Electrolyte additive for imparting fluorescence and visual observation properties to sei films and its use in lithium metal batteries

Abstract

This application provides an electrolyte additive that enables the SEI film to possess fluorescence and visualization observation properties, and its application in lithium metal batteries. The electrolyte additive's structural formula includes at least one polymerizable structural unit, at least one active ion transport structural unit, and at least one fluorescent tracer structural unit. The polymerizable structural unit contains a group with carbon-carbon unsaturated bonds, the active ion transport structural unit contains a polar group with heteroatoms, and the fluorescent tracer structural unit contains an aggregation-induced emission group. The electrolyte additive provided by this application can endow the solid electrolyte interphase (SEI film) on the lithium metal anode surface with the property of carrying its own fluorescence signal without interfering with the performance of the lithium metal battery. This allows for the visualization observation of the SEI film's formation-growth-destruction process, distribution area, and microstructure. It can also be used to perform semi-quantitative analysis of the SEI film abundance by measuring fluorescence intensity using a fluorescence spectrometer.

Description

Technical Field

[0001] This application relates to the field of battery energy technology, and in particular to an electrolyte additive that enables SEI films to have fluorescence and visualization observation properties and its application in lithium metal batteries. Background Technology

[0002] With increasing societal progress and technological advancements, the demands for energy storage, transportation, and efficient utilization are growing daily in human production and lifestyles. Currently, rechargeable batteries, represented by lithium-ion batteries, have become an indispensable part of our daily lives and various industrial sectors. However, the actual energy density of lithium-ion batteries (especially those with graphite anodes) is gradually approaching its theoretical upper limit (300Wh / kg), thus necessitating the development of new batteries with higher energy densities to meet future energy demands.

[0003] Lithium metal anodes possess extremely high theoretical capacity (3860 mAh / g) and the lowest electrode potential (-3.04 V vs. standard hydrogen electrode). Therefore, lithium metal batteries, using lithium metal as the anode material, have extremely high theoretical energy density and are highly likely to become the next generation of energy storage batteries. The cycle performance, lifespan, and capacity of lithium metal batteries are closely related to the uniformity and density of the solid electrolyte interphase (SEI) film on the surface of the lithium metal anode. Generally speaking, the SEI film determines the transport behavior of lithium ions. Non-uniformly grown SEI films lead to non-uniform lithium ion transport, resulting in problems such as uneven lithium deposition and rapid capacity decay. On the other hand, the density of the SEI film is related to the surface strength of the anode sheet. If the SEI film has structural defects, it is prone to repeated rupture and regeneration, continuously consuming lithium and electrolyte, and also leading to the formation of inactive "dead lithium." Therefore, characterizing the formation-growth-destruction process, uniformity, and density of the SEI film structure on the lithium anode surface is crucial for a deeper understanding of the SEI film and for evaluating the cycle performance and expected lifespan of lithium metal batteries.

[0004] Currently, there are many characterization or detection techniques used to study the SEI film structure on the surface of lithium anodes. These techniques can be broadly classified into two categories: physical methods (such as electron microscopy, X-ray diffraction, atomic Raman spectroscopy, nuclear magnetic resonance, etc.) and electrochemical methods (such as voltammetry, voltage / capacitance curve analysis, etc.). However, existing methods obtain information about the electrode surface through specific signals, lacking direct observation and intuitive results, which makes researchers and industrial personnel still have very little understanding of SEI films. Summary of the Invention

[0005] Based on this, this application provides an electrolyte additive that enables the SEI film to have fluorescence and visualization observation performance and its application in lithium metal batteries. It can endow the solid electrolyte interphase (SEI film) on the surface of the lithium metal anode with the property of carrying fluorescence signals without interfering with the performance of the lithium metal battery. This enables the visualization observation of the SEI film formation-growth-destruction process, distribution area and micromorphology. It can also achieve semi-quantitative analysis of the abundance of the SEI film by measuring the fluorescence intensity with a fluorescence spectrometer.

