium-ion transport, or they may polymerize after the silicon particles have already expanded in volume, leading to film rupture.

[0006] 3. Poor consistency: Due to slight differences in raw materials and assembly, there are batch-to-batch and cell-to-cell differences in the film formation kinetics of different batteries, making it difficult to ensure the consistency of the film formation window by immobilization curves.

[0007] Therefore, there is an urgent need for an intelligent SEI construction method that can "see" the interface growth state in real time and dynamically adjust the formation path accordingly to precisely trigger the film formation reaction. Summary of the Invention

[0008] This invention provides a method for preparing a silicon anode composite SEI film based on in-situ regulation of electrochemical impedance spectroscopy, which solves the problems of traditional formation processes being unable to sense the microscopic interface state and difficult to control the film formation timing. It realizes the intelligent and controllable preparation of composite SEI films, significantly reduces interface impedance, and improves the cycle life and consistency of silicon anode batteries.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy includes the following steps:

[0011] S1. Constructing a battery system: Assemble a lithium-ion battery containing a silicon anode, and add a certain amount of electrochemically active organic precursor and film-forming additive to the electrolyte of the battery.

[0012] S2. In-situ monitoring: The constructed battery is subjected to the first round of low-current formation, and at the same time, the battery is scanned in-situ by electrochemical impedance spectroscopy (EIS) at preset time intervals or capacity intervals to capture the growth dynamics of the SEI film in real time.

[0013] S3. Feature Recognition: Real-time analysis of EIS spectra to extract high-frequency impedance values ​​R, representing the ion transport impedance of the SEI membrane. SEI and its corresponding characteristic frequency f char and monitor R SEI growth rate | △R SEI / △t| The moment when the inflection point or the point of stabilization appears is the trigger point for induction;

[0014] S4. Dynamic induction: Apply a combination of electrochemical induction signal consisting of constant potential and high-frequency pulse to perform dynamic induction;

[0015] S5. Complete the first formation cycle to obtain the composite SEI membrane.

[0016] It should be noted that in step S1, the organic precursor can undergo electrochemical reduction polymerization or cross-linking at an appropriate potential to construct a flexible network, while the film-forming additive preferentially decomposes at higher potentials to form an SEI bottom layer rich in inorganic components. Step S2 involves applying small-signal AC perturbations to the battery at preset time intervals or capacity intervals, and collecting EIS data in situ from high frequency to low frequency.

[0017] Preferably, in step S1, the total mass fraction of the organic precursor and the film-forming additive is 2 to 10 wt% of the total mass of the electrolyte.

[0018] Preferably, the organic precursor is selected from polymerizable monomers containing acrylate, vinyl, epoxy or cyano groups, and more preferably, it is selected from at least one of methyl methacrylate (MMA), polyethylene glycol diacrylate (PEGDA), 1,3-dioxane (DOL) or acrylonitrile (AN).

[0019] Preferably, the film-forming additive is a mixture of fluoroethylene carbonate (FEC) and / or lithium difluorophosphate (LiDFP), more preferably a mixture of FEC and LiDFP, and more preferably, the mass ratio is 10:1.

[0020] It should be noted that: FEC preferentially decomposes at higher potentials to generate an inorganic SEI bottom layer rich in LiF and organic carbonates; PEGDA undergoes electrochemical reduction polymerization at lower potentials to form a flexible network; and LiDFP is conducive to further generating LiF and phosphorus-containing inorganic substances, forming a dense interface rich in LiF, improving SEI stability, and can also be used as a substrate.

[0021] Preferably, the small current in step S2 is 0.01C to 0.05C, and more preferably 0.02C to 0.05C.

[0022] Preferably, in step S4, R SEI The specific criteria for judging whether the growth rate reaches an inflection point or tends to stabilize are: within the voltage range of 1.5V to 0.5V corresponding to the equivalent potential of the silicon anode relative to Li / Li+, the R value sampled several times consecutively... SEI Rate of change | ΔR SEI / △t|≤0.5mΩ / min, preferably three consecutive samples; this indicates that the inorganic base layer has been completely covered and the silicon-based anode is in a low lithium intercalation potential >0.2V, which is the induction time for introducing the organic flexible layer.

