CN115579458A - Method for preparing electrode film of lithium ion battery by dry method - Google Patents

Abstract

The invention belongs to the technical field of battery material preparation, and mainly relates to a method for preparing an electrode film of a lithium ion battery by using a dry process. Modified Polytetrafluoroethylene (PTFE) with ultrahigh molecular weight is used as a binder, and is firstly uniformly mixed with an active material and a conductive agent at low temperature and low speed, and the mixed powder is subjected to high-speed shearing stirring after temperature rise and heat preservation to obtain the fibrous electrode powder. And conveying the fiberized mixed powder to a continuous rolling device through accurate metering to carry out hot pressing film forming, and controlling the mechanical precision, temperature and pressure of a hot pressing roller to obtain the electrode film with uniform thickness, high strength and toughness. According to the method for preparing the highly-fibrous electrode film by the dry method, the mechanical property of the PTFE binder is optimized by modifying and adjusting the particle size and the molecular weight of the PTFE binder, the fibrous mode, speed, temperature and time of the binder are regulated and controlled, and the precision of a hot pressing rod is used for producing the electrode film with good quality, so that the compaction density and the energy density of a battery can be improved, and the method has great potential in the lithium ion battery industry.

Description

Method for preparing electrode film of lithium ion battery by dry method

Technical Field

The invention belongs to the field of battery materials, and relates to a method for preparing an electrode film of a lithium ion battery by a dry method.

Background

The current lithium battery industry faces severe price competition, the gross profit rate of the power battery industry is generally lower than 15%, the competition is very fierce, and most enterprises face survival dilemma. With the rapid expansion of productivity, differentiation in product structure, client structure, productivity utilization rate, gross profit rate, and the like will inevitably occur, especially productivity utilization rate. Based on the innovative capacity, the efficient capacity meeting the future market demand is obtained. The key point of how to establish the method in the fierce new energy market is technical innovation and iteration. Dry electrode technology can bring about a 20% cost reduction. The battery enterprises which master the dry electrode process firstly have the advantages of the prior art and can further expand the market share. After more than twenty years of development, technological progress of the battery industry in China is focused on optimization of material and structure design, but the traditional wet process is still used for manufacturing the electrode.

In the process of increasingly developing new energy industries, the defects of the traditional wet electrode preparation are also in the step of gradually limiting the industrialization of lithium ion batteries. The wet coating, drying and solvent recovery processes require approximately 48% of the total energy required to produce the cell, greatly increasing the cost of cell production. A large amount of NMP (N-methylpyrrolidone) is used in the electrode slurry mixing process and volatilized at the time of drying, and thus a recovery device must be established, otherwise, environmental pollution is caused. This process also results in increased manufacturing costs. During the evaporation of the solvent, the binder and the conductive agent may diffuse near the electrode surface due to capillary action and form agglomerates, and the active material may precipitate. This can lead to delamination of the electrode, thereby impairing the construction of the conductive network in the electrode and reducing the strength of the bond between the active material and the current collector. Furthermore, electrodes made using wet coating techniques suffer from problems of cracking, delamination, and poor flexibility, which are magnified especially when thick electrodes are made. Therefore, the thickness of the electrode is limited, thereby affecting the capacity of the battery.

The dry electrode preparation technology is an electrode preparation technology which mixes an electrode active material, a conductive agent and a binder to obtain electrode powder and then obtains a pole piece through continuous rolling. However, research on dry-process electrodes is still in the beginning, and many technical problems are urgently needed to be solved, wherein fibrosis of the binder in the electrode material is one of the important factors affecting the performance of the dry-process electrode. The fiberization of the binder is affected by many factors, including the type of binder, the manner of mixing with the active material, and the time, temperature, magnitude of shear stress, etc. of the fiberization process. In the prior art, there is no effective solution to control the degree of fiberization of the binder in the electrode material. This problem affects the mass production development and large-scale application of dry electrodes.

Disclosure of Invention

The problem to be solved by the embodiment of the invention is to provide a method for preparing an electrode film by a dry method, so that a binder is fully fiberized in an electrode material, the internal resistance of an electrode pole piece is reduced, the ion transmission rate is improved, and the capacity and the cycle life of a lithium ion battery are effectively improved.

