Solid-state fluorescence imaging characterization method for silicon-based anodes

Abstract

The application relates to a solid-state fluorescence imaging characterization method of a silicon-based negative electrode. The solid-state fluorescence imaging characterization method of the silicon-based negative electrode comprises the following steps: reacting a fluorescent probe molecule with a lithium-silicon alloy in a silicon-based negative electrode to form a silicon-based negative electrode containing a lithium-based fluorescent compound; and performing solid-state fluorescence imaging characterization on the silicon-based negative electrode containing the lithium-based fluorescent compound; wherein the fluorescent probe molecule has a structure as shown in a general formula (I), and a hydroxyl group on Ar is located at an ortho position of an imine group; Ar is independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl at each occurrence. The characterization method can analyze the state of charge, lithium-silicon alloy distribution, silicon coating crack defects, lithium deposition particles and other key information of the silicon-based negative electrode, thereby providing a reference for diagnosing the interface state, battery cycle stability and safety of the silicon-based negative electrode, and being beneficial to the development of a next-generation high-energy-density lithium-silicon battery.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and in particular to a solid-state fluorescence imaging characterization method for silicon-based anodes. Background Technology

[0002] Lithium-ion batteries are among the most important energy storage devices today, widely used in mobile electronic devices, electric transportation, and large-scale energy storage. The energy density of lithium-ion batteries is largely limited by the specific capacity of the anode material. Currently, the specific capacity of mainstream commercial graphite anode products is around 350 mAh / g, close to the theoretical upper limit of 372 mAh / g, making the search for new anode materials with higher specific capacity an urgent priority.

[0003] Among numerous anode materials, silicon boasts a theoretical specific capacity of up to 4200 mAh / g, more than ten times that of graphite. It also provides channels for lithium ions to enter and dissolve from various directions, exhibiting excellent fast-charging performance and making it a promising next-generation anode material. The difference between silicon-based anodes and graphite anodes lies in the fact that lithium ions are not embedded in the interstices of silicon elements, but rather directly form a lithium-silicon alloy with silicon. Due to silicon's volume expansion rate exceeding 300%, silicon-based anodes experience repeated expansion and contraction during long-term charge-discharge cycles, leading to numerous cracks and defects at the electrode interface. This ultimately results in insulation of the anode active material and rapid capacity decay. Furthermore, silicon's conductivity is inferior to that of carbon materials, and the distribution of lithium-silicon alloys exhibits significant regional variations. These issues thus limit the large-scale application of silicon-based anodes. However, currently, there is a lack of effective characterization methods for silicon-based anodes, making it difficult to obtain crucial information such as the state of charge (SOC), lithium-silicon alloy distribution, silicon coating cracks and defects, and lithium deposition particles. Summary of the Invention

[0004] Therefore, it is necessary to provide a solid-state fluorescence imaging characterization method for silicon-based anodes to address the current lack of an effective characterization method for silicon-based anodes, which makes it difficult to obtain key information such as the state of charge, lithium-silicon alloy distribution, silicon coating crack defects, and lithium deposition particles.

[0005] The above-mentioned objective of this application is achieved through the following technical solution:

[0006] In a first aspect, this application provides a solid-state fluorescence imaging characterization method for silicon-based anodes, comprising the following steps:

[0007] The fluorescent probe molecules react with the lithium-silicon alloy in the silicon-based anode to form a silicon-based anode containing lithium-based fluorescent compounds;

[0008] Solid-state fluorescence imaging characterization was performed on the silicon-based anode containing the lithium-based fluorescent compound;

[0009] The fluorescent probe molecule has a structure as shown in general formula (Ⅰ):

[0010]

[0011] The hydroxyl group on Ar is located ortho to the imine group; each time Ar appears, it independently includes either a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

[0012] In one embodiment, each occurrence of Ar independently comprises an aryl group having 6 to 30 substituted or unsubstituted cyclic atoms, or a heteroaryl group having 5 to 30 substituted or unsubstituted cyclic atoms.

[0013] In one embodiment, each occurrence of Ar independently includes one of the following: benzene ring, naphthalene ring, pyridine, pyrrole, piperidine, pyrimidine, furan, thiophene, thiazole, imidazole, quinoline, and indole.

[0014] In one embodiment, the fluorescent probe molecule has a structure as shown in general formula (II):

[0015]

[0016] Each instance of R independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroalkyl, and substituted or unsubstituted heterocyclic.

[0017] In one embodiment, R is selected from H.

[0018] In one embodiment, reacting fluorescent probe molecules with a lithium-silicon alloy in a silicon-based anode includes the following steps:

[0019] The fluorescent probe molecules and organic solvent are mixed to prepare a mixture;

[0020] The mixture is applied to the surface of the silicon-based anode, and the organic solution is allowed to evaporate.

