Application of hydrazine hydrazone compound probe in detection of lithium metal negative electrode

Abstract

The application relates to application of a hydrazine dihydrazone compound as a probe in detection of a lithium metal negative electrode. The hydrazine dihydrazone compound has a structural formula shown in the following formula (1), wherein R1-R8 are each independently selected from one or more of a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an alkynyl group, an aryl group, a heteroalkyl group, a heterocyclic group, a heteroaryl group, an amino group, a nitro group, a cyano group, an isocyano group, a halogen, an alkylene group, an alkenylene group, an alkynylene group, a formyl group and an ester group. The hydrazine dihydrazone compound provided by the application can realize visual observation and semi-quantitative detection of the lithium metal negative electrode, and the detection process is simple, efficient, accurate, fast in response, good in stability and wide in applicability.

Description

Technical Field

[0001] This application relates to the field of battery energy technology, and in particular to the application of a hydrazine dihydrazone compound probe in the detection of lithium metal anodes. Background Technology

[0002] Lithium metal anodes have garnered significant attention from the scientific and industrial communities in recent years due to their theoretical potential to construct rechargeable secondary batteries with higher energy densities. However, lithium metal anodes face challenges during repeated cycling, including uneven lithium deposition (lithium dendrites), reduced coulombic efficiency, and the loss of active materials from the electrode and electrolyte due to side reactions. On one hand, the solid electrolyte interphase (SEI) layer formed between the lithium metal anode and the electrolyte through chemical and electrochemical reactions is considered a key factor determining the long-term stability of the battery. The structure, chemical, and thermodynamic properties of the SEI play a crucial role in achieving high levels of electrode reversibility in secondary batteries, especially in high-energy-density and low-cost battery systems where metal anodes are used. On the other hand, lithium dendrites are dendritic lithium crystals formed by the irregular electrodeposition of highly reactive lithium atoms at nucleation sites. They not only degrade battery performance, resulting in low coulombic efficiency and rapid capacity decay, but also pose serious safety hazards due to thermal runaway caused by internal short circuits. Furthermore, the nucleation and growth behavior of lithium dendrites is influenced by various factors due to the complexity of battery systems and the unique properties of lithium metal, making in-depth characterization and direct observation difficult. Therefore, studying the dendrite distribution, morphology, and relative abundance on the surface of lithium metal anodes is key to realizing next-generation high-energy-density and safe lithium metal batteries.

[0003] Traditional methods for studying the dendrite distribution, morphology, and relative abundance on the surface of lithium metal anodes lack direct observation and intuitive results. Therefore, developing a method for intuitive visual imaging and quantitative analysis of lithium metal anode surfaces is a key area of ​​focus for those skilled in the art. Summary of the Invention

[0004] Based on this, the present invention provides the application of hydrazine dihydrazone compound probes in the detection of lithium metal anodes. Using hydrazine dihydrazone compounds as probes, it is possible to achieve visual detection of lithium deposition, by-products, lithium dendrites, dead lithium, and solid electrolyte interface film on the surface of lithium metal anodes.

[0005] One aspect of this application provides the application of a hydrazine dihydrazone compound as a probe in the detection of lithium metal anodes, said hydrazine dihydrazone compound having the structural formula shown in formula (1):

[0006]

[0007] In formula (1), R1 to R8 are each independently selected from one or more of the following: hydrogen atom, alkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroalkyl, heterocyclic, heteroaryl, amino, nitro, cyano, isocyano, halogen, alkylene, alkenyl, alynyl, formyl, and ester.

[0008] In some embodiments, the hydrazine dihydrazone compound is selected from the structures described below:

[0009]

[0010] In some embodiments, the detection items include one or more of the following: deposited lithium, byproducts, lithium dendrites, dead lithium, and solid electrolyte interface film on the lithium metal anode surface.

[0011] In some embodiments, the byproducts include one or more of lithium fluoride, lithium chloride, lithium acetate, lithium carbonate, lithium hydroxide, lithium oxide, and lithium alkoxide.

[0012] In some embodiments, the lithium metal negative electrode is the lithium metal negative electrode in a lithium metal battery; the lithium metal battery is a lithium-oxygen battery, a lithium-sulfur battery, a lithium-oxide battery, a lithium-air battery, or a lithium-lithium battery.

