Boron naphthalene compounds, methods of making and using the same

Abstract

The present application relates to the field of lithium battery detection, in particular to a boron naphthalene compound, a preparation method and application thereof.The boron naphthalene compound has a structure as shown in general formula (1).The boron naphthalene compound can realize specific characterization of lithium fluoride in the SEI film without using high-cost experimental equipment, and the experimental condition threshold is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium battery detection, in particular to a boron naphthalene compound, a preparation method and application thereof, and more particularly to a boron naphthalene compound, a preparation method, a fluorescent detection agent and a method for detecting lithium fluoride in a solid electrolyte interphase film of a lithium metal negative electrode. BACKGROUND

[0002] The solid electrolyte interphase (SEI) film of the negative electrode of a lithium battery is one of the important electrode interface structures. The SEI film is directly related to the deposition behavior of lithium ions at the electrode interface, and a stable and dense SEI film helps to inhibit the growth of lithium dendrites of the negative electrode, thereby optimizing the cycle performance and service life of the lithium battery.

[0003] The fluorinated SEI film generally refers to an SEI film with a high content of lithium fluoride (LiF). A large number of research results have confirmed that the higher the content of lithium fluoride in the SEI film, the higher the stability and lithium ion conductivity of the SEI film, which can significantly improve the cycle stability and safety of the lithium battery. Therefore, detecting lithium fluoride in the SEI film has high research value and application prospect.

[0004] One of the most important links for detecting lithium fluoride in the SEI film is to achieve specific characterization of lithium fluoride. At present, specific characterization of lithium fluoride still needs to rely on 19 F NMR spectrum (fluorine nuclear magnetic resonance spectrum), XPS spectrum (X-ray photoelectron spectroscopy), SEM (scanning electron microscope) or cryo-TEM (cryogenic transmission electron microscope), and the experimental equipment cost is high, and the experimental condition threshold is high. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a boron naphthalene compound, a preparation method and application thereof, so as to solve the problem of high experimental equipment cost and high experimental condition threshold for specific characterization of lithium fluoride.

[0006] The first aspect of the present application provides a boron naphthalene compound, and the technical solution is as follows:

[0007] A boron naphthalene compound has a structure as shown in general formula (1):

[0008]

[0009] wherein R1 is selected from C 6-10 aryl;

[0010] R2 and R3 are each independently selected from H, C 1-6 alkyl, C 2-6 alkenyl, C 2-6alkyl, C 3-8 cycloalkyl, 3- to 8-membered heterocycloalkyl, C 6-10 aryl or 5- to 10-membered heteroaryl;

[0011] n is 0, 1, 2, or 3;

[0012] m is 0, 1, 2, or 3.

[0013] In some embodiments, R1is phenyl.

[0014] In some embodiments, R2and R3are each independently selected at each occurrence from H, C 1-3 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, amino, nitro, cyano, halogen, -C(O)CH3, -OC(O)CH3, cyclopropyl, or phenyl.

[0015] The second aspect of the present application provides a preparation method of boron substituted naphthyl compounds, and the technical scheme is as follows:

[0016] A preparation method of boron substituted naphthyl compounds, comprising the following steps:

[0017] reacting a compound having a structure as shown in general formula (II) with a compound having a structure as shown in general formula (III) to generate a compound having a structure as shown in general formula (I);

[0018]

[0019] wherein: R1is selected from C 6-10 aryl;

[0020] R2and R3are each independently selected at each occurrence from H, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, amino, nitro, cyano, halogen, -C(O)CH3, -OC(O)CH3, C 3-8 cycloalkyl, 3- to 8-membered heterocycloalkyl, C 6-10 aryl or 5- to 10-membered heteroaryl;

[0021] n is 0, 1, 2, or 3;

[0022] m is 0, 1, 2, or 3.

[0023] In some embodiments, R1is phenyl.

[0024] In some embodiments, R2and R3are each independently selected at each occurrence from H, C 1-3alkyl, C 2-4 alkenyl, C 2-4 alkynyl, amino, nitro, cyano, halogen, -C(O)CH3, -OC(O)CH3, cyclopropyl, or phenyl.