[0006] The first aspect of this application provides an electrolyte additive that enables SEI films to exhibit fluorescence and visualization observation properties. The electrolyte additive comprises at least one polymerizable structural unit, at least one active ion transport structural unit, and at least one fluorescent tracer structural unit. The polymerizable structural unit contains a group with carbon-carbon unsaturated bonds, the active ion transport structural unit contains a polar group with heteroatoms, and the fluorescent tracer structural unit contains an aggregation-induced emission group.

[0007] In some embodiments of this application, the group with carbon-carbon unsaturated bonds includes one of terminal olefins, vinylides, cyclopentenes, and terminal alkynes.

[0008] In some embodiments of this application, the aggregation-induced light-emitting group includes one of tetraphenylethylene, pentaphenylthiophene, dipyrrolemethylphenidate, and pyrandiene derivatives.

[0009] In some embodiments of this application, the polar group with heteroatoms includes one of thiamine, amide, thioester, phosphoester, ester group, ether bond, secondary amine and tertiary amine.

[0010] In some embodiments of this application, the heteroatom includes at least one of nitrogen, oxygen, sulfur and halogen atoms.

[0011] In some embodiments of this application, the electrolyte additive includes at least one of tetraphenylethylene acrylate, tetraphenylethylene acrylamide, pentaphenylthiophene acrylate, pentaphenylthiophene acrylamide, dipyrrolemethyl acrylate, and dipyrrolemethyl acrylate.

[0012] In some embodiments of this application, the electrolyte additive includes tetraphenylethylene-acrylate or tetraphenylethylene-acrylamide.

[0013] In some embodiments of this application, the electrolyte additive includes compounds represented by Formula 1 or Formula 2:

[0014]

[0015] The second aspect of this application provides an electrolyte additive that enables the SEI film to have fluorescence and visualization observation properties in lithium metal batteries.

[0016] In some embodiments of this application, the lithium metal battery includes at least one of lithium-sulfur batteries, lithium-air batteries, and lithium-oxide batteries.

[0017] In some embodiments of this application, the application includes:

[0018] The electrolyte additive that enables the SEI film to have fluorescence and visualization observation properties is added to the electrolyte to obtain the prepared electrolyte;

[0019] The prepared electrolyte is added to the lithium metal battery for charge-discharge cycling to obtain an SEI film with fluorescence and visualization performance.

[0020] The electrolyte additive provided in this application, which enables the SEI film to exhibit fluorescence and visualization properties, comprises polymerizable structural units, active ion transport units, and fluorescent tracer structural units. The polymerizable structural units (such as terminal olefins) ensure that the additive molecules participate in the formation of a chemically bonded SEI film during battery formation or early cycling. The heteroatoms within the active ion transport units (such as ester or amide groups) can form chemical complexes or polar van der Waals forces with active ions such as lithium ions, helping to maintain or enhance the lithium-ion conductivity of the SEI film. The fluorescent tracer structural units (such as tetraphenylethylene) are primarily aggregation-induced luminescent, endowing the SEI film with the ability to emit fluorescence signals under ultraviolet light irradiation. During charge-discharge cycling in the lithium metal battery electrolyte, the electrolyte additive can copolymerize with other commonly used additives (such as vinylene carbonate) on the surface of the lithium metal anode to participate in the formation of the SEI film. This process simultaneously introduces polar heteroatom groups that facilitate the transport of active ions such as lithium ions and aggregation-induced emission groups that emit solid-state fluorescence into the SEI film, thus forming a fluorescently traceable SEI film on the surface of the lithium metal anode.

[0021] The electrolyte additives provided in this application are used similarly to conventional electrolyte additives. These additives can be mixed into commercial electrolytes at a concentration of 1% by mass, and then added to lithium metal batteries to participate in charge-discharge cycles, thereby obtaining SEI films for fluorescence tracers. These electrolyte additives are easy to prepare, do not interfere with battery performance or SEI film growth, provide clear and intuitive fluorescence phenomena, have high sensitivity and fidelity, are compatible with various electrolytes, and are widely applicable. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the molecular structure of the electrolyte additives used in Examples 1 and 2 to enable the SEI film to exhibit fluorescence and visual observation properties.

