A lithium metal negative electrode mixed interface modification layer and a preparation method and application thereof

Abstract

The application discloses a lithium metal negative electrode mixed interface modification layer and a preparation method and application thereof, and comprises the following steps: mixing and grinding nano bismuth oxide and a binder in proportion, adding N-methyl pyrrolidone dropwise, stirring for a set time, and obtaining Bi2O3 slurry; uniformly coating the Bi2O3 slurry on a PE diaphragm, drying to obtain a diaphragm with a coating; adhering one side of the coating of the diaphragm to a lithium metal pole piece, assembling a battery under a set sealing pressure, standing for a set time, and generating a Li3Bi alloy-Li2O mixed interface modification layer on the surface of the lithium metal pole piece through pressure self-reaction; and disassembling the battery to obtain a lithium metal pole piece modified by the mixed interface modification layer. The mixed solid electrolyte interface layer composed of Li3Bi alloy and Li2O is prepared by spontaneous reaction to modify the metal lithium negative electrode, so as to promote uniform deposition of lithium ions.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal anode modification technology, and relates to a lithium metal anode hybrid interface modification layer, its preparation method and its application in lithium metal batteries. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium metal has an extremely high theoretical specific capacity (3860 mA hg). -1 With its low reduction electrode potential (-3.040V, relative to the standard hydrogen electrode), lithium metal anodes have become the most promising candidates for next-generation high-energy-density lithium-ion battery anodes. However, the practical application of lithium metal anodes still faces many obstacles. The main problems are the uncontrollable lithium nucleation and growth behavior during cycling, which leads to the formation of a large number of dendritic lithium metal on the surface of the lithium anode, a severe volume expansion effect, and continuous side reactions caused by the high reactivity between lithium metal and the electrolyte. This will lead to the continuous consumption of active lithium and electrolyte, and rapid degradation of battery performance.

[0004] Furthermore, the practical application of lithium metal anodes still faces many obstacles. The main problems lie in the high chemical activity of lithium metal and the huge volume changes during cycling. In long cycles, lithium dendrites and dead lithium are easily formed, leading to safety accidents and battery life degradation. Optimizing the composition of the lithium anode substrate can reduce the overpotential for lithium nucleation and deposition, and decrease lithium dendrite growth during cycling. However, current collector structure design and electrolyte optimization cannot solve the fundamental problem of side reactions between lithium metal and the electrolyte. Artificial protective layer strategies are a "preventive" measure that can directly address the problem of lithium metal dendrite growth and electrode-electrolyte side reactions. Artificial protective films are created by artificially constructing a stable protective layer at the interface of the lithium metal anode before battery cycling, thereby controlling the deposition behavior of lithium metal. Currently, most lithium anode interface design research uses direct surface treatment of lithium metal, such as solution reaction, vapor deposition, and surface coating. These methods require specific equipment and have complex experimental procedures, and the presence of these protective layers often affects the Li... + The diffusion rate of the battery can negatively impact its cycle performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a mixed solid electrolyte interphase (SEI) modification layer for lithium metal anodes, its preparation method, and its application. A mixed solid electrolyte interphase (SEI) layer composed of Li3Bi alloy and Li2O was prepared via a spontaneous reaction to modify the lithium metal anode, thereby promoting uniform deposition of lithium ions.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a lithium metal anode hybrid interface modification layer, comprising the following steps:

[0008] Nano-bismuth oxide and binder were mixed and ground in a certain proportion, N-methylpyrrolidone was added dropwise, and the mixture was stirred for a set time to obtain Bi2O3 slurry;

[0009] Bi2O3 slurry was uniformly coated onto a PE membrane, and after drying, a coated membrane was obtained.

[0010] After the coating side of the separator is attached to the lithium metal electrode, the battery is assembled under a set sealing pressure. After standing for a set time, a Li3Bi alloy-Li2O mixed interface modification layer is generated on the surface of the lithium metal electrode through pressure self-reaction. The battery is then disassembled to obtain the lithium metal electrode modified with the mixed interface modification layer.