[0021] In one embodiment, the concentration of the fluorescent probe molecules in the mixture is 0.1 mg / mL to 5.0 mg / mL; and / or,

[0022] The area of ​​the silicon-based negative electrode is 100 mm². 2 Under these conditions, the amount of the mixture used is 0.05 mL to 0.20 mL.

[0023] In one embodiment, the organic solvent includes one or more of diethyl ether, tetrahydrofuran, acetone, n-hexane, and cyclohexane.

[0024] In one embodiment, the material of the silicon-based anode includes one or more of silicon carbide, silicon oxide, silicon-based alloy, and nano-silicon materials.

[0025] In one embodiment, solid-state fluorescence imaging characterization of the silicon-based anode containing the lithium-based fluorescent compound includes the following steps:

[0026] The fluorescence phenomenon of the silicon-based anode containing the lithium-based fluorescent compound was observed under ultraviolet light irradiation.

[0027] And / or,

[0028] The fluorescence intensity of the silicon-based anode containing the lithium-based fluorescent compound was measured using a fluorescence spectrometer.

[0029] This application has at least the following beneficial effects:

[0030] The fluorescent probe molecule used in this application has an imine structure with ortho-hydroxyl groups, enabling proton transfer reactions via excited-state intramolecular proton transfer (ESIPT). Furthermore, the imine group forms a large conjugated π-electron system with the two aromatic rings (Ar), thus generating a strong and stable fluorescence signal in solid-state or poor solvent systems. The uncharged silicon-based anode does not contain lithium-silicon alloy and does not react with the fluorescent probe molecule, so the fluorescence signal remains unchanged. However, the charged silicon-based anode contains a highly chemically active lithium-silicon alloy, which reacts with the hydroxyl groups in the fluorescent probe molecule to form a deprotonated lithium-based fluorescent compound. This disrupts the ESIPT mechanism, resulting in a significant change in the fluorescence signal of the lithium-based fluorescent compound compared to the fluorescent probe molecule. The solid-state fluorescence imaging characterization method for silicon-based anodes provided in this application is based on the significant difference in fluorescence signals between fluorescent probe molecules and lithium-based fluorescent compounds. It can analyze key information such as the state of charge, lithium-silicon alloy distribution, silicon coating cracks and defects, and lithium deposition particles of the silicon-based anode, thus providing a reference for diagnosing the interface state, battery cycle stability, and safety of silicon-based anodes, which is beneficial for the development of next-generation high-energy-density lithium-silicon batteries. Furthermore, this solid-state fluorescence imaging characterization method has the advantages of simplicity, convenience, high sensitivity, fast response, stable light intensity, and applicability to various light sources, making it suitable for the rapid, large-scale, and batch characterization of silicon-based anodes. Attached Figure Description

[0031] Figure 1 Before and after the reaction of salicylaniline with lithium silicon alloy 1 H NMR spectrum;

[0032] Figure 2 Fluorescence images of salicylaniline before and after the reaction with lithium-silicon alloy;

[0033] Figure 3 The fluorescence spectra of salicylaniline before and after the reaction with lithium-silicon alloy are shown.

[0034] Figure 4 The fluorescence stability spectra of salicylaniline before and after the reaction with lithium-silicon alloy are shown.

[0035] Figure 5 Fluorescence images of silicon-based anodes in different charge states reacting with salicylaniline. Detailed Implementation

[0036] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0037] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0038] 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. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0039] the term

[0040] Unless otherwise stated or in case of conflict, the terms or phrases used in this application shall have the following meanings:

[0041] In this application, when a substituent of the same symbol appears multiple times, the substituents may be the same or different from each other. If the general formula contains multiple R, then the R may be the same or different from each other.

[0042] "Substituted or unsubstituted" indicates that the defined group may or may not be substituted. When the defined group is substituted, it should be understood that the defined group can be substituted by one or more substituents acceptable in the art. Suitable substituents include, but are not limited to: C1-C30 alkyl, cycloalkyl containing 3-20 ring atoms, heterocyclic group containing 3-20 ring atoms, aryl containing 6-20 ring atoms, heteroaryl containing 5-20 ring atoms, silyl, carbonyl, alkoxycarbonyl, aryloxycarbonyl, carbamoyl, halocarbamoyl, formyl, amino (-N(R)2), cyano, isocyano, isocyanate, thiocyanate, isothiocyanate, hydroxyl, trifluoromethyl, nitro, or halogen, and the above groups may also be further substituted by substituents acceptable in the art; it is understood that -N(R)2... In )2, each of the R groups is independently substituted by groups acceptable in the art, including but not limited to: H, alkyl groups containing 1 to 6 carbon atoms, cycloalkyl groups containing 3 to 8 ring atoms, heterocyclic groups containing 3 to 8 ring atoms, aryl groups containing 5 to 20 ring atoms, or heteroaryl groups containing 5 to 10 ring atoms; wherein the alkyl groups containing 1 to 6 carbon atoms, cycloalkyl groups containing 3 to 8 ring atoms, heterocyclic groups containing 3 to 8 ring atoms, aryl groups containing 5 to 20 ring atoms, or heteroaryl groups containing 5 to 10 ring atoms may optionally be further substituted by one or more of the following groups: alkyl groups containing 1 to 6 carbon atoms, cycloalkyl groups containing 3 to 8 ring atoms, heterocyclic groups containing 3 to 8 ring atoms, halogens, hydroxyl groups, nitro groups, or amino groups.