[0023] Figure 2 The images shown are the original microscopic images and fluorescence microscopic images of the lithium metal anode SEI films in Examples 1-2 and Comparative Example 1.

[0024] Figure 3 The graph shows the relationship between the fluorescence intensity of the lithium metal anode SEI film and the number of cycles in Examples 1 and 2. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0026] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value, or combined with other lower or upper limits, to form a range not explicitly stated.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be noted that, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, "above," "below," includes the stated number, and "one or more" with "multiple" means two or more.

[0028] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0029] Currently, to obtain direct observation and results of the SEI film on the negative electrode surface, methods exist that utilize aggregation-induced emission (AIE) molecules—catechol tetraphenylethylene—as solid-state fluorescent probes to analyze the SEI film structure, morphology, and distribution area of ​​lithium metal negative electrodes. This method typically involves disassembling the lithium metal battery after charge-discharge cycles, removing the lithium negative electrode, and introducing an exogenous solid-state fluorescent probe onto the lithium negative electrode surface. The AIE probe molecules generate fluorescence signal differences upon contact with the SEI film, uneven lithium deposition, or lithium dendrites, allowing for highly sensitive and high-contrast visualization of the negative electrode surface. However, the inventors discovered during their research that this method requires the introduction of an exogenous probe after battery disassembly and before observation, and the uniformity of the exogenous probe coating is crucial. Improper operation can easily lead to distortion of the observation results. Therefore, there is an urgent need to develop an endogenous probe that can act as an electrolyte additive. While the additive molecules participate in the formation of the SEI film, they can also enable the SEI film itself to carry and emit characteristic signals for tracking. Ultimately, this will enable in-situ observation and quantitative detection of the SEI film without any preparatory steps or the introduction of any exogenous impurities.

[0030] To address the aforementioned technical problems, the inventors have designed an electrolyte additive with a specific molecular structure through extensive research. This additive can endow the solid electrolyte interphase (SEI) film on the lithium metal anode surface with the property of carrying fluorescence signals without interfering with the performance of lithium metal batteries. This enables the visualization and observation of the SEI film formation-growth-destruction process, distribution area, and microstructure. It can also achieve semi-quantitative analysis of SEI film abundance by measuring fluorescence intensity using a fluorescence spectrometer. The design concept of the electrolyte additive's molecular structure is both the theoretical basis of this application and part of its original achievements.

[0031] A first aspect of this application provides an electrolyte additive that enables an SEI film to exhibit fluorescence and visualization properties. The electrolyte additive comprises at least one polymerizable structural unit, at least one active ion transport structural unit, and at least one fluorescent tracer structural unit. The polymerizable structural unit contains a group with carbon-carbon unsaturated bonds, the active ion transport structural unit contains a polar group with heteroatoms, and the fluorescent tracer structural unit contains an aggregation-induced emission group.

[0032] The electrolyte additive provided in this application, which enables the SEI film to possess fluorescence and visualization observation properties, includes a polymerizable structural unit, an active ion transport unit, and a fluorescent tracer structural unit. Its design concept primarily considers the three essential modules in the additive structure to achieve the function of a fluorescent tracer SEI film. Firstly, the polymerizable structural unit: during the battery formation and early cycling stages, unsaturated hydrocarbons in the electrolyte can electropolymerize on the lithium anode surface and become part of the SEI film. Therefore, introducing a polymerizable structural unit into the electrolyte additive can guide the additive molecules to form the SEI film and enhance the film strength. Secondly, the lithium-ion and other active ion transport unit: introducing polar, heteroatom-rich amide or ester groups into the molecular structure can effectively increase the conductivity of lithium-ions and other active ions at the SEI film. This design concept is similar to that of conventional ether and carbonate electrolytes. Thirdly, the fluorescent tracer structural unit: the aggregation-induced emission group portion of which enables the generated SEI film to possess fluorescent tracer imaging properties.