[0011] This invention modifies ordinary PE separators by coating them with a Bi2O3 layer, improving their thermal stability and other physical properties. During subsequent battery assembly and pressure application, the Bi2O3 coating directly contacts lithium metal and spontaneously reacts under internal battery pressure, generating a hybrid interface layer composed of Li3Bi alloy and Li2O. The Li3Bi alloy interface layer, with its three-dimensional porous morphology, provides abundant nucleation and growth sites for lithium metal deposition. Since the alloy components do not participate in the cycling process, electrode pulverization caused by alloy-dealloying is avoided. The electrochemical stability of the Li3Bi alloy also prevents structural damage to the interface pores during cycling. Li2O also promotes lithium-ion transport within the interface layer, homogenizing the lithium flux. Tests showed that adding this interface layer exhibited excellent lithium deposition regulation effects.

[0012] The reaction mechanism of pressure self-reaction is as follows:

[0013] (1) 6Li + Bi₂O₃ = Li₂O + 2Bi;

[0014] (2)Bi+3Li=Li3Bi.

[0015] In some embodiments, the adhesive is polyacrylic acid (PAA).

[0016] Preferably, the mass ratio of nano-bismuth oxide to polyacrylic acid is 5-10:1.

[0017] In some embodiments, after adding N-methylpyrrolidone, the stirring time is 10-12 hours to make the slurry more uniformly mixed.

[0018] In some embodiments, the coating thickness of the Bi2O3 slurry on the PE membrane is 7-12 μm.

[0019] Preferably, the Bi2O3 slurry is coated onto the PE membrane using a scraper with a thickness of 50-200 μm.

[0020] In some embodiments, the drying temperature is 60-80°C and the drying time is 24-48 hours.

[0021] In some embodiments, the sealing pressure is 40-60 kg / cm². -2 .

[0022] In some embodiments, the settling time is 10-15 hours.

[0023] Secondly, the present invention provides a lithium metal anode hybrid interface modification layer, which is prepared by the aforementioned preparation method.

[0024] Thirdly, the present invention provides a lithium metal anode, wherein at least one side of its surface is modified with the lithium metal anode mixed interface modification layer.

[0025] Fourthly, the lithium metal anode is used in the preparation of symmetrical cells, Li / / Cu half-cells, or full cells.

[0026] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0027] 1. In this invention, a Li3Bi alloy-Li2O mixed solid electrolyte interface modification layer can be generated through in-situ self-reaction with a lithium metal anode. The preparation method is low in cost and simple in operation.

[0028] 2. The mixed solid electrolyte interface layer prepared by this invention can not only inhibit the growth of lithium dendrites and induce uniform lithium deposition, but also isolate the direct contact between the lithium anode and the electrolyte, reducing the side reactions caused.

[0029] 3. The self-reaction of the membrane coating-lithium metal anode generates a Li3Bi alloy framework in situ. The generated Li3Bi alloy layer has a stronger affinity for lithium ions than pure metallic lithium. The stable and lithium-loving Li3Bi alloy framework provides abundant nucleation and growth sites for lithium metal. Therefore, lithium ions tend to be uniformly adsorbed on the alloy framework and reduced and deposited. The disordered growth of dendritic lithium in the space is suppressed and it turns to planar growth.

[0030] 4. The self-reactive in-situ formation of a Li₂O layer in the separator coating of the lithium metal anode provides high ionic conductivity and low diffusion energy when combined with other components at the nanoscale. This promotes parallel rather than perpendicular lithium-ion reduction deposition while also enabling the Li₂O layer to... +The diffusion kinetics are fast enough. This facilitates stable deposition and dissolution during cycling at lower overpotentials in Li||Li symmetric cells, and enables the full cell to achieve superior cycling stability and capacity retention. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 Characterization of the PE membrane coated with a Bi2O3 layer, including (a) SEM images of the PE membrane and (b) Bi2O3, (c) XRD image of Bi2O3, and (de) surface and (f) cross-sectional SEM images of the Bi2O3@PE membrane.

[0033] Figure 2 The morphology and elemental distribution of the Li3Bi alloy-Li2O mixed solid electrolyte interface layer prepared in Example 1 are shown in (a) surface, (bc) cross-sectional SEM images, (c) magnified area of ​​the white box in (b), (d) SEM image of the mixed solid electrolyte interface layer and (e) surface scan images of Bi and (f) O elements.

[0034] Figure 3 The following are characterizations of the mixed solid electrolyte interface layer generated in Example 1, including (a) the XRD pattern of the Li3Bi interface layer, and the XPS fine spectra of (b) O1s, (c) Li1s, and (d) Bi4f elements of the Li3Bi interface layer.

