CN101420032B - Combination pulp, preparation and application thereof - Google Patents

Abstract

The invention discloses a composition slurry for reducing battery polarization resistance, a preparation method and application thereof. The composition slurry includes carbon nanotubes, an aqueous binder and water, which are mixed and stirred for 1-4 hours After that, it can be coated on the negative electrode of the battery. The composition slurry provided by the invention has the advantages of simple preparation process and can significantly reduce the impedance of battery electrodes after high-temperature storage, and belongs to the field of lithium secondary battery electrodes.

Description

A kind of composition slurry, its preparation method and its application

technical field

The invention relates to a composition slurry for lithium secondary battery electrodes, in particular to a composition slurry for reducing battery polarization resistance. The present invention also relates to the preparation method and application of the composition paint.

Background technique

Lithium-ion batteries can be widely used in digital products, mobile phones, electric vehicles and other electronic products. Lithium-ion batteries are prone to electrode polarization in high-temperature environments, resulting in loss of battery capacity, which affects the application of electronic products in high-temperature environments and causes great troubles to users. Therefore, how to reduce the polarization impedance of lithium-ion batteries under high-temperature environment has become an urgent problem to be solved by various battery manufacturers.

The main method of researching the high-temperature storage performance of lithium-ion batteries is to store lithium-ion batteries under specific high-temperature conditions for a specific period of time, and to investigate the retention capacity and recovery ability of the batteries after storage. Generally, the battery is stored at 91°C for 5 hours, and the battery discharge capacity recorded after storage is defined as the retention capacity, and the re-discharge capacity after the battery is charged is defined as the recovery capacity of the battery after high-temperature storage. The capacity that the recovered capacity exceeds the initial discharge capacity after storage is defined as the reversible lost capacity. The difference between the recovered capacity and the initial capacity before battery storage is defined as the irreversible capacity loss of the battery after high-temperature storage. Through various studies, it is believed that there are two major causes of irreversible capacity loss: the consumption of lithium ions due to various chemical reactions in high temperature environments, which is an absolutely irreversible capacity loss, and the increase in electrode impedance due to high temperature environments , which causes the polarization phenomenon during the discharge process is another reason for the capacity loss of the battery after high-temperature storage. This part of the irreversible capacity loss is not absolutely irreversible. After storage, the battery is discharged with a very small current, and the discharge capacity is higher than the recovery capacity, which shows the existence of polarization caused by the electrode after high temperature.

CN1532141A discloses a nanotube-based high-energy material and its preparation method. It is a carbon-based material containing carbon allotropes, such as single-walled carbon nanotubes, and can accommodate doped alkali metals. The material exhibits a reversible capacity between about 650mAh/g-1000mAh/g. The material's high capacity makes it attractive for many applications, such as an electrode material for batteries. The method of producing single-walled carbon nanotubes includes purifying recovered nanotube material and depositing the purified material on a conductive substrate. The coated substrate is loaded into an electrochemical cell and its ability to accept a doped material, such as an alkali metal (eg lithium), is measured.

CN1588679A discloses a lithium ion secondary battery cathode material and a preparation method thereof, wherein the lithium ion secondary battery cathode material contains an active material and a nanoscale conductive agent, the conductive agent is a carbon nanotube, and the carbon nanotube is Multi-walled carbon nanotubes, the tube outer diameter distribution is 5-200nm. The preparation method of the cathode material of the lithium ion secondary battery comprises the following steps: (1) ultrasonically dispersing carbon nanotubes in water or an organic solvent, or in a solution containing a binder; (2) dispersing lithium cobaltate, nickel Lithium oxide, lithium nickel cobaltate or spinel lithium manganese oxide positive electrode material powder is added to it to disperse to obtain a uniform slurry; (3) coating the prepared uniform slurry on the collector; (4) drying Dry.

Both of the above two inventions prepare conductive substrates (i.e. electrodes) by doping carbon nanotubes with alkali metals. This method simply mixes carbon nanotubes into the negative electrode material, and all carbon nanotubes cannot be used for transportation. electrons, thus only partially improving the high-temperature storage performance of the battery.

Contents of the invention

The invention provides a composition slurry which has a simple preparation process and can significantly reduce the impedance of battery electrodes after high-temperature storage.

