Application of AIE molecules as probes in the detection of carbon material anodes

Abstract

The present invention provides an application of an AIE molecule as a probe in the detection of a carbon material negative electrode, wherein the detection object includes one or more of lithium insertion and surface lithium deposition of the carbon material negative electrode; the AIE molecule is a hydroxyl-modified AIE molecule; the carbon material used in the carbon material negative electrode is a carbon material with light absorption properties; the carbon material negative electrode is a carbon material negative electrode in a lithium ion battery, and the lithium ion battery is a lithium cobalt oxide battery, a lithium nickel oxide battery, a lithium iron phosphate battery or a lithium manganese dioxide battery. Aggregation-induced emission (AIE) molecules react with intercalation compounds formed after lithium insertion or surface lithium deposition, and the AIE changes in fluorescence color and intensity before and after the reaction, and when in contact with the carbon material itself, the AIE fluorescence is quenched due to the conjugated plane structure, thereby detecting and calibrating the morphology, distribution and concentration of the intercalation compound and surface lithium deposition.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to the application of an AIE molecule as a probe in the detection of a negative electrode of a carbon material. Background Art

[0002] With the continuous progress of society and technology, the demand for energy storage, transportation and efficient utilization in human production and lifestyle is increasing day by day. At present, lithium-ion batteries are the "main force" of secondary batteries, providing people with efficient and convenient energy, and have taken root in various fields such as mobile electronic devices, electric transportation, and aviation. However, lithium-ion batteries still have instability and safety hazards during use, and the accidents caused by them bring serious inconvenience to daily production and life.

[0003] Carbon materials are the most commonly used negative electrode materials in lithium-ion batteries. The common electrochemical processes of carbon material negative electrodes during cyclic use include lithium insertion and lithium precipitation. Lithium insertion is the process of lithium ions entering the gaps of carbon materials to form intercalation compounds. Due to factors such as the roughness and surface defects of the negative electrode materials, uneven electrolyte infiltration, and stress in battery manufacturing, lithium intercalation often shows regional differences. Uneven lithium insertion directly causes the rated capacity decay and local overheating of the negative electrode, and is more likely to induce lithium precipitation. Lithium precipitation refers to the reduction of lithium ions into active substances and deposition on the surface of the negative electrode, especially under low temperature, fast charging or extreme discharge. Lithium precipitation is very likely to occur. In the long-term cycle process, uneven lithium precipitation is prone to grow into lithium dendrites and pulverize, resulting in internal short circuits in the battery, causing thermal runaway, and then potential fire and explosion risks.

[0004] In addition, the exothermic reaction between the electrolyte and the surface lithium deposition may generate heat accumulation and byproducts, resulting in reduced Coulombic efficiency and capacity, and rapidly reduced safety. Therefore, how to visualize the distribution and concentration of lithium intercalation and how to accurately and intuitively image the lithium deposition process are of vital importance for studying the electrochemical behavior of graphite negative electrodes and predicting the life and safety hazards of lithium-ion batteries.

[0005] There are many characterization or detection technology studies on the phenomenon of lithium insertion and lithium deposition during the recycling process of lithium-ion batteries, which can be roughly divided into two categories: physical methods and electrochemical methods. Physical methods mainly detect the negative electrode based on the physical properties of the sample, such as morphology, interface properties, chemical composition and microstructure. Other physical methods such as X-ray diffraction (XRD), atomic Raman spectroscopy, in-situ nuclear magnetic resonance (in-situ NMR), etc. can obtain electrode surface information through specific signals, but direct observation is not possible. Electrochemical methods, including voltage / capacity curve analysis and Arrhenius method, use the difference in electrochemical behavior during lithium deposition to detect the negative electrode situation, but there is still a lack of direct observation and intuitive results. Therefore, it is urgent to develop a method that can simultaneously perform visual imaging and quantitative analysis of lithium insertion and deposition. Summary of the invention

[0006] Based on this, it is necessary to provide an application of AIE molecules as probes in the detection of carbon material negative electrodes, so as to enable visual imaging and quantitative analysis of lithium insertion and extraction at the same time.

[0007] An embodiment provides an application of an AIE molecule as a probe in the detection of a carbon material negative electrode, wherein the detection object includes one or more of lithium insertion and surface lithium deposition of the carbon material negative electrode.

[0008] In some embodiments, the AIE molecule is a hydroxyl-modified AIE molecule.

