Interface film as well as preparation method and application thereof

Abstract

The invention discloses an interface film and a preparation method and application thereof, and relates to the technical field of battery films. An amino acid analogue is introduced into a negative electrode interface layer, and a layer of uniform film is prepared by a film casting method. Strong electron withdrawing groups in the amino acid analogues are combined with active sites of an electrolyte layer through adsorption and coordination, a molecular-level protection layer is preferentially formed at the electrolyte, the surface of the electrolyte is passivated, and the direct contact reaction with a negative electrode is slowed down. And meanwhile, the amino acid analogue has hydrophobicity, so that electrolyte side reaction caused by water is reduced. The amino acid analogue contains fluorine atoms with high electronegativity, so that uniform flux of lithium ions can be guided. A uniform thin film is prepared through an amino acid analogue and a precursor solution of polyoxyethylene (PEO) molecules, and the introduction of PEO enhances the flexibility and deformability of the thin film, so that the thin film better adapts to the volume change and stress of a silicon negative electrode.

Description

Technical Field

[0001] This invention relates to the field of battery thin film technology, and more specifically, to an interface thin film, its preparation method, and its application. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic devices, and large-scale energy storage systems, the demand for rechargeable batteries with high energy density, high safety, and long cycle life is becoming increasingly urgent. Lithium-ion batteries, as the current mainstream energy storage technology, are gradually finding it difficult to meet the requirements of next-generation applications in terms of energy density and safety. Against this backdrop, all-solid-state batteries (ASSBs) have become an important development direction for next-generation energy storage technology due to their potential high energy density, excellent thermal stability, and lack of leakage risk. One of the core components of all-solid-state batteries is the solid electrolyte, which mainly includes sulfide electrolytes, oxide electrolytes, and polymer electrolytes. Among them, sulfide electrolytes are particularly valuable due to their high ionic conductivity (up to 10⁻⁶). -2 The all-solid-state battery has attracted widespread attention due to its high efficiency (on the order of S / cm) and excellent machinability. However, it still faces many challenges in practical applications, especially in the interface between the electrodes and the electrolyte.

[0003] On the one hand, there is thermodynamic instability between mainstream solid electrolytes (such as sulfides and oxides) and highly active anodes (such as lithium metal and silicon-based materials). When they come into contact, side reactions easily occur, generating high-resistivity interface layers such as Li₂S and Li₃P. This leads to continuous electrolyte decomposition, a sharp increase in interface impedance, and severe degradation of battery performance. On the other hand, high-capacity silicon anodes undergo drastic volume changes (>300%) during cycling. This repeated expansion and contraction disrupts the integrity of the interface structure, exacerbates side reactions, and causes electrode pulverization and detachment, resulting in rapid capacity decay. Existing technologies struggle to effectively suppress interface side reactions and adapt to volume changes while maintaining high ion conductivity.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide an interfacial thin film, its preparation method, and its applications. The present invention introduces an amino acid analog into the negative electrode interfacial layer, preparing a uniform thin film via a casting method. The strong electron-withdrawing groups of the amino acid analog preferentially form a molecular-level protective layer, passivating the electrolyte surface, mitigating direct contact reactions with the negative electrode, and reducing electrolyte side reactions through its hydrophobicity. Simultaneously, its high electronegativity guides a uniform ion flux. Furthermore, the mixing of the amino acid analog and polyethylene oxide enhances the film's flexibility and deformability, better adapting to volume changes and stresses of the silicon negative electrode.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing an interfacial film, comprising the following steps: adding polyethylene oxide and lithium salt to a solvent and stirring at high speed until uniform; then adding an amino acid analog; ultrasonicating and stirring until completely dispersed; then performing defoaming treatment to obtain a uniformly dispersed precursor solution; injecting the precursor solution into a polytetrafluoroethylene template; spontaneously forming a film by casting; allowing some solvent to evaporate by standing; and finally obtaining the interfacial film by vacuum drying. The general structural formula of the amino acid analog is H2N-CH(R)-COOH, wherein the R group is a phenyl compound substituted with at least three fluorine atoms.