[0033] Accordingly, the electrolyte additive provided in this application can endow the solid electrolyte interphase (SEI) film on the surface of the lithium metal anode with the property of carrying its own fluorescence signal without interfering with the performance of the secondary battery. This enables the visualization and observation of the SEI film formation-growth-destruction process, distribution area, and microstructure. It also allows for semi-quantitative analysis of the SEI film abundance by measuring fluorescence intensity using a fluorescence spectrometer. Furthermore, this application is the first to achieve in-situ observation and detection of the SEI film using the electrolyte additive as an endogenous probe, without altering the electrode surface structure or introducing any exogenous impurities.

[0034] It is understood that the active ions in the active ion transport unit described in this application correspond to active ions in a secondary battery that can undergo charge-discharge cycles, such as lithium ions.

[0035] It is understood that in the electrolyte additive provided in this application, there is no particular limitation on the bonding order between the polymerizable structural units, the active ion transport units, and the fluorescent tracer structural units. The bonding can be made according to actual needs, as long as the electrolyte additive includes interconnected structural units of the above three parts. For example, the polymerizable structural unit can be bonded to the active ion transport unit, and simultaneously bonded to the fluorescent tracer structural unit; or the polymerizable structural unit can be bonded to the fluorescent tracer structural unit, and simultaneously bonded to the active ion transport unit, etc., which will not be elaborated here. Furthermore, it should be noted that when the polymerizable structural unit is a terminal olefin or terminal alkyne, the polymerizable structural unit can be located at any end of the molecular structure of the electrolyte additive.

[0036] Furthermore, the bonding methods between the polymerizable structural units, the active ion transport units, and the fluorescent tracer structural units are not particularly limited and will vary depending on the actual raw materials and preparation process. For example, the polymerizable structural units and the active ion transport units may be connected by a straight chain, and the active ion transport units and the fluorescent tracer structural units may also be connected by a straight chain; alternatively, the polymerizable structural units and the active ion transport units may be connected by a straight chain, and the active ion transport units and the fluorescent tracer units may be connected by a branched chain, etc., which will not be elaborated here.

[0037] It is understood that the polymerizable structural unit provided in this application may be a single group with carbon-carbon unsaturated bonds, or it may be a segment containing multiple groups with carbon-carbon unsaturated bonds. When the polymerizable structural unit is a segment containing multiple groups with carbon-carbon unsaturated bonds, the groups may be linked by straight chains or by branched chains.

[0038] It is understood that the active ion transport unit provided in this application may consist of only one polar group with heteroatoms, or it may be a fragment containing multiple polar groups with heteroatoms. When the active ion transport unit is a fragment containing multiple polar groups with heteroatoms, the groups may be connected by straight chains or by branched chains. Furthermore, each polar group with heteroatoms may contain one or more heteroatoms.

[0039] It is understood that the fluorescent tracer structural unit provided in this application may consist of only one aggregation-induced emission group, or it may be a fragment containing multiple aggregation-induced emission groups. When the active ion transport unit is a fragment containing multiple aggregation-induced emission groups, the groups may be connected by straight chains or by branched chains.

[0040] In some embodiments, the type of group with carbon-carbon unsaturated bonds is not specifically limited, as long as it can be bonded to the active ion transport unit or the fluorescent tracer unit, and ensures that the electrolyte additive that enables the SEI film to have fluorescence and visual observation properties can copolymerize with other film-forming aids in the electrolyte (e.g., esters with carbon-carbon unsaturated double bonds) during the battery formation stage or the early stage of cycling, so that the electrolyte additive participates in the formation process of the SEI film. For example, the group with carbon-carbon unsaturated bonds may include one of terminal olefins, vinylenes, cyclopentenes, and terminal alkynes.