[0043] "Number of ring atoms" refers to the number of atoms in the ring itself of a compound formed by atomic bonds (e.g., monocyclic compounds, fused-ring compounds, cross-linked compounds, carbocyclic compounds, heterocyclic compounds). When the ring is substituted by a substituent, the atoms contained in the substituent are not included in the ring-forming atoms. The same applies to the "number of ring atoms" as described below unless otherwise specified. For example, the number of ring atoms in a benzene ring is 6, in a naphthalene ring it is 10, and in a thiophene group it is 5.

[0044] "Alkyl" refers to a monovalent residue formed by the loss of a hydrogen atom from a saturated hydrocarbon containing a primary (normal) carbon atom, a secondary carbon atom, a tertiary carbon atom, a quaternary carbon atom, or a combination thereof. Alkyl can represent straight-chain, branched, and / or cyclic alkyl. The number of carbon atoms in an alkyl group can be 1–50, 1–30, 1–20, 1–10, or 1–6. Phrases containing this term, such as "C1–C9 alkyl," refer to alkyl groups containing 1–9 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(C H3)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-3-pentyl (-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, octyl (-(CH2)7CH3).

[0045] "Cycloalkyl" refers to a monovalent residue formed by the loss of a hydrogen atom from a non-aromatic hydrocarbon containing a ring carbon atom. It can be a monocycloalkyl, spirocycloalkyl, or bridged cycloalkyl. Suitable examples include, but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclopentenyl, cyclohexenyl, cyclohexadienyl, and cyclobutadienyl.

[0046] "Alkenyl" refers to a group containing at least one unsaturated site, i.e., carbon-carbon sp. 2 A monovalent residue formed from a hydrogen atom of a hydrocarbon containing a double carbon atom, secondary carbon atom, tertiary carbon atom, or cyclic carbon atom. Suitable examples include, but are not limited to: vinyl (-CH=CH2), allyl (-CH2CH=CH2), cyclopentenyl (-C5H7), and 5-hexenyl (-CH2CH2CH2CH2CH=CH2).

[0047] "Alynyl" refers to a monovalent residue formed by the loss of a hydrogen atom from a hydrocarbon containing at least one unsaturated carbon-carbon sp triple bond, i.e., a carbon atom of the positive, secondary, tertiary, or cyclic carbon. Suitable examples include, but are not limited to: ethynyl (-C≡CH) and propynyl (-CH2C≡CH).

[0048] "Aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound containing only carbon atoms by removing one hydrogen atom. It can be a monocyclic aryl, a fused-ring aryl, or a polycyclic aryl; for polycyclic compounds, at least one is an aromatic ring system. For example, "substituted or unsubstituted aryl having 6 to 40 ring atoms" refers to a substituted or unsubstituted aryl containing 6 to 40 ring atoms, preferably 6 to 30 ring atoms, more preferably 6 to 18 ring atoms, and particularly preferably 6 to 14 ring atoms, with optional further substitution. Suitable examples include, but are not limited to: benzene, biphenyl, terphenyl, naphthalene, anthracene, fluoranthene, phenanthrene, benzo[a]phenanthrene, dinaphthalene-2, tetraphenylene, pyrene, benzo[a]pyrene, acenaphthene, fluorene, triphenylene and its derivatives. Understandably, multiple aryl groups can also be interrupted by short non-aromatic units (e.g., <10% non-H atoms, such as C, N, or O atoms), specifically acenaphthene, fluorene, or 9,9-diarylfluorene, triarylamine, and diaryl ether systems should also be included in the definition of aryl.

[0049] "Heteroaryl" refers to an aryl group in which at least one carbon atom is replaced by a non-carbon atom, which can be an N atom, an O atom, an S atom, etc. For example, "substituted or unsubstituted heteroaryl group having 5 to 40 ring atoms" refers to a substituted or unsubstituted heteroaryl group containing 5 to 40 ring atoms, preferably a heteroaryl group having 6 to 30 ring atoms, more preferably a heteroaryl group having 6 to 18 ring atoms, particularly preferably a heteroaryl group having 6 to 14 ring atoms, and the heteroaryl group may optionally be further substituted. Suitable examples include, but are not limited to: furan, thiophene, benzofuran, benzothiophene, pyrrole, pyrazole, pyridine, pyridine, pyrazine, pyridazine, pyrimidine, triazole, imidazole, oxazole, oxadiazole, thiazole, tetrazolium, carbazole, indole, triazine, pyrroloimidazole, pyrrolopyrrole, thiophenolopyrrole, thiophenolothiophene, furanolopyrrole, furanolofuran, thiophenolofuran, benzoisoxazole, benzoisothiazolium, quinoline, isoquinoline, o-diazonine, quinoxaline, phenanthridine, primidine, quinazoline, quinazolinone, dibenzothiophene, dibenzofuran, carbazole and their derivatives.