[0007] In some preferred embodiments, the molecular weight of the polyethylene oxide is 100,000-6,000,000; the solvent includes at least one of benzyl alcohol, dichloromethane, tetrahydrofuran, chloroform, N,N-dimethylformamide, N-methyl-2-pyrrolidone, acetonitrile, and ethylene carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide; and the amino acid analog includes at least one of 4-trifluoromethylphenylalanine, pentafluoropyridylalanine, and pentafluorophenylalanine.

[0008] In some preferred embodiments, the polyethylene oxide has a weight-average molecular weight of 600,000; the solvent is N,N-dimethylformamide; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide; and the amino acid analog is pentafluorophenylalanine.

[0009] In some preferred embodiments, the precursor solution contains 1%-10% lithium salt by mass, 1%-25% polyethylene oxide by mass, 1%-25% amino acid analog by mass, and the molar ratio of polyethylene oxide to lithium salt is (10-25):1.

[0010] In some preferred embodiments, the precursor solution contains 1%-6% lithium salt by mass, 5%-10% polyethylene oxide by mass, 3%-10% amino acid analog by mass, and 5%-20% polyethylene oxide and lithium salt by mass.

[0011] In some preferred embodiments, the frequency of the ultrasound is 500-2000Hz, the stirring speed is 500-2000rpm, and the time is 1-10h; the defoaming speed is 300-2000rpm, and the time is 1-10h.

[0012] In some preferred embodiments, the polytetrafluoroethylene mold plate has a thickness of 0.1-5 cm and a diameter of 2-15 cm.

[0013] In some preferred embodiments, the settling temperature is 20-35°C, the time is 1-10 hours, and the vacuum degree of the vacuum drying is 10. -1 Up to 10 -2 The drying time for pa is 12-24 hours, and the drying temperature is 60-80℃.

[0014] Secondly, the present invention proposes an interface film prepared by the above preparation method, wherein the thickness of the film is 0.5-5 mm.

[0015] Thirdly, this invention proposes the application of an interface thin film in the negative electrode of an all-solid-state battery.

[0016] The present invention has the following beneficial effects: (1) This invention introduces an amino acid analog into the interfacial thin film layer, which can bind to the active sites of the electrolyte layer to form a passivation layer, thereby mitigating or preventing interfacial side reactions caused by the contact between the electrolyte and the negative electrode. Simultaneously, as an electrolyte thin film layer, it improves ionic conductivity and enhances electrochemical cycling performance. Furthermore, the amino acid analog plays a role in uniformly distributing lithium ion flux, guiding the uniform deposition of lithium ions at the interface for the lithium negative electrode, resulting in a uniform current distribution at the interface and inhibiting the growth of lithium dendrites.

[0017] (2) The present invention prepares the precursor solution by simple mixing and prepares a uniform film by casting. The cost is low and the experimental process is simple and easy to operate.

[0018] (3) The present invention mixes amino acid analogs and polyethylene oxide to form a uniform, tough and viscous film that can effectively adapt to the repeated volume changes during the silicon anode cycling process, reduce interfacial stress, maintain the integrity of the anode structure, and improve the cycle capacity and life of the battery. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of an interface thin film provided in this application. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The following provides a detailed description of the interface thin film proposed in this invention, its preparation method, and its application.

[0023] In a first aspect, the present invention provides an interface film, the schematic diagram of which is shown below. Figure 1 The method involves introducing an amino acid analog molecule into the electrolyte interface layer and preparing a uniform thin film using a casting method. The amino acid analog's molecular side chain is a phenyl compound with at least three fluorine atoms substituted. This compound is a strong electron-withdrawing group, which facilitates binding to the active sites of the electrolyte layer, forming a protective layer at the electrolyte interface and preventing side reactions between the electrolyte and the negative electrode. The unique properties of the amino acid analog are dominated by its side chain, thus exhibiting strong hydrophobicity and lipophilicity. This is an advantage for water-sensitive sulfide electrolytes in solid-state batteries, avoiding the influence of moisture. Furthermore, the side chain substituents possess extremely high chemical stability, maintaining stable structure and chemical properties during cycling.