[0025] The third aspect of the present application provides a fluorescent detection agent, and the technical solution is as follows:

[0026] A fluorescent detection agent, comprising the boron-substituted naphthalene compound or the boron-substituted naphthalene compound prepared by the preparation method.

[0027] In some embodiments, a solvent is further included, and the solvent satisfies the following conditions:

[0028] (1) does not react chemically with the boron-substituted naphthalene compound; (2) can be volatilized; and (3) does not react chemically with components in the object to be detected.

[0029] The fourth aspect of the present application provides a method for detecting lithium fluoride in a lithium metal negative electrode solid electrolyte interface film, and the technical solution is as follows:

[0030] A method for detecting lithium fluoride in a lithium metal negative electrode solid electrolyte interface film, comprising the following steps:

[0031] The fluorescent detection agent is dispersed on the negative electrode solid electrolyte interface film to be detected, and under ultraviolet light irradiation, the lithium fluoride is detected according to the fluorescent signal.

[0032] In some embodiments, one or more of the following features is satisfied:

[0033] (1) the fluorescent detection agent further comprises a solvent, and after the fluorescent detection agent is dispersed, a step of volatilizing the solvent is further included;

[0034] (2) a step of detecting the content of the lithium fluoride according to the intensity value of the fluorescent signal is further included.

[0035] Advantages:

[0036] The present application provides a boron naphthalene compound, the substituted naphthalene in the structure of which has the property of aggregation induced emission (AIE), and under solid state or poor solvent system, it emits a fluorescent signal under ultraviolet excitation, on this basis, the boron ester in the structure has a 2p empty orbital and is a typical coordination acceptor, after the action of lithium fluoride, the electron-rich fluoride ion forms a coordination compound with the boron atom, resulting in a large change in the electron distribution and orbital energy of the boron naphthalene compound, which is manifested as the dual responsiveness of the fluorescent signal intensity and wavelength. Moreover, after the boron naphthalene compound reacts with other components in the SEI film such as lithium oxide and lithium acetate, it is difficult to effectively form a coordination bond, which is manifested as the maintenance of the intrinsic fluorescent signal. Therefore, the above-mentioned boron naphthalene compound can realize the specific characterization of lithium fluoride in the SEI film without using high-cost experimental equipment, and the experimental condition threshold is low. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, more completely understand the present application and its beneficial effects, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0038] Figure 1 Fluorescent emission intensity and imaging diagram of the fluorescent detection agent after reacting with lithium fluoride, lithium oxide, lithium chloride and lithium acetate;

[0039] Figure 2 Fluorine lithium imaging diagram and distribution diagram of the fluorescent detection agent on the surface of the lithium negative electrode sheet; wherein a is the fluorine lithium imaging diagram, and b is the fluorine lithium distribution diagram;

[0040] Figure 3 Wavelength and intensity comparison diagram of the fluorescent signal of the fluorescent detection agent of Comparative Example 1 before and after reacting with lithium fluoride. DETAILED DESCRIPTION

[0041] The present application will be further described in detail below in combination with specific embodiments. The present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0042] 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 the present application belongs. The terminology used in the description of the present application herein is only for the purpose of describing specific embodiments and is not intended to limit the present application.

[0043] the term

[0044] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0045] "alkyl" refers to straight-chain and branched saturated aliphatic hydrocarbon groups. "C 1-6 "Alkyl" refers to an alkyl group having 1 to 6 carbon atoms, preferably C16. 1-3 Alkyl groups, as defined similarly; non-limiting examples of alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, sec-butyl, n-pentyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl, n-hexyl, 1-ethyl-2-methylpropyl, 1,1,2-trimethylpropyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1,3-dimethylbutyl, 2-ethylbutyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 2,3-dimethylbutyl, and their various branched isomers.

[0046] "Alkenyl" refers to a straight-chain or branched unsaturated aliphatic hydrocarbon group with one or more carbon-carbon double bonds (C=C). 2-6 "Alkenyl" refers to an alkenyl group having 2 to 6 carbon atoms, preferably C. 2-4 Alkenyl, similarly defined; non-limiting examples of alkenyl include: vinyl, propenyl, isopropenyl, n-butenyl, isobutenyl, pentenyl, hexenyl, and their various branched isomers, etc.