[0050] "Heteroalkyl" refers to an alkyl group in which at least one carbon atom is replaced by a non-carbon atom, such as a nitrogen (N), oxygen (O), sulfur (S), etc. For example, if a carbon atom in an alkyl group is replaced by a non-carbon atom, the resulting heteroalkyl group is an alkoxy group (e.g., -OCH3), an amine (e.g., -NHCH3, -N(CH3)2), or a thioalkyl group (e.g., -SCH3). If no carbon atom in an alkyl group is replaced by a non-carbon atom, the resulting heteroalkyl group is an alkyl ether (e.g., -CH2CH2-O-CH3), an alkylamine (e.g., -CH2NHCH3, -CH2N(CH3)2), or a thioalkyl ether (e.g., -CH2-S-CH3). If the terminal carbon atom of an 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).

[0051] "Heterocyclic group" refers to a cycloalkyl group in which at least one carbon atom is replaced by a non-carbon atom. The non-carbon atom can be a nitrogen atom, an oxygen atom, a sulfur atom, etc., and can be a saturated ring or a partially unsaturated ring. Suitable examples include, but are not limited to: dihydropyridyl, tetrahydropyridyl (piperidinyl), tetrahydrothiophenyl, sulfur-oxidized tetrahydrothiophenyl, tetrahydrofuranyl, tetrahydroquinolinyl, tetrahydroisoquinolinyl, and dihydroindolyl.

[0052] "Halogen" or "halogen group" refers to F, Cl, Br or I.

[0053] "Amino" refers to a monovalent residue with the general formula -N(R)2. Each time R appears, it is independently selected from H, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heterocyclic group, etc.

[0054] "Imine group" refers to a divalent residue with the general formula -CR=N-, where R is selected from H, substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted heterocyclic groups, etc.

[0055] "Nitro" refers to -NO2.

[0056] "Cyano" refers to -CN or -C≡N.

[0057] "Isocyanate" refers to -NC or -N=C.

[0058] "Ester group" refers to a monovalent residue with the general formula -COOR, where R is selected from H, substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted heterocyclic groups, etc. For example, if R is selected from H, the resulting ester group is a carboxyl group. If R is selected from substituted or unsubstituted alkyl groups, the resulting ester group is an alkyl ester group, including but not limited to: methyl ester group (methyl ester group, -COOCH3) and ethyl ester group (ethyl ester group, -COOCH2CH3).

[0059] "Acyl" refers to a monovalent residue with the general formula -COR, where R is selected from H, substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted heterocyclic groups, etc. For example, if R is selected from H, the resulting acyl group is an aldehyde group. If R is selected from substituted or unsubstituted alkyl groups, the resulting ester group is an alkyl acyl group, including but not limited to: formyl (methyl acyl, -COCH3) and acetyl (ethyl acyl, -COCH2CH3).

[0060] Currently, reports have proposed using fluorescent probe molecules such as catecholtetraphenylene, chalcone, and benzoxazole to analyze the surface composition of lithium-based or graphite anode materials after charge-discharge cycles. This allows for the characterization of the solid-electrolyte interphase (SEI) film, lithium-carbon compounds, and lithium dendrite particles at the electrode, offering both visual characterization and quantitative detection capabilities. However, how to perform imaging characterization of silicon-based anodes remains one of the crucial problems that urgently need to be solved in the field of lithium-silicon batteries.

[0061] Based on this, this application provides a solid-state fluorescence imaging characterization method for silicon-based anodes to solve the problem that there is currently a lack of an effective characterization method for silicon-based anodes, making it difficult to obtain key information such as the state of charge, lithium-silicon alloy distribution, silicon coating crack defects, and lithium deposition particles.

[0062] In some embodiments, the solid-state fluorescence imaging characterization method for silicon-based anodes includes the following steps:

[0063] The fluorescent probe molecules react with the lithium-silicon alloy in the silicon-based anode to form a silicon-based anode containing lithium-based fluorescent compounds;

[0064] Solid-state fluorescence imaging characterization of silicon-based anodes containing lithium-based fluorescent compounds;

[0065] Among them, the fluorescent probe molecule has a structure as shown in general formula (Ⅰ):

[0066]

[0067] The hydroxyl group (-OH) on Ar is located ortho to the imine group (-CH=N-); each time Ar appears, it independently includes a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

