CN115347149A

CN115347149A - Ultra-dispersed nano composite conductive adhesive and preparation method and application thereof

Info

Publication number: CN115347149A
Application number: CN202110516586.7A
Authority: CN
Inventors: 申晓宇; 起文斌; 俞海龙; 黄学杰
Original assignee: Institute of Physics of CAS
Current assignee: Institute of Physics of CAS
Priority date: 2021-05-12
Filing date: 2021-05-12
Publication date: 2022-11-15

Abstract

The invention provides a method for preparing a super-dispersed nano composite conductive adhesive, which comprises the following steps: (1) Fully mixing a polymer binder, a solvent and a low-dimensional conductive agent to obtain a suspension; (2) When the polymer binder is dissolved in a solvent, completely removing the solvent in the suspension to obtain a powdery ultra-dispersed nano composite conductive binder; and when the polymer binder is insoluble in the solvent, removing 50-100% of the solvent in the suspension to obtain the ultra-dispersed nano composite conductive binder in a powdery or non-Newtonian fluid state. The invention also provides the ultra-dispersed nano composite conductive adhesive prepared by the method. The invention also provides a positive electrode. The invention also provides a negative electrode. The invention also provides a method for preparing the anode. The invention also provides a method for preparing the cathode. When the composite conductive adhesive is used for a dry electrode, the electrochemical performance of an ion energy storage device can be improved.

Description

Ultra-dispersed nano composite conductive adhesive and preparation method and application thereof

Technical Field

The invention belongs to the field of ion energy storage devices. In particular, the invention relates to a super-dispersed nano composite conductive adhesive and a preparation method and application thereof.

Background

At present, the problems of energy shortage, climate change, environmental pollution and the like are increasingly prominent, and the use of clean energy to replace the traditional energy is increasingly important. The related green chemical energy storage and energy conversion liquid gradually becomes a research hotspot in the fields of energy and environment, and a series of industrial chains are promoted, and play an irreplaceable role in the aspects of energy, environment, national economy and the like.

At present, despite the success of commercialization of ion energy storage devices, challenges remain as important indicators of ion energy storage devices, such as energy density, rate capability, and cycle performance. In an ion energy storage device, the surface capacity, the inactive material proportion, the active material voltage and the specific capacity of an electrode play a determining role in energy density. Currently, related research efforts are mainly focused on synthesis and modification of electrode active materials, and attention to a conductive agent, a binder, and an electrode structure in an electrode is less focused. However, the conductive agent and the binder directly affect the content of the active material, the electrode structure and the electrode conductivity, and have non-negligible influence on the energy density, the cycle performance and the rate performance of the energy storage device.

In addition, the traditional coating method for manufacturing the electrode needs to add a large amount of conductive agent and binder, the preparation process is complex and the surface capacity is low, and a current collector is needed, so that the production cost is increased, the proportion of the active material of the obtained electrode plate is low, and the distribution of the binder and the conductive agent is often not uniform. In addition, too much binder also increases the electrode impedance, limiting the performance of the electrode.

These problems limit the increase of energy density of the ion energy storage device and increase the production cost. Therefore, research and development on electrode-related conductive agents and binders and improvement in electrode preparation technology are very important. At present, it is a possible direction to solve the above problems to conduct compounding of a conductive agent and a binder and dry-process preparation of an electrode, and researchers have conducted related research and technical improvement.

Patent CN109755579B discloses a preparation method of a positive electrode composite conductive adhesive for a lithium ion battery, the composite conductive adhesive comprises a polyvinylidene fluoride substrate, a conductive polymer and a carboxylated carbon nanotube, wherein the conductive polymer has a certain specific capacity, and the electrode capacity can be slightly improved. However, the method uses a complex catalytic reaction method, the obtained composite conductive adhesive has poor dispersibility, needs a subsequent crushing process, and is only used for the coating method anode. In addition, the preparation method of the composite conductive adhesive is complex, has high cost and is difficult to be applied to actual production.

Patent CN111129499A discloses an aqueous conductive adhesive for a lithium battery and a preparation method thereof, wherein the aqueous conductive adhesive comprises a dispersant, an auxiliary conductive agent and a conductive polymer. The aqueous conductive adhesive has a simple production process, combines a conductive agent and an adhesive into a whole, is only suitable for coating electrodes of an active material system which is not sensitive to water, and has large limitation.