Another object of the present invention is to provide a preparation method of the above-mentioned composition slurry.

Another object of the present invention is to provide a method for preparing an electrode with low polarization resistance by using the slurry of the above composition.

In order to achieve the above-mentioned purpose of the invention, the inventors of the present invention have designed a composition slurry with simple preparation process and can significantly reduce the polarization resistance of the battery through a lot of research and creative work. The composition slurry is Prepared from the following components by weight:

Carbon nanotubes 5-15 Water-based binder 1 Water 30-50.

Preferably, the composition slurry is prepared from the following components in parts by weight: carbon nanotubes 5-8 water-based binder 1 water 38-45.

The outer diameter of the carbon nanotubes is 10-300nm, preferably 10-40nm.

The water-based binder is polytetrafluoroethylene, carboxymethylpropyl cellulose, polyvinyl alcohol, polyethylene oxide, methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl One or a mixture of methyl cellulose, styrene-butadiene rubber, and polyacrylate.

A method for preparing the composition slurry, the method is to mix and stir carbon nanotubes, water-based binder and water for 1-4 hours, preferably for 1.5-2.5 hours.

A method for preparing a low polarization impedance electrode, comprising the following steps: after baking the negative electrode sheet of the battery after drawing the slurry at 60°C-90°C for 5-15min, coating the surface with a thickness of 4-20 microns Said composition slurry is then baked, sheet-made, wound, liquid injected, chemically formed and sealed.

The battery negative electrode sheet is a battery graphite negative electrode sheet.

The inventors of the present invention have designed a method for preparing low polarization impedance electrodes through a large number of experiments. It is necessary to bake the negative electrode sheet of the battery after pulling the slurry at 60°C-90°C for 5-15min. If the baking time exceeds 15min , The surface layer of the negative electrode sheet of the battery after pulping is completely dry, the adhesion of the bottom layer is insufficient, and it is easy to fall off; if the baking time is less than 5 minutes, the surface layer of the negative electrode sheet of the battery after pulping has a high moisture content, which will cause calendering of the bottom layer when coating the surface layer. The conductivity of the carbon nanotubes coated on the baked battery negative electrode is better than that of graphite materials. After high temperature storage, the battery will further deteriorate due to reaction or contact between particles, etc., and the excellent conductivity of carbon nanotubes will be reduced. The degree of polarization caused by this reduces the loss of battery capacity, and at the same time protects the large-area contact between the electrolyte and the graphite material of the negative electrode, so that in the high-temperature storage stage, the reaction between graphite and electrolyte is reduced, and the thickness of the battery after high-temperature storage is improved. swell. The thicker the coating thickness of carbon nanotubes, the better. If carbon nanotubes are used in the negative electrode, the effect is the best, but the cost is expensive, generally 4-20 microns; if it is less than 4 microns, the effect is not ideal.

The batteries prepared in Examples 1-10 and the battery prepared in Comparative Example 1 were stored at 91°C for 5 hours, and the capacity retention rate and capacity loss rate of the two batteries after high-temperature storage were measured. The results are shown in Table 1. It can be seen from Table 1 that the capacity retention rate of the battery with carbon nanotube material added to the negative electrode after high-temperature storage is above 86%, the capacity loss rate is all lower than 14%, and the expansion thickness is all below 0.6mm, while the comparative example The capacity retention rate is only 70-78%, the capacity loss rate is as high as 30%, and the expansion thickness exceeds 1.0 mm, and some even as high as 3.8 mm. Therefore, the method provided by the invention can significantly improve the high-temperature storage performance of the battery.

Detailed ways

The determination methods of the capacity retention rate and capacity loss rate of the batteries of Examples 1-10 and Comparative Examples after high-temperature storage are as follows:

①Store the battery at 91°C for 5 hours;

②Charge the batteries at 950mA to 4.2V/0.1C (70mA) and discharge at 700mA to 3.1V to test their normal temperature capacity;

③Charge the battery to 4.2V and place it at room temperature for 1 hour to measure the initial data; put the battery in an oven at 91°C and store it for 5 hours;

④ After storage, test its thickness, voltage, internal resistance, remaining capacity, and do three recovery capacity.