[0068] The fluorescent probe molecule used in this application has an imine structure with ortho-hydroxyl groups, enabling proton transfer reactions via excited-state intramolecular proton transfer (ESIPT). Furthermore, the imine group forms a large conjugated π-electron system with the two aromatic rings (Ar), thus generating a strong and stable fluorescence signal in solid-state or poor solvent systems. The uncharged silicon-based anode does not contain lithium-silicon alloy and does not react with the fluorescent probe molecule, so the fluorescence signal remains unchanged. However, the charged silicon-based anode contains a highly chemically active lithium-silicon alloy, which reacts with the hydroxyl groups in the fluorescent probe molecule to form a deprotonated lithium-based fluorescent compound. This disrupts the ESIPT mechanism, resulting in a significant change in the fluorescence signal of the lithium-based fluorescent compound compared to the fluorescent probe molecule. The solid-state fluorescence imaging characterization method for silicon-based anodes provided in this application is based on the significant difference in fluorescence signals between fluorescent probe molecules and lithium-based fluorescent compounds. It can analyze key information such as the state of charge, lithium-silicon alloy distribution, silicon coating cracks and defects, and lithium deposition particles of the silicon-based anode, thus providing a reference for diagnosing the interface state, battery cycle stability, and safety of silicon-based anodes, which is beneficial for the development of next-generation high-energy-density lithium-silicon batteries. Furthermore, this solid-state fluorescence imaging characterization method has the advantages of simplicity, convenience, high sensitivity, fast response, stable light intensity, and applicability to various light sources, making it suitable for the rapid, large-scale, and batch characterization of silicon-based anodes.

[0069] In this application, each occurrence of Ar independently includes a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. Further, each occurrence of Ar independently includes a substituted or unsubstituted aryl group having 6 to 30 ring atoms, or a substituted or unsubstituted heteroaryl group having 5 to 30 ring atoms. Even further, each occurrence of Ar independently includes a substituted or unsubstituted aryl group having 6 to 20 ring atoms, or a substituted or unsubstituted heteroaryl group having 5 to 20 ring atoms. Still further, each occurrence of Ar independently includes a substituted or unsubstituted six-membered aryl group, a substituted or unsubstituted six-membered heteroaryl group, or a substituted or unsubstituted five-membered heteroaryl group.

[0070] In some embodiments, each occurrence of Ar independently includes one of the following: benzene ring, naphthalene ring, pyridine, pyrrole, piperidine, pyrimidine, furan, thiophene, thiazole, imidazole, quinoline, and indole.

[0071] Understandably, in the structure shown in general formula (I), Ar can be the same or different from each other. For example, Ar is selected from any one of benzene ring, naphthyl ring, pyridine, pyrrole, piperidine, pyrimidine, furan, thiophene, thiazole, imidazole, quinoline and indole; or, Ar is selected from substituted or unsubstituted aromatic rings, wherein the aromatic ring is selected from any two of benzene ring, naphthyl ring, pyridine, pyrrole, piperidine, pyrimidine, furan, thiophene, thiazole, imidazole, quinoline and indole.

[0072] In some embodiments, the fluorescent probe molecule has a structure as shown in general formula (II):

[0073]

[0074] Each instance of R independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroalkyl, and substituted or unsubstituted heterocyclic.

[0075] Understandably, in the structure shown in general formula (I), if all Ar are selected from the benzene ring, the fluorescent probe molecule has the structure shown in general formula (II), belonging to the salicylaldehyde Schiff base class. In the structure shown in general formula (II), R can be the same or different from each other. By modifying different sites on the benzene ring with different numbers and types of substituents, the wavelength and intensity of the fluorescence signal can be controlled and adjusted.

[0076] In this application, each occurrence of R on the benzene ring independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted heterocyclic, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroalkyl, and substituted or unsubstituted heterocyclic. Furthermore, each of R independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, substituted or unsubstituted C1-C20 alkyl, substituted or unsubstituted cycloalkyl containing 3-20 ring atoms, substituted or unsubstituted alkenyl containing 2-20 carbon atoms, substituted or unsubstituted alkynyl containing 2-20 carbon atoms, substituted or unsubstituted aryl containing 6-20 ring atoms, substituted or unsubstituted heteroaryl containing 5-20 ring atoms, substituted or unsubstituted heteroalkyl containing 1-20 carbon atoms, and substituted or unsubstituted heterocyclic group containing 3-20 ring atoms. Furthermore, each of R independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted cycloalkyl containing 3-10 ring atoms, substituted or unsubstituted alkenyl containing 2-10 carbon atoms, substituted or unsubstituted alkynyl containing 2-10 carbon atoms, substituted or unsubstituted aryl containing 6-10 ring atoms, substituted or unsubstituted heteroaryl containing 5-10 ring atoms, substituted or unsubstituted heteroalkyl containing 1-10 carbon atoms, and substituted or unsubstituted heterocyclic group containing 3-10 ring atoms. Further still, each of R independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, and substituted or unsubstituted C1-C6 alkyl.