[0013] A second aspect of this application provides a method for detecting lithium metal anodes, comprising the following steps:

[0014] Probe solutions were prepared by dissolving hydrazine dihydrazone compounds in organic solvents.

[0015] The probe solution is brought into contact with the surface of the lithium metal anode to be tested. After the organic solvent has evaporated to dryness, the analysis is performed under excitation light irradiation.

[0016] The hydrazine dihydrazone compound has the structural formula shown in formula (1):

[0017]

[0018] In formula (1), R1 to R8 are each independently selected from one or more of the following: hydrogen atom, alkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroalkyl, heterocyclic, heteroaryl, amino, nitro, cyano, isocyano, halogen, alkylene, alkenyl, alynyl, formyl, and ester.

[0019] In some embodiments, the hydrazine dihydrazone compound is selected from the structures described below:

[0020]

[0021] In some embodiments, the lithium metal negative electrode is the lithium metal negative electrode in a lithium metal battery; the lithium metal battery is a lithium-oxygen battery, a lithium-sulfur battery, a lithium-oxide battery, a lithium-air battery, or a lithium-lithium battery.

[0022] In some embodiments, the analysis steps include: visually observing the fluorescence of the lithium metal anode surface under test and / or using a fluorescence spectrometer to measure the fluorescence wavelength and fluorescence intensity.

[0023] In some embodiments, the concentration of hydrazine dihydrazone compounds in the probe solution is 1–10 mg / mL, optionally 2 mg / mL–4 mg / mL.

[0024] Compared with the prior art, this application has at least the following beneficial effects:

[0025] The hydrazine dihydrazone compounds provided in this application, when used as probes, can react with active lithium, unevenly deposited lithium, and lithium dendrites, respectively. The hydrazine dihydrazone compounds exhibit fluorescence changes before and after the reaction, while byproducts, SEI films, or dead lithium surrounded by byproducts do not react with the hydrazine dihydrazone compounds and show no fluorescence change. Therefore, deposited lithium, lithium dendrites, byproducts, dead lithium, and SEI films on the lithium metal anode surface can be visually detected and calibrated through fluorescence. In particular, the molecular structure of the hydrazine dihydrazone compounds provided in this application changes significantly before and after reacting with active lithium, unevenly deposited lithium, and lithium dendrites, resulting in a significant fluorescence emission shift and high readability and accuracy of the imaging results. Based on this, the hydrazine dihydrazone compounds provided in this application, as probes, can accurately detect the surface conditions of lithium metal anodes. Furthermore, this detection process is simple, efficient, accurate, fast-responding, stable, and widely applicable.

[0026] Furthermore, by combining fluorescence observation and fluorescence intensity detection, this application can semi-quantitatively and visually identify active lithium, lithium dendrites and their abundance, uneven lithium deposition, by-products and their accumulation, etc. It can also further link battery performance degradation and failure with the amount of lithium dendrites, uneven lithium deposition, and by-product accumulation, which is expected to provide a feasible method for analyzing the causes of battery failure and early prevention and warning of battery performance failure. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1The fluorescence spectrum of the salicylaldehyde hydrazide dihydrazone described in this application after interaction with lithium metal is shown. The fluorescence emission band of this probe molecule under 365 nm excitation light is relatively wide, with the maximum emission located at 539 nm, exhibiting yellow fluorescence. After interaction with lithium metal, the maximum emission blue shifts to 463 nm, the fluorescence response shift is as high as 76 nm, and the emission intensity increases.

[0029] Figure 2 The molecular structure and fluorescence changes of the salicylaldehyde-hydrazone fluorescent probe molecule described in this application before and after reaction with lithium metal are shown. The probe molecule does not exhibit fluorescence emission in solution, exhibits yellow fluorescence in solid state, and its fluorescence emission turns blue after interaction with lithium metal. Therefore, it has the ability to respond to active lithium and is suitable for imaging characterization of lithium anode interface species in lithium metal batteries.

