Solid-state lithium metal battery negative electrode interface layer and preparation method thereof

Abstract

The invention discloses a solid-state lithium metal battery negative electrode interface layer and a preparation method thereof, and belongs to the technical field of solid-state lithium batteries. According to the preparation method, PEGDE, LiDFOB and LiTFSI are taken as raw materials, an in-situ high-temperature polymerization reaction method is adopted, the ratio of PEGDE to LiTFSI is regulated, and the LiDFOB is utilized to catalyze PEGDE self-crosslinking reaction, so that an interface layer is constructed in situ on a lithium metal negative electrode. The interface layer shows excellent ionic conductivity within the range of 30-80 DEG C, has a wide electrochemical stability window, can form a hard SEI layer on the surface of a negative electrode, and provides a new idea for solving the problems of low interface compatibility and poor stability of an existing solid-state battery.

Description

Technical Field

[0001] The present invention relates to a negative electrode interface layer of a solid-state lithium metal battery and a preparation method thereof, belonging to the technical field of solid-state lithium batteries. Background Art

[0002] With the increasing demand for high-energy-density energy storage devices in electric vehicles and portable electronic devices, traditional lithium-ion batteries are limited by the theoretical capacity of graphite anodes and are difficult to meet the development requirements of next-generation battery technologies. Lithium metal is regarded as the most promising anode material due to its extremely high theoretical specific capacity and the lowest electrochemical potential. However, lithium metal is prone to uncontrollable side reactions with liquid electrolytes during cycling, forming an unstable solid electrolyte interface film (SEI), resulting in lithium dendrite growth, a sharp increase in interfacial impedance, and rapid capacity decay, and even causing safety hazards such as short circuits. Although the application of solid electrolytes (such as sulfide, oxide, or polymer-based materials) can suppress the problem of lithium dendrite piercing, challenges such as poor solid-solid interface contact between them and lithium metal and insufficient interfacial chemical / electrochemical stability still restrict the practical application process of the battery.

[0003] Therefore, the design of the negative electrode interface layer has become one of the core technologies for improving the performance of solid-state lithium metal batteries. Research shows that when traditional solid electrolytes are in direct contact with lithium metal, high-impedance decomposition products are easily generated at the interface, resulting in an increase in interfacial resistance and severely limiting the ion transport efficiency. In addition, the volume expansion of lithium metal during cycling will exacerbate interfacial mechanical failure and further reduce the battery cycle life. In the prior art, although artificial SEI modification or three-dimensional skeleton structures can partially alleviate the problems, they still face bottlenecks such as low ionic conductivity of the interface layer, insufficient long-term stability, or complex preparation processes. Therefore, the development of a negative electrode interface layer technology with high ionic conductivity, interfacial stability, and scalable preparation has become the key breakthrough for promoting the commercial application of solid-state lithium metal batteries. Summary of the Invention

[0004] Aiming at the problems of low ionic conductivity and poor cycling stability existing in the negative electrode interface layer of existing solid-state lithium metal batteries, the present invention provides a negative electrode interface layer of a solid-state lithium metal battery and a preparation method thereof.

[0005] The technical solution of the present invention:

[0006] One of the purposes of the present invention is to provide a negative electrode interface layer of a solid-state lithium metal battery and a preparation method thereof, and the method includes the following steps:

[0007] (1) Mix PEGDE (polyethylene glycol diglycidyl ether), LiDFOB (lithium difluorooxalate borate), and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), and stir evenly until LiDFOB and LiTFSI are completely dissolved to obtain an interface layer precursor solution;

[0008] (2) In a glove box, the interface layer precursor solution is drop-coated on the surface of the lithium sheet, the battery is encapsulated, and finally placed in a vacuum oven for reaction to obtain a solid-state battery with a negative electrode interface layer.

[0009] It is further defined that the mass ratio of LiTFSI is 10%, 15% and 20% of PEGDE.

[0010] It is further defined that the mass of LiDFOB is 10% of the mass of PEGDE.

[0011] It is further defined that the stirring conditions in (1) are 60° C. and the rotation speed is 800 r / min.

[0012] It is further defined that the solid electrolyte used in (2) is a PVDF-HFP based solid electrolyte.

[0013] It is further defined that the vacuum oven temperature in (2) is 80° C. and the reaction time is 4 h.

[0014] It is further defined that the oxygen content of the glove box in (2) is less than 0.1 ppm, and the water content is less than 0.1 ppm.

[0015] The second purpose of the present invention is to provide a solid-state battery negative electrode interface layer prepared by the above method.

