A porous conductive film negative current collector with in-hole enrichment type artificial SEI and a preparation method thereof

Abstract

The present application relates to the technical field of electrode material, and particularly relates to a porous conductive film negative electrode current collector with in-hole enrichment type artificial SEI and a preparation method thereof. The current collector comprises a porous high polymer conductive film, a first composite layer formed on the inner wall of the pores of the porous high polymer conductive film, and a second composite layer formed on the surface of the porous high polymer conductive film, wherein the first composite layer comprises Li3N and LiF, and the second composite layer comprises Li2CO3, ROCO2Li and Li2O. In the present application, the physical buffer space is provided by the porous high polymer skeleton, the lithium ions are uniformly deposited in the holes by LiF / Li3N, and the surface flexible layer is encapsulated, so that the battery volume expansion can be effectively inhibited; at the same time, the pre-prepared artificial SEI inside and outside the holes can effectively improve the initial efficiency.

Description

Technical Field

[0001] This invention relates to the field of electrode material technology, and in particular to a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI and its preparation method. Background Technology

[0002] With the development of technology, people's requirements for battery energy density are constantly increasing. Lithium-ion batteries, currently the mainstream power storage system for electric vehicles and smart grids, can no longer meet the development needs of emerging technologies. Lithium metal, due to its high theoretical specific capacity (3860 mAh / g) and low redox potential (-3.04V vs. standard hydrogen electrode), has become one of the key materials for improving battery energy density. However, lithium metal anodes have many problems. Existing lithium metal anodes generate a large number of lithium dendrites during charge and discharge. As the operating time increases, these lithium dendrites continue to grow and penetrate the separator, causing safety issues. Simultaneously, the repeated lithium insertion / extraction process of lithium metal anodes forms a large number of "dead lithium" deposits. These "dead lithium" deposits cause unlimited volume expansion of the electrode, leading to low battery coulombic efficiency and reduced cycle life.

[0003] To address these issues, researchers have explored various methods, such as optimizing electrolytes, designing artificial solid electrolyte interphase (SEI) films, using solid electrolytes, and introducing three-dimensional current collectors. Among these, three-dimensional current collectors, due to their high specific surface area, can effectively reduce local current density, thus helping to improve lithium dendrite growth. However, these methods still have some drawbacks, such as complex processes, high costs, and susceptibility to delamination. Therefore, developing a novel lithium metal anode material that can improve battery energy density while effectively addressing issues such as dendrite growth, volume expansion, and cycle life has become a key focus and challenge in current research.

[0004] Patent document CN115810720A discloses a composite anode for lithium secondary battery packs and its manufacturing method. The method includes: preparing an electrolyte containing lithium salt and solvent; arranging a working electrode and a counter electrode in the electrolyte, wherein the working electrode contains a porous conductor and the counter electrode contains lithium metal; and applying a voltage or current through a power source connected to the working electrode and the counter electrode to perform pulse electrodeposition of the lithium metal on the porous conductor; wherein the porous conductor includes one or more selected from carbon nanotubes, carbon felt, carbon paper, and carbon fibers. In this prior art, firstly, the porous conductor used is a carbon material, which reacts with Li ions during charge and discharge to form an SEI film, reducing initial efficiency; secondly, the deposition of lithium metal on the porous conductor only suppresses the formation of lithium dendrites, and lithium deposition and dissolution still occur on the surface during charge and discharge, resulting in battery volume expansion. Summary of the Invention

[0005] The present invention aims to solve the above-mentioned problems by providing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI that has high initial efficiency and can solve the problem of battery volume expansion, as well as its preparation method.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is, firstly, to provide a porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI, comprising a porous polymer conductive film, a first composite layer formed on the inner wall of the pores of the porous polymer conductive film, and a second composite layer formed on the surface of the porous polymer conductive film, wherein the first composite layer comprises Li3N and LiF, and the second composite layer comprises Li2CO3, ROCO2Li, and Li2O.