[0030] Figure 3 The 1H NMR spectra of the salicylaldehyde-hydrazone dihydrazone described in this application before and after its reaction with lithium metal are shown below. 1 (H NMR); After the reaction, the phenolic hydroxyl peak at a chemical shift of 11.09 ppm disappeared, the ESIPT mechanism failed, and therefore a significant difference in fluorescence signal was observed;

[0031] Figure 4 The fluorescence stability spectrum of the salicylaldehyde hydrazine dihydrazone described in this application before and after interaction with lithium metal is shown. After continuous excitation for one hour under a 365 nm excitation source, the fluorescence intensity of the probe molecule at 539 nm remains at 51.0%, and the fluorescence intensity of the product after interaction with lithium metal at 463 nm remains at 28.7% after continuous excitation for one hour under a 365 nm excitation source.

[0032] Figure 5 The fluorescence spectrum of the salicylaldehyde hydrazine dihydrazone described in this application after interaction with inorganic lithium salts; after the probe molecule interacts with byproduct species such as lithium fluoride, lithium acetate, and lithium carbonate, it can still maintain intrinsic emission at 539 nm, and the emission intensity remains basically unchanged, indicating its inertness to SEI and byproducts.

[0033] Figure 6 The Li||Li coin cell used in this embodiment of the application was subjected to 25 charge-discharge cycles (charge-discharge current: 1.0 mAh / cm²). 2 After that, the battery was disassembled, and a 1.0 mg / mL solution of salicylaldehyde hydrazine dihydrazone was sprayed onto the surface fluorescence image of the lithium metal anode. The lithium metal substrate, uneven lithium deposition, lithium dendrites, etc. showed blue fluorescence, while the by-reaction products (lithium carbonate, lithium fluoride, lithium acetate and other lithium salts and other organic polymers) showed yellow fluorescence. The fluorescence intensity was then measured by a fluorescence spectrometer to perform semi-quantitative analysis of various components.

[0034] Figure 7The fluorescence spectra of ethylenediamine Schiff base, propylenediamine Schiff base, and butylenediamine Schiff base in the comparative examples of this application before and after interaction with lithium metal are shown. The fluorescence response shifts of the three molecules before and after interaction with lithium metal are 17-26 nm, and the color distinction of the fluorescence signal is not obvious, indicating a weaker response capability than that of the examples. Detailed Implementation

[0035] 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.

[0036] 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 is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0037] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0038] In this article, "one or more" refers to any one, two or more of the listed items.

[0039] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0040] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0042] The term "alkyl" refers to a saturated hydrocarbon containing a primary (normal) carbon atom, or a secondary carbon atom, or a tertiary carbon atom, or a quaternary carbon atom, or a combination thereof. Phrases containing this term, such as "C1-C9 alkyl," refer to alkyl groups containing 1 to 9 carbon atoms, and each occurrence can independently be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, or C9 alkyl. Suitable examples include, but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(CH3)CH2CH3), 2-methyl-2-propyl (t-Bu) t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (-CH2CH2CH(CH3)2), 2-methyl-1-butyl (-CH2CH(CH3)CH2CH3), 1-hexyl ( -CH2CH2CH2CH2CH2CH3), 2-hexyl(-CH(CH3)CH2CH2CH2CH3), 3-hexyl(-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl(-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl(-CH(CH3)CH(CH3)CH2CH3), 4-methyl-2-pentyl(-CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl(-C(CH3)(CH2CH3)2), 2-methyl The groups are 2,3-dimethyl-2-butyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3), and octyl (-(CH2)7CH3). The term "alkylene" refers to a divalent group formed by losing a hydrogen atom from an alkyl group. For example, "C1-C5 alkylene" refers to a divalent group formed by losing a hydrogen atom from a C1-C5 alkyl group, including straight-chain C1-C5 alkylene and branched C3-C5 alkylene.

[0043] The term "cycloalkyl" refers to a non-aromatic hydrocarbon containing a ring of carbon atoms, which can be monocycloalkyl, spirocycloalkyl, or bridged cycloalkyl. Phrases containing this term, such as "C3-C9 cycloalkyl," refer to cycloalkyl compounds containing 3 to 9 carbon atoms, and each occurrence can independently be C3, C4, C5, C6, C7, C8, or C9 cycloalkyl. Suitable examples include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl. Additionally, "cycloalkyl" may contain one or more double bonds; representative examples of cycloalkyl compounds containing double bonds include cyclopentenyl, cyclohexenyl, cyclohexadienyl, and cyclobutadienyl.