[0047] "Alkyne" refers to a straight-chain or branched unsaturated aliphatic hydrocarbon group with one or more carbon-carbon triple bonds. 2-6 "Alkyne group" refers to an alkynyl group having 2 to 6 carbon atoms, preferably C64. 2-4 Alynyl group, similarly defined; non-limiting examples of alkynyl group include: ethynyl, propynyl, n-butynyl, isobutynyl, penynyl, hexynyl, and their various branched isomers, etc.

[0048] "Cycloalkyl" and "cycloalkyl ring" are used interchangeably, both referring to saturated monocyclic, bicyclic, or polycyclic cyclic hydrocarbon groups. "C 3-8 "Cycloalkyl" refers to a monocyclic cycloalkyl group having 3 to 8 carbon atoms, preferably C12. 3-6 Cycloalkyl groups are defined similarly; non-limiting examples of cycloalkyl groups include: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, etc.

[0049] "Heteroalkyl" and "heteroalkyl ring" are used interchangeably and refer to an alkyl group that contains at least one heteroatom selected from the group consisting of nitrogen, oxygen, and sulfur. "3 to 8 membered heteroalkyl" refers to a monocyclic cyclic hydrocarbon group having 3 to 8 ring atoms, wherein 1, 2, or 3 of the ring atoms are heteroatoms selected from the group consisting of nitrogen, oxygen, and sulfur. More preferably, 3 to 6 membered heteroalkyl, which has 3 to 6 ring atoms, wherein 1 or 2 of the ring atoms are heteroatoms selected from the group consisting of nitrogen, oxygen, and sulfur. More preferably, 4 to 6 membered heteroalkyl, which has 4 to 6 ring atoms, wherein 1 or 2 of the ring atoms are heteroatoms selected from the group consisting of nitrogen, oxygen, and sulfur. Non-limiting examples of heteroalkyl groups include aziridinyl, oxiranyl, azetidinyl, oxetanyl, tetrahydrofuranyl, tetrahydrothiophenyl, tetrahydropyrrolyl, oxazolidinyl, dioxolanyl, piperidinyl, piperazinyl, morpholinyl, dioxanyl, thiomorpholinyl, thiomorpholin-1,1-dioxide, tetrahydropyranyl, and the like.

[0050] "Aryl" and "aromatic ring" are used interchangeably and refer to an all-carbon monocyclic or fused polycyclic (that is, rings which share adjacent pairs of carbon atoms) groups having a completely conjugated pi-electron system. "C 6-10 "Aryl" and "aromatic ring" are used interchangeably and refer to an all-carbon monocyclic or fused polycyclic (that is, rings which share adjacent pairs of carbon atoms) groups having a completely conjugated pi-electron system. "C

[0051] "Heteroaryl" and "heteroaryl ring" are used interchangeably and refer to a monocyclic, bicyclic or polycyclic 4n+2 aromatic ring system (e.g., having 6 or 10 π electrons shared in a cyclic array) having ring carbon atoms and ring heteroatoms, wherein each heteroatom is independently selected from nitrogen, oxygen, and sulfur. "5- to 10-membered heteroaryl" refers to a monocyclic or bicyclic heteroaryl group having 5 to 10 ring atoms, wherein 1, 2, 3, or 4 of the ring atoms are heteroatoms. "5- to 6-membered heteroaryl" refers to a monocyclic heteroaryl group having 5 to 6 ring atoms, wherein 1, 2, 3, or 4 of the ring atoms are heteroatoms, non-limiting examples of which include thienyl, furanyl, thiazolyl, isothiazolyl, imidazolyl, oxazolyl, pyrrolyl, pyrazolyl, triazolyl, 1,2,3-triazolyl, 1,2,4-triazolyl, 1,2,5-triazolyl, 1,3,4-triazolyl, tetrazolyl, isoxazolyl, oxadiazolyl, 1,2,3-oxadiazolyl, 1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, thiadiazolyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazinyl, tetrazinyl. "8- to 10-membered heteroaryl" refers to a bicyclic heteroaryl group having 8 to 10 ring atoms, wherein 1, 2, 3, or 4 of the ring atoms are heteroatoms, non-limiting examples of which include indolyl, isoindolyl, indazolyl, benzotriazolyl, benzothienyl, isobenzothienyl, benzofuranyl, benzoisofuranyl, benzoimidazolyl, benzoxazolyl, benzoisoxazolyl, benzoxadiazolyl, benzothiazolyl, benzoisothiazolyl, benzothiadiazolyl, indoxazinyl, purinyl, pyrido[3,2-d]pyrimidinyl, pyrido[2,3-d]pyrimidinyl, pyrido[3,4-d]pyrimidinyl, pyrido[4,3-d]pyrimidinyl, 1,8-naphthyridinyl, 1,7-naphthyridinyl, 1,6-naphthyridinyl, 1,5-naphthyridinyl, pteridinyl, quinolinyl, isoquinolinyl, cinnolinyl, quinoxalinyl, phthalazinyl, and quinazolinyl. In heteroaryl groups containing one or more nitrogen atoms, the point of attachment can be a carbon or a nitrogen atom, as valency permits.