[0007] In this invention, a porous polymer framework provides a physical buffer space, LiF / Li3N induces uniform deposition of lithium ions within the pores, and a flexible surface layer encapsulates the components, effectively suppressing lithium metal expansion to inhibit battery volume expansion. Simultaneously, the pre-fabricated artificial SEI inside and outside the pores prevents direct contact between the electrolyte and highly reactive carbon materials or subsequently deposited lithium, thus avoiding side reactions. The ion conductivity of LiF / Li3N ensures efficient lithium transport and reversible deposition / stripping, thereby effectively improving initial efficiency.

[0008] Preferably, the thickness of the first composite layer is 50–200 nm, and the thickness of the second composite layer is no more than 100 nm. The first composite layer provides ion conduction and electron blocking functions, with an appropriate thickness to control the growth of lithium metal within the pores without affecting lithium ion conduction; the second composite layer provides encapsulation and guiding functions, with an appropriate thickness for flexible encapsulation and to induce lithium ions to enter the pores to avoid accumulation on the surface.

[0009] Preferably, the porous polymer conductive film is selected from at least one of porous PP conductive film and porous PE conductive film. The polymer film will not react with Li during charging and discharging. + The reaction forms an SEI film, reducing the first-efficiency effect.

[0010] Preferably, the porous polymer conductive film has an in-plane conductivity of 1×10⁻⁶. 4 ~1.5×10 4 S / cm, anisotropy ratio greater than 8. Improves the conductivity of the conductive film, provides a conductive network with low interfacial resistance, and synergistically enhances the interfacial stability of the electrode / electrolyte with artificial SEI.

[0011] As a preferred embodiment of the present invention, the porous polymer conductive film has a thickness of 5–50 μm and a porosity of 30%–80%. This ensures that lithium deposition / dissolution mainly occurs within the pores, avoiding surface accumulation; and provides sufficient volumetric buffer space for lithium metal insertion and extraction; thereby mitigating battery expansion, structural damage, and interface separation caused by drastic volume changes during cycling in traditional lithium anodes. For example, the thickness can be 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm; and the porosity can be 30%, 40%, 50%, 60%, 70%, or 80%.

[0012] Secondly, another objective of this invention is to provide a method for preparing the porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI, comprising the following steps:

[0013] The porous polymer conductive film is used to form the first and second composite layers in situ in an electrolyte using pulsed electrodeposition technology; the electrolyte includes LiTFSI, LiNH2, and carbonate; in the pulsed electrodeposition technology, the peak current is 3–8 mA / cm². 2 .

[0014] This invention utilizes pulsed current, pore structure and the resulting local electric field enhancement effect, and the Li-induced limited electrolyte diffusion. + Concentration gradients create different composite layers inside and outside the pores. Inside the pores: high local current density and limited space favor the formation of products with more negative reduction potentials, resulting in a first composite layer dominated by Li3N and LiF. Under pulsed current, Li... + Highly enriched, F - With N - The source preferentially reduces to form LiF and Li3N, exhibiting high ionic conductivity, high mechanical strength, and excellent interfacial stability. Outside the pores, the relatively uniform electric field and electrolyte environment favor the formation of conventional SEI components, resulting in a second composite layer dominated by traditional SEI components such as Li2CO3, ROCO2Li, and Li2O. It undergoes a common reduction reaction, with TFSI... - It mainly decomposes, producing an organic / inorganic mixture, with moderate ionic conductivity, weak mechanical strength, and average interfacial stability.