[0024] Polyethylene oxide (PEO) has a flexible segmental molecular structure that is semi-crystalline at room temperature and possesses a certain lithium-ion transport capability. PEO contains regularly shaped crystalline regions and irregularly shaped amorphous regions. Lithium ions primarily move through the amorphous regions. To improve the mobility of PEO segments and increase ion conductivity, small-molecule fillers can be doped into PEO. The introduction of small molecules hinders the regular arrangement of PEO segments through hydrogen bonding and steric hindrance, increasing the proportion of amorphous segments in the amorphous regions. Therefore, the segments have stronger mobility at room temperature, thus enhancing ion transport.

[0025] By introducing PEO molecules and amino acid analogs, a tough, viscous, and uniform thin film was prepared. This film effectively prevents side reactions between the electrolyte and the negative electrode at the interface, improves ion transport capacity, and ensures uniform ion flux. Simultaneously, it effectively adapts to the volume changes of the negative electrode during cycling, maintaining its structure and guaranteeing stable electrochemical cycling.

[0026] Secondly, the present invention provides a method for preparing an interface thin film, comprising the following steps: S1. Add polyethylene oxide and lithium salt to the solvent and stir at high speed until homogeneous. Then add amino acid analog, sonicate and stir until completely dispersed. Observe whether the mixed solution contains bubbles. If there are bubbles, use a degassing machine to degas and obtain a uniformly dispersed precursor solution.

[0027] In some preferred embodiments, the molecular weight of the polyethylene oxide is 100,000-6,000,000, preferably a polyethylene oxide with a weight-average molecular weight of 600,000. The solvent includes at least one of benzyl alcohol, dichloromethane, tetrahydrofuran, chloroform, N,N-dimethylformamide, N-methyl-2-pyrrolidone, acetonitrile, and ethylene carbonate, preferably N,N-dimethylformamide (DMF). The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(trifluoromethanesulfonyl)imide, preferably lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The amino acid analog has the general structural formula H2N-CH(R)-COOH, wherein the R group is a phenyl compound substituted with at least three fluorine atoms. Preferably, the amino acid analog includes at least one of 4-trifluoromethylphenylalanine, pentafluoropyridylalanine, and pentafluorophenylalanine. More preferably, the amino acid analog is pentafluorophenylalanine (PFPA), with the general structural formula H2N-CH(CH2-C6F5)-COOH.

[0028] In some preferred embodiments, the lithium salt in the precursor solution accounts for 1%-10% by mass, preferably 1%-6%; The mass percentage of the polyoxyethylene is 1%-25%, preferably 5%-10%; The mass percentage of the amino acid analog is 1%-25%, preferably 3%-10%; Preferably, the proportion of the polyethylene oxide and the lithium salt is 5%-20%; Preferably, the molar ratio of the polyethylene oxide to the lithium salt is (10-25):1.

[0029] In some preferred embodiments, the frequency of the ultrasound is 500-2000Hz, the stirring speed is 500-2000rpm, and the time is 1-10h; the defoaming speed is 300-2000rpm, and the time is 1-10h.

[0030] S2. The precursor solution is injected into the polytetrafluoroethylene template, and a film is formed spontaneously by casting. After standing, some of the solvent evaporates, and finally the interface film is obtained by vacuum drying. In some preferred embodiments, the polytetrafluoroethylene mold plate has a thickness of 0.1-5cm and a diameter of 2-15cm, preferably a thickness of 0.1-1cm and a diameter of 2-10cm; The settling temperature is 20-35℃, the time is 1-10 hours, preferably 5-8 hours, and the vacuum degree of the vacuum drying is 10. -1 Up to 10 -2The drying time for pa is 12-24 hours, and the drying temperature is 60-80℃.

[0031] In some preferred embodiments, the thickness of the interface film is 0.5-5 mm, preferably 1-5 mm.

[0032] Thirdly, this invention proposes the application of an interface thin film in the negative electrode of an all-solid-state battery.

[0033] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0034] Example 1 This embodiment provides a method for preparing an interface thin film, the steps of which include: 1 g of polyethylene oxide (Mw = 600,000) and 0.005 g of lithium bis(trifluoromethanesulfonyl)imide were dissolved in 20 mL of N,N-dimethylformamide and dispersed by high-speed stirring at 900 rpm to prepare a 5% polymer matrix solution. 5% PFPA was added to the above solution, and the mixture was ultrasonically treated at 1500 Hz in an ultrasonic water bath while stirring at 600 rpm for 1 h. The resulting solution was then degassed at 1000 rpm in a degassing machine to obtain a homogeneous PFPA precursor solution.