[0044] The term "alkenyl" refers to a compound containing at least one unsaturated site, i.e., a carbon-carbon sp group. 2 Hydrocarbons with a double bond consisting of a positive, secondary, tertiary, or cyclic carbon atom. Phrases containing this term, such as "C2–C9 alkenyl," refer to alkenyl groups containing 2–9 carbon atoms, which, each time appearing, can independently be C2, C3, C4, C5, C6, C7, C8, or C9 alkenyl. Suitable examples include, but are not limited to: vinyl (-CH=CH2), allyl (-CH2CH=CH2), cyclopentenyl (-C5H7), and 5-hexenyl (-CH2CH2CH2CH2CH=CH2). The term "alkenyl" refers to a divalent group formed by further losing a hydrogen atom from an alkenyl group. For example, "C2–C9 alkenyl" refers to a divalent group formed by losing a hydrogen atom from a C2–C9 alkenyl group, including straight-chain alkenyl groups and branched alkenyl groups from C2–C9.

[0045] The term "alkynyl" refers to a hydrocarbon containing at least one unsaturated carbon atom, i.e., a carbon-carbon sp triple bond, consisting of a positive, secondary, tertiary, or cyclic carbon atom. Phrases containing this term, such as "C2–C9 alkenyl," refer to alkynyl groups containing 2–9 carbon atoms, and each occurrence can be independently C2-alkynyl, C3-alkynyl, C4-alkynyl, C5-alkynyl, C6-alkynyl, C7-alkynyl, C8-alkynyl, or C9-alkynyl. Suitable examples include, but are not limited to, ethynyl (-C≡CH) and propynyl (-CH2C≡CH). The term "ynynyl" refers to a divalent group formed by further losing a hydrogen atom from an alkynyl group. For example, "C2–C9 ynynyl" refers to a divalent group formed by losing a hydrogen atom from a C2–C9 alkynyl group, including straight-chain ynynyl groups and branched ynynyl groups from C2–C9.

[0046] The term "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by losing one or more hydrogen atoms. Aryl groups can be monocyclic aryl, fused-ring aryl, two or more monocyclic aryl groups conjugated by carbon-carbon bonds, monocyclic aryl and fused-ring aryl groups conjugated by carbon-carbon bonds, or two or more fused-ring aryl groups conjugated by carbon-carbon bonds.

[0047] The term "heteroaryl" refers to a group formed by replacing at least one carbon atom of an aryl group with a heteroatom. The heteroatom can be at least one of O, N, P, Si, Se, and S, and the number of heteroatoms in a heteroaryl group can be one or more. Heteroaryl groups can be monocyclic heteroaryl, fused-ring heteroaryl, two or more monocyclic heteroaryl groups conjugated by carbon-carbon bonds, monocyclic heteroaryl and fused-ring heteroaryl groups conjugated by carbon-carbon bonds, two or more fused-ring heteroaryl groups conjugated by carbon-carbon bonds, monocyclic aryl and fused-ring heteroaryl groups conjugated by carbon-carbon bonds, etc.

[0048] The term "heteroalkyl" refers to an alkyl group in which at least one carbon atom is replaced by a non-carbon atom, which can be an N atom, O atom, S atom, etc. For example, if the carbon atom in the alkyl group that is attached to the parent nucleus is replaced by a non-carbon atom, the resulting heteroalkyl group is an alkoxy group (e.g., -OCH3, etc.), an amine (e.g., -NHCH3, -N(CH3)2, etc.), or a thioalkyl group (e.g., -SCH3). If the carbon atom in the alkyl group that is not attached to the parent nucleus is replaced by a non-carbon atom, the resulting heteroalkyl group is an alkyl ether (e.g., -CH2CH2-O-CH3, etc.), an alkylamine (e.g., -CH2NHCH3, -CH2N(CH3)2, etc.), or a thioalkyl ether (e.g., -CH2-S-CH3). If the terminal carbon atom of the alkyl group is replaced by a non-carbon atom, the resulting heteroalkyl group is a hydroxyalkyl group (e.g., -CH2CH2-OH), an aminoalkyl group (e.g., -CH2NH2), or an alkyl mercapto group (e.g., -CH2CH2-SH). Phrases containing this term, such as “C1-C9 heteroalkyl”, refer to heteroalkyl groups containing 1 to 9 carbon atoms, and each time they appear, they can be independently C2 heteroalkyl, C3 heteroalkyl, C4 heteroalkyl, C5 heteroalkyl, C7 heteroalkyl, C8 heteroalkyl, or C9 heteroalkyl.