[0015] In porous structures, the pore walls have sharp geometric edges and high curvature surfaces, leading to electric field concentration under the influence of an electric field. Driven by this electric field, Li⁺ migrates towards the negative electrode, creating a region with significantly enhanced local electric field strength within the high-curvature area of ​​the pores. This enhanced electric field preferentially attracts and accelerates Li⁺ accumulation towards the pore wall region, resulting in a higher Li⁺ flux at the pore wall and promoting the preferential nucleation and growth of Li₃N / LiF. Simultaneously, the porous structure exhibits a spatial confinement effect on electrolyte diffusion. Especially at high current densities, electrolyte transport into the pores is restricted, leading to rapid Li⁺ consumption within the channels, while external electrolyte replenishment lags behind. This results in a local Li⁺ concentration gradient within the pores (the Li⁺ concentration inside the pores is lower than outside). This concentration gradient drives continuous Li⁺ diffusion from outside to inside the pores, creating a self-sustaining Li⁺ enrichment environment. The thickness of the first composite layer is 50–200 nm, and the thickness of the second composite layer does not exceed 100 nm.

[0016] In pulsed electrodeposition, the porous polymer conductive film is used as the working electrode, and the counter electrode can be an inert electrode or a lithium electrode. Preferably, lithium is used as both the counter electrode and the reference electrode. Furthermore, since this invention aims to form a Li3N / LiF composite layer in situ rather than depositing a lithium metal layer, the peak current is 3–8 mA / cm². 2 The pulsed current can suppress hydrogen evolution side reactions and promote preferential nucleation of Li3N / LiF. For example, the current can be 3 mA / cm². 2 4 mA / cm 2 5 mA / cm 2 6 mA / cm 2 7 mA / cm 2 8 mA / cm 2 Excessive current density can lead to rapid nucleation on the surface, disrupting the enrichment structure within the pores.

[0017] As a preferred embodiment of the present invention, the electrolyte is obtained through the following steps: dissolving LiNH2 in DMSO to prepare a precursor solution, and preparing the precursor solution with LiTFSI and carbonate to prepare an electrolyte; the concentration of LiNH2 in the electrolyte is 0.2–0.3 M, and the concentration of LiTFSI in the electrolyte is 0.8–1.2 M. For example, the concentration of LiNH2 can be 0.2 M, 0.21 M, 0.22 M, 0.23 M, 0.24 M, 0.25 M, 0.26 M, 0.27 M, 0.28 M, 0.29 M, or 0.3 M; and the concentration of LiTFSI can be 0.8 M, 0.9 M, 1 M, 1.1 M, or 1.2 M.

[0018] Preferably, the concentration of LiNH2 in the precursor solution is 8 wt% to 12 wt%, for example, it can be 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%.

[0019] The concentration of the precursor solution in the electrolyte is 4 to 6 vol%, for example, it can be 4 vol%, 4.5 vol%, 5 vol%, 5.5 vol%, 6 vol%.

[0020] The choice of carbonate is not limited; for example, it may be at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. In some embodiments, the carbonate includes a fluorocarbonate to increase LiF formation. Preferably, the carbonate includes ethylene carbonate, dimethyl carbonate, or fluoroethylene carbonate; preferably, the volume ratio of EC / DMC / FEC is 1:1:0.1.

[0021] The parameters of pulsed electrodeposition affect the structure and performance of the composite layer. Preferably, in this invention, the duty cycle of the pulsed electrodeposition is 25%–35%, and the frequency is 80–120 Hz. Duty cycle refers to the percentage of the total cycle time during which the electrode is applied; frequency refers to the number of cycles completed per second. An appropriate duty cycle helps ensure sufficient ion diffusion time and avoids excessively rapid surface deposition. Medium to high frequencies match the diffusion timescale of ions in the electrolyte, contributing to the formation of a uniform and fine deposition structure. For example, the duty cycle can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%; the frequency can be 80 Hz, 85 Hz, 90 Hz, 95 Hz, 100 Hz, 105 Hz, 110 Hz, 115 Hz, or 120 Hz.

[0022] As a preferred embodiment of the present invention, the porous polymer conductive film is prepared by the following steps: mixing and heating a polymer material and a conductive agent for extrusion, applying an alternating electric field during the film formation process to obtain a polymer conductive film; then, through dry transverse stretching and longitudinal stretching, a porous polymer conductive film is obtained. In this invention, an alternating current battery drives the conductive agent to oriented along the electric field direction to form a through-type conductive pathway.