[0023] Preferably, the electrochemically induced signal in step S3 is a combination of potentiostatic polarization and high-frequency pulses, specifically:

[0024] (1) The negative electrode potential of the battery is clamped within the reduction polymerization potential window of the organic precursor, ranging from 0.4V to 0.9V vs. Li / Li. + ;

[0025] (2) A superimposed pulse voltage with a frequency of 10Hz to 1kHz and an amplitude of 10 to 100mV;

[0026] (3) The duration of applying the electrochemical induction signal is 1 to 5 hours, and the pulsed electric field is used to promote the penetration and polymerization of organic precursors into the pores of the inorganic layer.

[0027] It is important to note that the system switches to a constant potential mode within the region corresponding to a negative electrode potential of 0.4–0.9V (vs. Li / Li+), and superimposed high-frequency pulses of 10Hz–1kHz and 10–100mV are applied. The pulsed electric field promotes the penetration of organic precursors into the pores of the inorganic SEI layer, and simultaneously induces their in-situ polymerization or cross-linking on the silicon surface and within the inorganic layer through electrochemical reduction, forming a flexible organic network that penetrates the inorganic layer, thus achieving a composite SEI structure that combines rigidity and flexibility.

[0028] Preferably, the lithium-ion battery containing a silicon negative electrode in step S1 further includes: a positive electrode, a negative electrode, and a separator.

[0029] Preferably, the cathode is a nickel-cobalt-manganese ternary cathode material LiNi. 0.8 Co 0.1 Mn 0.1 O2;

[0030] The negative electrode is a silicon-carbon composite material, wherein the Si / C specific capacity is 450 mAh / g;

[0031] The diaphragm is a composite diaphragm of polypropylene (PP) and polyethylene (PE).

[0032] Preferably, the electrolyte in step S1 further includes a solvent and a lithium salt, wherein:

[0033] The solvent is ethylene carbonate EC, ethyl methyl carbonate EMC, and diethyl carbonate DEC;

[0034] The lithium salt is lithium hexafluorophosphate (LiPF6);

[0035] Preferably, the volume ratio of the solvent ethylene carbonate EC: ethyl methyl carbonate EMC: diethyl carbonate DEC is 3:5:2.

[0036] Preferably, the lithium salt concentration is 0.6-1.2M, and more preferably 1.0M.

[0037] Compared with existing technologies, this application achieves precise and controllable dynamic observation of the SEI membrane preparation process through a four-step closed-loop process of "construction-monitoring-identification-induction". The beneficial effects of this invention are:

[0038] (1) Achieve visualization and adaptive control of the SEI growth process: Real-time monitoring of R through EIS SEI with f char For the first time, the "SEI growth kinetic fingerprint" was used as a feedback variable in the formation process, realizing a shift from "fixing the curve" to "observing the interface and adjusting the curve" in closed-loop control.

[0039] (2) Precisely locate the flexible layer implantation window: using R SEI The growth rate inflection point identifies the time window when the inorganic bottom layer is "basically formed," while constraining the silicon anode to remain in a low lithium intercalation state, thus preventing the organic layer from polymerizing too early and blocking ion channels or polymerizing too late and cracking along with silicon expansion.

[0040] (3) Constructing a rigid-flexible composite SEI membrane: First, an inorganic-rich, high-rigidity base layer is constructed by film-forming additives. Then, organic precursors are induced to permeate along the pores and polymerize to form a flexible network through constant potential and high-frequency pulse, thereby realizing a "hard outer shell - soft inner phase" mechanical gradient and improving the interface stress resistance.

[0041] (4) Improve cell consistency: Since the conditions for triggering film formation are based on the EIS fingerprint of each cell rather than a uniform time / capacity formulation, it can adaptively absorb differences in materials, assembly and environment, significantly improving batch consistency.