[0016] The third object of the present invention is to provide an application of the above-mentioned negative electrode interface layer, specifically for solid-state lithium metal batteries.

[0017] Beneficial effects:

[0018] The present invention uses PEGDE, LiDFOB and LiTFSI as raw materials, and through a high temperature reaction method, adjusts the ratio between PEGDE and LiTFSI, and uses LiDFOB to catalyze the self-crosslinking reaction of PEGDE at high temperature to prepare a negative electrode interface layer with high ionic conductivity. The solid electrolyte material has the following advantages:

[0019] (1) The present invention utilizes LiDFOB to decompose during the battery cycle to form a SEI layer having LiF and Li2CO3 components to construct a negative electrode interface layer, and utilizes the catalytic self-crosslinking reaction of LiDFOB on PEGDE to make free PEGDE react with LiDFOB, thereby successfully preparing a solid negative electrode interface layer, which exhibits ideal ionic conductivity and excellent cycle performance at 60°C, thereby solving the problem of poor compatibility between the solid electrolyte and the negative electrode interface in lithium metal batteries.

[0020] (2) The present invention regulates the ratio of the above-mentioned PEGDE to LiTFSI not only to regulate the ionic conductivity of the interfacial layer. At the same time, due to the relaxation effect of LiTFSI on the epoxy groups of PEGDE at high temperatures, the ratio of LiTFSI with the best electrochemical stability is also determined.

[0021] (3) The negative electrode interfacial layer provided by the present invention has both excellent ionic conductivity and an electrochemical stability window, and has a simple preparation process, a short preparation cycle, and high repeatability, and is more suitable for large-scale production applications. Description of the Drawings

[0022] Figure 1 FT-IR comparison diagrams of the negative electrode interfacial layer and each raw material prepared in Example 1;

[0023] Figure 2 Variable-temperature ionic conductivity comparison diagram of the negative electrode interfacial material prepared in Comparative Example 2;

[0024] Figure 3 LSV diagrams of the negative electrode interfacial materials prepared in Examples 1 to 3;

[0025] Figure 4 Long-cycle test diagram of the solid-state battery prepared in Example 4;

[0026] Figure 5 XPS diagrams of the negative electrode interfacial layers prepared in Examples 1 to 3; Detailed Embodiments

[0027] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the specific embodiments of the present invention in detail with reference to the embodiments of the specification.

[0028] Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0029] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that excludes other embodiments.

[0030] The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in this field. Without special instructions, those skilled in the art can obtain them through commercial channels, and the purity of the solid and liquid reagents used is analytical pure.

[0031] Example 1

[0032] (1) Mix 2 g of PEGDE, 0.2 g of LiDFOB, and 0.08 g of LiTFSI evenly to obtain an interfacial layer precursor solution.

[0033] (2) Drop the precursor solution obtained in (1) on the negative electrode side of the PVDF-HFP solid electrolyte.

[0034] (3) Directly prepare the solid electrolyte dropped with the precursor solution in (2) into a button cell.

[0035] (4) Place the battery obtained in (3) in a common oven and heat it at 80 °C for 2 h to allow the precursor solution to react.

[0036] (5) Directly test the battery treated in (4), and name the SEI layer generated by the cyclic reaction as SEI-1.

[0037] Example 2

[0038] The difference between this example and Example 1 is that the mass of LiTFSI is 0.3 g, and the rest of the process steps and parameter settings are the same as those in Example 1, obtaining an interfacial layer named SEI-2.

[0039] Example 3

[0040] The difference between this example and Example 1 is that the mass of LiTFSI is 0.4 g, and the rest of the process steps and parameter settings are the same as those in Example 1, obtaining a solid electrolyte named SEI-3.

[0041] Comparative Example 1

[0042] The difference between this example and Example 1 is that no interfacial layer material is used, and the PVDF-HFP solid electrolyte is directly prepared into a button cell for testing, obtaining a solid battery named PVDF-HFP.

[0043] Effect Example

[0044] (1) Figure 1 FT-IR diagrams of the interfacial layer materials obtained in Examples 1 to 3, as well as PEGDE and LiDFOB. As can be seen from the figure, PEGDE is located at 1352 and 1455 cm -1The nearby peaks are respectively from the asymmetric stretching and bending vibrations of -CH2 and -CH, while the peak at 2868 cm -1 corresponds to the stretching vibration of C-H. After adding LiDFOB, the C=O epoxy group of PEGDE at 913.9 cm -1 disappears, and new characteristic peaks appear at 1759.7 and 1790.2 cm -1 . In addition, the intensity of the C-O-C absorption peak increases, proving that PEGDE undergoes a ring-opening reaction under the catalysis of LiDFOB to form a solid interface layer with a self-crosslinked structure.

