Preparation and application of ionic organic positive electrode material with high theoretical specific capacity and double redox active sites

Abstract

The invention discloses an ionic organic positive electrode material ethyl viologen dinaphthoquinone-2-sulfonate with high theoretical specific capacity and double oxidation reduction active sites. The synthesis method comprises the following steps: firstly, adding ethyl viologen dibromide powder into a 1, 2-naphthoquinone-4-sodium sulfonate aqueous solution to carry out ion exchange reaction; and cooling the faint yellow solution to room temperature, standing and precipitating at room temperature, filtering deep yellow solids, washing with excessive deionized water to remove impurities, and drying in vacuum. Compared with the prior art, the invention has the following advantages: NQ-anions which only contain two aromatic rings and two carbonyl groups at ortho-positions are innovatively introduced into an EV < 2 + > structure, so that the interaction between molecules can be enhanced, the dissolution of the NQ-anions in an ionic liquid electrolyte is inhibited, the cycle stability is favorably improved, and the two carbonyl groups are ortho-substituted, so that the service life of the NQ-anions is prolonged, and the service life of the NQ-anions is prolonged. The density of active sites is increased, the reaction activity and the capacity utilization rate of carbonyl active sites are also improved through ortho-substitution, and the electrochemical performance of the ionic organic positive electrode material is improved. In addition, the preparation method is simple to operate and low in cost, and the environment-friendly characteristic is shown while the cost is saved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum ion battery electrode materials, and in particular to the preparation and application of an ionic organic positive electrode material with high theoretical specific capacity and dual redox active sites. Background Art

[0002] The limited and uneven nature of lithium resources hinders the further development of lithium-ion batteries; the lithium-ion batteries currently developed still have safety hazards caused by thermal runaway and cannot meet people's needs for safety. Therefore, developing a new generation of secondary batteries with abundant resources, low cost and high safety to alleviate the excessive dependence on lithium-ion batteries has become an important direction for promoting the development of the energy field. Among the new secondary batteries, aluminum-ion batteries based on ionic liquid electrolytes have received increasing attention in recent years. This battery system has the following advantages: (1) Aluminum is the most abundant metal element in the earth's crust, with abundant reserves and low price; (2) The theoretical specific capacity of the aluminum negative electrode is huge, with mass and volume specific capacities reaching 2980mAh / g and 8063mAh / cm respectively. 3 (Lithium negative electrode: 3860mAh / g and 2062mAh / cm 3 ); (3) The aluminum anode and ionic liquid electrolyte are non-flammable and non-explosive, and have high safety. One of the most important challenges facing aluminum-ion batteries is the development of high-performance cathode materials that match the aluminum metal anode.

[0003] Organic cathode materials containing conjugated structures can store charge through the interaction between aluminum-based coordination ions and electron-donating / withdrawing active sites in the molecular structure. They have the characteristics of flexible structure, strong designability, multi-ion storage, low cost and environmental friendliness, showing great application potential. However, the electrochemical activity of organic cathodes in battery systems decreases, the reaction kinetics are slow, and the solubility in ionic electrolytes is high, which easily causes the loss of active substances and seriously affects the cycle performance of the battery. Copolymerization and grafting of organic materials is an effective method to reduce the solubility of active organic matter in electrolytes and improve the cycle performance; however, this method requires a complex synthetic route to introduce inactive substituents into the organic material. The introduction of inactive substituents will reduce the active site density, resulting in a lower specific capacity of the material. Therefore, it is urgent to find a method that can reduce the solubility of active organic matter in ionic liquid electrolytes and increase the active site density to improve the application of organic cathode materials in aluminum ion batteries.