[0023] Preferably, the conductive agent is selected from at least one of SP, CNT, and graphene. Preferably, the conductive agent includes SP, CNT, and graphene. Preferably, the mass ratio of SP, CNT, and graphene is (8-10):(2-4):1. For example, when the mass part of graphene is 1 part, the SP can be 8 parts, 8.5 parts, 9 parts, 9.5 parts, or 10 parts, and the mass part of CNT can be 2 parts, 2.5 parts, 3 parts, 3.5 parts, or 4 parts.

[0024] Preferably, the polymer material is selected from at least one of PP and PE.

[0025] Preferably, the mass ratio of the polymer material to the conductive agent is 100:(5-20). Examples include 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14, 100:15, 100:16, 100:17, 100:18, 100:19, and 100:20.

[0026] Preferably, the frequency of the alternating electric field is 1–5 kHz, and the field strength is 200–500 V / cm. For example, the frequency can be 1 kHz, 2 kHz, 3 kHz, 4 kHz, or 5 kHz; the field strength can be 200 V / cm, 250 V / cm, 300 V / cm, 350 V / cm, 400 V / cm, 450 V / cm, or 500 V / cm. The electric field strength cannot be too high, otherwise it may easily lead to breakdown or material degradation; the frequency cannot be too low, otherwise it will be difficult to effectively drive the orientation of the nanofiller.

[0027] Based on this, the SP / CNT / graphene composite conductive network in the conductive film achieves directional alignment under the action of an alternating electric field, forming a through-type conductive path with an in-plane conductivity of 1×10⁻⁶. 4 ~1.5×10 4 With an anisotropy ratio >8, the interfacial resistance is significantly reduced, and the rate performance is improved. Furthermore, through dry transverse and longitudinal stretching, the conductive film is prepared into a porous conductive film with a thickness of 5–50 μm and a porosity of 30%–80%.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention provides a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI. It effectively suppresses battery volume expansion by providing a physical buffer space through a porous polymer framework, inducing uniform lithium ion deposition within the pores through LiF / Li3N, and encapsulating it with a flexible surface layer. Simultaneously, the pre-fabricated artificial SEI inside and outside the pores prevents direct contact between the electrolyte and highly reactive carbon materials or subsequently deposited lithium, thus avoiding side reactions. The ion conductivity of LiF / Li3N ensures efficient lithium transport and reversible deposition / stripping, thereby effectively improving initial efficiency.

[0030] 2. In the Li3N / LiF composite layer, the ultra-high ionic conductivity of Li3N allows lithium ions to rapidly enter and exit, while the LiF layer ensures that only lithium ions can pass through while electrons are blocked. This allows the porous structure to retain active sites, which can still serve as Li+ sites during lithium dissolution. + The rebinding sites promote uniform redeposition of lithium metal. Combined with the ionic conductivity and chemical stability of the Li3N / LiF composite SEI, the system has a certain degree of interface self-healing ability, which effectively alleviates the problem of SEI layer cracking and failure during cycling and extends battery cycle life.

[0031] 3. This invention provides a method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI. By using pulsed current, the method utilizes the local electric field enhancement effect induced by the pore structure and the Li-induced Li-enriched ... + Concentration gradients enable preferential nucleation and selective growth of Li3N / LiF on pore walls.

[0032] In some implementations, a porous polymer conductive film is prepared using an alternating electric field. The conductive agent is oriented and aligned under the action of the alternating electric field to form a through-type conductive path, which significantly reduces the interface resistance and improves the rate performance and energy efficiency, providing key support for high energy density and long life lithium metal batteries. Detailed Implementation

[0033] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described, but the present invention is not limited to these embodiments.

[0034] Example 1

[0035] A porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI includes a porous PP conductive film, a first composite layer formed on the inner wall of the pores of the porous PP conductive film, and a second composite layer formed on the surface of the porous PP conductive film.

