Lithium ion battery negative electrode material with photochromic characteristic and preparation method thereof

Abstract

The invention discloses a lithium ion battery negative electrode material with a photochromic characteristic and a preparation method thereof. The molecular formula of the lithium ion battery negative electrode material with the photochromic characteristic is MVMo9O28. Wherein MV is a methyl viologen cation; according to the lithium ion battery negative electrode material with the photochromic characteristic, electron transfer from oxygen atoms to molybdenum atoms occurs under ultraviolet irradiation, and a two-year super-stable charge separation state is formed along with color change of crystals from colorless to blue; when the lithium ion battery negative electrode material with the photochromic characteristic is used as the lithium ion battery negative electrode material, the specific capacity of the battery can be improved in a colored state compared with an initial state; a new strategy is provided for developing a high-performance lithium ion battery negative electrode material, and the ever-increasing energy storage requirement is expected to be met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of crystal material synthesis and lithium ion battery, and particularly relates to a lithium ion battery negative electrode material with photochromic properties and a preparation method thereof. BACKGROUND

[0002] The increasing demand for advanced technologies such as large-scale energy storage systems, electric vehicles, and consumer electronics has led to a comprehensive requirement for rechargeable batteries with high safety, environmental friendliness, cost-effectiveness, and high energy density. Lithium ion batteries (LIBs) have been widely used in portable electronic devices and electric vehicles due to their high energy density and long cycle life. However, the theoretical capacity of commercial graphite anodes is limited (about 372 mAh g -1 ), and the lithium ion intercalation / deintercalation kinetics is slow, which restricts its potential to meet the growing energy and power demands of new-generation energy storage systems. Exploring new anode materials with high specific capacity and fast rate performance to meet the core requirements of lithium ion batteries is a long-term exploration direction for the scientific community.

[0003] It has been reported that many strategies can improve the capacity of the battery, including electrolyte optimization and electrode material modification. In recent years, decoupling strategies with additional H + / OH- pairs or electron-hole pairs provide an effective method to improve battery performance. For example, electrolyte decoupling allows the anode to work in alkaline electrolyte and the cathode to work in acidic electrolyte, with H + / OH- pairs participating in cathode / anode reactions, respectively, providing additional capacity to the system. In addition, photoactive semiconductor electrodes can generate photo-generated electron-hole pairs under light, and the efficient separation and transport of these photo-generated charge carriers can significantly improve the battery capacity. However, the former method requires a physical separator, which increases the complexity and cost of the battery, while the latter relies on continuous light to achieve capacity enhancement. Developing a low-cost, non-volatile decoupling strategy to improve the capacity of lithium ion batteries remains a challenge. SUMMARY

[0004] To solve the above problems, the application provides a lithium ion battery negative electrode material with photochromic properties and a preparation method thereof. The colored state of the lithium ion battery negative electrode material with photochromic properties significantly improves the specific capacity of the battery compared to the initial state. The application provides a new strategy for developing high-performance lithium ion battery negative electrode materials, which is expected to meet the growing demand for energy storage.

[0005] To achieve the above purpose, the application adopts the following technical solutions:

[0006] A lithium ion battery negative electrode material with photochromic properties, the molecular formula of the lithium ion battery negative electrode material with photochromic properties is MV Mo9O 28 ; wherein MV is a methyl viologen cation; the lithium ion battery negative electrode material with photochromic properties undergoes electron transfer from oxygen atoms to molybdenum atoms under ultraviolet light irradiation, accompanied by a color change from colorless to blue, forming a super-stable charge separation state lasting up to two years; as a lithium ion battery negative electrode material, the colored state of the lithium ion battery negative electrode material with photochromic properties can improve the specific capacity of the battery compared with the initial state.

[0007] Preferably, the crystal structure of the lithium ion battery negative electrode material with photochromic properties belongs to a monoclinic system, the space group is C2 / c, and the cell parameters are: a = 26.8624(16), b = 5.4839(2), c = 24.6339(6) α = 90°, β = 122.636°, γ = 90°.