[0052] "Amino" refers to -NH2.

[0053] "Nitro" refers to -NO2.

[0054] "Cyano" refers to -CN.

[0055] "Halo" refers to fluoro, chloro, bromo, or iodo.

[0056] "Substituted" means substituted with a substituent group as defined herein.

[0057] In the present application, a single bond between a substituent and a ring indicates that the substituent can be attached to any available position of the ring, e.g. where R is attached to any available position of the phenyl ring; indicates Fused to the benzene ring at any adjacent C atom.

[0058] In the present application, the same substituent group can be selected independently from different groups when it appears multiple times. For example, if the general formula contains multiple R2, R2 can be selected independently from different groups.

[0059] In view of the high cost and high threshold of experimental conditions of specific characterization experimental equipment for lithium fluoride, one embodiment of the present application provides a boron naphthalene compound having a structure as shown in general formula (1):

[0060]

[0061] R1 is selected from C 6-10 aryl;

[0062] R2 and R3 are each independently selected from H, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, amino, nitro, cyano, halogen, -C(O)CH3, -OC(O)CH3, C 3-8 cycloalkyl, 3-8 membered heterocycloalkyl, C 6-10 aryl or 5-10 membered heteroaryl;

[0063] n is 0, 1, 2 or 3;

[0064] m is 0, 1, 2 or 3.

[0065] Optionally, R1 can be phenyl or naphthyl. Preferably, R1 is phenyl.

[0066] Preferably, R2 and R3 are each independently selected from H, C 1-3 alkyl, C 2-4 alkenyl, C 2-4 alkynyl, amino, nitro, cyano, halogen, -C(O)CH3, -OC(O)CH3, cyclopropyl or benzene.

[0067] Preferably, n is 0 or 1.

[0068] Preferably, m is 0 or 1.

[0069] Referring to the following formula, the substituted naphthalene in the structure of the above boron-substituted naphthalene compound has the property of aggregation induced emission (AIE), and under solid state or poor solvent system, it will emit a fluorescence signal under ultraviolet excitation. On this basis, the boron ester in the structure has a 2p empty orbital and is a typical coordination acceptor. After the action of lithium fluoride, the electron-rich fluoride anion forms a coordination compound with the boron atom, resulting in a large change in the electron distribution and orbital energy of the boron-substituted naphthalene compound, which exhibits dual responsiveness of fluorescence signal intensity and wavelength. Moreover, after the boron-substituted naphthalene compound reacts with other components in the SEI film such as lithium oxide and lithium acetate, it is difficult to form a coordination bond effectively, and it exhibits the intrinsic fluorescence signal. Therefore, the above boron-substituted naphthalene compound can realize specific characterization of lithium fluoride in the SEI film without using high-cost experimental equipment, and the experimental condition threshold is low.

[0070]

[0071] An embodiment of the present application further provides a preparation method of the boron-substituted naphthalene compound, which comprises the following steps:

[0072] The compound having the structure shown in the general formula (II) is allowed to react with the compound having the structure shown in the general formula (III) to generate the compound having the structure shown in the general formula (I).

[0073]

[0074] wherein R1, R2, R3, n and m are as described above, which will not be repeated here.

[0075] Optionally, the method for allowing the compound having the structure shown in the general formula (II) to react with the compound having the structure shown in the general formula (III) can be a grinding method or a solution method.