[0041] In some embodiments, the type of polar group with heteroatoms is not specifically limited, as long as it can bond to the polymerization unit or the fluorescent tracer unit and form a chemical complex or polar van der Waals force with the active ions to help maintain or enhance the transport of the active ions at the negative electrode. For example, the polar group with heteroatoms may include one of thiamines, amides, thioesters, phospholipids, ester groups, ether bonds, secondary amines, and tertiary amines.

[0042] In some embodiments, the heteroatoms include at least one of nitrogen, oxygen, sulfur, and halogen atoms. Heteroatoms with higher electronegativity facilitate the guidance of active ions through the SEI film to the negative electrode via polar and electrostatic interactions, thereby helping to maintain or enhance the active ionic conductivity of the SEI film and preserve the electrochemical performance of the battery.

[0043] In some embodiments, the type of aggregation-induced emission group is not specifically limited, as long as it can be bonded to the polymerization unit or the active ion transport unit and has the function of emitting fluorescent signals itself. For example, the aggregation-induced emission group may include one of tetraphenylethylene, pentaphenylthiophene, dipyrrolemethyl ether, and pyrandiene derivatives.

[0044] In some embodiments, the electrolyte additive that imparts fluorescence and visualization properties to the SEI membrane comprises a polymerizable structural unit (A), an active ion transport structural unit (Z), and a fluorescent tracer structural unit (V), which are sequentially linked by single bonds. In this embodiment, the structural formula of the electrolyte additive may be represented as AZV.

[0045] Alternatively, A can be CH2=CH2-(CH2). n - where n represents an integer from 0 to 10.

[0046] Alternatively, Z can be -C(O)-O- or -C(O)-NH-.

[0047] Optionally, V is tetraphenylvinyl, pentaphenylthiophenyl, or dipyrrolidinyl.

[0048] In some embodiments, the type of electrolyte additive that imparts fluorescence and visualization properties to the SEI film can be determined based on the types of three structural units contained in the electrolyte additive. The electrolyte additive may include tetraphenylethylene-acrylate and tetraphenylethylene-acrylamide, as well as acryloyltetraphenyl molecules linked by heteroatom groups such as thioesters, phospholipids, and ether bonds, and polysubstituted acryloyltetraphenyl molecules.

[0049] For example, electrolyte additives may include at least one of tetraphenylethylene acrylate, tetraphenylethylene acrylamide, pentaphenylthiophene acrylate, pentaphenylthiophene acrylamide, dipyrrolemethyl acrylate, and dipyrrolemethyl acrylate. Preferably, electrolyte additives include tetraphenylethylene acrylate and tetraphenylethylene acrylamide.

[0050] More preferably, the electrolyte additive can be a compound represented by Formula 1 or Formula 2:

[0051]

[0052] The electrolyte additives provided in this application, which enable the SEI film to exhibit fluorescence and visualization properties, allow the SEI film itself to carry fluorescence signals. This enables the direct acquisition of high-contrast images of the SEI film distribution area and microstructure. Semi-quantitative analysis of the SEI film abundance can be achieved by measuring the fluorescence intensity using a fluorescence spectrometer. This method can also be combined with various parameters such as current density, cycle number, operating temperature, and cell formulation to study the formation, growth, and degradation of SEI films under different conditions.

[0053] Furthermore, this type of electrolyte additive not only endows the SEI film with fluorescence tracing and imaging capabilities but also maintains the electrochemical performance of the battery without interfering with the electrode interface structure and cycling behavior. The resulting SEI film inherently possesses visible light optical signals, enabling visual observation and semi-quantitative / quantitative detection of crucial information such as the formation-growth-destruction process, distribution area, microstructure, and surface abundance of the SEI film. This provides a novel design approach and research direction for studying the electrochemical behavior of the battery anode and analyzing the intrinsic relationship between SEI film properties and parameters such as cycling conditions and cell formulation. This type of electrolyte additive is convenient to prepare, does not interfere with battery performance or SEI film growth, provides intuitive and obvious fluorescence phenomena, exhibits high sensitivity and fidelity, is compatible with various electrolytes, and has a wide range of applications.