[0008] A preparation method of a lithium ion battery negative electrode material with photochromic properties, comprising the following steps:

[0009] S1, 151mg of Na2MoO4·2H2O and 65mg of methyl viologen chloride are dissolved in 8mL of water, stirred at room temperature for 5 minutes to obtain a transparent liquid;

[0010] S2, the pH value of the transparent liquid is adjusted to 1 with a 4mol·L -1 of HCl solution, the transparent liquid becomes turbid, and is stirred at room temperature for 1 hour to obtain a mixture;

[0011] S3, after the stirring is completed, the mixture is placed in a 25mL polytetrafluoroethylene kettle, and is placed at 140℃ for 72 hours for hydrothermal reaction;

[0012] S4, the polytetrafluoroethylene kettle after the hydrothermal reaction is cooled to room temperature, filtered, and dried in a vacuum drying box to obtain a colorless block crystal, which is the lithium ion battery negative electrode material with photochromic properties.

[0013] Preferably, the lithium ion battery negative electrode material with photochromic properties obtained in step S4 is irradiated with ultraviolet light, and a color change from colorless to blue occurs, the lithium ion battery negative electrode material with photochromic properties in the colorless state is named 1a, and the lithium ion battery negative electrode material with photochromic properties in the blue state is named 1b.

[0014] After the above technical solution is adopted, the present application has the following beneficial effects: the present application designs a new crystalline photochromic polyoxymolybdate MV[Mo9O 28As the negative electrode of lithium ion battery (LIB), the electron transfer from O to Mo occurs after UV irradiation, accompanied by the color change from colorless to blue, with an ultra-stable charge-separated state for up to 2 years under ambient conditions. After coloring, the observed capacity increased from 147 mAh g -1 to 1245 mAh g -1 at a current density of 0.1 Ag -1 . The charge-separated state not only accelerated the Li + ion transfer, achieving excellent rate capacity, but also provided additional holes to increase the amount of Li + insertion. This makes the electron transfer photochromic successfully applied in LIB to achieve capacity increase, opening up a new way to improve the performance of LIBS. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The crystal structure diagram of the lithium ion battery negative electrode material with photochromic properties prepared in the application;

[0016] Figure 2 The powder diffraction diagram of the lithium ion battery negative electrode material with photochromic properties prepared in the application;

[0017] Figure 3 The infrared spectrum diagram of the lithium ion battery negative electrode material with photochromic properties prepared in the application;

[0018] Figure 4 The ultraviolet absorption spectrum diagram of the lithium ion battery negative electrode material with photochromic properties prepared in the application;

[0019] Figure 5 The lithium ion battery cyclic voltammetry comparison diagram of the lithium ion battery negative electrode material with photochromic properties prepared in the application;

[0020] Figure 6 The lithium ion battery constant current charge and discharge comparison diagram of the lithium ion battery negative electrode material with photochromic properties prepared in the application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the application and not to limit the application.

[0022] As shown in the following. Figures 1 to 6

[0023] Example 1

[0024] Example 1

[0025] MV[Mo9O​28 Preparation of the compound of formula (I):

[0026] S1, dissolve 151 mg of Na2MoO4·2H2O and 65 mg of methyl viologen chloride in 8 mL of water, stir at room temperature for 5 minutes to obtain a transparent liquid;

[0027] S2, adjust the pH value of the transparent liquid to 1 with 4 mol·L-1 HCl solution, the transparent liquid becomes turbid, and stir at room temperature for 1 hour to obtain a mixture; -1

[0028] S3, after stirring, put the mixture into a 25 mL polytetrafluoroethylene kettle, and place it at 140℃ for 72 hours for hydrothermal reaction;

[0029] S4, cool the polytetrafluoroethylene kettle after hydrothermal reaction to room temperature, filter, and dry in a vacuum drying oven to obtain a colorless block crystal, which is a lithium ion battery negative electrode material with photochromic properties.

[0030] Characterization and performance test of the crystal:

[0031] (1) Crystal structure determination

[0032] The lithium ion battery negative electrode material with photochromic properties prepared in Example 1 was selected under a microscope to obtain single crystals with appropriate size, regular shape and transparency. The crystal structure was analyzed by a Rigaku XtaLAB Synergy-R diffractometer at 175(2) K, using a graphite monochromator monochromatized Mo-Kα ray as an incident light source to collect crystal diffraction data. In the structure analysis, the Shelextl-97 program was used to analyze and refine the crystal structure by direct method, and the non-hydrogen atoms and their anisotropic treatment parameters were corrected by full matrix least squares method, and all hydrogen atoms were obtained by theoretical hydrogenation. Part of the crystallographic data and refinement parameters are shown in Table 1.