[0036] The porous PP conductive film has a thickness of 25 μm, a porosity of 50%, and an in-plane conductivity of 1.2 × 10⁻⁶. 4 The S / cm ratio and the anisotropy ratio of the pore structure are greater than 8. The first composite layer consists of Li3N and LiF with a thickness of 70 nm; the second composite layer consists of Li2CO3, ROCO2Li, and Li2O with a thickness of 85 nm.

[0037] Prepared by the following steps:

[0038] S1. PP and conductive agent (SP, CNT, graphene in a mass ratio of 9:3:1) are mixed at a mass ratio of 100:10 and added to a screw extruder. Through heating and screw extrusion, an alternating electric field (frequency 2kHz, field strength 350V / cm) is applied during film formation, driving the conductive agent to align along the electric field direction to form a through-type conductive pathway, achieving an in-plane conductivity of 1.2 × 10⁻⁶. 4 With an anisotropy ratio >8, a uniformly mixed PP conductive film was prepared.

[0039] A porous PP conductive film with a thickness of 25 μm and a porosity of 50% was prepared by dry transverse stretching and longitudinal stretching.

[0040] S2. Dissolve LiNH2 in DMSO to prepare a precursor solution with a concentration of 10 wt%. Prepare an electrolyte solution with the precursor solution, LiTFSI, and carbonate; the carbonate solution consists of EC / DMC / FEC in a volume ratio of 1:1:0.1; the concentration of the precursor solution in the electrolyte is 5 vol%, resulting in a LiNH2 concentration of 0.24 M in the electrolyte; the concentration of LiTFSI in the electrolyte is 1 M.

[0041] In this electrolyte, a porous PP conductive film is used as the working electrode, and lithium is used as both the counter and reference electrodes. A pulsed current with a peak value of 5 mA / cm is applied. 2 With a duty cycle of 30% and a frequency of 100Hz, a first composite layer with a thickness of 70 nm is formed on the inner wall of the pore, while the second composite layer on the surface of the current collector has a thickness of 85 nm.

[0042] Examples 2-5

[0043] This embodiment is basically the same as embodiment 1, except that the AC electric field strength is different during the film formation process in step S1, as shown in Table 1 below.

[0044] Table 1. Example Field strength V / cm Example 1 350 Example 2 200 Example 3 500 Example 4 100 Example 5 600

[0045] Examples 6-9

[0046] This embodiment is basically the same as embodiment 1, except that the frequency of the alternating electric field is different during the film formation process in step S1, as shown in Table 2 below.

[0047] Table 2. Example frequency kHz Example 1 2 Example 6 1 Example 7 5 Example 8 0.5 Example 9 6

[0048] Examples 10-13

[0049] This embodiment is basically the same as embodiment 1, except that the peak value of the pulse current in step S2 is different, as shown in Table 3 below.

[0050] Table 3. Example <![CDATA[Peak mA / cm 2 > Example 1 5 Example 10 3 Example 11 8 Example 12 1 Example 13 10

[0051] Example 14

[0052] This embodiment is basically the same as embodiment 1, except that the pulse duty cycle in step S2 is different.

[0053] Specifically, in step S2, the pulse duty cycle is adjusted to 25%. A first composite layer with a thickness of approximately 50 nm is formed on the inner wall of the porous PP conductive film, and a second composite layer with a thickness of approximately 70 nm is formed on the surface. Furthermore, X-ray photoelectron spectroscopy depth profiling shows that the relative content of Li3N in the first composite layer is higher than that in Example 1.

[0054] Example 15

[0055] This embodiment is basically the same as embodiment 1, except that the pulse duty cycle in step S2 is different.

[0056] Specifically, in step S2 only, the pulse duty cycle is adjusted to 35%. A first composite layer with a thickness of approximately 75 nm is formed on the inner wall of the porous PP conductive film, and a second composite layer with a thickness of approximately 95 nm is formed on the surface. Furthermore, X-ray photoelectron spectroscopy depth profiling shows that the relative content of LiF in the first composite layer is higher than that in Example 1.