[0076] In some examples: the compound having the structure shown in the general formula (II) is allowed to react with the compound having the structure shown in the general formula (III) by the grinding method. The grinding method comprises the following steps: taking the same stoichiometric amount of the compound solid having the structure shown in the general formula (II) and the compound solid having the structure shown in the general formula (III), mixing and grinding to obtain the compound having the structure shown in the general formula (I).

[0077] Optionally, the grinding can be performed in a mortar.

[0078] Optionally, the grinding time is greater than or equal to 20 minutes.

[0079] In some examples, the compound having the structure as shown in general formula (II) is reacted with the compound having the structure as shown in general formula (III) by a solution method. The solution method comprises the following steps: taking the same stoichiometric amount of the compound having the structure as shown in general formula (II) and the compound having the structure as shown in general formula (III), dissolving them in a solvent, stirring, removing the solvent, and obtaining the compound having the structure as shown in general formula (I).

[0080] Optionally, the solvent for dissolving the two reactants is an organic solvent. Further optionally, the solvent for dissolving the two reactants is selected from one or more of dichloromethane, tetrahydrofuran and acetone.

[0081] Optionally, the temperature for stirring is 20-50℃, for example, it can be 20℃, 30℃, 40℃ or 50℃. Preferably, it is 30℃.

[0082] Optionally, the time for stirring is greater than or equal to 20 minutes.

[0083] Optionally, the method for removing the solvent is evaporation drying.

[0084] The boron-substituted naphthyl compound having the above-mentioned function can be prepared by the above-mentioned method.

[0085] The embodiment of the present application also provides a fluorescent detection agent comprising the above-mentioned boron-substituted naphthyl compound or the boron-substituted naphthyl compound prepared by the above-mentioned preparation method.

[0086] When the fluorescent detection agent of the embodiment is used, the fluorescent detection agent can be dispersed on the object to be detected. Under the condition of solid state or poor solvent system and under the condition of excitation by ultraviolet light, the boron-substituted naphthyl compound in the fluorescent detection agent reacts with lithium fluoride to form a coordination compound, which exhibits double responsiveness of fluorescence signal intensity and wavelength. Therefore, the lithium fluoride in the object to be detected can be detected according to the fluorescence signal. Specifically, the lithium fluoride can be efficiently identified according to the change of fluorescence color on the surface of the object to be detected, and the approximate distribution area of the lithium fluoride on the surface of the object to be detected can be determined according to the distribution of the fluorescence signal.

[0087] The fluorescent detection agent of the embodiment can realize specific characterization of lithium fluoride without using high-cost experimental equipment, and the experimental condition threshold is low.

[0088] Optionally, the fluorescent detection agent further comprises a solvent, and the solvent satisfies the following conditions:

[0089] (1) no chemical reaction occurs between the solvent and the boron-substituted naphthyl compound; (2) the solvent can be volatilized; and (3) no chemical reaction occurs between the solvent and the components in the object to be detected.

[0090] The boron-substituted naphthyl compound is dispersed by using the solvent first, and then the solution is dispersed on the object to be detected, which is beneficial to uniform dispersion.

[0091] Further optionally, the solvent can be an organic solvent.

[0092] Further optionally, the solvent is selected from one or more of diethyl ether, n-hexane and tetrahydrofuran.

[0093] Optionally, the concentration of the boron-substituted naphthalene compound in the fluorescent detection agent is 0.5 mg / mL to 5 mg / mL. For example, it can be 0.5 mg / mL, 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL or 5 mg / mL.

[0094] It can be understood that, optionally, the object to be detected can be a lithium metal negative electrode solid electrolyte interface film. The components in the object to be detected include lithium metal, lithium oxide, lithium chloride, lithium acetate and other by-products.

[0095] In view of the important role of lithium fluoride in SEI film stability and lithium battery negative electrode cycle performance, an embodiment of the present application also provides a method for detecting lithium fluoride in a negative electrode solid electrolyte interface film (SEI film), comprising the following steps:

[0096] Dispersing the above-mentioned fluorescent detection agent on the negative electrode SEI film to be detected, and detecting the lithium fluoride according to the fluorescent signal under ultraviolet light irradiation.