[0077] In some embodiments, R is selected from H, and the fluorescent probe molecule has a structure as shown in general formula (III):

[0078]

[0079] Understandably, the chemical name of a fluorescent probe molecule with the structure shown in general formula (III) is salicylideneaniline, CAS number 779-84-0. It has good solubility and chemical reactivity, is soluble in water, alcohol solvents and ether solvents, and has a very stable fluorescence signal under ultraviolet light.

[0080] Optionally, the raw materials for salicylaniline include salicylaldehyde and aniline. Salicylaldehyde and aniline can be directly condensed to form salicylaniline. Both raw materials are inexpensive and readily available, and the synthesis method is simple, which helps to reduce the detection cost of silicon-based anodes.

[0081] In some embodiments, reacting fluorescent probe molecules with a lithium-silicon alloy in a silicon-based negative electrode includes the following steps:

[0082] A mixture of fluorescent probe molecules and organic solvents was prepared.

[0083] The mixture is applied to the surface of the silicon-based anode, and the organic solution is allowed to evaporate.

[0084] Dissolving or dispersing fluorescent probe molecules in organic solvents to form a mixture facilitates the uniform coating of fluorescent probe molecules on the surface of the silicon-based anode, reduces the inhomogeneity and incompleteness of the reaction, and improves the accuracy and detection speed of solid-state fluorescence imaging characterization.

[0085] In some embodiments, the concentration of fluorescent probe molecules in the mixture is 0.1 mg / mL to 5.0 mg / mL, including but not limited to: 0.1 mg / mL, 0.2 mg / mL, 0.5 mg / mL, 0.8 mg / mL, 1.0 mg / mL, 1.5 mg / mL, 2.0 mg / mL, 2.5 mg / mL, 3.0 mg / mL, 3.5 mg / mL, 4.0 mg / mL, 4.5 mg / mL, and 5.0 mg / mL, preferably 0.5 mg / mL to 1.5 mg / mL.

[0086] In some embodiments, the area of ​​the silicon-based anode is 100 mm². 2 Under these conditions, the volume of the mixture used is 0.05 mL to 0.20 mL, including but not limited to: 0.05 mL, 0.08 mL, 0.10 mL, 0.12 mL, 0.15 mL, 0.18 mL, and 0.20 mL, preferably 0.08 mL to 0.12 mL.

[0087] Controlling the concentration and amount of fluorescent probe molecules per unit area can ensure the complete reaction of the lithium-silicon alloy in the silicon-based anode, thereby improving the accuracy of solid-state fluorescence imaging characterization.

[0088] In some embodiments, the organic solvent includes one or more of diethyl ether, tetrahydrofuran, acetone, n-hexane, and cyclohexane, preferably diethyl ether.

[0089] Understandably, the aforementioned organic solvents exhibit good solubility for fluorescent probe molecules and demonstrate excellent chemical inertness, meaning they do not react with the fluorescent probe molecules, silicon-based anodes, lithium-silicon alloys, or lithium-based fluorescent compounds. Furthermore, these organic solvents are highly volatile, rapidly evaporating after the mixture coats the surface of the silicon-based anode, requiring no heat treatment or prolonged settling. This ensures they do not affect the fluorescent probe molecules, silicon-based anodes, lithium-silicon alloys, or lithium-based fluorescent compounds, making them highly suitable for the rapid characterization of silicon-based anodes.

[0090] In some embodiments, the method for coating the silicon-based anode surface with the mixture includes one or more of spraying, coating, and dipping. The coating method includes one or more of spin coating, blade coating, and drop coating. Preferably, the method for coating the silicon-based anode surface with the mixture is spraying.

[0091] In some embodiments, the silicon-based anode material includes one or more of silicon carbide, silicon oxide, silicon-based alloy and nano-silicon materials, preferably silicon oxide.

[0092] In some embodiments, solid-state fluorescence imaging characterization of a silicon-based anode containing a lithium-based fluorescent compound includes the following steps:

[0093] The fluorescence phenomenon of a silicon-based anode containing a lithium-based fluorescent compound was observed under ultraviolet light irradiation.

[0094] And / or,

[0095] The fluorescence intensity of a silicon-based anode containing a lithium-based fluorescent compound was measured using a fluorescence spectrometer.

[0096] By directly observing fluorescence phenomena under ultraviolet light irradiation, key information such as the state of charge of the silicon-based anode, lithium-silicon alloy distribution, silicon coating cracks and defects, and lithium deposition particles can be qualitatively analyzed visually. Quantitative analysis of the lithium-silicon alloy content can be achieved by measuring fluorescence intensity using a fluorescence spectrometer.

[0097] In some embodiments, when irradiated with ultraviolet light at a wavelength of 365±5 nm, the fluorescent probe molecules produce yellow fluorescence at a wavelength of 552±5 nm, and the lithium-based fluorescent compound produces blue fluorescence at a wavelength of 460±5 nm.

