Photo-assisted lithium ion battery positive electrode slurry based on dye sensitization and preparation method of photo-assisted lithium ion battery positive electrode slurry

Abstract

The invention discloses photo-assisted lithium ion battery positive electrode slurry based on dye sensitization and a preparation method thereof, and relates to lithium ion battery positive electrode slurry and a preparation method thereof. The invention aims to solve the technical problems of large size, complex structure and high cost of the existing photo-rechargeable lithium ion battery. According to the positive electrode paste, N719 dye, N3 dye, black dye or titanyl phthalocyanine dye is added into the positive electrode paste with lithium iron phosphate, nickel-rich layered oxide Li [Ni0. 8Co0. 1Mn0. 1] O2, lithium cobalt oxide or lithium manganate as active substances. The preparation method comprises the following steps: adding the carbon black into a dye solution, then adding the active substance and the polyvinylidene fluoride, and uniformly stirring to obtain positive electrode slurry; after illumination, the capacity of a positive electrode prepared from the slurry is increased from 135.87 mAh g <-1 > to 144.77 mAh g <-1 > to 155.27 mAh g <-1 >, and is increased by 6.55%-14.72%. The invention can be used in the field of lithium ion batteries.

Description

Technical Field

[0001] The invention relates to lithium ion battery positive electrode slurry and a preparation method thereof, belonging to the technical field of lithium ion battery charging. Background Art

[0002] Lithium-ion batteries have become the energy solution of choice for portable electronic devices, electric vehicles, and large-scale energy storage systems, but they have problems such as limited charging methods, low efficiency, and large environmental impact. Solar cells can convert solar energy into electrical energy, but they are intermittent and cannot store electrical energy continuously. Currently, photorechargeable batteries solve these problems by connecting separate solar photovoltaic devices in series with lithium-ion batteries or integrating solar cells and batteries in a single device based on three electrodes. However, photorechargeable batteries have problems such as large size, complex structure, energy loss, and high cost. Summary of the invention

[0003] The present invention aims to solve the technical problems of existing light-rechargeable lithium-ion batteries, such as large size, complex structure, energy loss and high cost, and provides a dye-sensitized light-assisted lithium-ion battery positive electrode slurry and a preparation method thereof.

[0004] The present invention is based on dye-sensitized light-assisted lithium-ion battery positive electrode slurry, which is based on lithium iron phosphate, nickel-rich layered oxide Li[Ni 0.8 Co 0.1 Mn 0.1 ]Dyes are added to the positive electrode slurry of lithium-ion batteries with ]O2 (NCM811), lithium cobalt oxide or lithium manganese oxide as active materials, wherein the dye is one or more of N719 dye, N3 dye, black dye and oxytitanium phthalocyanine.

[0005] Furthermore, the amount of dye added is 0.8% to 1.2% of the mass of the active substance.

[0006] The above-mentioned method for preparing the dye-sensitized light-assisted lithium-ion battery positive electrode slurry is carried out according to the following steps:

[0007] 1. Place N-methylpyrrolidone (NMP) in a brown glass bottle, then add the dye into the N-methylpyrrolidone, and stir evenly at room temperature to obtain a dye-NMP solution; wherein the dye is one or more of N719 dye, N3 dye, black dye and oxytitanium phthalocyanine;

[0008] 2. Adding conductive carbon black to the dye-NMP solution obtained in step 1, stirring evenly at room temperature to obtain a dye-sensitized conductive carbon black-NMP solution;

[0009] 3. Add the active material and polyvinylidene fluoride (PVDF) in a mass ratio of (7.5-8.5):1 to the dye-sensitized conductive carbon black-NMP solution obtained in step 2, and stir at room temperature for 10-12 hours to obtain a dye-sensitized light-assisted lithium-ion battery positive electrode slurry; wherein the active material is lithium iron phosphate, nickel-rich layered oxide Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2(NCM811), lithium cobalt oxide or lithium manganese oxide.

[0010] Furthermore, the mass of the dye in the dye-NMP solution in step one is 0.8% to 1.2% of the mass of the active substance in step three.

[0011] Furthermore, the mass of the conductive carbon black in the dye-sensitized conductive carbon black-NMP solution in step one is 12% to 13% of the mass of the active material in step three.