[0035] Figure 4 The Li / Bi2O3@PE / Cu battery corresponding to Example 1 at 1mAh cm⁻¹ -2 5mAh cm -2 10mAh cm -2 Lithium deposition morphology at the Li3Bi alloy-Li2O mixed interface layer under different deposition capacities. The deposition capacity is 1 mAh cm⁻¹. -2 SEM images of the interface layer (a) upper surface, (d) bottom surface and (g) cross-section, with a deposition capacity of 5 mAh cm⁻¹. -2 SEM images of the interface layer (b) upper surface, (e) bottom surface and (h) cross-section, with a deposition capacity of 10 mAh cm⁻¹. -2 SEM images of the interface layer (c) upper surface, (f) bottom surface and (i) cross section.

[0036] Figure 5The results show the calculated adsorption energies of lithium ions on the vacancy faces of lithium metal and Li3Bi alloy (100), with (a) the lithium adsorption model and the calculated adsorption energy for Li3Bi and (b) Li.

[0037] Figure 6 The Li / / Cu half-cells Li / Bi₂O₃@PE / Cu and Li / PE / Cu corresponding to Example 1 and Comparative Example 1 were assembled at 1 mA cm⁻¹. -2 0.5mAh cm -2 Coulombic efficiency and deposition overpotential were tested under the specified conditions, including (a) the coulombic efficiency of Li / Bi2O3@PE / Cu and (b) the Li / PE / Cu half-cell, (c) the first-cycle capacity-voltage curves of Li / Bi2O3@PE / Cu and Li / PE / Cu half-cells, (d) the partial-cycle capacity-voltage curves of Li / Bi2O3@PE / Cu and (e) the Li / PE / Cu half-cells, and (f) a partial magnified view of the tenth-cycle capacity-voltage curve of Li / Bi2O3@PE / Cu and Li / PE / Cu half-cells.

[0038] Figure 7 To compare the lithium symmetric batteries corresponding to Example 1 and Comparative Example 1 at 1 mA cm -2 1mAh cm -2 SEM characterization of the relevant electrodes after 200 hours of cycling under test conditions was performed to analyze the surface lithium deposition morphology, including (ac) SEM images of the Li3Bi alloy-Li2O mixed layer modified anode and (df) ordinary lithium anode.

[0039] Figure 8 The cycling performance tests of the LFP / / Li full cells corresponding to Example 1 and Comparative Example 1 are shown, where (a) the long-cycle performance of the LFP / Bi2O3@PE / Li cell and the LFP / PE / Li cell is tested at a current density of 1C, and (b) and (c) the partial cycle capacity-voltage curves of the LFP / Bi2O3@PE / Li cell and the LFP / PE / Li cell are shown.

[0040] Figure 9 The rate performance tests of the LFP / / Li full cells corresponding to Example 1 and Comparative Example 1 are shown, including (a) the rate performance of the LFP / Bi2O3@PE / Li cell and the LFP / PE / Li cell, (b) the capacity-voltage curves of the LFP / Bi2O3@PE / Li cell and (c) the LFP / PE / Li cell at different current densities.

[0041] Figure 10The following are the cycle performance tests of LCO / / Li full cells corresponding to Example 1 and Comparative Example 1, where (a) the long cycle performance of LCO / Bi2O3@PE / Li battery and LCO / PE / Li battery tested at a current density of 1C, (b) and (c) partial cycle capacity-voltage curves of LCO / Bi2O3@PE / Li battery and LCO / PE / Li battery. Detailed Implementation

[0042] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0043] The present invention will be further described below with reference to the embodiments.

[0044] Example 1

[0045] A method for preparing a lithium metal anode alloy-oxide hybrid solid electrolyte interface layer includes the following steps:

[0046] (1) Preparation of Bi2O3 slurry: Commercial nano bismuth oxide and polyacrylic acid (PAA) binder were mixed and ground at a mass ratio of 6:1. An appropriate amount of N-methylpyrrolidone was added dropwise and stirred for 10 hours to form a yellow slurry.

[0047] (2) Diaphragm coating and scraper: Use a 200μm scraper to evenly coat the mixed slurry onto the commercial PE diaphragm, and put it into a 60℃ vacuum drying oven to dry for 24h. Cut the dried diaphragm into 16mm round pieces and put them into a glove box for later use.

[0048] (3) After bonding the lithium sheet to the separator coating obtained in step (2), assemble them into a button battery with a sealing pressure of 50 kg / cm². -2 Before testing, the battery was left to stand for 12 hours. After 12 hours of pressure self-reaction, a Li3Bi alloy-Li2O mixed interface modification layer was generated on the original lithium metal anode surface.