[0098] Under ultraviolet light with a wavelength of 365±5nm, the yellow fluorescence of the fluorescent probe molecules and the blue fluorescence of the lithium-based fluorescent compound show a clear contrast, making it easy to directly observe the distribution and relative abundance of lithium-silicon alloys.

[0099] The present application will be further described in detail below with reference to specific embodiments.

[0100] Unless otherwise specified, the raw materials used in the following specific embodiments and comparative examples are all commercially available products; the instruments used are all commercially available products; and the processes used are all conventionally selected by those skilled in the art unless otherwise specified.

[0101] Example 1

[0102] In this embodiment, the fluorescent probe molecule is salicylaniline, which reacts with lithium-silicon alloy as follows:

[0103]

[0104] As can be seen from the reaction formula, the phenolic hydroxyl group in salicylaniline reacts with the highly reactive lithium-silicon alloy (Li... x After Si reacts, it loses a proton to form a lithium-based fluorescent compound, which disrupts the ESIPT mechanism of the imine structure of the ortho-hydroxyl group, thus causing a significant change in the fluorescence signal.

[0105] The physicochemical properties of salicylaniline before and after the reaction with lithium-silicon alloy were tested as follows:

[0106] (1) Nuclear magnetic resonance hydrogen spectrum ( 1 H NMR): Figure 1 Before and after the reaction of salicylaniline with lithium silicon alloy 1 H NMR spectrum. Figure 1 In the diagram, curve A represents salicylaniline. 1 H NMR curves, curve B represents the H NMR curves obtained within minutes of the reaction between salicylaniline and lithium-silicon alloy. 1 In the 1H NMR curves, the circles in curves A and B both represent the phenolic hydroxyl peak at a chemical shift of 13.05. The phenolic hydroxyl peak in curve B disappears completely, indicating that the phenolic hydroxyl group is the reaction site, and that the reaction between the phenolic hydroxyl group and the lithium-silicon alloy is rapid and complete.

[0107] (2) Solid-state fluorescence imaging characterization: Figure 2 These are fluorescence images of salicylaniline before and after the reaction with lithium-silicon alloy. Figure 3 The fluorescence spectra of salicylaniline before and after the reaction with lithium-silicon alloy are shown. Figure 2 The region indicated by arrow A contains only salicylaniline, which emits yellow fluorescence under ultraviolet light at a wavelength of 365 nm, corresponding to... Figure 3 The fluorescence emission peak at 552 nm is the curve A. Figure 2 The region indicated by arrow B contains the reaction product of salicylaniline and lithium-silicon alloy, which emits blue fluorescence under ultraviolet light at a wavelength of 365 nm, corresponding to... Figure 3 The fluorescence emission peak at 460 nm is the curve B. Figure 3 The response shift of the two fluorescence emission peaks is Δλ = 92 nm, and the color contrast is high, making it very suitable for qualitative and quantitative analysis of lithium-silicon alloys.

[0108] (3) Characterization of fluorescence stability: Figure 4 The fluorescence stability spectra of salicylaniline before and after the reaction with lithium-silicon alloy are shown. Figure 4In the figure, curve A shows the fluorescence intensity change of salicylaniline at 552 nm under a 365 nm excitation source. After continuous excitation for 1 hour, its fluorescence intensity can be maintained at 82.3%. Curve A also shows the fluorescence intensity change of salicylaniline after reacting with lithium-silicon alloy at 460 nm under a 365 nm excitation source. After continuous excitation for 1 hour, its fluorescence intensity can be maintained at 44.1%. Both before and after the reaction of salicylaniline with lithium-silicon alloy, it exhibits strong anti-photobleaching properties, which is helpful for long-term fluorescence imaging characterization of the interface of silicon-based anodes.

[0109] Example 2

[0110] The lithium-silicon battery used in this embodiment is SiO₂. x @C|Li button cell. Among them, the silicon-based anode is SiO₂. x @C refers to carbon-coated silicon-oxygen material; the electrolyte formulation is 1 mol / L LiPF6 / EC+DEC+EMC (mass ratio 2:1:1), meaning the concentration of LiPF6 in the electrolyte is 1 mol / L, and the electrolyte solvent consists of ethylene glycol carbonate (EC), propylene glycol carbonate (DEC), and methyl propylene glycol carbonate (EMC) in a mass ratio of 2:1:1; the separator is a Celgard 2500 polypropylene membrane. The above lithium-silicon battery was subjected to charge-discharge cycles using a Blue Electric device. The charge-discharge program was a 12-hour rest period followed by a 2.5 mAh / cm³ charge-discharge cycle. 2 The energy density was charged to half-charged state (i.e., SOC 50%) and fully charged state (i.e., SOC 100%), respectively. Then the lithium silicon battery was disassembled and the silicon-based negative electrode with different charge states was taken out.