[0097] The above-mentioned method for detecting lithium fluoride in a negative electrode SEI film utilizes the fact that, under the conditions of solid or poor solvent system and ultraviolet light excitation, the boron-substituted naphthalene compound in the fluorescent detection agent reacts with lithium fluoride to form a coordination compound, which exhibits dual responsiveness of fluorescence signal intensity and wavelength, while the boron-substituted naphthalene compound reacts with other components (such as by-products) in the SEI film such as lithium oxide, lithium chloride and lithium acetate, which is difficult to form a coordination bond effectively, and exhibits intrinsic fluorescence signal, so that the lithium fluoride in the negative electrode SEI film can be detected according to the fluorescence signal. Specifically, the lithium fluoride can be efficiently identified from the numerous components of the SEI film according to the change of the fluorescence color on the negative electrode surface, and the approximate distribution area of the lithium fluoride on the negative electrode surface can be determined according to the fluorescence signal distribution.

[0098] Optionally, the negative electrode can be a lithium metal negative electrode, and further can be the negative electrode of a Li|Li symmetric button cell, a lithium-sulfur battery, a lithium-oxygen battery, a lithium-oxide battery and a lithium-air battery.

[0099] Optionally, the negative electrode SEI film to be detected can be obtained by the following method:

[0100] Disassembling the battery after charge-discharge cycle to expose the SEI film on the surface of the negative electrode.

[0101] It can be understood that the battery can be a Li|Li symmetric coin cell, a lithium-sulfur battery, a lithium-oxygen battery, a lithium-oxide battery, and a lithium-air battery.

[0102] In some examples, the fluorescent detection agent further comprises a solvent, and the method further comprises a step of evaporating the solvent after dispersing the fluorescent detection agent. The solvent is as described above and will not be repeated here.

[0103] Optionally, the concentration of the boron-substituted naphthalene compound in the fluorescent detection agent is 0.5 mg / mL to 5 mg / mL. For example, it can be 0.5 mg / mL, 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, or 5 mg / mL.

[0104] Optionally, the step of dispersing the fluorescent detection agent comprises the following steps:

[0105] The fluorescent detection agent is coated on the anode SEI film to be detected.

[0106] Further optionally, the coating method can be spraying.

[0107] The boron-substituted naphthalene compound is first dispersed with a solvent, and then the solution is dispersed on the object to be detected. This is beneficial to uniform dispersion, and the solvent is removed later to obtain a solid boron-substituted naphthalene compound that emits a specific fluorescent signal when excited by ultraviolet light.

[0108] Optionally, the ultraviolet light can be provided by a handheld ultraviolet lamp.

[0109] The method of the present embodiment can realize specific characterization of lithium fluoride in the SEI film without using high-cost experimental equipment, and has low experimental condition threshold. At the same time, the method is simple and convenient, has high sensitivity, wide applicability, and accurate detection results.

[0110] In addition, unlike the use of 19 The F NMR spectrum (fluorine nuclear magnetic resonance spectrum) and the XPS spectrum (X-ray photoelectron spectrum) obtain electrode surface information through the transformation of specific signals. The method for detecting lithium fluoride in the anode SEI film can realize visual analysis of the detection results of lithium fluoride, and the approximate distribution area of lithium fluoride in the SEI film on the surface of the electrode can be determined according to the distribution of the fluorescent signal.

[0111] Further, unlike the use of SEM (scanning electron microscope) and cryo-TEM (cryogenic transmission electron microscope) to realize visual analysis of the detection results of lithium fluoride, the method for detecting lithium fluoride in the anode SEI film does not require complex sample preparation steps.

[0112] Further, the accumulation degree of lithium fluoride can be reflected due to the difference in intensity of the fluorescence signal. Therefore, in some embodiments, the method further comprises a step of detecting the content of lithium fluoride according to the intensity value of the fluorescence signal. Compared with SEM (scanning electron microscope) and cryo-TEM (cryogenic transmission electron microscope), the method of detecting lithium fluoride in the negative electrode SEI film can realize quantitative analysis of lithium fluoride.

[0113] Optionally, the detection of the content of lithium fluoride according to the intensity value of the fluorescence signal can be realized in combination with a fluorescence spectrometer.