[0049] Example 2

[0050] A method for preparing a lithium metal anode alloy-oxide hybrid solid electrolyte interface layer includes the following steps:

[0051] (1) Preparation of Bi2O3 slurry: Commercial nano bismuth oxide and polyacrylic acid (PAA) binder were mixed and ground at a mass ratio of 8:1. An appropriate amount of N-methylpyrrolidone was added dropwise and stirred for 12 hours to form a yellow slurry.

[0052] (2) Diaphragm coating and scraper: Use a 50μm scraper to evenly coat the mixed slurry onto the commercial PE diaphragm, and put it into an 80℃ vacuum drying oven to dry for 24h. Cut the dried diaphragm into 16mm round pieces and put them into a glove box for later use.

[0053] (3) After bonding the lithium sheet to the separator coating obtained in step (2), assemble them into a button battery with a sealing pressure of 60 kg / cm². -2 Before testing, the battery was left to stand for 15 hours. After 15 hours of pressure self-reaction, a Li3Bi alloy-Li2O mixed interface modification layer was formed on the original lithium metal anode surface.

[0054] Example 3

[0055] A method for preparing a lithium metal anode alloy-oxide hybrid solid electrolyte interface layer includes the following steps:

[0056] (1) Preparation of Bi2O3 slurry: Commercial nano bismuth oxide and polyacrylic acid (PAA) binder were mixed and ground at a mass ratio of 5:1, and an appropriate amount of N-methylpyrrolidone was added. After stirring for 11 hours, a yellow slurry was formed.

[0057] (2) Diaphragm coating and scraper: Use a 100μm scraper to evenly coat the mixed slurry onto the commercial PE diaphragm, and put it into a 70℃ vacuum drying oven to dry for 24h. Cut the dried diaphragm into 16mm round pieces and put them into a glove box for later use.

[0058] (3) After bonding the lithium sheet to the separator coating obtained in step (2), assemble them into a button battery with a sealing pressure of 40 kg / cm². -2 Before testing, the battery was left to stand for 15 hours. After 15 hours of pressure self-reaction, a Li3Bi alloy-Li2O mixed interface modification layer was formed on the original lithium metal anode surface.

[0059] Comparative Example 1

[0060] The separator used in the comparative example was a commercially available PE separator, without the coating process involved in steps (1) and (2) of Example 1. It was directly cut into 16mm round pieces and placed in the glove box for later use. During the battery assembly process, since the surface was not coated, the lithium metal sheet surface did not undergo a reaction to generate a solid electrolyte interface modification layer.

[0061] To test the cycle stability and lithium deposition morphology of the Li3Bi alloy-Li2O mixed solid electrolyte interface modified and unmodified lithium metal sheets assembled in Example 1 and Comparative Example 1, the specific methods are as follows:

[0062] (1) Synthesis and morphology characterization: To characterize the deposition morphology of lithium metal on the Cu foil side, the battery needs to be disassembled. The battery is disassembled using a matching battery disassembly equipment. The electrode to be further characterized needs to be immersed in DMC solution to remove the electrolyte and lithium salt components on the surface. The immersion time is about 24 hours.

[0063] (2) Assembly and testing of Li / / Li symmetric cells: Since the separator is only coated on one side, the electrode sheet modified with a mixed solid electrolyte interface layer needs to be obtained first through a pressure method during the symmetric cell testing process. Specifically, the lithium sheet is attached to the separator coating side and then assembled into a button cell using a 50kg cm⁻¹ pressure method. -2 The button cell is sealed under pressure. After 12 hours of pressure self-reaction, the cell is disassembled to obtain a lithium metal anode modified with a mixed solid electrolyte interface layer, which is then used as an electrode. When assembling a lithium symmetric cell, a fresh lithium sheet is attached to the separator coating side, and the electrode modified with the mixed solid electrolyte interface layer is attached to the other side. LS-001 lithium-sulfur electrolyte was used in all symmetric cell tests, with an addition amount of 50 μL.

[0064] The constant current charge-discharge test for symmetrical batteries involves repeatedly charging and discharging the battery with a constant current for a fixed duration, recording the overpotential throughout the process to evaluate the battery's cycle stability. Rate testing (step current cycle performance) involves increasing or decreasing the current density and adjusting the charge / discharge capacity during the test to assess the battery's stability under different current densities and capacities.