[0054] The second aspect of this application provides an electrolyte additive that enables the SEI film to have fluorescence and visualization observation properties in lithium metal batteries.

[0055] In some embodiments, the lithium metal battery includes at least one of lithium-sulfur batteries, lithium-air batteries, and lithium-oxide batteries.

[0056] In some embodiments, the application includes: adding the electrolyte additive that imparts fluorescence and visualization properties to the SEI film to an electrolyte to obtain a prepared electrolyte;

[0057] The prepared electrolyte is added to the lithium metal battery for charge-discharge cycling to obtain an SEI film with fluorescence and visualization performance.

[0058] In some embodiments, the specific detection steps of the SEI film are as follows: after the lithium metal battery is charged and discharged, the battery is disassembled and the lithium metal negative electrode is removed. The electrode is then placed under a fluorescence microscope under the illumination of a 365nm handheld ultraviolet lamp. This allows for the visualization of the SEI formation-growth-destruction process, the film distribution area, and the microstructure. Alternatively, a fluorescence spectrometer can be used to measure the fluorescence intensity to achieve a semi-quantitative analysis of the SEI film abundance.

[0059] As examples of electrolyte additives that enable SEI films to exhibit fluorescence and visualization properties, and their application in lithium metal batteries, see the appendix. Figure 1 The figures shown represent structural formulas of tetraphenylethylene acrylate and tetraphenylethylene acrylamide, respectively. The molecular structures of both tetraphenylethylene acrylate and tetraphenylethylene acrylamide follow the pattern of "polymerizable unit-active ion transport unit-tracer unit" (corresponding to...). Figure 1 The design principles (corresponding to ①, ②, and ③ in the text) are as follows: the propylene structure ensures that the electrolyte additive molecules polymerize to form the SEI film, enabling fluorescence and visualization of the SEI film; amide and ester groups guide active ions (such as lithium ions) through the SEI film to the negative electrode; and the tetraphenylethylene structure is a typical aggregation-induced emission source, emitting blue-green fluorescence signals in solid or poor solvents. Tetraphenylethylene-acrylate or tetraphenylethylene-acrylamide is mixed at a concentration of 1% by mass into a commercial electrolyte, which is then added to a lithium metal battery for charge-discharge cycling to prepare an SEI film for fluorescence tracking. Afterward, the respective lithium negative electrode is removed for observation. The lithium metal battery is disassembled, and the lithium metal negative electrode is observed under a fluorescence microscope under 365nm handheld UV light. This allows for visualization of the SEI film formation-growth-destruction process, film distribution area, and microstructure. Semi-quantitative analysis of SEI film abundance can also be achieved by measuring fluorescence intensity using a fluorescence spectrometer.

[0060] Example

[0061] The following are specific embodiments, which describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0062] Example 1

[0063] Preparation of electrolyte additives that enable SEI films to exhibit fluorescence and visualization properties

[0064] 1.85 g of 4-(1,2,2-triphenylyl)phenol (CAS No. 76115-06-5) and 1.07 g of triethylamine were dissolved in 10 mL of anhydrous tetrahydrofuran, and the solution was cooled to -30°C. 624 mg of acryloyl chloride was slowly added dropwise over ten minutes. The reaction mixture was then heated to room temperature (approximately 20°C) and stirred for 24 hours. After the reaction was complete, the solution was evaporated to dryness under vacuum, washed with ethyl acetate and saturated brine, and the organic phase was separated to obtain the crude product. The crude product was purified by silica gel chromatography (eluent ratio: petroleum ether / dichloromethane = 4 / 1) to obtain 4-(1,2,2-triphenylvinyl)phenyl acrylate (yield 37.5%).