[0057] Comparative Example 1

[0058] The porous PP conductive film prepared in Example 1 was used.

[0059] Comparative Example 2

[0060] This comparative example is basically the same as Example 1, except that lithium metal layers are deposited inside and outside the porous PP conductive film.

[0061] The electrolyte was prepared by the following steps: In the electrolyte prepared in Example 1, the porous PP conductive film prepared in Example 1 was used as the working electrode, and lithium was used as the counter electrode and reference electrode. A pulse voltage of 1.5V relative to the reduction of Li was applied, with a duty cycle of 30% and a frequency of 100Hz.

[0062] Comparative Example 3

[0063] This comparative example is basically the same as Example 1, except that the porous PP conductive film is replaced with commercial porous carbon fiber.

[0064] Performance testing

[0065] The materials obtained in the examples and comparative examples were cut and used as negative electrodes, and then combined with commercial lithium iron phosphate positive electrodes, separators, and electrolytes to form batteries.

[0066] The assembled battery was charged at a constant current and constant voltage of 0.1C to 3.65V, and then charged at a constant voltage of 3.65V until the current dropped to 0.01C. The initial charge capacity was recorded. After resting for 30 minutes, the battery was discharged at a constant current of 0.1C to a voltage of 2.5V, and the initial discharge capacity was recorded. The initial coulombic efficiency was calculated. The test results are shown in Table 4 below.

[0067] After two activation cycles at 0.1C, the battery underwent a constant current charge-discharge long-cycle test at 1C, with a voltage range of 2.5–3.65 V. The discharge capacity was recorded, and the capacity retention rate after 500 cycles was calculated based on the discharge capacity of the second cycle. The test results are shown in Table 4 below.

[0068] Table 4. experimental group First-time effect (%) 1C cycle 500 cycles capacity retention rate (%) Example 1 94.5 88.2 Example 2 93 85.1 Example 3 93.8 86.7 Example 4 91.2 78.5 Example 5 92.5 82.3 Example 6 92.8 84 Example 7 94 87.5 Example 8 90.5 75 Example 9 93.2 85.5 Example 10 93.5 86 Example 11 92 81.5 Example 12 90 72 Example 13 91.8 79 Example 14 95 89.5 Example 15 94.2 87 Comparative Example 1 88.5 75 Comparative Example 2 86 68 Comparative Example 3 85 65

[0069] As shown in Table 4, comparing the embodiments and comparative examples, it can be seen that in this invention, constructing an artificial SEI structure inside and outside the porous polymer conductive film not only improves the initial efficiency but also effectively inhibits dendrite growth and lithium metal expansion, thus improving the cycle stability of the battery. In Comparative Example 1, only a conductive framework exists without an artificial SEI, causing the electrolyte to react directly with the carbon material, resulting in severe dendrite growth, expansion, and side reactions, and leading to a lower initial efficiency. In Comparative Example 2, by controlling the voltage to ensure that lithium metal deposition is the primary process, with the lithium metal layer mainly deposited on the outside, problems such as surface accumulation, severe volume expansion, and uneven SEI occur in the current collector, leading to battery capacity decay and shortened lifespan. In Comparative Example 3, commercial porous carbon fibers lack directional conductive pathways, have low conductivity, and high interfacial impedance, which is detrimental to interfacial stability. Furthermore, their insufficient stability and flexibility can cause them to react with Li... + The reaction forms an SEI film, reducing the first-efficiency effect.