[0049] The term "heterocyclic group" refers to a cycloalkyl group in which at least one carbon atom is replaced by a non-carbon atom, which can be an N atom, O atom, S atom, etc., and can be a saturated ring or a partially unsaturated ring. Phrases containing this term, such as "C4-C9 heterocyclic group," refer to heterocyclic groups containing 4 to 9 carbon atoms, and each occurrence can be independently C4, C6, C7, C8, or C9 heteroalkyl. Suitable examples include, but are not limited to: dihydropyridyl, tetrahydropyridyl (piperidinyl), tetrahydrothiophenyl, sulfur-oxidized tetrahydrothiophenyl, tetrahydrofuranyl, tetrahydroquinolinyl, tetrahydroisoquinolinyl, and dihydroindolyl.

[0050] The term "amino" refers to a derivative of ammonia, characterized by the formula -N(X)2, where each "X" is independently H, a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted heterocyclic group, etc. Non-limiting types of amino groups include -NH2, -N(alkyl)2, -NH(alkyl), -N(cycloalkyl)2, -NH(cycloalkyl), -N(heterocyclic)2, -NH(heterocyclic), -N(aryl)2, -NH(aryl), -N(alkyl)(aryl), -N(alkyl)(heterocyclic), -N(cycloalkyl)(heterocyclic), -N(aryl)(heteroaryl), -N(alkyl)(heteroaryl), etc.

[0051] The term "halogen" or "halogen group" refers to F, Cl, Br, or I.

[0052] Regarding the study of lithium metal anode surfaces, the applicant first proposed using fluorescent molecules to analyze the surface composition of cycled lithium metal anodes, achieving visualized tracking and detection of surface components. Various fluorescent molecules, such as catechol tetraphenylene, acryloyltetraphenylamine, tetraphenyl acrylate, o-hydroxybenzoxazole, and chalcone, have been studied. However, these fluorescent molecules contain only a single response site, exhibiting minimal changes in molecular structure before and after the response, resulting in insignificant fluorescence emission shifts and unsatisfactory readability and accuracy of the imaging results.

[0053] To address the aforementioned problems, a first aspect of this application provides an application of a hydrazine dihydrazone compound as a probe in the detection of lithium metal anodes. The hydrazine dihydrazone compound has the structural formula shown in formula (1):

[0054]

[0055] In formula (1), R1 to R8 are each independently selected from one or more of the following: hydrogen atom, alkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroalkyl, heterocyclic, heteroaryl, amino, nitro, cyano, isocyano, halogen, alkylene, alkenyl, alynyl, formyl, and ester.

[0056] Understandably, the lithium metal anode to be tested refers to the lithium metal anode of the battery after normal use (charge and discharge cycles).

[0057] In some specific examples, R1 to R8 are each independently selected from one or more of hydrogen atoms, triphenylamine groups, nitro groups, and maleimide groups. Further, at least four of R1 to R8 are selected from hydrogen atoms, and optionally at least five are selected from hydrogen atoms.

[0058] In some specific examples, the hydrazine dihydrazone compounds are selected from the structures described in formula (1-1):

[0059]

[0060] In equation (1-1), R 1 R 2 Each of R1 to R8 is independently selected from one or more of the following groups: hydrogen atom, alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, heteroalkyl group, heterocyclic group, heteroaryl group, amino group, nitro group, cyano group, isocyano group, halogen group, alkylene group, alkenylene group, alkynyl group, formyl group, and ester group. Optionally, R1 to R8 are each independently selected from one or more of the following groups: hydrogen atom, triphenylamine group, nitro group, and maleimide group.

[0061] In some specific examples, the hydrazine dihydrazone compounds are selected from the structures described below:

[0062] Salicylaldehyde-hydrazide dihydrazone.