[0004] By salting the organic materials and rationally designing the structure and electron-donating / withdrawing active sites of organic anions and cations, the density of active sites can be increased while reducing the solubility of the organic active components in the ionic liquid electrolyte, thereby improving the specific capacity and cycle performance of the battery. Studies have shown that when ethyl viologen dianthraquinone-2-sulfonate, which is partially coupled with anthraquinone-2-sulfonate and ethyl viologen, is used as the positive electrode material of organic lithium-ion batteries, the ethyl viologen cation (EV 2+ ) and anthraquinone-2-sulfonic acid anion (AQ - ) can provide multiple reversible active sites, showing excellent cycle stability and outstanding rate performance. However, the anion of this ionic organic compound has more aromatic rings, which limits the density of active sites to a certain extent; and the two carboxyl groups in the anion are in the para position, which limits the utilization of this group. Studies have shown that the ortho-position carbonyl group reaction activity in the organic quinone positive electrode material of aluminum ion batteries is higher, and the capacity contribution rate is greater. In summary, the electrochemical performance of ionic organic compound positive electrode materials is expected to be further improved by optimizing the structure of organic anions (including reducing the number of aromatic rings and adjusting the carbonyl substitution position). Summary of the Invention

[0005] In response to the above problems, the present invention provides a preparation method and application of an ionic organic cathode material with high theoretical specific capacity and dual redox active sites, and prepares ethyl viologen dinaphthoquinone-2-sulfonate (EV-NQ2) cathode material by partial coupling of 1,2-naphthoquinone-4-sulfonate sodium (NA-NQ) and ethyl viologen dibromide (EV-Br2). Each chemical formula unit of the cathode material provides six active sites, and six electron transfers can occur during the charge and discharge process, which corresponds to the electron transfer from a pair of redox pairs EV. 2+ / EV 0 The transfer of two electrons from four redox-active NQ - Transfer of four electrons from anions. - With AQ - Compared to the conventional method, the method has one less benzene ring and the two carbonyl groups are substituted at the ortho position, which not only increases the active site density, but also enhances the reactivity of the carbonyl active sites, which is beneficial to improving the specific capacity of the ionic organic positive electrode material. The aluminum ion battery positive electrode material prepared by the method has good cycle stability and high specific capacity.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for preparing an ionic cathode material having high theoretical specific capacity and dual redox active sites comprises the following steps:

[0008] S1. Prepare EV-NQ2 by ion exchange reaction, prepare NA-NQ aqueous solution, and sonicate and stir for 0.5-1h until NA-NQ is completely dissolved.

[0009] S2. Add EV-Br2 to the S1 solution and stir for 0.5-1h.

[0010] S3. Transfer the S2 solution to a water bath for ion exchange reaction at a water bath temperature of 80°C.

[0011] S4. Let the solution after reaction in S3 stand for 2-3 hours to obtain a milky white precipitate.

[0012] S5. Filter, wash, and dry the precipitate from S4 to obtain EV-NQ2.

[0013] Preferably, the concentration of the NA-NQ aqueous solution is independently 0.2 mol / L.

[0014] Preferably, the molar ratio of NA-NQ to EV-Br2 is 2:1.

[0015] Preferably, the reaction temperature of the ion exchange reaction is 80°C.

[0016] Preferably, the ion exchange reaction is carried out under high-speed stirring to ensure that NA-NQ and EV-Br2 fully react.

[0017] Preferably, the ion exchange reaction time is 5-6 hours, starting from when the temperature rises to 80°C; the static precipitation time is 2-3 hours; the ion exchange reaction and static precipitation are both carried out under air; and the vacuum drying time is 48-72 hours.

[0018] Preferably, the washing detergent is deionized water; the drying temperature is preferably 80° C., and the drying time is preferably 48 hours; and the drying is preferably vacuum drying.

[0019] Preferably, the EV-NQ2 has a block-like morphology and a particle size of 0.2-0.5 μm.

[0020] Preferably, the present invention can also regulate the size of EV-NQ2 particles by adjusting parameters such as reactant concentration and ion exchange reaction temperature.