[0009] In some embodiments, the AIE molecule comprises a hydroxyl-modified tetraphenylethylene molecule.

[0010] In some embodiments, the carbon material used for the carbon material negative electrode is a carbon material with light absorbing properties.

[0011] In some embodiments, the carbon material used for the carbon material negative electrode is selected from graphite, hard carbon, soft carbon, carbon nanotubes or graphene.

[0012] In some embodiments, the carbon material negative electrode is a graphite negative electrode.

[0013] In some of the embodiments, the lithium intercalated in the carbon material negative electrode is a graphite intercalation compound.

[0014] In some embodiments, the carbon material negative electrode is a carbon material negative electrode with light-absorbing properties in a lithium-ion battery.

[0015] In some embodiments, the lithium-ion battery is a lithium cobalt oxide battery, a lithium nickel oxide battery, a lithium iron phosphate battery, or a lithium manganese dioxide battery.

[0016] In some embodiments, when performing detection, the concentration of the AIE molecule as a probe is 1.0-10 mg / mL.

[0017] The above-mentioned AIE molecules are used as probes in the detection of carbon material negative electrodes, and the detection objects include one or more of lithium insertion and surface lithium deposition in the carbon material negative electrode; aggregation-induced emission (AIE) molecules react with intercalation compounds formed after lithium insertion or surface lithium deposition, and the AIE fluorescence color and intensity change before and after the reaction, and when in contact with the carbon material itself, the AIE fluorescence is quenched due to the conjugated planar structure, thereby detecting and calibrating the morphology, distribution and concentration of the intercalation compound and surface lithium deposition. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the mechanism of using fluorescent molecular probe to detect the components of graphite negative electrode;

[0019] Figure 2 Schematic diagram of the fluorescence color change after the fluorescent molecular probe comes into contact with the graphite intercalation compound;

[0020] Figure 3 The NCM622|Gr soft-pack lithium-ion battery provided in the embodiment is charged to a certain state of charge (SOC) after 3 charge and discharge cycles. The battery is then disassembled, the negative electrode is taken out, and the ether solution of dihydroxytetraphenylethylene is sprayed on the graphite negative electrode. This is a surface fluorescence image. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented 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 understanding of the disclosure of the present invention more thorough and comprehensive.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0023] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0024] As used herein, "one or more" refers to any one or a combination of any two or more of the listed items.

[0025] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0026] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 1.0-10 mg / mL means that the units of the left endpoint "1.0" and the right endpoint "10" are both mg / mL.

[0027] The present invention provides an application of an AIE molecule as a probe in the detection of a carbon material negative electrode, wherein the detection object includes one or more of lithium insertion and surface lithium deposition of the carbon material negative electrode.

[0028] It should be noted that the carbon material negative electrode to be tested is the carbon material negative electrode of the battery after charge and discharge.

[0029] During the cyclic use of carbon material negative electrodes, lithium insertion occurs, that is, lithium ions enter the gaps between carbon material layers to form intercalation compounds; taking graphite negative electrodes as an example, lithium insertion occurs during the cyclic use of graphite negative electrodes, and lithium ions enter the gaps between graphite layers to form lithium-graphite intercalation compounds (Li-GIC for short).

[0030] Understandably, intercalation compounds refer to highly reactive lithium-carbon compounds in carbon material negative electrodes, and their chemical formula is LiC x (x≥6); the main chemical components of the solid electrolyte layer (SEI film) grown on the surface of the lithium metal negative electrode used in lithium metal batteries are lithium salts such as LiF and LiOAc, and the main chemical components of the lithium dendrites grown on the surface of the lithium metal negative electrode used in lithium metal batteries are lithium element; the chemical composition and properties of the intercalation compound of the carbon material negative electrode are different from the SEI film and lithium dendrites on the surface of the lithium metal negative electrode.

[0031] AIE molecular probes can react with highly active intercalation compounds or surface lithium deposition and are accompanied by fluorescence changes. When in contact with carbon materials, the AIE fluorescence is quenched due to the conjugated planar structure of the carbon material itself. The surface components (uneven lithium insertion areas, lithium deposition particles, etc.) are distinguished according to the fluorescence emission area; the regional distribution of uneven lithium insertion in the negative electrode of the carbon material and the morphology of lithium deposition on the surface of the carbon material are judged according to the depth of the fluorescence color, so as to realize the visual analysis of the negative electrode surface of the carbon material; the fluorescence intensity is measured by a fluorescence spectrometer to quantitatively analyze the amount of lithium insertion in the negative electrode of the carbon material and the amount of lithium deposition on the surface.