[0042] By combining real-time EIS monitoring with dynamic induction, the bottleneck of "blind control" in traditional SEI film preparation is broken, achieving precise matching of film structure and performance. At the same time, the synergistic construction of inorganic base layer and organic flexible layer can effectively alleviate the SEI film rupture problem caused by silicon anode volume expansion, realizing intelligent and controllable preparation of composite SEI film, significantly reducing interface impedance, and improving the cycle life and consistency of silicon anode battery. Attached Figure Description

[0043] Figure 1 : Process flow diagram of an embodiment of the present invention.

[0044] Figure 2 The equivalent potential curve of the negative electrode during the formation process in this embodiment of the invention and the in-situ R SEI A schematic diagram illustrating the relationship between the evolution curves.

[0045] Figure 3 Comparison chart of the cycle capacity retention rate of the batteries in the embodiments of the present invention and Comparative Examples 1-3 at a rate of 0.5C.

[0046] Figure 4 Comparison of the AC impedance spectra (Nyquist plots) of the cells after formation of the embodiments of the present invention and Comparative Examples 1-3. Detailed Implementation

[0047] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0048] Example

[0049] The entire closed-loop formation process of SEI membrane preparation in the embodiments of this application, namely "monitoring-feedback-control", is as follows: Figure 1 As shown. The specific implementation steps are as follows:

[0050] S1. The constructed battery system is a 1Ah pouch-pack stacked battery (nominal capacity). Specifically:

[0051] Cathode: LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811);

[0052] Anode: Silicon-carbon composite material, wherein the Si / C specific capacity is 450 mAh / g;

[0053] Separator: PP and PE composite separator.

[0054] Functional electrolyte: Solvent: EC: EMC: DEC volume ratio is 3:5:2;

[0055] Lithium salt: 1.0M LiPF6;

[0056] Film-forming additives: 5.0 wt% fluoroethylene carbonate (FEC), lithium difluorophosphate

[0057] The content of LiDFP is 0.5 wt%.

[0058] Organic precursor: 3.0 wt% polyethylene glycol diacrylate (PEGDA).

[0059] Mw = 250;

[0060] Among them, FEC preferentially decomposes at higher potentials to generate LiF-rich inorganic SEI layers, PEGDA undergoes electrochemical reduction polymerization at lower potentials to form a flexible network, and LiDFP is conducive to further generating LiF and phosphorus-containing inorganic substances, thereby improving SEI stability.

[0061] Test equipment: A high-precision charge and discharge test system equipped with EIS function, such as a battery test cabinet with a frequency response analysis module, which can realize small signal impedance testing in the frequency range of 100kHz to 0.1Hz.

[0062] S2. In-situ monitoring (intelligent closed-loop formation based on EIS fingerprint), the specific steps are as follows:

[0063] a. Immersion and Pretreatment

[0064] After electrolyte injection, the battery is left to stand at 45°C for 24 hours to ensure that the electrolyte fully wets the electrodes and separator.

[0065] b. Initial constant current stage and in-situ monitoring

[0066] During the first cycle of formation, the battery was charged with a constant current of 0.02C, and the constant current was stopped every 5 minutes to apply a small signal AC disturbance to the battery. The test frequency range was 100kHz to 0.1Hz EIS.

[0067] Based on the "full cell voltage – negative electrode equivalent potential" mapping relationship established in advance through three-electrode calibration or model fitting, the current full cell voltage is converted into the equivalent potential of the silicon negative electrode relative to Li / Li+, and it is determined whether it is in the equivalent potential window of 1.5V to 0.5V.

[0068] By fitting high-frequency semicircles, the R value of each EIS is obtained. SEI and corresponding characteristic frequency f char And record R SEIThe curve of evolution over time.

[0069] S3. Feature Recognition (TriggerPoint)

[0070] In the early stages of formation, from the open-circuit state to the equivalent potential of approximately 1.5V at the corresponding negative electrode, R SEI It is almost zero, and the high-frequency region in the EIS plot is almost a straight line.