The lithium ion secondary battery positive electrode material of embodiment 1-10 contains lithium cobaltate and carbon nanotubes, and the consumption of described carbon nanotubes is 1wt% of positive electrode material, and the outer diameter of carbon nanotubes is 10-40nm, and its preparation process for the conventional process.

Tablet making, winding, liquid injection, chemical formation and sealing in Examples 1-10 are all conventional processes.

Example 1

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 10-25nm 5 Polytetrafluoroethylene 1 Deionized water 40

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder polytetrafluoroethylene and deionized water for 2 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the pulp at 70°C for 10 minutes, coat the surface with the composition slurry with a thickness of 10 microns, and then bake it at 110°C for 5 minutes, and then make Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 2

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 15-40nm 11 Carboxymethyl propyl cellulose 1 Deionized water 50

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder carboxymethylpropyl cellulose and deionized water for 1.5 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the slurry at 90°C for 5 minutes, coat the surface with the composition slurry with a thickness of 5 microns, and then bake it at a temperature of 110°C for 5 minutes, and then prepare Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 3

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 20-100nm 8 Polyvinyl alcohol 1 Deionized water 30

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based adhesive polyvinyl alcohol and deionized water for 3 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the slurry at 60°C for 15 minutes, coat the surface with the composition slurry with a thickness of 20 microns, and then bake it at a temperature of 105°C for 8 minutes, and then prepare Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 4

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 80-150nm 15 Polyethylene oxide 1 Deionized water 45

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based adhesive polyethylene oxide and deionized water for 4 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the slurry at 80°C for 12 minutes, coat the surface with the composition slurry with a thickness of 15 microns, and then bake it at a temperature of 110°C for 5 minutes, and then make Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 5

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 100-300nm13 Methylcellulose1 Deionized water34

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder methylcellulose and deionized water for 2.5 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the slurry at 75°C for 8 minutes, coat the surface with the composition slurry with a thickness of 12 microns, and then bake it at a temperature of 115°C for 4 minutes, and then prepare Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 6

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 200-300nm 6 Hydroxyethyl cellulose 0.5 Hydroxyethyl methyl cellulose 0.5 Deionized water 38

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder hydroxyethyl cellulose and deionized water for 1 hour;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after pulling the paste at 65°C for 15 minutes, coat the surface with the composition slurry with a thickness of 4 microns, and then bake it at a temperature of 112°C for 5 minutes, and then prepare Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 7

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 10-40nm 14 Hydroxypropyl methylcellulose 1 Deionized water 47

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder hydroxypropyl methylcellulose and deionized water for 2 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the slurry at 85°C for 14 minutes, coat the surface with the composition slurry with a thickness of 8 microns, and then bake it at 100°C for 10 minutes, and then make Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 8

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 10-60nm 10 Styrene-butadiene rubber 0.2 Sodium polyacrylate 0.8 Deionized water 42

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder styrene-butadiene rubber, sodium polyacrylate and deionized water for 3.5 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after pulling the paste at 78°C for 7 minutes, coat the surface with the composition slurry with a thickness of 18 microns, and then bake it at 110°C for 5 minutes, and then make Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 9

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 50-100nm 12 polyethylene oxide 0.2 methylcellulose 0.6 polytetrafluoroethylene 0.2 deionized water 32

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder polyethylene oxide, methylcellulose, polytetrafluoroethylene and deionized water for 2 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after pulling the pulp at 82°C for 7 minutes, coat the surface with the composition slurry with a thickness of 16 microns, and then bake it at a temperature of 110°C for 5 minutes, and then prepare Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Example 10

The weight ratio of each component of composition slurry:

Carbon nanotubes with an outer diameter of 100-200nm 7 Polyvinyl alcohol 0.1, hydroxyethyl cellulose 0.4, hydroxyethyl methyl cellulose polytetrafluoroethylene 0.5 Deionized water 36

Preparation method of composition slurry:

The method is to mix and stir carbon nanotubes, water-based binder polyvinyl alcohol, hydroxyethyl cellulose, hydroxyethyl methyl cellulose polytetrafluoroethylene and deionized water for 2.5 hours;

A method for preparing a low polarization impedance electrode using the above composition slurry:

After baking the graphite negative electrode sheet of the battery after drawing the slurry at 76°C for 9 minutes, coat the surface with the composition slurry with a thickness of 13 microns, and then bake it at a temperature of 110°C for 5 minutes, and then prepare Sheet, winding, liquid injection, formation, sealing.