[0021] The advantages of the present invention compared with existing viologen-based ionic cathode materials are:

[0022] The present invention will contain only two aromatic rings and two carbonyl groups in the ortho position of NQ - Anions are innovatively introduced into EVs 2+The structure can enhance the interaction between molecules, inhibit its dissolution in ionic liquid electrolyte, and help improve the cycle stability. - Anions and AQ - Compared to the anion, the anion has one less benzene ring, and the two carbonyl groups are ortho-substituted, which not only increases the active site density, but also improves the reactivity and capacity utilization of the carbonyl active sites, which is beneficial to improving the electrochemical performance of the ionic organic cathode material. In addition, the preparation method provided by the present invention has the significant advantages of simple operation, low cost, and large-scale production.

[0023] The results of the embodiment show that the EV-NQ2 prepared by the present invention can provide six reversible active sites and has a high theoretical specific capacity. The EV-NQ2 prepared by the present invention is applied to aluminum ion batteries and exhibits excellent electrochemical properties. -1 At a current density of 1.5 GHz, its specific capacity can reach 336 mAh g -1 , at 500mA g -1 Under the current density, the capacity retention rate is above 90.2% after 800 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the synthetic route of Example 1EV-NQ2.

[0025] Figure 2 This is the SEM image of Example 1EV-NQ2;

[0026] Figure 3 This is the SEM image of comparative example 1EV-Br2;

[0027] Figure 4 This is the SEM image of comparative example 2NA-NQ;

[0028] Figure 5 FTIR spectra of the positive electrode materials of Example 1, Comparative Example 1 and Comparative Example 2;

[0029] Figure 6 When EV-NQ2 is used as the positive electrode of aluminum ion battery in Example 1, the -1 First cycle charge and discharge data graph under current density;

[0030] Figure 7 For comparative example 1, when EV-Br2 is used as the positive electrode of aluminum ion battery, at 200mAg -1 First cycle charge and discharge data graph under current density;

[0031] Figure 8 For comparative example 2NA-NQ as an aluminum ion battery electrode, at 200mAg -1First cycle charge and discharge data graph under current density;

[0032] Figure 9 When Example 1, Comparative Example 1 and Comparative Example 2 are used as the positive electrode of aluminum ion batteries, at 500mAg -1 Plot of cycling data at current density. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing an ionic organic cathode material having dual redox active sites with a high theoretical specific capacity, comprising the following steps:

[0034] EV-Br2 powder was added to the Na-NQ aqueous solution to perform an ion exchange reaction. The pale yellow solution was then cooled to room temperature and allowed to settle. The dark yellow solid was filtered, washed with excess deionized water to remove impurities, and dried under vacuum.

[0035] In the present invention, EV-Br2 is added to a Na-NQ aqueous solution to perform an ion exchange reaction. In the present invention, the concentration of the Na-NQ aqueous solution is preferably 0.2 mol / L; the Na-NQ aqueous solution is preferably prepared from Na-NQ and deionized water. In the present invention, Na-NQ is preferably dissolved in deionized water under air to obtain the Na-NQ aqueous solution.

[0036] In the present invention, the molar ratio of Na-NQ to EV-Br2 is preferably 2:1.

[0037] In the present invention, the temperature of the ion exchange reaction is preferably 80° C. The time of the ion exchange reaction is preferably 5-6 hours, and the time of the ion exchange reaction is counted from the time when the reaction temperature reaches 80° C. The ion exchange reaction is carried out under high-speed stirring.

[0038] After the ion exchange reaction is completed, the present invention allows the reaction solution to settle. In the present invention, the settling time is preferably 2-3 hours.

[0039] After the static precipitation is completed, the present invention preferably filters, washes and dries the obtained liquid in sequence to obtain EV-NQ2; the washing detergent is preferably deionized water; the drying temperature is preferably 80°C, and the time is preferably 48 hours; the drying is preferably vacuum drying.

[0040] In order to make the contents of the present invention more clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention.

[0041] A specific embodiment of the present invention provides an ethyl viologen dinaphthoquinone-2-sulfonate positive electrode material, whose chemical formula is EV-NQ2.

[0042] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art.