[0071] Subsequently, R SEI The value of [value] underwent an evolution from low to high and then tended to stabilize. Specifically:

[0072] When the negative electrode potential is >1.5V, since no interface film has yet formed on the silicon negative electrode surface, the electrochemical impedance spectroscopy (EIS) in the high-frequency region exhibits extremely small impedance characteristics, and the fitted R... SEI The value is only about 5mΩ, which mainly represents the ohmic contact resistance of the system;

[0073] As the negative electrode potential decreases to the 1.5V–0.8V range, film-forming additives (such as FEC) in the electrolyte preferentially undergo electrochemical reduction and decomposition. The resulting LiF-rich inorganic products deposit on the silicon particle surface, rapidly constructing an ion transport barrier. This leads to a significant increase in the semi-circular feature in the high-frequency region of the EIS spectrum, and R... SEI The value then rapidly increased from 5mΩ;

[0074] When R SEI When it grows to approximately 35 mΩ, its growth rate (|ΔR) SEI The value of / △t|) shows a clear inflection point and tends to level off. This numerical change indicates that the inorganic decomposition products have completed a dense coverage of the silicon anode surface at the microscopic level, forming a stable inorganic base layer. This is the optimal time to introduce an organic flexible layer.

[0075] When the equivalent potential of the negative electrode further drops to near the full cell voltage of approximately 0.75V, R is detected. SEI The growth rate has slowed significantly, and the |△R| of three consecutive samples has decreased. SEI |≈0.2mΩ / 5min, corresponding to |△R SEI / △t|≈0.04mΩ / min. Meanwhile, the silicon anode potential is still above 0.2V (vs.Li / Li+), and has not yet entered the large-scale lithium intercalation expansion stage.

[0076] Therefore, this moment is designated as the "induction trigger point," such as Figure 2 As shown in the image.

[0077] S4. Dynamic Electrochemical Induction (Action)

[0078] Once a trigger point that meets the above conditions is detected, the system will automatically perform the following operations:

[0079] 1) Immediately interrupt the 0.02C constant current charging mode;

[0080] 2) Switch to constant potential mode to fix the equivalent potential of the negative electrode at about 0.7V (vs. Li / Li+), and the corresponding full cell voltage is controlled by the mapping relationship;

[0081] 3) Superimpose a square wave pulse with a frequency of 500Hz and an amplitude of 50mV onto a constant potential.

[0082] A constant potential combined with a high-frequency pulse was continuously applied for 3 hours. During this period, polyethylene glycol diacrylate (PEGDA) underwent electrochemical reduction polymerization within this potential window. The pulsed electric field promoted the migration of PEGDA monomers into the pores of the inorganic SEI layer and crosslinked them on the silicon surface and inside the inorganic layer, constructing a continuous flexible network that interpenetrates with the LiF-rich inorganic layer to form a rigid-flexible composite SEI film.

[0083] S5. Complete transformation

[0084] After the induction phase, the charge was switched back to 0.1C constant current charging until the upper limit voltage of 4.2V was reached, completing the first formation cycle and yielding a low-impedance composite SEI film. This film was then used for capacity retention and impedance evaluation in subsequent cycles at a 0.5C rate.

[0085] To verify the effectiveness of the method of the present invention, the following comparative examples were designed. Except for the different formation strategies, the other material systems, electrolyte formulations and test conditions were the same as those in the examples.

[0086] Comparative Example 1 (Traditional Constant Current Formation):

[0087] No EIS in-situ monitoring was performed, nor were constant potential or high-frequency pulse induction applied. During the first formation cycle, the cells were charged to the specified termination conditions using a conventional 0.02C constant current-constant voltage procedure. The resulting cell is designated as Comparative Example 1.

[0088] Comparative Example 2 (Premature Induction of Interference with Inorganic Layer):

[0089] When the negative electrode equivalent potential just enters the region before FEC decomposition (approximately 1.8V), a constant potential + high-frequency pulse induction signal, the same as in the example, is forcibly applied to induce PEGDA polymerization before the inorganic SEI layer has formed. The resulting cell is designated as Comparative Example 2.

[0090] Comparative Example 3 (Induction Too Late - Repair After Deep Lithium Intercalation in Silicon):

[0091] After the equivalent potential of the silicon anode had dropped to approximately 0.1V (indicating deep lithium intercalation and significant volume expansion), the same constant potential + high-frequency pulse induction signal as in the example was applied. The resulting battery is designated as Comparative Example 3.