[0033] Table 1: Crystal parameters of the compound

[0034]

[0035]

[0036] (2) Powder diffraction characterization:

[0037] Take an appropriate amount of single crystal prepared in Example 1 above, and grind it into powder. The powder diffraction pattern of the material was measured at room temperature (as shown in Figure 2). Figure 2 ​​The comparison between the experimental results and the diffraction peaks simulated according to the single crystal diffraction data shows that the experimental results are in good agreement with the fitting results of the Mercury software, thus indicating that the compound is a pure phase. The anisotropy of the crystal causes some differences in peak intensity of the diffraction peaks.

[0038] (3) Infrared spectroscopic characterization:

[0039] As shown in Figure 3 , the peaks at 3122 cm -1 , 3050 cm -1 are attributed to the stretching vibration of =C-H; the peaks at 1639 cm -1 , 1562 cm -1 , 1503 cm -1 are attributed to the stretching vibration of the pyridine skeleton; the peak at 1442 cm -1 is attributed to the C-H bending vibration in -CH3; the peaks at 1350-1100 cm -1 are mainly attributed to the stretching vibration of C-N; the peaks below 1000 cm -1 are mainly attributed to the Mo-O stretching vibration, and partly to the =C-H bending vibration.

[0040] (4) Ultraviolet absorption spectroscopic characterization:

[0041] As shown in Figure 4 , under ambient conditions, the colorless crystal (1a) becomes blue (1b) when irradiated with a 500 W Hg lamp (about 110 mW·cm -2 , the default light source hereinafter). The time-dependent electronic absorption spectrum shows that 1b has a new broad absorption band, spanning 400-1200 nm, with the maximum absorption wavelength concentrated at 681 nm. The coloration reaches saturation after 35 minutes of irradiation.

[0042] Figure 5 is a lithium ion battery negative electrode material with photochromic properties and a cyclic voltammetry comparison chart of the lithium ion battery after discoloration; Figure 6 is a lithium ion battery negative electrode material with photochromic properties and a galvanostatic charge-discharge comparison chart of the lithium ion battery after discoloration.

[0043] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed by the present application can be easily conceived by those skilled in the art, and should be encompassed within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A lithium-ion battery negative electrode material with photochromic properties, characterized in that: The molecular formula of the lithium-ion battery negative electrode material with photochromic properties is MVMo9O 28 ; Wherein, MV is a methyl viologen cation; the lithium-ion battery negative electrode material with photochromic properties undergoes electron transfer from oxygen atoms to molybdenum atoms under ultraviolet light irradiation, accompanied by a color change of the crystal from colorless to blue, forming an ultra-stable charge separation state for up to two years; when the lithium-ion battery negative electrode material with photochromic properties is used as a lithium-ion battery negative electrode material, the colored state can improve the battery specific capacity compared with the initial state.

2. The lithium-ion battery negative electrode material having photochromic properties according to claim 1, wherein: The crystal structure of the lithium-ion battery negative electrode material with photochromic properties belongs to the monoclinic system, the space group is C2 / c, and the unit cell parameters are: a=26.8624(16), b=5.4839(2), α=90°, β=122.636°, γ=90°.

3. A method for preparing a lithium-ion battery negative electrode material having photochromic properties according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Dissolve 151 mg of Na2MoO4·2H2O and 65 mg of methyl viologen chloride in 8 mL of water and stir at room temperature for 5 minutes to obtain a clear liquid. S2, use 4mol·L -1 The pH value of the transparent liquid was adjusted to 1 by adding HCl solution, and the transparent liquid became turbid, and stirred at room temperature for 1 hour to obtain a mixture; S3. After stirring, the mixture was placed in a 25 mL polytetrafluoroethylene kettle and placed at 140°C for 72 hours for hydrothermal reaction; S4. Cool the polytetrafluoroethylene kettle after the hydrothermal reaction to room temperature, filter, and dry in a vacuum drying oven to obtain colorless block crystals, which are lithium-ion battery negative electrode materials with photochromic properties.

4. The method for preparing a lithium-ion battery negative electrode material having photochromic properties according to claim 3, wherein: The lithium-ion battery negative electrode material with photochromic properties obtained in step S4 is irradiated with ultraviolet light to change color from colorless to blue. The lithium-ion battery negative electrode material with photochromic properties in the colorless state is named 1a, and the lithium-ion battery negative electrode material with photochromic properties in the blue state is named 1b.

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