[0114] The method of the present embodiment can quantitatively and visually identify the regional distribution and relative abundance of lithium fluoride in the SEI film, and in combination with the adjustment structure, the lithium fluoride can be associated with the interface stability, compactness and cycle performance of the pole piece, thereby providing a new idea and direction for evaluating the interface state of the pole piece and the growth of the SEI film.

[0115] Example 1

[0116] The present embodiment provides a boron-substituted naphthalene compound and a preparation method thereof, and the steps are as follows:

[0117]

[0118] Mix the same stoichiometric amounts of compound 1 solid and compound 2 solid in an agate mortar for 20 min to obtain compound 3.

[0119] Example 2

[0120] The present embodiment provides a fluorescence detection agent and a preparation method thereof, and the steps are as follows:

[0121] Dissolve compound 3 in diethyl ether to obtain a fluorescence detection agent with a concentration of 1 mg / mL.

[0122] Example 3

[0123] Investigate the fluorescence signal of the fluorescence detection agent of Example 2 after reacting with lithium fluoride, lithium oxide, lithium chloride and lithium acetate, and the steps are as follows:

[0124] Control group: spray the fluorescence detection agent of Example 2, and after the diethyl ether evaporates, irradiate the solid state under a 365 nm handheld ultraviolet lamp. The solid state emits blue-purple fluorescence with a wavelength of 428 nm.

[0125] Experimental group: take lithium fluoride, lithium oxide, lithium chloride and lithium acetate powders, and respectively spray the fluorescence detection agent of Example 2. After the diethyl ether evaporates, irradiate the solid state under a 365 nm handheld ultraviolet lamp. See Figure 1The solid state material after acting with lithium fluoride powder presents bright cyan fluorescence, the wavelength of fluorescence is red shifted to 464 nm, and the fluorescence emission intensity at 464 nm is significantly improved, which is beneficial to the imaging characterization of lithium fluoride component; the solid state material after acting with lithium oxide, lithium chloride and lithium acetate powder still presents relatively dim blue-violet intrinsic fluorescence signal, and the fluorescence emission intensity at 464 nm is basically the same as that of the control group.

[0126] It can be seen that lithium oxide, lithium chloride and lithium acetate as common components in SEI film do not cause the boron naphthalene compound to produce a response, and the specificity of the boron naphthalene compound to lithium fluoride can be utilized for the detection of lithium fluoride in the SEI film.

[0127] Example 4

[0128] The present embodiment provides a method for detecting lithium fluoride in the negative electrode SEI film, and the steps are as follows:

[0129] Take Li||Li symmetrical button cells, and the positive and negative electrodes are both lithium sheets. The electrolyte is 1 mol / L LiPF6 / EC+DEC+EMC (mass ratio 1:1:1), and the separator is Celgard 2500. The battery is subjected to charge and discharge cycles by using a blue light equipment. The charge and discharge program is as follows: 2 h of standing, 0.5 mAh / cm 2 2 h of discharging, 1 h of charging, and 10 cycles. Then, the battery is disassembled, the SEI film on the surface of the negative electrode is exposed, and the fluorescent detection agent of Example 2 with a concentration of 1.0 mg / mL is sprayed on the surface of the lithium metal negative electrode. After the ether is volatilized, the solid state material is irradiated under a 365 nm handheld ultraviolet lamp, as shown in Figure 2 a. As Figure 2 a shows, after the lithium fluoride in the negative electrode SEI film contacts the fluorescent detection agent, the lithium fluoride is “lit up” by the fluorescent molecules, and presents bright cyan fluorescence. The cyan fluorescence region can directly reflect the distribution and accumulation degree of lithium fluoride in the SEI film, as shown in Figure 2 b, which is the distribution diagram of lithium fluoride.

[0130] According to the difference in fluorescence intensity, the accumulation degree of lithium fluoride can be observed. After the fluorescence intensity is measured by a fluorescence spectrometer, the interface relative abundance of lithium fluoride can be quantitatively analyzed.

[0131] Comparative Example 1

[0132] The present comparative example provides a method for detecting lithium fluoride in the negative electrode SEI film, which is basically the same as Example 4, and the main difference is that compound 3 in the fluorescent detection agent of Example 2 is replaced by compound 1.