[0032] Taking the carbon material negative electrode as a graphite negative electrode, the intercalation compound as a graphite intercalation compound, and the AIE molecular probe as a catechol-based tetraphenylethylene as an example, the reaction process is as follows: Figure 1 shown.

[0033] like Figure 1 As shown, catechol-based tetraphenylethylene exhibits blue fluorescence under 365nm excitation, but after reacting with active lithium species (graphite intercalation compounds or lithium deposition on the graphite surface), the product (lithium-containing AIE compound) exhibits yellow fluorescence under 365nm excitation; on the pure graphite surface, the fluorescent molecular probe does not emit light.

[0034] like Figure 2As shown, a graphite intercalation compound LiC6 is taken, and after 10 seconds, catechol-based tetraphenylethylene is sprayed on the surface of the graphite intercalation compound LiC6. The fluorescent color is blue, and after 20 seconds, the fluorescent color changes from blue to yellow.

[0035] like Figure 2 As shown, the aqueous dispersion of dihydroxytetraphenylethylene exhibits blue fluorescence under 365nm excitation. After 15s, the graphite intercalation compound LiC6 is added to the aqueous dispersion of dihydroxytetraphenylethylene, and the fluorescence changes from blue to yellow after 30s.

[0036] In some embodiments, the AIE molecule may be a hydroxyl-modified AIE molecule, including AIE molecules modified with a single hydroxyl group or multiple hydroxyl groups, and AIE molecules modified with hydroxyl groups at different substitution positions.

[0037] In some embodiments, the AIE molecule may include a hydroxyl-modified tetraphenylethylene molecule; further, the AIE molecule is selected from a class of polyphenolic hydroxyl-modified tetraphenylethylene represented by catechol-based tetraphenylethylene.

[0038] In some embodiments, the carbon material used in the carbon material negative electrode can be a carbon material with light absorbing properties. When the AIE molecular probe contacts the carbon material negative electrode, the fluorescence of AIE will be quenched, and when the AIE molecule reacts with lithium insertion or lithium precipitation, the fluorescence of AIE will change, so the AIE molecular probe can be used to analyze the lithium insertion and surface lithium precipitation of the carbon material negative electrode.

[0039] In some embodiments, the carbon material used in the carbon material negative electrode can be selected from graphite, hard carbon, soft carbon, carbon nanotubes or graphene.

[0040] In some embodiments, the carbon material negative electrode is a graphite negative electrode.

[0041] In some embodiments, the lithium intercalated in the carbon material negative electrode is a graphite intercalation compound.

[0042] In some embodiments, the carbon material negative electrode may be a carbon material negative electrode with light absorbing properties in a lithium ion battery.

[0043] In some embodiments, the lithium-ion battery may be a lithium cobalt oxide battery, a lithium nickel oxide battery, a lithium iron phosphate battery or a lithium manganese dioxide battery.

[0044] A method for detecting a carbon material negative electrode provided in an embodiment may include the following steps:

[0045] The AIE molecules are mixed with an organic solvent to form an AIE molecular probe solution;

[0046] contacting the AIE molecular probe solution with the negative electrode surface of the carbon material, observing the fluorescence of the negative electrode surface of the carbon material, and measuring the fluorescence intensity;

[0047] Based on the fluorescence intensity, the lithium content on the surface of the carbon material negative electrode is quantitatively analyzed.

[0048] In some embodiments, the concentration of the AIE molecular probe solution is 1.0 to 10 mg / mL; for example, it can be 1.0 mg / mL, 2.0 mg / mL, 3.0 mg / mL, 4.0 mg / mL, 5.0 mg / mL, 6.0 mg / mL, 7.0 mg / mL, 8.0 mg / mL, 9.0 mg / mL or 10.0 mg / mL, etc., without specific limitation.

[0049] In some embodiments, the organic solvent includes a volatile inert organic solvent; for example, diethyl ether or dichloromethane, etc., which are not specifically limited.

[0050] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0051] It should be noted that the following detailed description of the detection method is given by taking a graphite negative electrode as an example, but the detection method is not limited to being applicable only to a graphite negative electrode. The detection method is applicable to all lithium-ion batteries containing light-absorbing carbon materials.