[0012] Furthermore, the stirring time at room temperature in step 1 is 5 to 15 minutes.

[0013] Furthermore, the stirring time at room temperature in step 2 is 5 to 15 minutes.

[0014] The present invention adds a photosensitive dye to the positive electrode slurry to prepare a dye-sensitized light-assisted lithium ion positive electrode. When exposed to light during the charging process, the photosensitive dye is excited to generate abundant photogenerated electron-hole pairs, which promote the occurrence of oxidation reactions of active substances, reduce the polarization effect of the electrode, reduce the impedance of the battery, and reduce the charging voltage. At the same time, the photoelectrons will travel to the anode side through the external circuit and react with the migrated Li from the cathode side. + During the discharge process, the photoelectrons excited by the dye promote the Li + The embedding, i.e., reduction reaction, reduces the polarization effect of the electrode, reduces voltage loss, and increases the discharge voltage. At the same time, the photogenerated holes combine with the electrons released by the oxidation reaction occurring on the negative electrode side and then quench. Different dyes absorb light of different wavelengths. Using two or more different dye molecules enables the battery to absorb light over a wider spectral range. In the case of dye co-sensitization, a wider spectral range can be covered, the photoelectric conversion efficiency is improved, and more efficient electron transfer can be promoted to reduce energy loss.

[0015] The positive electrode prepared by the dye-sensitized light-assisted lithium-ion battery positive electrode slurry of the present invention has a capacity increased from 135.87 mAh g -1 Increased to 144.77mAh g -1 ~155.27mAh g -1, increased by 6.55% to 14.72%. The discharge capacity increased by 6.55% to 35.45% after illumination at different current densities. It can be used in the field of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The capacity-voltage curve of the N719 dye-sensitized LFP positive electrode prepared by the slurry of Example 1 during the charging process; Figure 2 The capacity-voltage curve of the N719 dye-sensitized LFP positive electrode prepared by the slurry of Example 1 during the discharge process;

[0017] Figure 3 The cycle and coulombic efficiency curves of the N719 dye-sensitized LFP positive electrode prepared using the slurry of Example 1;

[0018] Figure 4 The charge and discharge curve of the N719 dye-sensitized LFP positive electrode prepared using the slurry of Example 1;

[0019] Figure 5 The charge and discharge curve of the LFP positive electrode sensitized by the oxytitanium phthalocyanine dye prepared by the slurry of Example 2;

[0020] Figure 6 Capacity comparison of the N719 dye-sensitized LFP positive electrode prepared using the slurry of Example 1 before and after illumination at different current densities. DETAILED DESCRIPTION

[0021] The beneficial effects of the present invention are verified by the following examples.

[0022] Example 1: The preparation method of the dye-sensitized light-assisted lithium-ion battery positive electrode slurry of this example is carried out according to the following steps:

[0023] 1. Place 2.3 mL of N-methylpyrrolidone (NMP) in a brown glass bottle, then add 5 mg of N719 dye to the N-methylpyrrolidone and stir at room temperature for 10 minutes to obtain a dye-NMP solution;

[0024] 2. Add 75 mg of conductive carbon black to the dye-NMP solution obtained in step 1, and stir at room temperature for 10 minutes to obtain a dye-sensitized conductive carbon black-NMP solution;

[0025] 3. Add 600 mg of lithium iron phosphate and 75 mg of polyvinylidene fluoride (PVDF) to the dye-sensitized conductive carbon black-NMP solution obtained in step 2, and stir at room temperature for 12 hours to obtain a dye-sensitized light-assisted lithium-ion battery positive electrode slurry.

[0026] Example 2: The preparation method of the dye-sensitized light-assisted lithium-ion battery positive electrode slurry of this example is carried out according to the following steps:

[0027] 1. Place 2.3 mL of N-methylpyrrolidone (NMP) in a brown glass bottle, then add 5 mg of oxytitanium phthalocyanine dye to the N-methylpyrrolidone and stir at room temperature for 10 minutes to obtain a dye-NMP solution;

[0028] 2. Add 75 mg of conductive carbon black to the dye-NMP solution obtained in step 1, and stir at room temperature for 10 minutes to obtain a dye-sensitized conductive carbon black-NMP solution;

[0029] 3. Add 600 mg of lithium iron phosphate and 75 mg of polyvinylidene fluoride (PVDF) to the dye-sensitized conductive carbon black-NMP solution obtained in step 2, and stir at room temperature for 12 hours to obtain a dye-sensitized light-assisted lithium-ion battery positive electrode slurry.