Patent CN111436199a discloses a composition and method for an energy storage device with improved performance. The method is similar to other dry method electrode preparation technologies, the active material, the conductive agent and the binder are respectively added and mixed, more conductive agent and binder are required to be added, the obtained electrode surface capacity is not high, and the improvement is limited relative to the coating electrode.

Patent CN110563904A discloses a polymer-coated carbon nanotube composite material, a preparation method and application. First, a monomer containing an aldehyde functional group is reacted with an aminated carbon nanotube through a schiff base reaction. Secondly, adding a proper molar amount of monomer containing amino functional groups, and preparing the composite material of the high molecular polymer coated carbon nano tube through chemical reaction and hydrogen bond acting force. On the one hand, the process of this patent requires a complex reaction; on the other hand, the preparation method of the patent results in a product of polymer-coated carbon nanotubes, which easily causes agglomeration of the carbon nanotubes and the polymer.

At present, a composite conductive adhesive capable of adapting to a dry electrode is urgently needed, and when the composite conductive adhesive is used for preparing the dry electrode of an ion energy storage device, only a very small amount of the composite conductive adhesive is needed, and the surface capacity, the energy density, the cycle performance and the rate capability of the ion energy storage device can be improved.

Disclosure of Invention

The invention aims to provide an ultra-dispersed nano composite conductive adhesive. When the composite conductive adhesive is used for an ion energy storage device, only a small amount of the composite conductive adhesive is needed, and the surface capacity, the energy density, the cycle performance and the rate capability of the ion energy storage device can be improved. In addition, the preparation method of the composite conductive adhesive is simple, and the manufacturing cost of the ion energy storage device can be effectively reduced.

The above object of the present invention is achieved by the following means.

In the context of the present invention, the term "low-dimensional" means that at least one dimension is less than 100nm in size.

In a first aspect, the present invention provides a method of preparing a super-dispersed nanocomposite conductive binder, comprising the steps of:

(1) Fully mixing a polymer binder, a solvent and a low-dimensional conductive agent to obtain a suspension;

(2) When the polymer binder is dissolved in a solvent, completely removing the solvent in the suspension to obtain a powdery ultra-dispersed nano composite conductive binder; and when the polymer binder is insoluble in the solvent, removing 50-100% of the solvent in the suspension to obtain the ultra-dispersed nano composite conductive binder in a powdery or non-Newtonian fluid state.

In a specific embodiment of the present invention, a method of preparing an ultra-dispersed nanocomposite conductive binder of the present invention may comprise the steps of:

(1) Preparing a polymer binder and a solvent into an emulsion or a solution;

(2) Adding a low-dimensional conductive agent into the emulsion or the solution of the binder, and dispersing by adopting mechanical stirring and ultrasonic to obtain uniform suspension;

(3) And transferring the suspension, and removing the solvent in a freeze drying, vacuum suction or vacuum heating mode to obtain the ultra-dispersed nano composite conductive adhesive.

Preferably, in the method of the present invention, the mass ratio of the low dimensional conductive agent, the polymer binder and the solvent is 1.

Preferably, in the method of the present invention, the low dimensional conductive agent is selected from one or more of carbon nanotubes, nitrocarbon nanotubes, graphene, silicon nanowires, and metal nanofibers.

Preferably, in the method of the present invention, the low dimensional conductive agent is carbon nanotubes and/or graphene.

Preferably, in the method of the present invention, the polymer binder is selected from one or more of Polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polytetrafluoroethylene, sodium carboxymethylcellulose (CMC), and a copolymer of Styrene and Butadiene (SBR); more preferably one or more of Polytetrafluoroethylene (PTFE) dispersion, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and polyvinylidene fluoride (PVDF) powder.

Preferably, in the method of the present invention, the solvent is selected from deionized water, ethanol, acetone, butanone (methyl ethyl ketone), tetrahydrofuran (THF), N-dimethylformamide (NMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP).

Preferably, in the method of the present invention, the mixing of the polymer binder, the solvent and the low dimensional conductive agent in the step (1) is performed by stirring or ultrasound.

Preferably, in the method of the present invention, the step (2) of completely removing the solvent from the suspension or removing 50% -100% of the solvent from the suspension is performed by: freeze drying, vacuum pumping, vacuum heating or heating under normal pressure.