[0092] Performance testing:

[0093] The following tests were performed on the batteries of the embodiments and comparative examples, and the test results are shown in Table 1:

[0094] (1) After formation, EIS was tested under the same conditions, and the charge transfer resistance Rct was obtained by fitting.

[0095] (2) Perform 200 cycles at a 0.5C rate and record the capacity retention rate;

[0096] (3) Statistical analysis of R for different battery cells SEI Variance characterizes the uniformity of the SEI film;

[0097] (4) Measure the coulomb efficiency of the first cycle.

[0098] Table 1 Performance Test Results

[0099]

[0100] Conclusion Analysis:

[0101] Figure 3 This is a comparison chart of the cycle capacity retention rates of the batteries in the Example and Comparative Examples 1-3 at a 0.5C rate. Figure 4 This section compares the post-formation AC impedance spectra (Nyquist plots) of the cells in the examples and comparative examples 1-3. From... Figure 3 Comparison curves of cycling performance between the examples and comparative examples. Figure 4 The following can be seen from the comparison curves of the transformed Nyquist plot:

[0102] Compared with Comparative Example 1, the Rct of Example 1 decreased from 35.8 mΩ to 22.5 mΩ, a reduction of more than 20%; the capacity retention rate of Example 1 after 200 cycles was 93.5%, which is about 12.5 percentage points higher than that of Comparative Example 1 (81.0%).

[0103] Compared with Comparative Example 2, in Comparative Example 2, due to the induction of PEGDA polymerization before the formation of the inorganic SEI base layer, the polymer blocked the ion channels, the Rct was as high as 156.0 mΩ, and the cycling capacity decayed rapidly.

[0104] Compared to Comparative Example 3, in Comparative Example 3, the flexible layer was formed only after the silicon particles had expanded significantly. The SEI was damaged before being repaired, making it difficult for the interface to remain stable in the long term. The cycle performance was between that of the Example and Comparative Example 1.

[0105] In summary, the cycle performance comparison between the examples and the comparative examples shows that the examples are superior to Comparative Example 3, which is superior to Comparative Example 1, which is superior to Comparative Example 2. Regarding charge transfer resistance (Rct), the examples are superior to Comparative Example 1, which is superior to Comparative Example 3, which is superior to Comparative Example 2. Regarding SEI film uniformity, the examples are superior to Comparative Example 1, which is superior to Comparative Example 3, which is superior to Comparative Example 2. In conclusion, premature induced failure has the most significant impact on battery performance. Analyzing the failure mechanism, the SEI film of the examples has a rigid-flexible interpenetrating structure, exhibiting low impedance and resistance to expansion. The SEI film of Comparative Example 1 has an uneven distribution of the organic layer and insufficient pore filling. The SEI film of Comparative Example 3 shows initial damage followed by repair, resulting in an unstable interface. The worst performing SEI film in Comparative Example 2 exhibits polymer blockage of ion channels and severe polarization.

[0106] The overall results show that this invention, by identifying the film formation state of the inorganic SEI substrate through EIS fingerprinting and triggering organic layer polymerization within the optimal window before lithium intercalation expansion of the silicon anode, can construct a rigid-flexible composite SEI film with low impedance and good uniformity. This significantly reduces interface impedance and improves the cycle life and consistency of silicon anode batteries. Compared to the traditional constant current formation process without EIS control, the method of this invention reduces the charge transfer resistance Rct after formation by at least 20% and improves the capacity retention rate after 200 cycles at 0.5C by at least 10%.

[0107] The above description is merely an example of the embodiments of this application. It should be noted that, for those skilled in the art, various equivalent substitutions or modifications can be made to this invention without departing from the spirit and essence of this invention, and such equivalent substitutions or modifications should all fall within the protection scope of the claims of this invention.