[0045] (2) Figure 2 Figure 2 shows the variable-temperature ionic conductivity diagrams of the SEI layers prepared in Examples 1 to 3. It can be seen from the figure that as the proportion of LiTFSI increases, the lithium source in the overall material increases, and the ionic conductivity of the interfacial material improves. The highest ionic conductivity is shown in SEI-3, which can reach 1.44×10 -5 S cm -1 at 30 °C and 2.86×10 -4 S cm -1 at 80 °C. PLE-3 is slightly lower than PLE-4, but it can still reach 1.14×10 -5 S cm -1 at 30 °C and 1.95×10 -4 S cm -1 at 80 °C.

[0046] (3) Figure 3 Figure 3 shows the LSV comparison diagrams of the SEI layer materials prepared in Examples 1 to 3. It can be seen from the figure that due to the large amount of LiTFSI in SEI-3, after the reaction is completed, TFSI - will still attack the unreacted PEGDE, resulting in a decrease in stability, and the electrochemical stability window of SEI-3 is only 4.53 V. While the components of SEI-2 interact reasonably, and under the promotion of an appropriate amount of LiTFSI, PEGDE reacts appropriately with LiDFOB, achieving a higher electrochemical stability window of 4.69 V.

[0047] (4) Figure 4 Figure 4 shows the long-cycle test diagrams of the solid-state batteries with the interfacial layer PVDF-HFP electrolyte and the solid-state battery with the PVDF-HFP electrolyte without the interfacial layer prepared in Example 2 and Comparative Example 1 at 60 °C and 1C. It can be seen that the PVDF-HFP solid-state battery with the interfacial treatment shows significantly better stability and specific capacity than the untreated interface. Among them, the solid-state battery with the SEI-2 interface layer formed after treatment forms a stable SEI layer during the first 20 cycles of reaction, and the discharge specific capacity reaches 144.4 mAh g-1 , and after 100 cycles, there is still a discharge specific capacity of 138.8 mAh g -1 . The capacity retention rate is as high as 96.1%, while the initial discharge specific capacity of the untreated solid-state battery is only 44.3 mAh g -1 . Thus, it can be seen that the interface layer formed by the combination of PEGDE and LiDFOB not only provides a stable interface for the solid-state battery, but also the cross-linking reaction between PEGDE and LiDFOB forms an electrolyte structure, providing additional capacity for the solid-state battery.

[0048] (5) Figure 5 FIG. XPS diagrams of the negative electrodes of the batteries prepared in Examples 1 to 3 are shown. As can be seen from the figure, after long-term cycling tests, according to the XPS analysis of the C1s, O 1s, and F1s spectra, it can be seen that signals of Li2CO3 and LiF are detected on the surface of the negative electrode. This indicates that after the cyclic reaction, the interface layer material formed by the combination of PEGDE and LiDFOB forms a SEI layer mainly composed of Li2CO3 and LiF, providing excellent interface stability for the solid-state battery.

[0049] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A negative electrode interface layer of a solid-state lithium metal battery and a preparation method thereof, characterized in that, Comprising: (1) Mix PEGDE, LiDFOB and LiTFSI, and stir to obtain an interfacial layer precursor solution; (2) Drop the interfacial layer precursor solution onto the surface of a lithium metal sheet, encapsulate the battery, and finally place it in a vacuum oven for reaction to obtain a solid-state battery with a treated negative electrode interface.

2. The preparation method according to claim 1, wherein The mass of LiDFOB is 10% of that of PEGDE:1; the mass of LiTFSI is (10%, 15%, 20%) of the mass of PEGDE.

3. The preparation method according to claim 1, characterized in that, (1) The mixing of the three materials does not require any solvent, and LiDFOB and LiTFSI are directly dissolved in PEGDE.

4. The preparation method according to claim 1, characterized in that, (1) The stirring condition is to stir at 60 °C and a rotation speed of 800 r / min until LiDFOB and LiTFSI are completely dissolved.

5. The preparation method according to claim 1, characterized in that, (2) The selected solid electrolyte is a PVDF-HFP-based solid electrolyte.

6. The preparation method according to claim 1, wherein (2) The heating reaction temperature is 80 °C and the time is 4 h.

7. The preparation method according to claim 1, wherein, (3) The oxygen content in the glove box is less than 0.1 ppm, and the water content is less than 0.1 ppm.

8. A negative electrode interface layer of a solid-state battery prepared by the method according to any one of claims 1 to 7.

9. An interface layer according to claim 8 for use in preparing a solid-state lithium metal battery.

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