[0043] Example 1

[0044] Through ion exchange reaction, NQ - and EV 2+ The ionic organic compound EV-NQ2, which has six reversible active sites, was prepared by partial coupling as follows: EV-Br2 and Na-NQ were synthesized in a 1:2 molar ratio. EV-Br2 powder was added to a deionized Na-NQ solution. After addition, the mixture was stirred at 80°C for 5 hours. The pale yellow solution was then cooled to room temperature and then maintained at room temperature for an additional 2-3 hours. The dark yellow solid was filtered, washed with excess deionized water, and dried in vacuo at 80°C for 48 hours.

[0045] Comparative Example 1

[0046] EV-Br2 is one of the precursors for preparing EV-NQ2, providing EV 2+ In aluminum ion batteries, AlCl3 / Et3NHCl ionic liquid electrolyte will undergo irreversible decomposition at voltages of 2.3V and above. Br in EV-Br2 - / Br 0 The reversible conversion potential is 2.71V, so EV-Br2 is only used as the positive electrode material of aluminum ion batteries. 2+ It is an active component, and its two C=N double bonds participate in the reaction as reversible active sites.

[0047] Comparative Example 2

[0048] Na-NQ is one of the precursors for preparing EV-NQ2, providing NQ - Anion, this material only has NQ - The anion is the active component, in which the four carbonyl groups act as reversible active sites to participate in the reaction.

[0049] Morphology test:

[0050] Figure 1 The synthetic route of Example 1EV-NQ2 is as follows: Figure 1 It can be seen that NA-NQ is partially coupled with EV-Br2 to prepare EV-NQ2.

[0051] Figure 2 This is the SEM image of Example 1EV-NQ2, according to Figure 2 It can be seen that the EV-NQ2 prepared in this example exhibits a uniform block morphology, and the particle size is about 0.2-0.5 μm.

[0052] Figure 3 This is the SEM image of comparative example 1EV-Br2. Figure 3 It can be seen that agglomeration occurs between the grains, and the particle size is about 0.5-1 μm.

[0053] Figure 4 The SEM image of comparative example 2Na-NQ is shown in FIG. Figure 4 It can be seen that the comparative example exhibits a block-like morphology, and the particle size is about 1-2 μm.

[0054] Figure 5 The FTIR spectra of the positive electrode materials prepared in Comparative Example 1 / Comparative Example 2 and Example 1 are as follows. Figure 5 It can be seen that in EV-Br2 and EV-NQ2, 804 cm -1 and 1558cm -1 The peaks at 1640 cm-1 are attributed to the in-plane bending vibration and stretching vibration of the C-H bond of pyridine, respectively. -1 The peak at is attributed to the stretching vibration of the C=N double bond, indicating that EV 2+ The presence of ; in Na-NQ and EV-NQ2 1667cm -1 The peak at 1032 cm is attributed to the stretching vibration of the C=O double bond. The stretching vibration peak of the sulfonate substituent also appears at 1032 cm -1 At, indicating NQ - exist

[0055] Electrochemical performance test

[0056] Prepare the DMF solutions of Example 1, Comparative Example 1, and Comparative Example 2, respectively, with a preferred concentration of 5 mg / mL. Graphene aerogels were immersed in the solutions for 6 hours, then removed and dried in an 80°C oven for 12 hours. The active material loading was 0.5 mg to 1.0 mg. The electrolyte used was an AlCl3 / Et3NHCl ionic liquid electrolyte, with a preferred molar ratio of Et3NHCl to AlCl3 of 1:1.5. The aluminum ion battery mold used was a Swaglok-type mold. Because the electrolyte is not resistant to water and oxygen, it must be stored in an argon-filled vacuum glove box, and thus the battery assembly also required completion in the glove box. A high-purity aluminum foil was placed as the negative electrode at the bottom layer of the battery, followed by a glass fiber separator. 150 μL of electrolyte was dripped onto the separator, and the graphene aerogel loaded with active material was placed on the top layer. The battery mold was tightened and sealed with an insulating film to prevent contact with air. The battery was then removed from the glove box for testing. Then use the Blue Electric test system to perform corresponding charge and discharge tests with a voltage window of 0.1 to 2.2V.