[0063] In some specific examples, the detected items include one or more of the following on the lithium metal anode surface: deposited lithium, byproducts, lithium dendrites, dead lithium, and SEI film. Hydrazine dihydrazone compounds can react with active lithium, unevenly deposited lithium, and lithium dendrites, accompanied by fluorescence changes, but do not react with byproducts, SEI film, or dead lithium surrounded by byproducts, and maintain unchanged fluorescence. Surface components (such as active lithium and byproducts) are distinguished based on different fluorescence colors; the intensity and distribution of fluorescence color indicate the uneven deposition of lithium, distribution of lithium dendrites, dead lithium, degree of byproduct accumulation, and the growth and distribution area of ​​the SEI film on the lithium metal anode surface, achieving visual analysis of the lithium metal surface. Specifically, byproducts include one or more of lithium fluoride, lithium chloride, lithium acetate, lithium carbonate, lithium hydroxide, lithium oxide, and lithium alkoxide.

[0064] In some specific examples, the lithium metal anode is the lithium metal negative electrode in a lithium metal battery. Further, the lithium metal battery is a lithium-oxygen battery, a lithium-sulfur battery, a lithium-oxide battery, a lithium-air battery, or a lithium-lithium battery.

[0065] A second aspect of this application also provides a method for detecting lithium metal anodes, comprising the following steps:

[0066] Dissolve any of the hydrazine dihydrazone compounds mentioned above in an organic solvent to prepare a probe solution;

[0067] The probe solution is brought into contact with the surface of the lithium metal anode to be tested. After the organic solvent has evaporated to dryness, the analysis is performed under excitation light irradiation.

[0068] Understandably, the wavelength of the excitation light is the wavelength capable of exciting the hydrazine dihydrazone compound to emit fluorescence, and can be any wavelength between 300 nm and 365 nm. In some specific examples, the excitation light is ultraviolet light, which can be ultraviolet light of 355 nm to 365 nm, and more specifically, ultraviolet light of 365 nm.

[0069] In some specific examples, the metal anode is the lithium metal anode in a lithium metal battery. Further, the lithium metal battery is a lithium-oxygen battery, a lithium-sulfur battery, a lithium-oxide battery, a lithium-air battery, or a lithium-lithium battery.

[0070] In some specific examples, the concentration of hydrazine dihydrazone compounds in the probe solution is 1–10 mg / mL. Concentrations that are too high or too low will lead to decreased detection efficiency. Specifically, the concentration of hydrazine dihydrazone compounds in the probe solution may include, but is not limited to: 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, 6 mg / mL, 7 mg / mL, 8 mg / mL, 9 mg / mL, and 10 mg / mL. Further, the concentration of hydrazine dihydrazone compounds in the probe solution is between 2 mg / mL and 4 mg / mL. Better detection results can be obtained within this concentration range.

[0071] In some specific examples, the organic solvent is selected from volatile solvents. Specific examples include, but are not limited to, one or more of diethyl ether, acetonitrile, tetrahydrofuran, acetone, n-hexane, and cyclohexane.

[0072] In some specific examples, the analytical steps include: visually observing the fluorescence on the surface of the lithium metal anode to be tested and / or measuring the fluorescence wavelength and intensity using a fluorescence spectrometer. Measuring the fluorescence wavelength and intensity using a fluorescence spectrometer allows for semi-quantitative analysis of the aforementioned detection items.

[0073] Taking salicylaldehyde-hydrazone (CAS No. 959-36-4) as an example, its reaction with lithium metal is described in detail below.

[0074] Salicylaldehyde-hydrazide dihydrazone, when excited by a 365 nm UV lamp, does not exhibit fluorescence in solution but shows yellow fluorescence in the solid state, with the maximum emission peak located at 539 nm (e.g., ...). Figure 1 As shown); and the molecular structure changes after reacting with lithium metal (as shown). Figure 2 As shown), the product, lithium salicylaldehyde hydrazine dihydrazone, exhibits a blue fluorescence signal under 365nm ultraviolet light excitation (as shown). Figure 1 As shown in the figure, the maximum emission peak is located at 463 nm. Before and after the interaction of salicylaldehyde-hydrazone with lithium metal, the fluorescence response shift is as high as 76 nm, and the emission intensity increases. (See figure for reference.) Figure 3 As shown, the phenolic hydroxyl peak at chemical shift 11.09 ppm disappears, indicating that the phenolic hydroxyl group is the reaction site, and the reaction is rapid and complete. The 1H NMR spectrum shows that elemental lithium disrupts the proton donor in the ESIPT mechanism, meaning that both phenolic hydroxyl groups (δ 11.2 ppm) participate in the reaction, leading to a significant change in the fluorescence signal. Figure 4 , 5 As shown, salicylaldehyde hydrazide dihydrazone maintained its intrinsic yellow fluorescence emission after reacting with several common lithium salt byproducts in SEI, with a maximum emission of 539 nm and the emission intensity remained basically unchanged, indicating that salicylaldehyde hydrazide dihydrazone is reactively inert to SEI and byproducts. After one hour of continuous excitation, the fluorescence intensity remained at 51.0%. However, after reacting with lithium metal, the fluorescence signal intensity increased, with the maximum emission blue-shifted to 463 nm, and the fluorescence intensity remained at 28.7% after one hour of continuous excitation.