The present invention has been made to solve the above-mentioned problems occurring in the prior art, and provides a method for dry-process production of a fibrous electrode material, comprising:

step 1: premixing an active material and a conductive agent through mixing equipment, wherein the stirring time is 10-60min, and the stirring speed is 1000-10000 r/min, so as to obtain mixed powder; the conductive agent is 3-10% of the conductive agent and the active substance is 90-97% of the conductive agent, and the active substance is a positive electrode material or a negative electrode material;

step 2: adding the powder mixed in the step 1, a PTFE adhesive and an auxiliary agent into mixing equipment, stirring and mixing at a low temperature and a low speed to obtain a premixed electrode material, wherein the stirring and mixing time is 1-3min, the stirring and mixing temperature is 0-10 ℃, and the stirring and mixing speed is 50r/min-100 r/min; wherein, the weight percentage of the powder, the PTFE adhesive and the auxiliary agent is 2 percent to 5 percent of PTFE, 0.05 percent to 0.1 percent of auxiliary agent and 94.9 percent to 97.5 percent of powder.

And 3, step 3: and (3) carrying out heat treatment on the premixed electrode material obtained in the step (2) at the temperature of 80-200 ℃ for 60-100min to obtain premixed heat-insulating electrode powder.

And 4, step 4: and (3) shearing the premixed heat-insulating electrode powder obtained in the step (3) at a high speed to obtain the uniformly mixed highly fibrous electrode material, wherein the shearing time is 5-20min, the shearing temperature is 80-200 ℃, and the shearing speed is 10000r/min-20000r/min.

And 5: and (4) transferring the highly-fibrillated electrode material obtained in the step (4) to a continuous rolling device for hot-pressing film forming to obtain an electrode piece.

2. The dry process for preparing a fiberized electrode according to claim 1, wherein the PTFE binder is a modified PTFE binder powder having a standard relative density (SSG) of 2.14 to 2.18, a tensile strength of 3.5 to 4.5MPa, an elongation of 300% to 500%, and an average particle size of 3 to 10 μm. A (c)

3. The dry-process fiberization electrode preparation method according to claim 1, wherein the auxiliary agent is a mixture of one or more of silicon oxide, titanium oxide, graphene, and ceramic powder.

4. The dry-process method for preparing the fiberized electrode according to claim 1, wherein the conductive agent is one or more of conductive carbon black, ketjen black, conductive graphite, carbon fiber, carbon nanotube, graphene and superconducting carbon black.

Further, the electrode material is one or a mixture of more of lithium iron phosphate, nickel cobalt manganese ternary material-523 type, 811 type, 622 type, lithium cobaltate, lithium manganate and graphite.

5. The dry-process fiberizing electrode of claim 1, wherein the shear mixing device is one of a single screw extruder, a twin screw extruder, and a supersonic jet mill.

6. The dry-process fiberization electrode preparation method according to claim 1, wherein the continuous rolling film-forming process is carried out under a pressure of 5-200T and at a heating temperature of 100-300 ℃, and the thickness of the electrode sheet is 50-3000 μm.

Has the advantages that:

compared with the prior art of preparing the electrode plate by wet coating, the method has the beneficial effects that: according to the method, the dry-process electrode plate is directly obtained by the mixture containing the electrode material, the conductive carbon and the modified PTFE adhesive through the in-situ fibrosis of the modified PTFE adhesive, the uniform mixing of a jet mill and the continuous dry-process roll forming. The preparation process is simple, the electrode has high tap density, and a solvation process is avoided, so that the cost for drying the electrode is saved. The modified PTFE adhesive exists in a highly fibrous state, so that the contact between active material particles and conductive carbon particles is tighter, the powder is not easy to fall off, and the electrode conductivity is improved; by adopting the continuous rolling forming method, the pressure is gradually increased in the rolling process, and the speed difference is set between the two counter-pressing rollers, so that the pole piece generates internal acting force in the forming process, the forming effect is improved, and the obtained electrode film has uniform thickness, high strength and excellent mechanical property.

Drawings

FIG. 1 is a scanning electron micrograph of the electrode material before fiberization in example 1.