[0133] The fluorescent detection agent of the present comparative example is sprayed on the surface of the lithium metal negative electrode. After the ether is volatilized, the solid state material is irradiated under a 365 nm handheld ultraviolet lamp, and the wavelength and intensity of the fluorescence signal are recorded, as shown inFigure 3 Figure 3 The wavelength and intensity of the fluorescence signal of the fluorescence detection agent of Comparative Example 1 before and after the reaction with lithium fluoride are compared.

[0134] As can be seen from the comparison, compound 1, as a synthetic raw material of compound 3, is similar to compound 3 in the skeleton structure and fluorescence performance, and only differs in the borate structure. Figure 3 As shown in the figure, the fluorescence emission peak position and intensity of compound 1 before and after the reaction with lithium fluoride do not change significantly, and compound 1 does not show specific response ability to lithium fluoride. It is proved that the borate structure is the response site combined with fluoride ions, and the molecular design and post-modification of compound 3 are reasonable and necessary.

[0135] The technical features of the above-described embodiments can be combined arbitrarily. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not contradict, they should be considered as the scope of the description.

[0136] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.​

Claims

1. A boron-substituted naphthalene compound, characterized in that, It has the structure shown in general formula (1): （1） Wherein: R1 is a phenyl group; Each time R2 and R3 appear, they are each independently selected from H; n is 0, 1, 2, or 3; m can be 0, 1, 2, or 3.

2. A method for preparing a boron-substituted naphthalene compound, characterized in that, Includes the following steps: A compound having the structure shown in general formula (II) is reacted with a compound having the structure shown in general formula (III) to generate a compound having the structure shown in general formula (I); Equation (II) Equation (III) (1) Wherein: R1 is a phenyl group; Each time R2 and R3 appear, they are each independently selected from H; n is 0, 1, 2, or 3; m can be 0, 1, 2, or 3.

3. The method for preparing boron-substituted naphthalene compounds according to claim 2, characterized in that, The compound having the structure shown in general formula (II) is reacted with the compound having the structure shown in general formula (III) by a grinding method. The grinding method includes the following steps: taking the same stoichiometric amounts of the solid compound having the structure shown in general formula (II) and the solid compound having the structure shown in general formula (III), mixing and grinding them to obtain a compound having the structure shown in general formula (I).

4. The method for preparing boron-substituted naphthalene compounds according to claim 2, characterized in that, The compound having the structure shown in general formula (II) is reacted with the compound having the structure shown in general formula (III) by a solution method. The solution method includes the following steps: taking the same stoichiometric amounts of the solid compound having the structure shown in general formula (II) and the solid compound having the structure shown in general formula (III), dissolving them in a solvent, stirring, removing the solvent, and obtaining the compound having the structure shown in general formula (I).

5. The method for preparing boron-substituted naphthalene compounds according to claim 4, characterized in that, The solvent for dissolving the solid compound having the structure shown in general formula (II) and the solid compound having the structure shown in general formula (III) is an organic solvent.

6. A fluorescent detection reagent, characterized in that, Includes the boronized naphthalene compounds of claim 1 or the boronized naphthalene compounds prepared by the preparation method of any one of claims 2 to 5.

7. The fluorescent detection agent according to claim 6, characterized in that, It also includes a solvent, wherein the solvent in the fluorescent detection agent satisfies the following conditions: (1) It does not react chemically with the boronized naphthalene compounds; (2) It is volatile; (3) It does not react chemically with the components in the test object.

8. A method for detecting lithium fluoride in the interface film of a negative electrode solid electrolyte, characterized in that, Includes the following steps: The fluorescent detection agent according to any one of claims 6 to 7 is dispersed on the negative electrode solid electrolyte interface film to be tested, and lithium fluoride is detected based on the fluorescence signal under ultraviolet light irradiation.

9. The method for detecting lithium fluoride in the negative electrode solid electrolyte interface film according to claim 8, characterized in that, The fluorescent detector also includes a solvent, and after dispersing the fluorescent detector, the step further includes evaporating the solvent in the fluorescent detector; 10. The method for detecting lithium fluoride in the negative electrode solid electrolyte interface film according to claim 8, characterized in that, It also includes the step of detecting the content of lithium fluoride based on the intensity value of the fluorescence signal.

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