[0057] Figure 6 When the EV-NQ2 prepared in Example 1 is used as an aluminum ion battery electrode,-1 The first cycle charge and discharge data under current density. Figure 6 It can be seen that the aluminum ion battery assembled in Example 1EV-NQ2 has a -1 The first cycle can provide 336.5mAh g -1 reversible capacity.

[0058] Figure 7 For comparative example 1, when EV-Br2 is used as an aluminum ion battery electrode, at 200mAg -1 The first cycle charge and discharge data under current density. Figure 7 It can be seen that the aluminum ion battery assembled in Comparative Example 1EV-Br2 has a -1 The first cycle can provide 201.7 mAh g -1 reversible capacity.

[0059] Figure 8 For comparative example 2, when Na-NQ is used as an aluminum ion battery electrode, at 200 mAg -1 The first cycle charge and discharge data under current density. Figure 8 It can be seen that the aluminum ion battery assembled by Comparative Example 2Na-NQ has a -1 The first cycle can provide 124.3mAh g -1 reversible capacity.

[0060] Figure 9 When Example 1, Comparative Example 1 and Comparative Example 2 are used as the positive electrode of aluminum ion batteries, the -1 Cycling data at current density. Figure 9 It can be seen that the aluminum ion battery assembled with EV-NQ2 prepared in Example 1 has a -1 The capacity retention rate is about 90.2% after 800 cycles at a current density of 500mAg. -1 The capacity retention rate after 800 cycles at a current density of 10000mAg is only 65.7%. -1 After 800 cycles at a current density of , the capacity retention rate is only 76.2%.

[0061] The reason why Example 1 has excellent electrochemical performance as the positive electrode of aluminum ion battery is that: π framework NQ – Introducing EV 2+ The structure enhances the interaction between molecules, reduces the solubility of the cathode material in the ionic liquid electrolyte, and is beneficial to improving the cycle performance; NQ - Anions and EVs 2+The cations can provide redox reversible active sites, and NQ - The density of carbonyl active sites in the anion is high, and the reaction activity of the adjacent carbonyl groups is strong, which improves the capacity utilization of the positive electrode material and the electrochemical performance of the aluminum ion battery.

[0062] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. Preparation and application of an ionic organic cathode material with high theoretical specific capacity and dual redox active sites, characterized by: The following steps are involved: An ion exchange reaction was performed by adding ethyl viologen dibromide (EV-Br2) powder to an aqueous solution of sodium 1,2-naphthoquinone-4-sulfonate (Na-NQ). The pale yellow solution was cooled to room temperature and then allowed to settle. The dark yellow solid was filtered, washed with excess deionized water to remove impurities, and dried under vacuum to obtain the ethyl viologen dinaphthoquinone-2-sulfonate cathode material (EV-NQ2).

2. The preparation method according to claim 1, characterized in that The Na-NQ aqueous solution is independently 0.2 mol / L.

3. The preparation method according to claim 1, characterized in that The molar ratio of Na-NQ to EV-Br2 is 2:

1.

4. The preparation method according to claim 1, characterized in that The ion exchange reaction is carried out under high-speed stirring to ensure that Na-NQ and EV-Br2 react fully.

5. The preparation method according to claim 1, characterized in that The ion exchange reaction temperature is independently 80° C. The vacuum drying temperature is independently 80° C.

6. The preparation method according to claim 1, characterized in that The ion exchange reaction time is 5-6 hours, starting from when the temperature reaches 80°C; the static precipitation time is 2-3 hours; the ion exchange reaction and static precipitation are both carried out under air; and the vacuum drying time is 48-72 hours.

7. The preparation method according to claim 1, characterized in that The EV-NQ2 has a blocky morphology and a particle size of 0.2-0.5 μm.

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