[0065] (3) In the Li / / Cu half-cell test, the positive electrode was copper foil, and the negative electrode was a fresh lithium metal sheet. When assembling the battery, the copper foil was attached to the coating side of the separator. The electrolyte used was lithium-sulfur electrolyte LS-009, with an addition amount of 50 μL. During the charge-discharge test, the battery was discharged at a constant current for a fixed time, and then charged to a fixed potential with the same current. The overpotential and the ratio of charge-discharge capacity (coulombic efficiency) during the process can reflect the reversibility of lithium deposition stripping, etc.

[0066] (4) LFP / / Li and LCO / / Li full cell tests: Taking LiCoO2 as an example, the preparation process of the positive electrode is as follows: The active material, conductive agent, and binder are mixed in NMP solvent at a ratio of 8:1:1 (mass ratio). Super P is used as the conductive agent and PVDF is used as the binder. After stirring evenly, the mixture is coated on aluminum foil and vacuum dried at 80°C for 12 hours. The resulting small circular pieces with a diameter of 14 mm are then cut into LCO positive electrodes. Using LFP as the active material, LFP positive electrodes can be obtained under the same experimental steps. The separator is pre-cut into 16 mm circular pieces and stored in a glove box for later use. Using the LFP or LCO obtained above as the positive electrode, the Li metal sheet as the negative electrode, and the separator loaded with 50 μL of electrolyte, CR2025 button cells are assembled sequentially. When assembling the cells, the coated side of the separator faces the lithium metal negative electrode, and the cells are left to stand for 12 hours after assembly to allow for interface self-reaction. All cell assemblies are completed under glove box conditions (H2O and O2 content are both below 0.1 ppm).

[0067] The current density of a lithium metal full battery is determined by the capacity of the positive electrode. The current required to charge the positive electrode from zero to full in one hour is denoted as 1C, and full batteries are typically expressed using this current rating. Simultaneously, the charge / discharge cutoff condition for a full battery changes from a time-based cutoff to a voltage-based cutoff. Rate performance testing involves gradually increasing the current and then reverting to a lower current value to test stability. The rate performance of a full battery is evaluated by the capacity retention rate at different rates.

[0068] All batteries used in this article were tested using the LANDCT2001A battery charge / discharge system from Wuhan Landian Electronics Co., Ltd. The battery testing temperature was room temperature.

[0069] First, the PE membrane before coating was characterized by SEM. Figure 1 Image a shows a SEM image of the PE membrane surface, revealing its porous structure. Subsequently, commercially available Bi2O3 was characterized using SEM and XRD to verify its morphology and composition. Figure 1 b is its SEM image, which shows that the particles are relatively fine and include some spherical particles, with a particle size range of 0.5-2μm. Figure 1 c is the XRD pattern of Bi2O3, which matches the PDF card and shows no impurity peaks, indicating that the phase is relatively pure. After coating modification, the membrane surface is pale yellow and the color is relatively uniform. Figure 1 Images d and e are SEM images of the Bi2O3@PE membrane surface. The coating surface in the images is relatively rough, composed of Bi2O3 particles of different sizes, with a certain porosity structure and good particle dispersion. Figure 1 f is a cross-sectional SEM image of the Bi2O3@PE membrane, with a coating thickness of approximately 9 μm and a relatively uniform thickness distribution.

[0070] To clarify the surface morphology and actual thickness of the interface layer, the synthesized negative electrode was characterized by SEM. Figure 2 a and d are surface SEM images of the negative electrode modified with a mixed solid electrolyte interface layer. The lithium sheet surface is loaded with a relatively flat and porous interface layer, which maintains a similar porous structure to the separator coating, but with a flatter morphology. Meanwhile... Figure 2 The EDS images of e and f show that Bi and O elements are uniformly distributed on the surface. Figure 2 b and c are cross-sectional SEM images of the Li3Bi alloy layer negative electrode, further revealing a porous structure in the interface layer, and the thickness of the mixed interface layer was measured to be approximately 10 μm.