[0070] Furthermore, comparisons within the examples show that appropriately adjusting the parameters during the fabrication process is beneficial for improving cycle stability and first-efficiency. Comparisons of Examples 1, 2-5 show that the electric field strength affects the formation of the conductive network. Within the appropriate range of 200-500 V / cm, increasing or decreasing the electric field strength may affect the uniformity or orientation of the conductive network, leading to changes in cycle stability and first-efficiency, but all remain within the optimal range. However, if the electric field strength is too low, insufficient driving will result in discontinuous guiding pathways; while if the electric field strength is too high, it may lead to material degradation or electrode damage; both of which will seriously affect the cycle stability and first-efficiency of the battery. Comparisons of Examples 1, 6-9 show that the frequency of the alternating current field affects the anisotropy. Adjusting the frequency within the appropriate range of 1-5 kHz can optimize the guiding network. However, if the frequency is too low, it will be difficult to effectively drive the orientation of the nanofiller; if the frequency is too high, it may cause local overheating or non-uniform deposition, both of which will adversely affect the battery. Comparisons of Examples 1, 10-13 show that the peak current affects the formation of the composite layer inside and outside the pores; within the appropriate range of 3-8 mA / cm... 2 Internally, the increase or decrease of the peak current density affects the enrichment structure within the pores or the integrity of the internal and external SEI formation. However, when the peak current density is too low, it will greatly reduce the thickness of the SEI, while when the peak current density is too high, it will trigger side reactions (such as H2 precipitation) and local short circuits, which will have a significant adverse effect on the battery. Comparing Examples 1, 14, and 15, it can be seen that the duty cycle affects the thickness of the composite layer and the composition ratio. At a duty cycle of 25%, ion diffusion is sufficient, Li3N enrichment is better, and the SEI is more stable. At a duty cycle of 35%, the relative content of LiF is higher, the mechanical strength is slightly better, but the ion conduction is slightly worse.

[0071] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI, characterized in that: It includes a porous polymer conductive film, a first composite layer formed on the inner wall of the pores of the porous polymer conductive film, and a second composite layer formed on the surface of the porous polymer conductive film. The first composite layer comprises Li3N and LiF. The second composite layer includes Li2CO3, ROCO2Li, and Li2O.

2. The porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI according to claim 1, characterized in that: The thickness of the first composite layer is 50–200 nm, and the thickness of the second composite layer is no more than 100 nm.

3. The porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI according to claim 1, characterized in that: The porous polymer conductive film is selected from at least one of porous PP conductive film and porous PE conductive film.

4. The porous conductive film negative electrode current collector with an in-pore enrichment type artificial SEI according to claim 1, characterized in that: The in-plane conductivity of the porous polymer conductive film is 1×10⁻⁶. 4 ~1.5×10 4 S / cm, anisotropy ratio greater than 8.

5. A method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI as described in any one of claims 1 to 4, characterized in that: Includes the following steps: The porous polymer conductive film is used to form the first and second composite layers in situ in an electrolyte using pulsed electrodeposition technology; the electrolyte includes LiTFSI, LiNH2, and carbonate; in the pulsed electrodeposition technology, the peak current is 3–8 mA / cm². 2 .

6. The method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI according to claim 5, characterized in that: In the pulsed electrodeposition technique, the duty cycle is 25%–35% and the frequency is 80–120 Hz.

7. The method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI according to claim 5, characterized in that: The electrolyte is obtained through the following steps: dissolving LiNH2 in DMSO to prepare a precursor solution, and preparing the precursor solution with LiTFSI and carbonate to prepare an electrolyte; the concentration of LiNH2 in the electrolyte is 0.2-0.3 M, and the concentration of LiTFSI in the electrolyte is 0.8-1.2 M.

8. A method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI according to claim 5 or 7, characterized in that: The carbonates include fluorocarbonates.

9. The method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI according to claim 5, characterized in that: The porous polymer conductive film is prepared by the following steps: mixing polymer materials and conductive agents, heating and extruding, applying an alternating electric field during the film formation process to obtain a polymer conductive film; and then obtaining a porous polymer conductive film by dry transverse stretching and longitudinal stretching.

10. The method for preparing a porous conductive film negative electrode current collector with an in-pore enriched artificial SEI according to claim 9, characterized in that: The frequency of the alternating electric field is 1–5 kHz, and the field strength is 200–500 V / cm.