[0111] Salicylate aniline was dissolved in diethyl ether to prepare a mixed solution with a concentration of 1.0 mg / mL. (The remaining text appears to be incomplete and requires further context.) 2 A mixture of 0.10 mL was sprayed onto the silicon-based anode surface at different charge states. After the ether evaporated, the fluorescence of the silicon-based anode at different charge states was observed under ultraviolet light at a wavelength of 365 nm. The results are shown in [Figure number missing]. Figure 5 .

[0112] Figure 5 Figure (a) shows the fluorescence image of a silicon-based anode with a SOC of 50% after reacting with salicylaniline. Figure 5Figure (b) shows the fluorescence phenomenon of a 100% SOC silicon-based anode reacting with salicylaniline. A comparison reveals significant differences in the fluorescence signal color of the silicon-based anode under different charge states. The 50% SOC silicon-based anode is greenish, falling between blue and yellow, indicating a lower lithium-silicon alloy content and insufficient reaction of the salicylaniline fluorescent probe molecule. The 100% SOC silicon-based anode is blue, very close to... Figure 2 The fluorescence signal of the reaction product of salicylaniline in the lithium-silicon alloy was observed. This demonstrates a strong correlation between the fluorescence signal and the relative abundance of the lithium-silicon alloy. Furthermore, Figure 5 The fluorescence signals in Figures (a) and (b) show non-uniformity. The fluorescence signals at the creases or morphological defects are significantly weakened or even completely disappeared, indicating that there is a distribution difference in the alloying process of the silicon-based anode. This distribution difference is closely related to the interface state of the silicon-based anode.

[0113] In summary, using fluorescent probe molecules with an imine structure containing ortho-hydroxyl groups to characterize silicon-based anodes via solid-state fluorescence imaging allows for direct analysis of key information such as the state of charge, lithium-silicon alloy distribution, silicon coating cracks and defects, and lithium deposition particles. This provides a reference for diagnosing the interface state of silicon-based anodes, battery cycle stability, and safety.

[0114] 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.

[0115] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are 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 application should be determined by the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A solid-state fluorescence imaging characterization method for silicon-based anodes, characterized in that, Includes the following steps: The fluorescent probe molecules react with the lithium-silicon alloy in the silicon-based anode to form a silicon-based anode containing lithium-based fluorescent compounds; Solid-state fluorescence imaging characterization was performed on the silicon-based anode containing the lithium-based fluorescent compound; The fluorescent probe molecule has a structure as shown in general formula (I): （Ⅰ）； The hydroxyl group on Ar is located ortho to the imine group; each occurrence of Ar independently includes one of the following: benzene ring, naphthyl ring, pyridine, pyrrole, piperidine, pyrimidine, furan, thiophene, thiazole, imidazole, quinoline, and indole; and the fluorescent probe molecule has ESIPT fluorescence properties in solid state or in poor solvent system. After reacting with the lithium silicon alloy, the ESIPT mechanism is destroyed, resulting in a significant change in the fluorescence signal.

2. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in claim 1, characterized in that, Each occurrence of Ar independently includes either a 6-30 substituted or unsubstituted aryl group or a 5-30 substituted or unsubstituted heteroaryl group.

3. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in claim 1, characterized in that, The fluorescent probe molecule has a structure as shown in general formula (II): （Ⅱ）； Each instance of R independently includes one of H, halogen, amino, nitro, cyano, isocyano, acyl, ester, substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heteroalkyl, and substituted or unsubstituted heterocyclic.

4. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in claim 3, characterized in that, R is selected from H.

5. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in any one of claims 1 to 4, characterized in that, The reaction of fluorescent probe molecules with a lithium-silicon alloy in a silicon-based anode includes the following steps: The fluorescent probe molecules and organic solvent are mixed to prepare a mixture; The mixture is applied to the surface of the silicon-based anode, and the organic solution is allowed to evaporate.

6. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in claim 5, characterized in that, The concentration of fluorescent probe molecules in the mixture is 0.1 mg / mL to 5.0 mg / mL; and / or, The area of ​​the silicon-based negative electrode is 100 mm². 2 Under these conditions, the amount of the mixture used is 0.05 mL to 0.20 mL.

7. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in claim 5, characterized in that, The organic solvent includes one or more of diethyl ether, tetrahydrofuran, acetone, n-hexane, and cyclohexane.

8. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in any one of claims 1 to 4, characterized in that, The silicon-based anode material includes one or more of silicon carbide, silicon oxide, silicon-based alloy, and nano-silicon materials.

9. The solid-state fluorescence imaging characterization method for silicon-based anodes as described in any one of claims 1 to 4, characterized in that, Solid-state fluorescence imaging characterization of the silicon-based anode containing the lithium-based fluorescent compound includes the following steps: The fluorescence phenomenon of the silicon-based anode containing the lithium-based fluorescent compound was observed under ultraviolet light irradiation. And / or, The fluorescence intensity of the silicon-based anode containing the lithium-based fluorescent compound was measured using a fluorescence spectrometer.

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