[0065] Preparation of lithium metal batteries

[0066] The lithium metal battery used is a Li|Li symmetrical coin cell, with lithium plates as both positive and negative electrodes. The electrolyte is 1 mol / L LiPF6 / EC+DEC+EMC (mass ratio 1:1:1), with 1 wt% vinylene carbonate and 1 wt% tetraphenylethylene acrylate added. The separator is Celgard 2500.

[0067] Example 2

[0068] Preparation of electrolyte additives that enable SEI films to exhibit fluorescence and visualization properties

[0069] 1.38 g of potassium carbonate was dissolved in 2.5 mL of ice water, and 905 mg of acryloyl chloride was dissolved in 10 mL of anhydrous acetone. The two solutions were mixed to form the reaction system, which was then cooled to 0 °C. 1.737 g of 4-(1,2,2-triphenylyl)aniline (CAS No. 919789-80-3) was dissolved in 5 mL of anhydrous acetone and added dropwise to the reaction system. The system was maintained at 0 °C and stirred for 12 hours. After the reaction was completed, the mixture was evaporated to dryness under vacuum, washed with a small amount of ethyl acetate and saturated brine, and the organic phase was separated to obtain the crude product. The crude product was purified by silica gel chromatography (eluent ratio: petroleum ether / dichloromethane = 1 / 1) to obtain 4-(1,2,2-triphenylvinyl)phenylacrylamide (yield 72.7%).

[0070] Preparation of lithium metal batteries

[0071] The lithium metal battery used is a Li|Li symmetrical coin cell, with lithium sheets as both positive and negative electrodes. The electrolyte is 1 mol / L LiPF6 / EC+DEC+EMC (mass ratio 1:1:1), the separator is Celgard 2500, and 1 wt% vinylene carbonate and 1 wt% tetraphenylethylene-acrylamide are added to the electrolyte.

[0072] Comparative Example 1

[0073] The preparation method of Comparative Example 1 is similar to that of Example 1, except that the electrolyte of the lithium metal battery does not contain the electrolyte additives provided in this application that enable the SEI film to have fluorescence and visualization observation performance.

[0074] The lithium metal batteries prepared in Examples 1-2 and Comparative Example 1 were subjected to charge-discharge cycles. The charge-discharge program was: rest for 2 hours, 1.0 mAh / cm³. 2 Charge for 1 hour, discharge for 1 hour, repeat 5 times. Afterwards, disassemble the lithium metal battery and remove the negative electrode. Observe the electrode under a fluorescence microscope under a 365nm handheld UV lamp. The results are shown in the attached figure. Figure 2 As shown, (a1), (b1) and (c1) are the original microscopic images of the lithium anode surface, while (a2), (b2) and (c2) are the fluorescence microscopic images of the lithium anode surface.

[0075] like Figure 2 As shown, the lithium metal anode surface (a2) without the electrolyte additives provided in this application shows almost no fluorescence signal, requiring other characterization methods to study its surface SEI film. In contrast, the SEI films (b2 and c2) on the lithium metal anode surface with added tetraphenylethylene-acrylate or tetraphenylethylene-acrylamide inherently possess fluorescence signals, allowing direct observation of the SEI film's distribution area and microstructure. After measuring the fluorescence intensity using a fluorescence spectrometer, a semi-quantitative analysis of the overall SEI growth on the electrode surface can be performed. When the battery is cycled with different numbers of cycles and different charge / discharge current densities, this method can visualize and perform semi-quantitative or quantitative analysis of the distribution, morphology, and concentration of the SEI film on the lithium anode surface under different conditions. Figure 3 As shown, the correlation between the number of cycles and the growth of the SEI film was observed under a fixed current density. The semi-quantitative abundance of the SEI film under different number of cycles can be given by fluorescence intensity.