[0035] The PFPA precursor solution was injected into a polytetrafluoroethylene mold with a thickness of 1.4 cm and a diameter of 8 cm, and the solution spontaneously cast into a film. After being placed at room temperature for 8 hours, it was transferred to a vacuum drying oven and dried under vacuum at 60°C for 12 hours to obtain the PFPA film.

[0036] Example 2 This embodiment provides a method for preparing an interface film, the steps of which are the same as those in Example 1, except that: 0.5 g of polyethylene oxide (Mw=600,000) is mixed with 0.005 g of lithium bis(trifluoromethanesulfonyl)imide to prepare a 2.5% polymer matrix solution.

[0037] Example 3 This embodiment provides a method for preparing an interface film, the steps of which are the same as those in Example 1, the only difference being that polyethylene oxide with Mw=300,000 is used.

[0038] Example 4 This embodiment provides a method for preparing an interface film, the steps of which are the same as those in Example 1, the only difference being that the amount of PFPA added is 3%.

[0039] Example 5 This embodiment provides a method for preparing an interface film, the steps of which are the same as those in Example 1, the only difference being that: the PFPA precursor solution is injected into a polytetrafluoroethylene mold with a thickness of 2 cm and a diameter of 6 cm, and the solution spontaneously flows and forms a film.

[0040] Comparative Example 1 This comparative example provides a method for preparing an interface film, the steps of which are the same as those in Example 1, except that: no PFPA molecules are added, and the precursor solution is composed of PEO and LiTFSI.

[0041] Comparative Example 2 This comparative example provides a method for preparing an interface film, the steps of which are the same as those in Example 1, except that the amount of PFPA added is 10%.

[0042] Test case The interface films prepared in Examples 1-5 and Comparative Examples 1-2 were used to assemble batteries, and the batteries were subjected to performance testing.

[0043] Battery assembly method: The molded full cell was assembled in a glove box. The protective gas inside the glove box was argon, and the partial pressures of water and oxygen were both below 1 ppm. The positive electrode material was NCM811 powder, the negative electrode material was silicon powder, and the solid electrolyte was a sulfide. A prepared PFPA film was added at the electrolyte-negative electrode interface. The N / P ratio of the positive and negative electrodes was 1.2. Battery testing method: Cut-off voltage 2.0~4.25 V, first charge and discharge at 0.1 C rate for 2 cycles, then charge and discharge at 1.0 C rate for 100 cycles, record the capacity retention rate, and the data are shown in Table 1.

[0044] All-solid-state battery assembly method: Solid-state all-solid-state batteries are assembled in a glove box. The protective gas in the glove box is argon, and the partial pressures of water and oxygen are both below 1 ppm. NCM811 and silicon are used as the positive and negative electrodes, respectively. A PFPA thin film is introduced at the interface between the negative electrode and the electrolyte. All-solid-state batteries are assembled using the thin films from the various embodiments and comparative examples.

[0045] Full battery testing method: Set the charging and discharging rates. First, perform two charge-discharge cycles at a current rate of 0.1C, followed by a long charge-discharge cycle at a current rate of 1.0C. The voltage cutoff range is 2.0V~4.25V. Record the discharge capacity of the first cycle and the capacity retention rate after 100 cycles, as shown in Table 1.

[0046] Table 1. Capacity retention rate of button cell after 30 cycles and cycle count of symmetrical cell under short circuit.