In a specific embodiment of the present invention, the solvent is preferably removed by freeze-drying, so that the polymer binder is uniformly deposited on the low-dimensional conductive agent such as carbon nanofibers to obtain the composite conductive binder.

In a second aspect, the present invention provides an ultra-dispersed nanocomposite conductive adhesive prepared by the method of the present invention.

In a specific embodiment of the invention, the polymer binder of the invention is distributed on the surface of the low-dimensional conductive agent, and the main body of the composite conductive binder keeps the original shape of the low-dimensional conductive agent, does not agglomerate, does not form a film or does not form a block.

In a particular embodiment of the invention, the composite conductive adhesive is less than 100nm in size in at least one dimension.

In a third aspect, the present invention provides a positive electrode comprising a positive electrode material, wherein the positive electrode material comprises a positive electrode active material and the ultra-dispersed nanocomposite conductive binder of the invention.

Preferably, in the positive electrode of the present invention, the mass percentage of the positive electrode active material is 50 to 99.9%, more preferably 80 to 99%, based on the total mass of the positive electrode.

Preferably, in the positive electrode of the present invention, the mass percentage of the composite conductive binder is 0.1% to 20%, and more preferably 0.5% to 10%, based on the total mass of the positive electrode.

In a fourth aspect, the present invention provides an anode comprising an anode material, wherein the anode material comprises an anode active material and the ultra-dispersed nanocomposite conductive binder of the invention.

Preferably, in the anode of the present invention, the mass percentage of the anode active material is 50 to 99.9%, preferably 80 to 99%, based on the total mass of the anode.

Preferably, in the negative electrode of the present invention, the mass percentage of the composite conductive binder is 0.1% to 20%, preferably 0.5% to 10%, based on the total mass of the negative electrode.

In a fifth aspect, the present invention provides a method of preparing a positive electrode of the invention, comprising the steps of:

(1) Uniformly mixing the positive active material and the ultra-dispersed nano composite conductive adhesive;

(2) And (2) preparing the mixture obtained in the step (1) into a positive electrode by pressurizing.

In a sixth aspect, the present invention provides a method of preparing the anode of the present invention, comprising the steps of:

(1) Uniformly mixing a negative electrode active material and the ultra-dispersed nano composite conductive binder;

(2) And (2) preparing the mixture obtained in the step (1) into a negative electrode by pressurizing.

In a specific embodiment of the present invention, the electrode (including the positive electrode and the negative electrode) of the present invention may be prepared without any solvent and without forming a slurry, and the electrode may be prepared by uniformly mixing the active material and the composite conductive binder of the present invention and then applying pressure thereto.

In particular embodiments of the present invention, the active material may be mechanically mixed with the composite conductive binder, such as by shearing, milling, ball milling, and pneumatic dispersion; then, the sheet is rolled, cut, and rolled to form a sheet. The sheet is an electrode and no additional current collector is required.

In a specific embodiment of the present invention, the sheet of the present invention may be combined with a current collector to form a final electrode, according to actual requirements, such as bonding, spraying or depositing metal foils, carbon materials and other conductive materials as current collectors on the sheet.

In a specific embodiment of the present invention, the method for preparing the electrode of the present invention comprises the steps of:

(1) Weighing an electrode active material into a mortar, adding the super-dispersed nano composite conductive adhesive, and grinding to fully mix the electrode active material and the composite conductive adhesive;

(2) Transferring the mixture obtained in the step (1), and obtaining the dry electrode with high surface capacity and high active material ratio by rolling, extruding or cutting.

In a specific embodiment of the present invention, the electrode active materials are divided into a positive electrode active material and a negative electrode active material. In the present invention, the positive electrode active material and the negative electrode active material are not particularly limited, and those conventional in the art may be used. Common positive electrode active materials are lithium cobaltate, lithium nickelate, lithium iron phosphate, nickel cobalt manganese oxide, sodium vanadate, and sulfides. Common negative active materials such as graphite, silicon carbon, and silicon.