[0052] Example

[0053] A method for detecting graphite negative electrodes in lithium-ion batteries, wherein the lithium-ion batteries used are NCM622|Gr soft-pack batteries, the negative electrodes are graphite, the positive electrodes are ternary materials of lithium nickel oxide / lithium cobalt oxide / lithium manganese oxide, the electrolyte is 1 mol / L LiPF6 / EC+DEC+EMC (volume ratio 1:1:1), and the separator is a commercial PE film. The detection method comprises the following steps:

[0054] (1) The battery was charged and discharged using a blue-power device, using a constant current (0.1C, 1C = 100mA) - constant voltage (4.2V, 0.02C cut-off) charging and constant current discharge (0.1C) mode. After three cycles, the battery was charged to a certain state of charge (SOC) at 0.1C, and the battery was disassembled to obtain the cycled graphite negative electrode material.

[0055] (2) Spray a 3.0 mg / mL catechol tetraphenylethylene ether solution on the surface of the graphite negative electrode. After the ether evaporates, illuminate the graphite negative electrode under a 365 nm ultraviolet lamp to observe the fluorescence on the surface of the graphite negative electrode. The fluorescence intensity is measured using a fluorescence spectrometer to quantitatively analyze the lithium content on the surface of the graphite negative electrode. The results are as follows: Figure 3 shown.

[0056] Depend on Figure 3 From the fluorescence spectrum, we can see that the intrinsic emission of the catechol-based tetraphenylethylene coating has a strong emission peak near 475nm, but the emission peak weakens and red-shifts to around 530nm after contacting with graphite interlayer compounds or active lithium such as lithium metal. After contacting with pure graphite, the fluorescence is quenched and there is no emission peak. Figure 3 From the fluorescence imaging results, it can be seen that the uneven lithium deposition area shows yellow fluorescence, and the graphite part with less lithium content does not show fluorescence due to quenching. And the depth of yellow can reflect the lithium content in this area. After measuring the fluorescence intensity with a fluorescence spectrometer, the overall lithium content on the electrode surface can be quantitatively analyzed. When the battery is charged and discharged with different cycle numbers and different charge and discharge current sizes, this method can visualize and quantitatively analyze the battery conditions under different conditions.

[0057] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0058] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An application of an AIE molecule as a probe in the detection of a negative electrode of a carbon material, characterized in that: The detection object includes one or more of lithium insertion and surface lithium deposition in the negative electrode of the carbon material; the AIE molecule includes a hydroxyl-modified tetraphenylethylene molecule.

2. The use of the AIE molecule according to claim 1 as a probe in the detection of carbon material negative electrode, characterized in that: The AIE molecules include tetraphenylethylene molecules modified with polyphenolic hydroxyl groups.

3. The use of the AIE molecule according to claim 1 or 2 as a probe in the detection of carbon material negative electrode, characterized in that: The AIE molecules include catechol-based tetraphenylethylene molecules.

4. The use of the AIE molecule according to claim 1 as a probe in the detection of a negative electrode of a carbon material, characterized in that: The carbon material used in the carbon material negative electrode is a carbon material with light absorbing properties.

5. The use of the AIE molecule according to claim 4 as a probe in the detection of carbon material negative electrode, characterized in that: The carbon material used in the carbon material negative electrode is selected from graphite, hard carbon, soft carbon, carbon nanotubes or graphene.

6. The use of the AIE molecule according to claim 4 or 5 as a probe in the detection of carbon material negative electrode, characterized in that: The carbon material negative electrode is a graphite negative electrode.

7. The use of the AIE molecule according to claim 6 as a probe in the detection of carbon material negative electrode, characterized in that: The lithium intercalation of the carbon material negative electrode is a graphite intercalation compound.

8. Use of the AIE molecule according to any one of claims 1 to 2, 4 to 5 and 7 as a probe in the detection of carbon material negative electrode, characterized in that: The carbon material negative electrode is a carbon material negative electrode with light-absorbing properties in a lithium-ion battery.

9. The use of the AIE molecule according to claim 8 as a probe in the detection of carbon material negative electrode, characterized in that: The lithium ion battery is a lithium cobalt oxide battery, a lithium nickel oxide battery, a lithium iron phosphate battery or a lithium manganese dioxide battery.

10. Use of the AIE molecule according to any one of claims 1 to 2, 4 to 5, 7 and 9 as a probe in the detection of carbon material negative electrode, characterized in that: When performing the detection, the concentration of the AIE molecule as a probe is 1.0 to 10 mg / mL.

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