[0047] Table 1 shows that the prepared interfacial films all exhibited certain electrochemical performance in all-solid-state batteries, but the performance varied under different preparation conditions. Overall, Examples 1, 3, and 5 showed higher first-cycle discharge specific capacities (187.6, 185.1, and 190.1 mAh g⁻¹, respectively). -1 The films prepared under these conditions exhibited excellent capacity retention after 100 cycles, at 87.3%, 86.1%, and 90.2%, respectively, indicating good interfacial stability and cycle durability. Example 5 showed the best overall performance, possibly due to optimized film thickness or film formation conditions contributing to a more stable electrode-electrolyte interface. In Examples 2 and 4, reduced polymer concentration or PEPA addition slightly decreased capacity and cycle retention, but still outperformed the comparative examples. Comparative Example 1, without PEPA, showed a significant decrease in electrochemical performance, demonstrating the crucial role of PEPA in improving interfacial compatibility and battery cycle stability. In Comparative Example 2, with PEPA addition increased to 10%, although the capacity retention was higher than Comparative Example 1, it was still lower than most examples, suggesting that excessive PEPA may adversely affect film structure or ion conduction.

[0048] In summary, the PFPA interface film prepared in this application can significantly improve the cycle performance of the battery, which is attributed to the unique properties of PFPA. The electron-withdrawing groups in PFPA preferentially protect the electrolyte, reducing side reactions caused by contact between the electrolyte and the negative electrode. PFPA contains a large number of F atoms, which can guide the uniform flux of lithium ions during cycling and reduce the growth of lithium dendrites. Furthermore, the introduction of flexible PEO segments helps to alleviate rigid stress on the negative electrode during cycling, promoting battery cycle stability and cycle life.

[0049] 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 an interfacial thin film, characterized in that, Includes the following steps: Polyethylene oxide and lithium salt were added to a solvent and stirred at high speed until homogeneous. Then, an amino acid analog was added, and the mixture was ultrasonically stirred until completely dispersed. Defoaming was then performed to obtain a uniformly dispersed precursor solution. The precursor solution was injected into a polytetrafluoroethylene template, and a film was formed spontaneously by casting. After standing, some of the solvent was evaporated, and finally, the interfacial film was obtained by vacuum drying. The general structural formula of the amino acid analog is H2N-CH(R)-COOH, wherein the R group is a phenyl compound substituted with at least three fluorine atoms.

2. The method for preparing an interface thin film according to claim 1, characterized in that, The molecular weight of the polyethylene oxide is 100,000-6,000,000; the solvent includes at least one of benzyl alcohol, dichloromethane, tetrahydrofuran, chloroform, N,N-dimethylformamide, N-methyl-2-pyrrolidone, acetonitrile, and ethylene carbonate; the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide; the amino acid analog includes at least one of 4-trifluoromethylphenylalanine, pentafluoropyridylalanine, and pentafluorophenylalanine.

3. The method for preparing an interface thin film according to claim 2, characterized in that, The weight-average molecular weight of the polyethylene oxide is 600,000; the solvent is N,N-dimethylformamide; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide; and the amino acid analog is pentafluorophenylalanine.

4. The method for preparing an interface thin film according to claim 1, characterized in that, The precursor solution contains 1%-10% lithium salt by mass, 1%-25% polyethylene oxide by mass, 1%-25% amino acid analog by mass, and the molar ratio of polyethylene oxide to lithium salt is (10-25):

1.

5. The method for preparing an interface thin film according to claim 4, characterized in that, The precursor solution contains 1%-6% lithium salt by mass, 5%-10% polyethylene oxide by mass, 3%-10% amino acid analog by mass, and 5%-20% polyethylene oxide and lithium salt by mass.

6. The method for preparing an interface thin film according to claim 1, characterized in that, The ultrasonic frequency is 500-2000Hz, the stirring speed is 500-2000rpm, and the time is 1-10h; the defoaming speed is 300-2000rpm, and the time is 1-10h.

7. The method for preparing an interface thin film according to claim 1, characterized in that, The thickness of the polytetrafluoroethylene mold plate is 0.1-5cm, and the diameter is 2-15cm.

8. The method for preparing an interface thin film according to claim 1, characterized in that, The settling temperature is 20-35℃, the time is 1-10 hours, and the vacuum degree of the vacuum drying is 10. -1 Up to 10 -2 The drying time for pa is 12-24 hours, and the drying temperature is 60-80℃.

9. An interfacial thin film obtained by the preparation method according to any one of claims 1-8, characterized in that, The thickness of the film is 0.5-5 mm.

10. The application of the interface film as described in claim 9 in the negative electrode of an all-solid-state battery.

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