The invention has the following beneficial effects:

the inventors of the present invention found that when the proportion of the active material is the same, the surface capacity of the electrode of the present invention is far higher than that of the electrode obtained by the conventional coating method, and at this time, the electrode of the present invention has a higher energy density than that of the electrode obtained by the coating method. Without wishing to be bound by theory, the surface capacity of the electrode of the present invention far exceeds that of electrodes obtained by traditional coating methods, probably because: i) In the composite conductive adhesive, the adhesive is uniformly dispersed, and nanoparticles are attached to the surface of the conductive agent, and the conductive agent keeps the original state, is well dispersed and is not agglomerated; ii) when the dosage of the composite conductive adhesive is small, the composite conductive adhesive can still be uniformly distributed in the electrode; iii) The binder in the composite conductive binder of the present invention can perform "wire drawing" due to pressure when preparing an electrode, and form an interlaced network structure with a conductive agent such as carbon nanotubes, supporting active material particles to form a dense electrode with high surface capacity.

Drawings

Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a SEM topography of a super-dispersed nano-composite conductive adhesive numbered DN1 in example 1 of the invention.

FIG. 2 is a transmission electron microscope image of a polymer coated carbon nanotube composite prepared by the prior art (CN 110563904A).

FIG. 3a is an SEM topography of a positive plate numbered A1-1 in example 2 of the invention;

fig. 3a shows that the composite conductive binder is uniformly distributed inside the electrode, and the binder "strings" and carbon nanotubes form a three-dimensional network to entangle and bind the active material particles together.

FIG. 3B is an SEM topography of the positive plate numbered B1-1 in example 5 of the invention.

Fig. 4 is a charge-discharge curve diagram of the assembled button cell battery E-02 of the present invention.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.

Example 1

Preparation of super-dispersed nano composite conductive adhesive

In this embodiment, polytetrafluoroethylene (PTFE) is used as the binder and deionized water is used as the solvent. Carbon Nanotubes (CNTs) act as conductive agents.

1. (1) taking 10g of multi-wall carbon nano-tube into a spherical reaction bottle, adding 50ml of concentrated nitric acid, heating to 150 ℃, and refluxing for 4h. Vacuum-filtering with a buchner filter flask, washing with deionized water for three times, and freeze-drying to obtain nitrated carbon Nanotube (NO) ₂ -MWNT). (2) 1.667g of 60wt% Polytetrafluoroethylene (PTFE) concentrated dispersion is weighed into a beaker, and 20ml of deionized water is added for dilution, and then 1g of nitrated carbon nanotube is added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) putting the fully dispersed suspension into a freeze dryer, freezing for 12h at-50 ℃, vacuumizing, maintaining for 24h, and removing the solvent to obtain the ultra-dispersed nano composite conductive adhesive, wherein DN1 is recorded.

2. 1.667g of 60 wt.% concentrated dispersion of Polytetrafluoroethylene (PTFE) was weighed into a beaker, diluted with 20ml of deionized water, and then 2g of nanotubes were added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) freezing the fully dispersed suspension in a freeze dryer at-50 ℃ for 12h, vacuumizing, maintaining for 24h, and removing the solvent to obtain the ultra-dispersed nano composite conductive adhesive, namely DN2.

3. 1.667g of 60wt% Polytetrafluoroethylene (PTFE) concentrated dispersion is put into a beaker, and 20ml of deionized water is added for dilution, and then 4g of carbon nanotubes are added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) freezing the fully dispersed suspension in a freeze dryer at-50 ℃ for 12h, vacuumizing, maintaining for 24h, and removing the solvent to obtain the ultra-dispersed nano composite conductive adhesive, namely DN3.

4. 1.667g of 60wt% polyvinylidene fluoride (PVDF) concentrated dispersion is weighed into a beaker, and 20ml of deionized water is added for dilution, and then 1g of carbon nanotubes is added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) placing the fully dispersed suspension in a freeze dryer, freezing for 12 hours at-50 ℃, vacuumizing, maintaining for 24 hours, and removing the solvent to obtain the ultra-dispersed nano composite conductive adhesive, wherein DN4 is recorded.

5. 1g of polyvinylidene fluoride (PVDF) powder is weighed into a beaker, 10ml of acetone is added, the mixture is magnetically stirred for 24 hours to be fully dissolved, and then 2g of carbon nano tubes are added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) putting the fully dispersed suspension into a vacuum box, vacuumizing for 1h to remove the solvent, and marking the obtained ultra-dispersed nano composite conductive adhesive as DN5.

