Organic lithium battery positive electrode material and preparation method, preparation of positive electrode sheet and lithium battery

Abstract

The present invention discloses an organic lithium battery positive electrode material and a preparation method, as well as the preparation of a positive electrode sheet and a lithium battery. The present invention uses TFCZ as the structural skeleton of COFs and DMDA as a connecting unit, and chemically weaves the two to form an ordered COFs (CZ-DM-COF) with a grid framework structure. The material can simultaneously inherit the excellent electrochemical properties of carbazole and the lithium storage function of DMDA. The nitrogen atom of the connecting bond (-C=N-) has a pair of lone pairs of electrons, which can form n-doping with lithium ions during the discharge process, also providing lithium storage capacity. The ordered covalent bond grid framework structure provides a stable lithium ion migration channel and can also give it excellent physical and chemical stability, solving the problems of instability, low solubility, and structural disorder of traditional conductive polymer materials. In addition, the polymerization reaction uses acetic acid instead of precious metals as a catalyst, reducing preparation costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries and relates to positive electrode materials, in particular to an organic lithium battery positive electrode material based on an organic covalent framework of bicarbazole and a preparation method thereof, as well as the preparation of positive electrode sheets and lithium batteries. Background Art

[0002] Conductive polymers are a class of polymers with large conjugated π bonds. Delocalized π electrons can move freely along the polymer chain, resulting in insulating or semiconducting states in their native state. Through oxidative doping (p-doping) or reductive doping (n-doping), they can achieve electrical conductivity comparable to that of metals. Common conductive polymers include polyaniline, polypyrrole, polythiophene, and their derivatives. Conductive polymers offer diverse and diverse structures, are environmentally friendly, and are highly controllable and processable. Pre-engineered structures can yield lithium battery cathode materials with high specific capacitance and fast electrochemical reaction kinetics.

[0003] Conductive polymers are mostly amorphous, with disordered and irregular linear or network structures and small specific surface area. This disordered structure is not conducive to the migration of lithium ions, reducing the actual lithium storage capacity of the material. The reaction of the polymer requires the addition of a metal palladium catalyst, which is costly and difficult to control. It is easy to form oligomers, resulting in impure products and affecting electrochemical performance. Although oligomers can be removed using a Soxhlet extractor, it is necessary to screen out low-boiling point solvents that can only dissolve oligomers. Improper screening may cause high polymers to dissolve at the same time, reducing the yield. Amorphous conductive polymers are easy to decompose under high operating voltages and have poor cycle stability. In summary, traditional conductive polymers still have many problems that need to be improved and are not suitable for large-scale production applications for the time being. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides an organic lithium battery positive electrode material and preparation method based on an organic covalent framework of bicarbazole, the preparation of a positive electrode sheet and a lithium battery. The high specific capacity lithium battery positive electrode material and preparation method of the present invention have both orderly and regular lithium ion migration channels and good structural and electrochemical stability to ensure the battery cycle life. At the same time, the preparation process is controllable and suitable for industrial production applications.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides an organic lithium battery positive electrode material, which is a covalent organic framework CZ-DM-COF based on bicarbazole. The organic lithium battery positive electrode material is formed by condensing the building unit [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde and the connecting unit 2,5-dimethoxybenzene-1,4-diamine through a Schiff base reaction.

[0007] In this invention, [9,9'-dicarbazole]-3,3',6,6'-tetracarboxaldehyde (TFCZ) is used as the structural skeleton of COFs, and 2,5-dimethoxybenzene-1,4-diamine (DMDA) is used as the connecting unit. The two are chemically woven to form an ordered COF with a grid framework structure (CZ-DM-COF). This material inherits both the excellent electrochemical properties of carbazole and the lithium storage function of DMDA. The nitrogen atom in the connecting bond (-C=N-) has a pair of lone electrons, which can form n-doping with lithium ions during discharge, also providing lithium storage capacity. The ordered covalently bonded grid framework structure provides a stable lithium ion migration channel and also imparts excellent physical and chemical stability, solving the problems of instability, low solubility, and structural disorder of traditional conductive polymer materials. In addition, the polymerization reaction uses acetic acid instead of precious metals as a catalyst, reducing preparation costs.