[0071] Furthermore, phase analysis was performed on the Li3Bi alloy-Li2O mixed artificial solid electrolyte interface modification layer generated by the self-reaction. Figure 3 Figure a shows the XRD characterization results of the mixed interface layer. The larger amorphous peak originates from the polyimide tape coating the sample. The remaining diffraction peaks correspond to the Li3Bi phase and are in high agreement with the PDF card. Lithium metal diffraction peaks were also observed, but no Li2O diffraction peaks were found, possibly due to the low content of in-situ generated Li2O. To further clarify the composition and valence state of the interface layer, XPS characterization was performed on the Li3B interface layer anode. Figure 3 b is the O1s fine spectrum of the sample. The characteristic peak at 532.12 eV corresponds to Li2O, and the other characteristic peaks correspond to the oxygen element in the carboxyl group of PAA. Figure 3 c is the fine spectrum of the Li1s sample, where the characteristic peak of Li2O is located at 55.1 eV, while the peak of the Li3Bi alloy is located at 55.8 eV. In addition, the characteristic peak of metallic lithium can also be obtained. Figure 3 Image d shows the fine spectrum of Bi 4f in the sample. The characteristic peaks of Bi 4f7 / 2 and Bi 4f5 / 2 at 158.1 eV and 163.4 eV correspond to those of the Li3Bi alloy. XRD and XPS results confirm the completion of the interfacial reaction, resulting in a mixed interfacial layer of Li3Bi alloy and Li2O.

[0072] To investigate the guiding effect of the Li3Bi alloy-Li2O hybrid artificial solid electrolyte interface modification layer on lithium metal deposition, Li / / Cu half-cells were assembled using Bi2O3@PE membranes and PE membranes, respectively, for lithium metal deposition testing. The two half-cells were designated Li / Bi2O3@PE / Cu and Li / PE / Cu, respectively, and the measured deposition amount was 1 mAh cm⁻¹. -2 5mAh cm -2 and 10mAh cm -2 The tested battery was disassembled and the electrodes were characterized using SEM. Figure 4SEM images of lithium deposition at the Li3Bi alloy-Li2O mixed interface layer after lithium deposition in Li / Bi2O3@PE / Cu half-cells with three different capacities. Due to the high electronic conductivity of the copper foil surface and the difference in lithiophilicity between the Li3Bi alloy-Li2O mixed interface layer and the copper foil, lithium metal first uniformly nucleates on the alloy framework on the lower surface of the Li3Bi alloy-Li2O mixed interface layer (the side in contact with the copper foil) and grows along the pore structure, resulting in lithium metal not being deposited on the copper foil surface.

[0073] like Figure 4 As shown in a, the deposition amount is 1 mAh cm⁻¹ -2 At that time, no lithium deposition occurred on the upper surface of the interface layer, so the surface structure of the upper surface remained basically consistent with that of the mixed solid electrolyte interface layer mentioned above. Figure 4 Image d shows the SEM image of the lower surface of the Li3Bi interface layer. The deposition layer on the lower surface has a high density and grows laterally. Large, tightly packed lithium blocks can be observed at high magnification. Figure 4 g is 1mAh cm -2 A cross-sectional SEM image of the interface layer is shown, revealing the deposition layer beneath the interface layer. When the deposition amount is increased to 5 mAh cm⁻¹... -2 and 10mAh cm -2 At that time, the pores in the interface layer are occupied by deposited lithium, and the upper surface deposit layer also exhibits a relatively dense state.

[0074] like Figure 4 As shown in b and c, the lithium deposited on the upper surface of the interface layer remains tightly packed, with no obvious lithium dendrites observed, and maintains overall lateral growth. At this point, the deposited layer on the lower surface of the interface layer ( Figure 4 e and f) remain in a dense state. Figure 4 h and i are respectively 5mAhcm -2 and 10mAh cm -2 The SEM image of the lower interface layer shows that lithium metal fills and encapsulates the pores inside the interface layer, making it difficult to distinguish the multi-layer deposition structure.

[0075] like Figure 5 As shown in a and b, the vacancy adsorption energies of lithium ions on the crystal planes of lithium metal and Li3Bi alloy (100) were calculated to reveal the reasons for the differences in lithium deposition morphology. The adsorption energy of lithium ions on Li3Bi is -2.467 eV, while that on the lithium substrate is -1.496 eV. Therefore, lithium ions tend to be uniformly adsorbed on the alloy framework and reduced and deposited, reducing the occurrence of lithium metal self-aggregation and thus avoiding dendrite growth, which is consistent with the results of deposition experiments.