[0076] Based on the above comparison, it can be seen that the electrolyte additive of this application does not interfere with the growth of the SEI film on the surface of the lithium metal anode, and endows the SEI film with the function of exhibiting fluorescence signals under ultraviolet light irradiation. Based on the luminescence of the SEI film itself, its distribution area and microstructure can be visualized and observed, and the abundance of the SEI film can be semi-quantitatively analyzed by measuring the fluorescence intensity using a fluorescence spectrometer. In other words, the electrolyte additive provided by this application not only endows the SEI film with fluorescence tracing and imaging functions, but also maintains the electrochemical performance of the lithium metal battery and does not interfere with the interface structure and cycling behavior of the lithium metal electrode. The resulting SEI film inherently possesses optical signals in the visible light band, enabling visual observation and semi-quantitative / quantitative detection of important information such as the formation-growth-destruction process, distribution area, microstructure, and surface abundance of the SEI film. This provides a novel design approach and research direction for studying the electrochemical behavior of the battery anode and analyzing the intrinsic relationship between SEI film properties and parameters such as cycling conditions and cell formulation.

[0077] To date, research on the SEI film in lithium metal batteries has largely focused on micromorphology control, electrolyte formulation adjustment, and modification of exogenous composite materials. The method provided in this application for direct observation and detection of the SEI film using electrolyte additives and fluorescence tracer technology is unprecedented. Apart from fluorescent probe methods, no other characterization method can clearly and intuitively observe and detect the distribution area and micromorphology of the SEI film without altering the electrode surface structure or affecting battery cycle performance. Therefore, this application offers advantages such as simplicity, convenience, intuitiveness, high sensitivity and fidelity, and wide applicability.

[0078] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. Use of an electrolyte additive that imparts fluorescent and visual observation properties to an SEI film in a lithium metal battery, characterized in that, The electrolyte additive comprises at least one polymerizable structural unit, at least one active ion transport structural unit, and at least one fluorescent tracer structural unit. The polymerizable structural unit contains a group with carbon-carbon unsaturated bonds, the active ion transport structural unit contains a polar group with heteroatoms, and the fluorescent tracer structural unit contains an aggregation-induced emission group. The group containing carbon-carbon unsaturated bonds includes one of terminal alkenes, vinylides, cyclopentenes, and terminal alkynes; The aggregation-induced light-emitting group includes one of tetraphenylethylene, pentaphenylthiophene, dipyrrolemethyl ether, and pyrandiene derivatives; The polar groups with heteroatoms include one of thiamines, amides, thioesters, phospholipids, ester groups, ether bonds, secondary amines, and tertiary amines; The heteroatom includes at least one of nitrogen, oxygen, sulfur and halogen atoms.

2. The application of the electrolyte additive described in claim 1, which imparts fluorescence and visualization performance to the SEI film, in lithium metal batteries, characterized in that... The electrolyte additive includes at least one of tetraphenylethylene acrylate, tetraphenylethylene acrylamide, pentaphenylthiophene acrylate, pentaphenylthiophene acrylamide, dipyrrolemethyl acrylate, and dipyrrolemethyl acrylate.

3. The application of the electrolyte additive according to claim 1 or 2, which imparts fluorescence and visualization performance to the SEI film, in lithium metal batteries, characterized in that... The electrolyte additives include tetraphenylethylene-acrylate or tetraphenylethylene-acrylamide.

4. The application of the electrolyte additive described in claim 2, which imparts fluorescence and visualization performance to the SEI film, in lithium metal batteries, characterized in that... The electrolyte additive includes compounds represented by Formula 1 or Formula 2: Formula 1, Formula 2.

5. The application of the electrolyte additive according to claim 1 or 2, which imparts fluorescence and visualization performance to the SEI film, in lithium metal batteries, characterized in that... The lithium metal battery includes at least one of lithium-sulfur batteries, lithium-air batteries, and lithium oxide batteries.

6. The application of the electrolyte additive according to claim 1 or 2, which imparts fluorescence and visualization performance to the SEI film, in lithium metal batteries, characterized in that... The applications include: The electrolyte additive that enables the SEI film to have fluorescence and visualization observation properties is added to the electrolyte to obtain the prepared electrolyte; The prepared electrolyte is added to the lithium metal battery for charge-discharge cycling to obtain an SEI film with fluorescence and visualization performance.

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