[0075] The following are specific embodiments. They are intended to provide a more detailed description of this application to help those skilled in the art and researchers better understand it. The technical conditions described do not constitute any limitation on this application. Any modifications made within the scope of the claims of this application are protected by the claims of this application.

[0076] Unless otherwise stated, all raw materials and reagents used in the following examples are commercially available or can be prepared by known methods. All instruments are conventionally selected in the art. Experimental methods not specifically described in the examples were performed under conventional conditions, such as those described in literature, books, or methods recommended by the manufacturer.

[0077] Example 1

[0078] This embodiment describes a method for detecting the lithium metal anode in a lithium metal battery. The lithium metal battery used is a Li||Li symmetrical coin cell, with lithium sheets as both the positive and negative electrodes. The electrolyte is 1 mol / L LiPF6 / EC+DEC+EMC (mass ratio 1:1:1), and the separator is Celgard 2500. The specific steps are as follows:

[0079] (1) The battery was charged and discharged using a blue-chip device. The charge and discharge program was: rest for 2 hours, 1.0 mAh / cm³. 2 Charge for 1 hour, discharge for 1 hour, repeat 25 times to simulate the battery's condition after use. Then, disassemble the battery and remove the negative lithium electrode.

[0080] (2) Dissolve salicylaldehyde dihydrazone in diethyl ether to prepare a solution with a concentration of 3.0 mg / mL to obtain the probe solution.

[0081] (3) Spray the probe solution prepared in step (2) onto the surface of the negative lithium electrode after charge-discharge cycles. After the ether evaporates (within 10 seconds), a fluorescence image can be obtained under 365nm ultraviolet light. See Figure 6 .

[0082] Depend on Figure 6 It is known that lithium metal, uneven lithium deposition, and lithium dendrites exhibit blue fluorescence, while byproducts (lithium acetate, lithium carbonate, lithium fluoride, etc.), SEI films, and dead lithium surrounded by byproducts exhibit yellow fluorescence. The two fluorescence signals are significantly different and can be directly observed by the naked eye. The intensity of the blue and yellow fluorescence can reflect the degree of uneven lithium deposition or lithium dendrite formation, and the degree of byproduct accumulation in different regions. Furthermore, fluorescence spectroscopy can determine that the blue fluorescence wavelength of lithium metal, uneven lithium deposition, and lithium dendrites is around 463 nm, while the yellow fluorescence wavelength of byproducts (lithium acetate, lithium carbonate, lithium fluoride, etc.), SEI films, and dead lithium surrounded by byproducts is around 539 nm. The degree of uneven lithium deposition or lithium dendrite formation and the degree of byproduct accumulation can be semi-quantitatively analyzed by measuring the fluorescence intensity.

[0083] When the battery is charged and discharged with different numbers of cycles and different charge and discharge currents, the aforementioned steps can be applied to visualize and semi-quantitatively analyze the battery conditions under different conditions. Furthermore, a valuable scientific framework can be established between the detection of deposited lithium, byproducts, lithium dendrites, dead lithium, and solid electrolyte interfacial films on the lithium metal anode surface and various cycling conditions.

[0084] Comparative Examples 1-3

[0085] Similar to Example 1, except that ethylenediamine Schiff base, propylenediamine Schiff base, and butylamine Schiff base of the same mass concentration were used instead of salicylaldehyde hydrazine dihydrazone. (The fluorescence image is shown below.) Figure 7 As shown.