6. 1g of ethylene oxide (PEO) was weighed into a beaker, 10ml of deionized water was added, and then 1g of carbon nanotubes was added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) freezing the fully dispersed suspension in a freeze dryer at-50 ℃ for 12h, vacuumizing, maintaining for 24h, and removing the solvent to obtain the ultra-dispersed nano composite conductive adhesive, wherein DN6 is recorded.

7. 1g of sodium carboxymethylcellulose (CMC) was weighed into a beaker, 10ml of deionized water was added, and then 1g of carbon nanotubes was added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) placing the fully dispersed suspension in a vacuum oven, heating for 6 hours under vacuum to remove the solvent, and marking the obtained ultra-dispersed nano composite conductive adhesive as DN7.

8. 1.667g of 60wt% Styrene Butadiene Rubber (SBR) emulsion is weighed into a beaker, 20ml of deionized water is added for dilution, and then 1g of carbon nano tube is added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. And (3) placing the fully dispersed suspension in a freeze dryer, freezing for 12 hours at-50 ℃, vacuumizing, maintaining for 24 hours, and removing the solvent to obtain the ultra-dispersed nano composite conductive adhesive, wherein DN8 is recorded.

9. 1.667g of 60wt% Polytetrafluoroethylene (PTFE) concentrated dispersion is taken to be put into a beaker, 20ml of deionized water is added for dilution, and then 1g of nitrated carbon nano tube is added. The primary dispersion was carried out by magnetic stirring for 30 minutes, and then ultrasonic dispersion was carried out by a cell disruptor for 30 minutes. Heating the fully dispersed suspension to 80 ℃ at normal pressure, evaporating, removing part of the solvent (80%), and obtaining the non-Newtonian fluid ultra-dispersed nano composite conductive adhesive which is marked as DN9.

Example 2

Preparation of lithium cobaltate positive plate

1. 4.9g of lithium cobaltate powder was weighed into a mortar, and 0.1g of the prepared composite conductive binder (DN 1) was weighed and added to the mortar for grinding and mixing. Rolling the mixture into tablets, rolling the tablets to 1000 mu m, then using a tablet punching machine to punch the tablets into wafers with the diameter of 10mm, weighing the wafers, and quickly transferring the wafers into a glove box filled with argon for storage. The obtained LCO positive plate is marked as A1-1.

2. 4.9g of lithium cobaltate powder was weighed into a mortar, and 0.1g of the prepared composite conductive binder (DN 1) was weighed and added to the mortar for grinding and mixing. Rolling the mixture into tablets, rolling the tablets to 500 mu m, then using a tablet punching machine to punch the tablets into wafers with the diameter of 10mm, weighing the wafers, and quickly transferring the wafers into a glove box filled with argon for storage. The obtained LCO positive plate is marked as A1-2.

3. 4.9g of lithium cobaltate powder was weighed into a mortar, and 0.1g of the prepared composite conductive binder (DN 1) was weighed and added to the mortar for grinding and mixing. Rolling the mixture into tablets, rolling the tablets to 280 mu m, then using a tablet punching machine to punch the tablets into wafers with the diameter of 10mm, weighing the wafers, and quickly transferring the wafers into a glove box filled with argon for storage. The obtained LCO positive plate is marked as A1-3.

4. The non-Newtonian fluid composite conductive adhesive (DN 9) with the solid content of 0.1g is weighed into a mortar, and 4.9g of lithium cobaltate powder is added into the mortar for grinding, mixing and beating into a mass. The mixture was rolled to a sheet size of 280 μm and placed in a vacuum oven. Drying at 120 deg.C for 6h to remove residual solvent, then punching into 10mm diameter round piece with a punching machine, weighing, and rapidly transferring into a glove box filled with argon gas for storage. The obtained LCO positive plate is marked as A1-5.

5. 4.95g of lithium cobaltate powder was weighed into a mortar, and 0.05g of the prepared composite conductive binder (DN 2) was weighed and added to the mortar for grinding and mixing. Rolling the mixture into sheets, rolling to 160 μm, punching into 10mm diameter circular sheets with a punching machine, weighing, and storing in a glove box filled with argon gas. The obtained LCO positive plate is marked as A1-6.