[0008] Covalent organic frameworks (COFs) are a class of porous polymers with high specific surface area and crystallinity, which are formed by the polymerization of small molecules. The polymerization process of COFs is like fine weaving, forming a periodic and ordered porous grid array structure. Studies have found that COFs often inherit the characteristics of the building blocks, so COFs are very easy to functionalize. By using structural units with electrochemical properties as building blocks of COFs, they can be given corresponding properties. Due to the good stability, abundant pores, ordered channels and easy electrochemical modification of COFs, COFs have become a promising energy storage material. These properties of COFs can be used to prepare lithium battery positive electrode materials with high stability and high specific capacity.

[0009] Carbazole has excellent redox and hole transport properties, numerous structural modification sites, abundant sources, and is environmentally friendly, making it an ideal electrochemical material. However, the high solubility of small organic compounds like carbazole prevents its direct application as a lithium-ion battery cathode material. While conventional linear carbazole polymers have improved solubility while retaining the excellent electrochemical properties of carbazole, they still decompose under high voltage, limiting their application.

[0010] Paraphenylenediamine is a more commonly used linking unit. There are four vacant substitution sites on its benzene ring. By connecting functional groups (such as methoxy) that can form coordination with lithium ions to the substitution sites, the lithium storage sites of COFs can be increased, further improving the specific capacity of COFs positive electrode materials.

[0011] As a preferred embodiment of the present invention, the mass ratio of the [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde to the 2,5-dimethoxybenzene-1,4-diamine is 20-25:15-18.

[0012] In a second aspect, the present invention provides a method for preparing the above-mentioned organic lithium battery positive electrode material, the preparation method comprising the following steps:

[0013] 1) Weigh [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde and 2,5-dimethoxybenzene-1,4-diamine, add them to a reaction kettle, and add a reaction solvent and a catalyst;

[0014] 2) In a protective gas atmosphere, the temperature was raised to the reaction temperature for reaction. After the reaction was completed, the reaction product was filtered and washed, and then subjected to Soxhlet extraction for 24 hours and then vacuum dried to obtain a yellow fluffy CZ-DM-COF solid powder.

[0015] As a preferred embodiment of the present invention, in step 1), the reaction solvent is a mixed solvent of mesitylene and dioxane in a volume ratio of 1:1.

[0016] As a preferred embodiment of the present invention, in step 1), the catalyst is an acetic acid solution with a concentration of 6 mol / L.

[0017] As a preferred embodiment of the present invention, in step 2), the protective gas is nitrogen, the reaction temperature is 120° C., the reaction time is 72 h, and the Soxhlet extraction reagent is tetrahydrofuran.

[0018] In a third aspect, the present invention provides a method for preparing an organic lithium battery positive electrode sheet comprising the above-mentioned organic lithium battery positive electrode material, the preparation method comprising the following steps:

[0019] 1) Slurry preparation: NMP, PVDF, acetylene black and the above-mentioned CZ-DM-COF are added to a stirring tank respectively, and stirred for a period of time to obtain a uniformly dispersed positive electrode slurry;

[0020] 2) Coating: The positive electrode slurry obtained in step 1) is fed into the trough from the bottom of the trough by rewinding and unwinding at a certain speed, and then adhered to the aluminum foil moving at a constant speed;

[0021] 3) Drying: The aluminum foil coated with the slurry in step 2) is uniformly fed into a drying tunnel for drying to remove NMP, thereby obtaining a rolled CZ-DM-COF positive electrode sheet.

[0022] As a preferred embodiment of the present invention, in step 1), the stirring speed is 100 rpm to 400 rpm, and the stirring time is 2-6 hours; the mass ratio of CZ-DM-COF, PVDF, and acetylene black is 95:3:2.

[0023] As a preferred embodiment of the present invention, in step 3), the drying temperature is 70-110°C.

[0024] In a fourth aspect, the present invention provides a lithium button battery, comprising a CZ-DM-COF positive electrode sheet, a negative electrode, an electrolyte and a separator prepared by the above method; wherein the negative electrode is a lithium sheet, the electrolyte is LiPF6, and the separator is a polypropylene (PP) separator.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The bicarbazole-based covalent organic framework material (CZ-DM-COF) of the present invention has very good thermal stability, remaining stable at 300°C and having a thermal weight loss of <5% at 400°C. It also has good chemical stability and its structure remains stable under strong acid and strong base conditions.

[0027] 2) The specific surface area of ​​CZ-DM-COF of the present invention is as high as 1358m 2 / g, the dense carbazolyl-based repeating redox centers, abundant pores and open two-dimensional channels provide it with abundant lithium ion binding sites and transport channels.