[0086] Depend on Figure 7 It can be seen that the maximum emission peak of the ethylenediamine Schiff base before reacting with lithium metal (intrinsic) is located at 503 nm, and the maximum emission peak of the ethylenediamine Schiff base after reacting with lithium metal (lithiation) is located at 486 nm, with a fluorescence response shift of 17 nm.

[0087] The maximum emission peak of the propylenediamine Schiff base before reacting with lithium metal (intrinsic) is located at 503 nm, and the maximum emission peak of the propylenediamine Schiff base after reacting with lithium metal (lithiation) is located at 477 nm, with a fluorescence response shift of 26 nm.

[0088] The maximum emission peak of the ethylenediamine Schiff base before interaction with lithium metal (intrinsic) is located at 497 nm, and the maximum emission peak of the ethylenediamine Schiff base after interaction with lithium metal (lithiation) is located at 476 nm, with a fluorescence response shift of 21 nm.

[0089] Before and after the interaction of ethylenediamine Schiff base, propylenediamine Schiff base and butylenediamine Schiff base with lithium metal (intrinsic and lithiation), the color distinction of the fluorescence signal is not obvious, and the response ability is weaker than that of Example 1.

[0090] 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.

[0091] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection 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 scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. The application of a hydrazine dihydrazone compound as a probe in the detection of lithium metal anodes, characterized in that, The detection items include one or more of the following: deposited lithium, by-products, lithium dendrites, dead lithium, and solid electrolyte interface film on the surface of lithium metal anode. The hydrazine dihydrazone compounds have the structural formula shown in formula (1): （1） In formula (1), R1 to R8 are each independently selected from one or more of hydrogen atoms, triphenylamine groups, nitro groups and maleimide groups.

2. The application of the hydrazine dihydrazone compound as a probe in the detection of lithium metal anodes according to claim 1, characterized in that, The hydrazine dihydrazone compounds are selected from the structures described below: 。 3. The application of the hydrazine dihydrazone compound as a probe in the detection of lithium metal anodes according to claim 1, characterized in that, The byproducts include one or more of lithium fluoride, lithium chloride, lithium acetate, lithium carbonate, lithium hydroxide, lithium oxide, and lithium alkoxide.

4. The application of hydrazine dihydrazone compounds according to any one of claims 1 to 3 as probes in the detection of lithium metal anodes, characterized in that, The lithium metal anode is the lithium metal anode in the lithium metal battery; the lithium metal battery is a lithium-oxygen battery, a lithium-sulfur battery, a lithium-oxide battery, a lithium-air battery, or a lithium-lithium battery.

5. A method for detecting lithium metal anodes, characterized in that, Includes the following steps: Probe solutions were prepared by dissolving hydrazine dihydrazone compounds in organic solvents. The probe solution is brought into contact with the surface of the lithium metal anode to be tested. After the organic solvent has evaporated to dryness, the analysis is performed under excitation light irradiation. The hydrazine dihydrazone compound has the structural formula shown in formula (1): （1） In formula (1), R1 to R8 are each independently selected from one or more of hydrogen atoms, triphenylamine groups, nitro groups and maleimide groups; The detection items of the detection method include one or more of the following: deposited lithium, by-products, lithium dendrites, dead lithium, and solid electrolyte interface film on the surface of the lithium metal anode.

6. The method for detecting lithium metal anodes according to claim 5, characterized in that, The hydrazine dihydrazone compounds are selected from the structures described below: 。 7. The method for detecting lithium metal anodes according to claim 5, characterized in that, The lithium metal anode is the lithium metal anode in the lithium metal battery; the lithium metal battery is a lithium-oxygen battery, a lithium-sulfur battery, a lithium-oxide battery, a lithium-air battery, or a lithium-lithium battery.

8. The method for detecting lithium metal anodes according to any one of claims 5 to 7, characterized in that, The analytical steps include: visually observing the fluorescence on the surface of the lithium metal anode to be tested and / or using a fluorescence spectrometer to measure the fluorescence wavelength and fluorescence intensity.

9. The method for detecting lithium metal anodes according to any one of claims 5 to 7, characterized in that, The concentration of hydrazine dihydrazone compounds in the probe solution is 1~10 mg / mL.

10. The method for detecting lithium metal anodes according to any one of claims 5 to 7, characterized in that, The concentration of hydrazine dihydrazone compounds in the probe solution is 2 mg / mL to 4 mg / mL.

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