Example 3

Preparation of lithium iron phosphate positive plate

4.9g of lithium iron phosphate powder was weighed into a mortar, and 0.1g of the prepared composite conductive adhesive (DN 1) was weighed and added into the mortar for grinding and mixing. Rolling the mixture into tablets, rolling the tablets to 500 mu m, then using a tablet punching machine to punch the tablets into wafers with the diameter of 10mm, weighing the wafers, and quickly transferring the wafers into a glove box filled with argon for storage. The obtained positive electrode sheet was designated as A2-1.

Example 4

Preparation of graphite negative plate

4.8g of graphite was weighed into a mortar, and 0.2g of the prepared composite conductive adhesive (DN 1) was weighed and added into the mortar for grinding and mixing. Rolling the mixture into tablets, rolling the tablets to 500 mu m, then using a tablet punching machine to punch into circular tablets with the diameter of 10mm, weighing the circular tablets, and quickly transferring the circular tablets into a glove box filled with argon for storage. The obtained negative electrode sheet was recorded as A3-1 in terms of thickness.

Example 5

Preparation of lithium cobaltate contrast pole piece

3.92g LCO, 0.04g super-P, 0.04g polyvinylidene fluoride (PVDF) were weighed into a stirred tank, and 1.2ml dimethyl pyrrolidone (NMP) was added. The slurry is prepared by mixing with a stirrer at the rotating speed of 2000r/min for 30min. The mixed slurry was knife coated on aluminum foil with a 400 μm doctor blade and then transferred to a 55 ℃ forced air oven for drying for 4h. And then, punching into a wafer with the diameter of 10mm by using a punching machine, weighing, transferring into a vacuum oven, preserving heat for 6 hours at 120 ℃, and rapidly transferring the pole piece into a glove box filled with argon for storage after the temperature is reduced to 30 ℃. The resulting pole piece was recorded as B1-1.

3.84g LCO, 0.08g super-P, 0.08g polyvinylidene fluoride (PVDF) were weighed into a stirred tank, followed by 1.2ml dimethyl pyrrolidone (NMP). The slurry is prepared by mixing with a stirrer at the rotating speed of 2000r/min for 30min. The mixed slurry was knife coated on aluminum foil with a 400 μm doctor blade and then transferred to a 55 ℃ forced air oven for drying for 4h. Then, a punching machine is used for punching into a wafer with the diameter of 10mm, the wafer is weighed and then transferred into a vacuum oven to be insulated for 6 hours at the temperature of 120 ℃, and the pole piece is rapidly transferred into a glove box filled with argon to be stored after the temperature is reduced to 30 ℃. The resulting pole piece was recorded as B1-2.

0.92g LCO, 0.04g super-P, 0.04g polyvinylidene fluoride (PVDF) were weighed into a stirred tank, and 0.6ml dimethyl pyrrolidone (NMP) was added. The slurry is prepared by mixing with a stirrer at the rotating speed of 2000r/min for 30min. The mixed slurry was knife coated on aluminum foil with a 400 μm doctor blade and then transferred to a 55 ℃ forced air oven for drying for 4h. And then, punching into a wafer with the diameter of 10mm by using a punching machine, weighing, transferring into a vacuum oven, preserving heat for 6 hours at 120 ℃, and rapidly transferring the pole piece into a glove box filled with argon for storage after the temperature is reduced to 30 ℃. The resulting pole piece was recorded as B1-3.

0.8g LCO, 0.1g super-P, 0.1g polyvinylidene fluoride (PVDF) were weighed into a stirring pot, and then 0.6ml dimethyl pyrrolidone (NMP) was added. The slurry is prepared by mixing a stirrer at the rotating speed of 2000r/min for 30min. The mixed slurry was knife coated on aluminum foil with a 400 μm doctor blade and then transferred to a 55 ℃ forced air oven for drying for 4h. Then, a punching machine is used for punching into a wafer with the diameter of 10mm, the wafer is weighed and then transferred into a vacuum oven to be insulated for 6 hours at the temperature of 120 ℃, and the pole piece is rapidly transferred into a glove box filled with argon to be stored after the temperature is reduced to 30 ℃. The resulting pole piece was recorded as B1-4.