[0076] The above results demonstrate that the Li3Bi alloy-Li2O hybrid artificial solid electrolyte interface modification layer can effectively guide the homogeneous deposition of lithium metal. Subsequently, Li / Bi2O3@PE / Cu and Li / PE / Cu half-cells were assembled and tested at 1 mA cm⁻¹. -2 0.5mAh cm -2 Coulomb efficiency and deposition overpotential were tested under the given conditions. Figure 6 a and b represent the coulombic efficiencies of the two sets of half-cells. The coulombic efficiency of the Li / Bi2O3@PE / Cu half-cell corresponding to Example 1 remained stable at around 98% after 250 cycles, while the coulombic efficiency of the Li / PE / Cu half-cell corresponding to Comparative Example 1 became unbalanced after 110 cycles, and the change gradually increased, dropping to 80% after 250 cycles.

[0077] Figure 6 Figures d and 6e show the capacity-voltage curves of the Li / Bi₂O₃@PE / Cu and Li / PE / Cu half-cells at different time points, respectively. With increasing cycle count, the charging capacity of the PE group gradually decreases. This is because lithium dendrites formed during discharge become dead lithium that does not participate in cycling during charging. In contrast, the charging capacity of the Li / Bi₂O₃@PE / Cu half-cell remains stable throughout the cycle. This is attributed to the Li₃Bi alloy-Li₂O hybrid artificial solid electrolyte interface modification layer on the separator side, which modifies the lithium metal deposition process, thus reducing the formation of dendrites and dead lithium. This aligns with the deposition morphology observed in the deposition experiments. Furthermore, the deposition stripping overpotential of the Li / Bi₂O₃@PE / Cu half-cell is slightly lower than that of the Li / PE / Cu half-cell, indicating that the interface layer also plays a role in mitigating interfacial polarization during cycling.

[0078] To investigate the effect of the interface layer on the lithium nucleation overpotential, two sets of half-cell capacity-voltage curves were plotted. For example... Figure 6 As shown in Figure c, during the first discharge of the Li / Bi2O3@PE / Cu half-cell, Bi2O3 underwent a reduction reaction, generating Li3Bi and Li2O. Furthermore, no dealloying voltage plateau was observed in the Li3Bi alloy when charged to 0.5V. Figure 6 f represents the capacity-voltage curves of the two sets of cycles at the 10th cycle. The measured lithium nucleation overpotential of the Li / Bi2O3@PE / Cu half-cell was 55.6 mV, while that of the Li / PE / Cu half-cell was 72.5 mV. This indicates that the Li3Bi alloy-Li2O mixed artificial solid electrolyte interface modification layer can reduce the lithium nucleation overpotential, thereby enabling uniform lithium nucleation and growth.

[0079] Figure 7 The lithium metal anodes of Example 1 and Comparative Example 1 (lithium metal anode modified with a Li3Bi alloy-Li2O mixed interface layer and original lithium metal anode) were respectively assembled into symmetrical cells, and tested at 1 mA cm⁻¹.-2 1mAh cm -2 SEM image of lithium deposition morphology on the surface of the negative electrode after 200 h of cycling. Figure 7 Image ac is a surface SEM image of the Li3Bi alloy-Li2O mixed layer modified negative electrode after 200h cycling. The surface deposited layer is relatively dense, and at high magnification, some areas of the deposited layer show a stacked growth pattern, with a small proportion of dendritic lithium. Figure 7 Image df is a surface SEM image of a typical lithium metal anode. The deposition layer is generally loose, with numerous pores, which increases the electrode's specific surface area. At high magnification, dendritic lithium with a high specific surface area can be observed.

[0080] Figure 8 The graphs show the cycle performance of LFP / / Li full cells assembled with lithium metal anodes corresponding to Example 1 and Comparative Example 1 (i.e., lithium iron phosphate LFP full cells assembled with Bi2O3@PE membrane and PE membrane respectively). Figure 8 a represents the 1C cycle results of LFP full cells using Bi2O3@PE membrane and PE membrane. The Bi2O3@PE group exhibited high cycle stability, with an average coulombic efficiency of 98.7% during cycling. After 600 cycles, the discharge specific capacity still reached 120.4 mAh g⁻¹. -1 The capacity retention rate was 84%. The PE group had an average coulombic efficiency of 98.3% during cycling, slightly lower than the Bi2O3@PE group, and experienced efficiency fluctuations and significant capacity decay around 370 cycles, with a discharge capacity of only 86.6 mAh g after 400 cycles. -1 The capacity-voltage curves of the Bi2O3@PE group and the PE group are shown below. Figure 8 b and Figure 8 As shown in Figure c, the full cell using the Bi2O3@PE separator exhibits less capacity decay and a smaller overpotential increase. The interfacial layer introduced by the Bi2O3@PE separator effectively improves the cycle performance of the full cell.