[0028] 3) The CZ-DM-COF of the present invention has a high gram capacity (260 mAh / g) and good cycle stability. The capacitance retention is >85% after 5000 cycles at a current density of 100 mA / g. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the synthesis of CZ-DM-COF.

[0030] Figure 2 is the SEM image of CZ-DM-COF powder.

[0031] Figure 3 It is the discharge capacity of the button battery at room temperature of 100mA / g.

[0032] Figure 4 It is the discharge capacity retention rate of the button battery at 100mA / g at room temperature. DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, purpose and efficacy of the present invention easy to understand, the present invention is further described below in conjunction with specific examples, but the following examples are only preferred embodiments of the present invention, not all. Based on the examples in the embodiments, other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention. The experimental methods in the following examples, unless otherwise specified, are conventional methods, and the materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0034] In the present invention, [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde (TFCZ) has a CAS number of 2227477-88-3.

[0035] 2,5-Dimethoxybenzene-1,4-diamine (DMDA), CAS number: 17626-02-7.

[0036] Example 1

[0037] This example provides the preparation of a covalent organic framework material CZ-DM-COF based on bicarbazole:

[0038] 22.2g of [9,9'-dicarbazole]-3,3',6,6'-tetracarbaldehyde (TFCZ) and 16.8g of 2,5-dimethoxybenzene-1,4-diamine (DMDA) were added to a small reactor, along with 500mL of mesitylene / dioxane (volume ratio 1:1) and 50mL of acetic acid solution (6mol / L). Under nitrogen protection, the reaction was carried out at 120°C for 72h without stirring. After the reaction, the product was filtered and washed twice with tetrahydrofuran. After Soxhlet extraction for 24h, the product was vacuum-dried to obtain a yellow, fluffy solid powder of CZ-DM-COF. The Soxhlet extraction solvent was tetrahydrofuran. The preparation route and SEM images of CZ-DM-COF are shown in [ 1 ]. Figure 1 and Figure 2 .

[0039] from Figure 2 It can be seen that the material has a regular spherical morphology.

[0040] Example 2

[0041] This embodiment provides the preparation of a lithium-ion battery electrode comprising the bicarbazole-based covalent organic framework material CZ-DM-COF:

[0042] Weigh 950 mg of the two-dimensional covalent organic framework material CZ-DM-COF based on bicarbazole prepared in Example 1 into a stirring tank, then continue to add 20 mg of acetylene black, 30 mg of PVDF, and 30 mL of N-methylpyrrolidone (NMP), and stir at 3600 rpm for 10 min. The sample mixed in the stirrer is coated on the current collector Al foil into a 250 μm thick film, dried at 80 ° C for 12 h, and the dried electrode film is cut into circular electrode pole pieces with a diameter of 12 mm to obtain the lithium ion battery pole piece of the bicarbazole-based covalent organic framework material CZ-DM-COF.

[0043] To characterize the electrochemical performance of CZ-DB-COF, the CZ-DM-COF cathode prepared in this example was assembled into a symmetrical blocked button cell. A stainless steel gasket was used as the blocking electrode. The cell was subjected to an AC impedance test with a frequency range of 2 MHz to 0.1 Hz and an amplitude of 10 mV. Based on the obtained AC impedance spectrum, the room temperature ionic conductivity of the cathode was calculated to be 1.6 × 10 -3 S / cm.

[0044] The CZ-DM-COF cathode prepared in this example was assembled into a stainless steel / Li button cell with a PP film as a separator and LiPF6 as the electrolyte. A linear sweep voltammetry test was performed on the cell with a voltage range of open circuit voltage (OCP) to 6 V (vs. Li / Li + ), with a scan rate of 1mV / s, the electrochemical stability window of the electrode was measured to be 4.5V.

[0045] See also Figure 3 and Figure 4 The CZ-DM-COF positive electrode sheet was assembled into a stainless steel / Li button battery, with a PP film as the separator and LiPF6 as the electrolyte. The assembled button battery was then subjected to a room temperature 100mA / g charge and discharge cycle. The initial gram capacity was 260mAh / g, and the capacity retention rate was 95% after 250 cycles.

[0046] Therefore, this aspect develops a high specific capacity lithium battery positive electrode material and its preparation method, which has both ordered and regular lithium ion migration channels and good structural and electrochemical stability to ensure the battery cycle life. At the same time, the preparation process is controllable and suitable for industrial production applications.