Claims

1. A method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy, characterized in that: Includes the following steps: S1. Constructing a battery system: Assemble a lithium-ion battery containing a silicon anode, and add an electrochemically active organic precursor and a film-forming additive to the electrolyte of the battery; S2. In-situ monitoring: The constructed battery is subjected to the first round of low-current formation, the low current being 0.01C~0.1C. At the same time, the battery is scanned in-situ by electrochemical impedance spectroscopy (EIS) at preset time intervals or capacity intervals to capture the growth dynamics of the SEI film in real time. S3. Feature Recognition: Real-time analysis of EIS spectra to extract high-frequency impedance values ​​R, representing the ion transport impedance of the SEI membrane. SEI and its corresponding characteristic frequency f char and monitor R SEI growth rate | △R SEI / △t| The moment when the inflection point or the point of stabilization appears is the trigger point for induction, and R is the trigger point. SEI The criterion for determining when the growth rate reaches an inflection point or tends to stabilize is: within the voltage range of 1.5V to 0.5V corresponding to the equivalent potential of the silicon anode relative to Li / Li+, the R value is continuously sampled several times. SEI Rate of change | ΔR SEI / △t|≤0.5mΩ / min; S4. Dynamic induction: Apply a combination of electrochemical induction signal consisting of constant potential and high-frequency pulse to perform dynamic induction; S5. Complete the first formation cycle to obtain the composite SEI membrane.

2. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 1, characterized in that, In step S1, the total mass fraction of the organic precursor and film-forming additive is 2-10 wt% of the total mass of the electrolyte.

3. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 2, characterized in that, The organic precursor is selected from polymerizable monomers containing at least one functional group selected from acrylate, vinyl, epoxy, or cyano groups. The film-forming additive is one or both of fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiDFP).

4. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 3, characterized in that, The organic precursor is selected from at least one of methyl methacrylate (MMA), polyethylene glycol diacrylate (PEGDA), 1,3-dioxolane (DOL), or acrylonitrile (AN). The film-forming additive is a mixture of FEC and LiDFP, with a mass ratio of FEC to LiDFP of 10:

1.

5. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 1, characterized in that, In step S2, the small current is 0.02C~0.05C.

6. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 1, characterized in that, In step S3, three consecutive samples are taken within the voltage range of 1.5V to 0.5V corresponding to the equivalent potential of the silicon anode relative to Li / Li+. At this time, the inorganic base layer has been completely covered, and the silicon-based anode is in a low lithium intercalation state with a potential >0.2V, which is the induction time for introducing the organic flexible layer.

7. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 1, characterized in that: In step S4, the electrochemically induced signal is a combination of constant potential and high-frequency pulse, specifically: (1) The negative electrode potential of the battery is clamped within the reduction polymerization potential window of the organic precursor, ranging from 0.4V to 0.9V vs. Li / Li + ; (2) A superimposed pulse voltage with a frequency of 10Hz to 1kHz and an amplitude of 10 to 100mV; (3) The duration of applying the electrochemical induction signal is 1 to 5 hours, and the pulsed electric field is used to promote the penetration and polymerization of organic precursors into the pores of the inorganic layer.

8. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 1, characterized in that: The lithium-ion battery containing a silicon negative electrode in step S1 includes: a positive electrode, a negative electrode, and a separator, wherein: The cathode is a nickel-cobalt-manganese ternary cathode material, LiNi. 0.8 Co 0.1 Mn 0.1 O2; The negative electrode is a silicon-carbon composite material, wherein the Si / C specific capacity is 450 mAh / g; The diaphragm is a composite diaphragm of polypropylene (PP) and polyethylene (PE).

9. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 1, characterized in that, The electrolyte in step S1 further includes a solvent and a lithium salt, wherein: The solvent is ethylene carbonate EC, ethyl methyl carbonate EMC, and diethyl carbonate DEC; The lithium salt is lithium hexafluorophosphate (LiPF6).

10. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 9, characterized in that: The volume ratio of ethylene carbonate EC: ethyl methyl carbonate EMC: diethyl carbonate DEC is 3:5:

2.

11. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 9, characterized in that: The lithium salt concentration is 0.6-1.2M.

12. The method for preparing a silicon anode composite SEI film based on in-situ regulation using electrochemical impedance spectroscopy according to claim 11, characterized in that: The lithium salt concentration is 1.0M.

Images