[0030] The positive electrode sheet is prepared by using the dye-sensitized light-assisted lithium-ion battery positive electrode slurry prepared in Example 1 and Example 2, respectively, in the following steps:

[0031] 1. The dye-sensitized light-assisted lithium-ion battery cathode slurry was coated on the ITO-PET film with a conductive coating using a coating machine with a thickness of 300 μm;

[0032] 2. Put the prepared electrode into a vacuum drying oven and vacuum dry it at 80°C for 12 hours to obtain a dry electrode;

[0033] 3. Place the dried electrode on a manual punching machine to make a circular positive electrode with a diameter of 12 mm, and obtain the dye-sensitized light-assisted positive electrode, which are respectively recorded as N719 dye-sensitized LFP positive electrode and oxytitanium phthalocyanine dye-sensitized LFP positive electrode, and weigh and record them with an electronic balance.

[0034] The CR2032 half-cell was assembled using a dye-sensitized light-assisted positive electrode. The button battery was assembled in the order of negative electrode shell, spring, gasket, lithium sheet, diaphragm, aluminum foil gasket, dye-sensitized light-assisted positive electrode, and positive electrode shell. The battery was then pressed by a tablet press. The battery was kept at a constant temperature for 8 hours before the electrochemical performance test was performed. Among them, the positive electrode shell was a perforated positive electrode shell with an 8mm window. The transparent PET film was fixed on the hole with epoxy resin glue to prevent the electrolyte from evaporating. The electrolyte was obtained by adding lithium hexafluorophosphate and fluoroethylene carbonate (FEC) to a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 as a solvent, wherein the concentration of lithium hexafluorophosphate (LiPF6) was 1 mol / L, and the mass percentage concentration of fluoroethylene carbonate (FEC) was 5%.

[0035] Electrical performance test of the battery: The charge and discharge capacity and cycle performance test of the battery adopts the form of constant current charge and discharge. The test uses the Xinwei test system, and different test voltages are selected according to different positive electrode materials. The charge and discharge capacity of all materials is calculated based on the total mass of the active material in the electrode. The battery is activated for two cycles at a rate of 0.2C, and the charge and discharge capacity and cycle performance of the battery are tested at rates of 0.5C / 1C / 2C / 3C / 4C / 5C. The power of the xenon lamp used in the test is 350W.

[0036] The capacity-voltage curve of the N719 dye-sensitized LFP positive electrode prepared by the slurry of Example 1 during the charging process is as follows: Figure 1 As shown in the figure, the capacity-voltage curve during the discharge process is as follows Figure 2 As shown, from Figure 1 and Figure 2 It can be seen that the photoelectrode is exposed to light, generating abundant photogenerated electron-hole pairs, which promote the positive electrode Li + The removal and embedding of ions reduce the polarization effect of the electrode, the charging voltage decreases, and the discharge voltage increases.

[0037] The cycle and coulombic efficiency curves of the N719 dye-sensitized LFP positive electrode prepared using the slurry of Example 1 are as follows: Figure 3 As shown, from Figure 3 It can be seen that under illumination conditions, the discharge specific capacity is significantly improved, and the capacity remains stable after illumination.

[0038] The charge and discharge curves of the N719 dye-sensitized LFP positive electrode prepared using the slurry of Example 1 are as follows: Figure 4 As shown, from Figure 4 It can be seen that the capacity of the N719 dye-sensitized LFP cathode increased from 135.87 mAh g -1 Increased to 144.77mAh g -1 , an increase of 6.55%.

[0039] The charge and discharge curves of the LFP positive electrode sensitized by oxytitanium phthalocyanine dye prepared by the slurry of Example 2 are as follows: Figure 5 As shown, from Figure 5 It can be seen that the capacity of the LFP cathode sensitized by oxytitanium phthalocyanine dye increased from 135.35 mAh g -1 Increased to 155.27mAh g -1 , an increase of 14.72%.