[0081] To further investigate the impact of the Li3Bi alloy-Li2O hybrid interface modification layer on the rate performance of the battery, rate performance tests were conducted on two groups of LFP full cells, such as... Figure 9 As shown. Figure 9 a represents the capacity retention of the two battery groups under stepped current conditions. At a low rate of 0.5-1C, the discharge capacities of the two groups are similar; at 4C, the full cell discharge capacity using Bi2O3@PE is 98.6 mAh g. -1 This shows a significant difference compared to the PE group; even with the current increased to 5C, the Bi2O3@PE group still maintains 80.6mAh g⁻¹. -1The porous interface layer effectively promotes lithium-ion transport, reduces local current density, and slows down polarization, thus preventing the charge / discharge cutoff voltage from being reached earlier. This allows the assembled full cell to exhibit good rate performance. Figure 9 b and c are the capacity-voltage curves of the two rate tests. The capacity decay and overpotential rise of the Bi2O3@PE group are smaller than those of the PE group.

[0082] Subsequent long-cycle tests were conducted on the LCO / / Li full cells corresponding to Example 1 and Comparative Example 1, and the performance was as follows: Figure 10 As shown. Figure 10 a represents the 1C long-cycle results of the two LCO batteries. After 200 cycles, the full cell using the Bi2O3@PE separator had a discharge capacity of 109.1 mAh g. -1 The capacity retention rate reached 78.4%, and the coulombic efficiency remained stable above 98.2% during cycling. The PE diaphragm group, however, exhibited rapid capacity decay, with significant fluctuations in coulombic efficiency at 180 cycles. The capacity-voltage curves for the two groups are shown below. Figure 10 As shown in Figures b and c, the Bi₂O₃@PE group exhibits better capacity and overpotential changes than the PE group during cycling. The test results demonstrate that the Li₃Bi interface layer can still improve battery cycling performance in the lithium cobalt oxide full-cell system.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium metal anode mixed interface modification layer, characterized in that: Includes the following steps: Nano-bismuth oxide and binder were mixed and ground in a certain proportion, N-methylpyrrolidone was added dropwise, and the mixture was stirred for a set time to obtain Bi2O3 slurry; Bi2O3 slurry was uniformly coated onto a PE membrane, and after drying, a coated membrane was obtained. After the coating side of the separator is attached to the lithium metal electrode, the battery is assembled under a set sealing pressure. After standing for a set time, a Li3Bi alloy-Li2O mixed interface modification layer is generated on the surface of the lithium metal electrode through pressure self-reaction. The battery is then disassembled to obtain the lithium metal electrode modified with the mixed interface modification layer.

2. The method for preparing the lithium metal anode mixed interface modification layer according to claim 1, characterized in that: The adhesive is polyacrylic acid.

3. The method for preparing the lithium metal anode hybrid interface modification layer according to claim 2, characterized in that: The mass ratio of nano-bismuth oxide to polyacrylic acid is 5-10:

1.

4. The method for preparing the lithium metal anode hybrid interface modification layer according to claim 1, characterized in that: After adding N-methylpyrrolidone, stir for 10-12 hours.

5. The method for preparing the lithium metal anode mixed interface modification layer according to claim 1, characterized in that: The coating thickness of Bi2O3 slurry on PE membrane is 7-12 μm.

6. The method for preparing the lithium metal anode mixed interface modification layer according to claim 5, characterized in that: Bi2O3 slurry is coated onto the PE membrane using a doctor blade with a thickness of 50-200 μm.

7. The method for preparing the lithium metal anode mixed interface modification layer according to claim 1, characterized in that: The drying temperature is 60-80℃, and the drying time is 24-48h.

8. The method for preparing the lithium metal anode mixed interface modification layer according to claim 1, characterized in that: The sealing pressure is 40-60 kg / cm². -2 .

9. The method for preparing the lithium metal anode mixed interface modification layer according to claim 1, characterized in that: The settling time is 10-15 hours.

10. A lithium metal anode hybrid interface modification layer, characterized in that: It is prepared by any one of the preparation methods described in claims 1-9.

11. A lithium metal anode, characterized in that: At least one side of its surface is modified with the lithium metal anode mixed interface modification layer as described in claim 10.

12. The application of the lithium metal anode of claim 11 in the preparation of symmetrical cells, Li / / Cu half cells or full cells.

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