Example 6

Preparation of lithium iron phosphate contrast pole piece

0.98g of lithium iron phosphate powder, 0.01g of super-P and 0.01g of polyvinylidene fluoride (PVDF) were weighed in a stirring tank, and then 0.6ml of dimethylpyrolidone (NMP) was added. The slurry is prepared by mixing with a stirrer at the rotating speed of 2000r/min for 30min. The mixed slurry was knife coated on aluminum foil with a 400 μm doctor blade and then transferred to a 55 ℃ forced air oven for drying for 4h. Then, a punching machine is used for punching into a wafer with the diameter of 10mm, the wafer is weighed and then transferred into a vacuum oven to be insulated for 6 hours at the temperature of 120 ℃, and the pole piece is rapidly transferred into a glove box filled with argon to be stored after the temperature is reduced to 30 ℃. The resulting pole piece was recorded as B2-1.

Example 7

Preparation of graphite contrast pole piece

0.98g of graphite powder, 0.01g of super-P and 0.01g of polyvinylidene fluoride (PVDF) were weighed in an agitating pot, and then 0.6ml of dimethyl pyrrolidone (NMP) was added. The slurry is prepared by mixing with a stirrer at the rotating speed of 2000r/min for 30min. The mixed slurry was knife coated on aluminum foil with a 400 μm doctor blade and then transferred to a 55 ℃ forced air oven for drying for 4h. Then, a punching machine is used for punching into a wafer with the diameter of 10mm, the wafer is weighed and then transferred into a vacuum oven to be insulated for 6 hours at the temperature of 120 ℃, and the pole piece is rapidly transferred into a glove box filled with argon to be stored after the temperature is reduced to 30 ℃. The resulting pole piece was recorded as B3-1.

Example 8

Assembly of lithium ion secondary battery

The inventors of the present invention assembled the positive electrode sheets prepared in examples 1 to 7 into a battery by the method provided in this example.

In a glove box filled with inert atmosphere, a lithium metal sheet with a diameter of 15mm and a thickness of 0.6mm was used as the negative electrode of the cell, a double-layer film of PVDF was used as a separator between the positive electrode and the negative electrode, and non-additive nonaqueous electrolyte (purchased from institute of Process engineering) was added dropwise to assemble the electrode sheets A1-2, A1-3, B1-1, A2-1, B2-1, A3-1, B3-1 and the lithium metal negative electrode prepared in examples 2, 3, 5, 6 and 7 into button cells of type CR2032, which are labeled as E-01, E-02, E-03, E-04, E-05, E-06 and E-07, respectively. The assembled button cell was tested for charge and discharge using a blue test system at a test voltage ranging from 3V to 4.3V, with E-01 providing the first 30 cycles of data and the remainder 100 cycles of data due to slower charge and discharge. E-02 and E-03 adopt a test mode of multiplying power charging and discharging firstly and then constant current circulation.

Results

FIG. 1 is a SEM topography of a super-dispersed nano-composite conductive adhesive numbered DN1 in example 1 of the invention. Fig. 1 shows that the binder is uniformly dispersed and attached to the surface of the carbon nanotube as nanoparticles. In addition, the carbon nanotubes maintain the original shape, and the carbon nanotubes are well dispersed without forming agglomeration.

FIG. 2 is a transmission electron microscope image of a polymer coated carbon nanotube composite prepared by the prior art (CN 110563904A). Fig. 2 shows that the carbon nanotubes and the polymer have an agglomeration phenomenon, that the individual carbon tubes exist only at the edge portion and that the dispersibility of the carbon nanotubes is poor.

TABLE 1 ultra-dispersed nanocomposite conductive binders

From table 1, it can be seen that various binders and conductive agents can be used to prepare the ultra-dispersed nanocomposite conductive binder, and have good compatibility with both solvents and drying methods. The drying method is most effective in freeze drying.

FIG. 3a is an SEM topography of a positive plate numbered A1-1 in example 2 of the invention; fig. 3a shows that the composite conductive binder is uniformly distributed inside the electrode, and the binder "strings" and carbon nanotubes form a three-dimensional network to entangle and bind the active material particles together. The adhesive wire drawing and the carbon nano tube form a staggered network structure, and active material particles are supported to form a compact pole piece with high surface capacity.