[0040] The capacity comparison of the N719 dye-sensitized LFP positive electrode prepared by the slurry of Example 1 before and after illumination at different current densities is shown in the figure below: Figure 6 As shown, from Figure 6It can be seen that the discharge capacity of the N719 dye-sensitized LFP cathode is enhanced after illumination at different current densities. With the increase of current density, the light-assisted discharge capacity increase ratio increases significantly, from 6.55% at 0.5C to 18.96% at 3C. Even at higher 4C and 5C rates, the light-assisted capacity ratio is still at a high level of 32.62% and 35.45%, respectively.

[0041] As a new type of energy conversion and storage method, light-assisted charging technology combines the advantages of photovoltaic effect and electrochemical energy storage, directly converts light energy into electrical energy, and stores it in the battery, thereby partially replacing traditional external power charging. The present invention adds photosensitizing dyes to the positive electrode slurry to make a light-assisted charging electrode, directly converts light energy into electrical energy under light, can effectively reduce the polarization effect of the electrode, effectively improve the battery capacity density under different current densities, and has no effect on the performance of the battery system under no light conditions, improves the gram capacity of lithium-ion commercial positive electrodes and battery life, and achieves partial replacement of traditional external power charging with solar energy, solves the problem of limited charging methods for lithium-ion batteries and reduces dependence on traditional energy sources. The dye-sensitized light-assisted charging technology of the present invention has a simple process, is easy to implement, and is easy to achieve direct matching with emerging improvement schemes for electrodes or diaphragms.

Claims

1. A dye-sensitized light-assisted lithium-ion battery cathode slurry, characterized in that The slurry is prepared by mixing lithium iron phosphate, nickel-rich layered oxide Li[Ni 0.8 Co 0.1 Mn 0.1 ]Dyes are added to the positive electrode slurry of lithium-ion batteries with lithium ion oxide, lithium cobalt oxide or lithium manganese oxide as active materials, wherein the dye is one or more of N719 dye, N3 dye, black dye and oxytitanium phthalocyanine.

2. The dye-sensitized light-assisted lithium-ion battery positive electrode slurry according to claim 1, characterized in that The amount of dye added is 0.8% to 1.2% of the mass of the active substance.

3. The method for preparing a dye-sensitized light-assisted lithium-ion battery positive electrode slurry according to claim 1, characterized in that: The method proceeds as follows:

1. Place N-methylpyrrolidone in a brown glass bottle, then add the dye into the N-methylpyrrolidone, and stir evenly at room temperature to obtain a dye-NMP solution; wherein the dye is one or more of N719 dye, N3 dye, black dye and oxytitanium phthalocyanine; 2. Adding conductive carbon black to the dye-NMP solution obtained in step 1, stirring evenly at room temperature to obtain a dye-sensitized conductive carbon black-NMP solution; 3. Add the active material and polyvinylidene fluoride in a mass ratio of (7.5-8.5):1 to the dye-sensitized conductive carbon black-NMP solution obtained in step 2, and stir at room temperature for 10-12 hours to obtain a dye-sensitized light-assisted lithium-ion battery positive electrode slurry; wherein the active material is lithium iron phosphate, nickel-rich layered oxide Li[Ni 0.8 Co 0.1 Mn 0.1 ]O2, lithium cobalt oxide or lithium manganese oxide.

4. The method for preparing a dye-sensitized light-assisted lithium-ion battery positive electrode slurry according to claim 3, characterized in that: The mass of the dye in the dye-NMP solution in step one is 0.8% to 1.2% of the mass of the active substance in step three.

5. The method for preparing a dye-sensitized light-assisted lithium-ion battery positive electrode slurry according to claim 3 or 4, characterized in that: The mass of the conductive carbon black in the dye-sensitized conductive carbon black-NMP solution in step one is 12% to 13% of the mass of the active material in step three.

6. The method for preparing a dye-sensitized light-assisted lithium-ion battery positive electrode slurry according to claim 3 or 4, characterized in that: The stirring time at room temperature in step 1 is 5 to 15 minutes.

7. The method for preparing a dye-sensitized light-assisted lithium-ion battery positive electrode slurry according to claim 3 or 4, characterized in that: The stirring time at room temperature in step 2 is 5 to 15 minutes.

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