[0047] The present invention uses [9,9'-dicarbazole]-3,3',6,6'-tetracarboxaldehyde (TFCZ) as the structural skeleton of COFs and 2,5-dimethoxybenzene-1,4-diamine (DMDA) as the connecting unit. The two are chemically woven to form an ordered COF with a grid framework structure (CZ-DM-COF). This material inherits both the excellent electrochemical properties of carbazole and the lithium storage function of DMDA. The nitrogen atom in the connecting bond (-C=N-) has a pair of lone electrons, which can form n-doping with lithium ions during discharge, also providing lithium storage capacity. The ordered covalently bonded grid framework structure provides a stable lithium ion migration channel and also imparts excellent physical and chemical stability, solving the problems of instability, low solubility, and structural disorder of traditional conductive polymer materials. In addition, the polymerization reaction uses acetic acid instead of precious metals as a catalyst, reducing preparation costs.

[0048] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. An organic lithium battery positive electrode material, characterized in that: The organic lithium battery positive electrode material is a covalent organic framework CZ-DM-COF based on bicarbazole, and the organic lithium battery positive electrode material is formed by condensing the building unit [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde and the linking unit 2,5-dimethoxybenzene-1,4-diamine through a Schiff base reaction; The mass ratio of the [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde to the 2,5-dimethoxybenzene-1,4-diamine is 20-25:15-18; The method for preparing the organic lithium battery positive electrode material comprises the following steps: 1) Weigh [9,9'-bicarbazole]-3,3',6,6-tetracarbaldehyde and 2,5-dimethoxybenzene-1,4-diamine, add them to a reaction kettle, and add a reaction solvent and a catalyst; 2) In a protective gas atmosphere, the temperature was raised to the reaction temperature. After the reaction was completed, the reaction product was filtered and washed, and then subjected to Soxhlet extraction for 24 hours and then vacuum dried to obtain a yellow fluffy CZ-DM-COF solid powder; In step 2), the protective gas is nitrogen, the reaction temperature is 120° C., the reaction time is 72 h, and the Soxhlet extraction reagent is tetrahydrofuran.

2. A method for preparing an organic lithium battery positive electrode material according to claim 1, characterized in that: The preparation method comprises the following steps: 1) Weigh [9,9'-bicarbazole]-3,3',6,6'-tetracarbaldehyde and 2,5-dimethoxybenzene-1,4-diamine, add them to a reaction kettle, and add a reaction solvent and a catalyst; 2) In a protective gas atmosphere, the temperature was raised to the reaction temperature for reaction. After the reaction was completed, the reaction product was filtered and washed, and then subjected to Soxhlet extraction for 24 hours and then vacuum dried to obtain a yellow fluffy CZ-DM-COF solid powder.

3. The method for preparing an organic lithium battery cathode material according to claim 2, wherein: In step 1), the reaction solvent is a mixed solvent of mesitylene and dioxane in a volume ratio of 1:

1.

4. The method for preparing an organic lithium battery cathode material according to claim 2, wherein: In step 1), the catalyst is acetic acid solution with a concentration of 6 mol / L.

5. A method for preparing an organic lithium battery positive electrode sheet, characterized in that: The preparation method comprises the following steps: 1) Slurry preparation: NMP, PVDF, acetylene black and the CZ-DM-COF according to claim 1 are added to a stirring tank respectively, and stirred for a period of time to obtain a uniformly dispersed positive electrode slurry; 2) Coating: The positive electrode slurry obtained in step 1) is fed into the trough from the bottom of the trough by rewinding and unwinding at a certain speed, and then adhered to the aluminum foil moving at a constant speed; 3) Drying: The aluminum foil coated with the slurry in step 2) is uniformly fed into a drying tunnel for drying to remove NMP, thereby obtaining a rolled CZ-DM-COF positive electrode sheet.

6. The method for preparing an organic lithium battery positive electrode sheet according to claim 5, characterized in that: In step 1), the stirring speed is 100 rpm to 400 rpm, and the stirring time is 26 hours; the mass ratio of CZ-DM-COF, PVDF, and acetylene black is 95:3:

2.

7. The method for preparing an organic lithium battery positive electrode sheet according to claim 5, characterized in that: In step 3), the drying temperature is 70-110°C.

8. A lithium button battery, characterized in that: The invention comprises a CZ-DM-COF positive electrode sheet, a negative electrode, an electrolyte and a separator prepared by the method of any one of claims 5 to 7.

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