The low polarization impedance electrode and the positive electrode of the battery are prepared into a battery by a conventional method.

Comparative example 1

With the positive and negative electrode materials used in Example 1, no carbon nanotube material is added to the surface of the positive and negative electrodes, and the processes of batching-drawing-sheet-making-winding-liquid injection-chemical formation-sealing and other processes are carried out according to the normal production process. Produce batteries.

Comparative example 2:

With the positive and negative electrode materials used in Example 1, no carbon nanotube material is added to the positive electrode, and carbon nanotubes are added as the conductive agent at the negative electrode, wherein the mass ratio of graphite, carbon nanotubes, and binder PTFE is 92:5 : 3, produce the battery according to the normal process.

The measurement result of table 1 embodiment electrode and comparative example electrode

type of battery   Capacity retention Capacity loss rate Expansion thickness/mm Example 1 92% 8% 0.4 92% 8% 0.5 91% 9% 0.5 Example 2 90% 10% 0.4 90% 10% 0.5 91% 9% 0.4 Example 3 89% 11% 0.4 91% 9% 0.3 88% 12% 0.5 Example 4 89% 11% 0.4 88% 12% 0.4 98% 12% 0.5 Example 5 89% 11% 0.5 89% 11% 0.5 88% 12% 0.6 Example 6 89% 11% 0.4 89% 11% 0.5 89% 11% 0.4 Example 7 86% 14% 0.5 87% 13% 0.6 88% 12% 0.4 Example 8 88% 12% 0.5 88% 12% 0.5 87% 13% 0.6 Example 9 89% 11% 0.4 90% 10% 0.4 91% 9% 0.3

Example 10 88% 12% 0.6 88% 12% 0.4 90% 10% 0.5 Comparative example 1 70% 30% 2.5 70% 30% 3.8 71% 29% 3.5 Comparative example 2 78% twenty two% 1.0 78% twenty two% 1.2 79% twenty one% 0.9

It can be seen from Table 1 that the capacity retention rate of the battery with carbon nanotube material added to the negative electrode after high-temperature storage is above 86%, the capacity loss rate is all lower than 14%, and the expansion thickness is all below 0.6mm, while the comparative example The capacity retention rate is only 70-78%, the capacity loss rate is as high as 30%, and the expansion thickness exceeds 1.0 mm, and some even as high as 3.8 mm. Therefore, the method provided by the invention can significantly improve the high-temperature storage performance of the battery.

Claims (6)

1. method for preparing the hypopolarization impedance electrodes, it is characterized in that: described method comprises the steps: the anode plate for lithium ionic cell after the slurry behind baking 5-15min under 60 ℃-90 ℃, at its surface-coated thickness is 4-20 micron combination pulp, toasts, film-making, coiling, fluid injection, changes into, seals; Described combination pulp is to be prepared from by following components by part by weight:

Carbon nano-tube 5-15 water system binder 1 water 30-50.

2. the method for preparing the hypopolarization impedance electrodes according to claim 1 is characterized in that: described anode plate for lithium ionic cell is the silicon/carbon/graphite in lithium ion batteries negative plate.

3. the method for preparing the hypopolarization impedance electrodes according to claim 1 is characterized in that: described combination pulp is to be prepared from by following components by part by weight:

Carbon nano-tube 5-8 water system binder 1 water 38-45.

4. according to claim 1 or the 3 described methods that prepare the hypopolarization impedance electrodes, it is characterized in that: the external diameter of pipe of described carbon nano-tube is 10-300nm.

5. the method for preparing the hypopolarization impedance electrodes according to claim 4 is characterized in that: the external diameter of pipe of described carbon nano-tube is 10-40nm.

6. according to claim 1 or the 3 described methods that prepare the hypopolarization impedance electrodes, it is characterized in that: described water system binder is a kind of or wherein several mixture in polytetrafluoroethylene, carboxymethyl propyl cellulose, polyvinyl alcohol, polyethylene glycol oxide, methylcellulose, hydroxyethylcellulose, HEMC, hydroxypropyl methylcellulose, butadiene-styrene rubber, the polyacrylate.