FIG. 3B is an SEM topography of the positive electrode plate numbered B1-1 in example 5 of the invention. In the lithium cobaltate positive electrode B1-1 prepared by coating shown in fig. 3B, the carbon nanotubes are mainly distributed in the corners of some particles, the dispersibility is poor, and the microstructure is loose.

TABLE 2-1 major technical parameters of the dry electrode

TABLE 2-2 Main technical parameters of the coated electrodes

As can be seen from tables 2-1 and 2-2, the use of the ultra-dispersed nanocomposite conductive binder of the present invention can greatly reduce the amount of conductive agent and binder used to prepare an electrode film, greatly increase the active material content, and obtain a dry electrode several times the theoretical surface capacity of the coated electrode (all data calculated as 140mAh/g specific capacity). Meanwhile, the dependence on a current collector/aluminum foil is avoided, and the energy density (calculated according to the mass of the anode, including the current collector) can be further improved. In addition, the dry-method electrode also has good flexibility and is expected to be applied to flexible devices.

As shown in table 2-2, with the conventional coating method, there is a significant limit in coating thickness due to the slurry gravity, and it is difficult to prepare an electrode sheet having a high active material content and a high surface capacity. When the contents of the conductive agent and the binder are decreased, the active material is easily peeled off from the current collector.

TABLE 3 Battery Performance index

* The graphite half-cell is only used for verifying the capacity performance, and the energy density of the half-cell is meaningless because the graphite is used as a negative electrode in the actual cell.

FIG. 4 is a charge-discharge curve of battery E-02. Fig. 4 shows that when a dry electrode prepared by using the ultra-dispersed nano composite conductive binder of the present invention is used for assembling a battery, the assembled battery has higher energy density and surface capacity, and simultaneously has good cycle performance and rate performance.

Claims

1. A method of preparing a super-dispersed nanocomposite conductive adhesive comprising the steps of:

2. The method according to claim 1, wherein the mass ratio of the low dimensional conductive agent, the polymer binder and the solvent is 1.1 to 10;

preferably, the low-dimensional conductive agent is selected from one or more of carbon nanotubes, nitrocarbon nanotubes, graphene, nano silicon wires and nano metal fibers;

preferably, the low dimensional conductive agent is carbon nanotubes and/or graphene;

preferably, the polymer binder is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylpyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, sodium carboxymethylcellulose and a copolymer of styrene and butadiene;

preferably, the solvent is one or more selected from water, ethanol, acetone, butanone, tetrahydrofuran, N-dimethylformamide, dimethyl sulfoxide and N-methyl-2-pyrrolidone;

preferably, the intensive mixing of the polymer binder, the solvent and the low dimensional conductive agent in the step (1) is performed by stirring or ultrasound.

3. The method of claim 1, wherein the step (2) of completely removing the solvent from the suspension or removing 50% -100% of the solvent from the suspension is performed by: freeze drying, vacuum pumping, vacuum heating or heating under normal pressure.

4. An ultra-dispersed nanocomposite conductive binder prepared by the method of any one of claims 1-3.

5. A positive electrode comprising a positive electrode material, wherein the positive electrode material comprises a positive electrode active material and the ultra-dispersed nanocomposite conductive binder of claim 4.

6. The positive electrode according to claim 5, wherein the mass percentage of the positive electrode active material is 50 to 99.9%, preferably 80 to 99%, based on the total mass of the positive electrode;

preferably, the mass percent of the composite conductive adhesive is 0.1-20%, preferably 0.5-10%, based on the total mass of the positive electrode.

7. An anode comprising an anode material, wherein the anode material comprises an anode active material and the ultra-dispersed nanocomposite conductive binder of claim 4.

8. The negative electrode according to claim 7, wherein the negative electrode active material is in a mass percentage of 50 to 99.9%, preferably 80 to 99%, based on the total mass of the negative electrode;

preferably, the mass percent of the composite conductive adhesive is 0.1-20%, preferably 0.5-10%, based on the total mass of the negative electrode.

9. A method of making the positive electrode of any one of claims 5-6, comprising the steps of:

(1) Uniformly mixing a positive electrode active material and the ultra-dispersed nanocomposite conductive binder of claim 4;

10. A method of preparing the anode of any one of claims 7-8, comprising the steps of:

(1) Uniformly mixing a negative electrode active material and the ultra-dispersed nanocomposite conductive binder of claim 4;