FIG. 2 is a scanning electron micrograph of the electrode material after fiberization in example 1.

Fig. 3 shows a high-precision continuous rolling apparatus.

Detailed Description

The present invention will be further described with reference to the following embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claims appended to the present application.

Example 1

Dry preparation of fiberized cathode material

Weighing 900g of lithium manganate and 100g of superconducting carbon black, premixing in a mixing device, and stirring at the speed of 800r/min for 5min to obtain mixed powder. And (3) weighing 20g of modified PTFE (polytetrafluoroethylene) binder and 0.8g of silicon oxide auxiliary agent, adding into mixing equipment, stirring and mixing at a low speed at a low temperature for 2min at a stirring and mixing temperature of 5 ℃ and a stirring and mixing speed of 70r/min to obtain the premixed electrode material. And (3) carrying out heat treatment on the premixed electrode material in an oven at 100 ℃ for 80min to obtain premixed heat-insulating electrode powder. And (3) carrying out high-speed shearing on the premixed heat-insulating electrode powder in a supersonic airflow pulverizer at the shearing speed of 15000r/min at 100 ℃ for 10min to obtain the uniformly mixed highly fibrous electrode material. And transferring the highly-fibrillated electrode material to continuous rolling equipment for hot-pressing film formation, wherein the first-stage rolling pressure is 50T, the temperature is 100 ℃, the second-stage rolling pressure is 100T, the temperature is 150 ℃, the third-stage rolling pressure is 200T, and the temperature is 200 ℃, and finally obtaining the dry-method-prepared fibrillated anode piece.

Example 2

Dry preparation of fiberized cathode material

Weighing 900g of lithium iron phosphate and 100g of superconducting carbon black, and premixing in mixing equipment, wherein the stirring time is 6min, and the stirring speed is 900r/min, so as to obtain well-mixed powder. And (3) weighing 20g of modified PTFE (polytetrafluoroethylene) binder and 0.7g of silicon oxide auxiliary agent, adding into mixing equipment, stirring and mixing at a low speed at a low temperature for 2min at a stirring and mixing temperature of 3 ℃ and a stirring and mixing speed of 80r/min to obtain the premixed electrode material. And (3) carrying out heat treatment on the premixed electrode material in an oven at 100 ℃ for 80min to obtain premixed heat-insulating electrode powder. And (3) carrying out high-speed shearing on the premixed heat-insulating electrode powder in a supersonic airflow pulverizer at the shearing speed of 15000r/min at 100 ℃ for 10min to obtain the uniformly mixed highly fibrous electrode material. And transferring the highly-fibrillated electrode material to continuous rolling equipment for hot-pressing film formation, wherein the first-stage rolling pressure is 50T, the temperature is 120 ℃, the second-stage rolling pressure is 100T, the temperature is 150 ℃, the third-stage rolling pressure is 200T, and the temperature is 200 ℃, and finally obtaining the dry-method-prepared fibrillated anode piece.

Mechanical property testing and physical property analysis are carried out on the above embodiment and the traditional wet electrode pole piece, and the obtained data are as follows:

sample(s)	Thickness of electrode	Density of compaction	Tensile strength	Surface defect
					Example 1	150μm	3.35g cm -3	1.3MPa	Whether or not
Example 2	150μm	3.07g cm -3	1.21MPa	Whether or not
					Conventional wet process electrode	220μm	2.33g cm -3	0.6MPa	Is that

Claims (6)

1. A method for preparing an electrode film of a lithium ion battery by a dry method is characterized by comprising the following steps:

step 1: premixing the active material and the conductive agent by mixing equipment, wherein the stirring time is 10-60min, and the stirring speed is 1000 r/min-10000 r/min, so as to obtain uniformly mixed powder; the conductive agent is 3-10% of the conductive agent and the active substance is 90-97% of the conductive agent, and the active substance is a positive electrode material or a negative electrode material;

and 2, step: adding the powder mixed in the step 1, a PTFE adhesive and an auxiliary agent into mixing equipment, stirring and mixing at a low temperature and a low speed to obtain a premixed electrode material, wherein the stirring and mixing time is 1-3min, the stirring and mixing temperature is 0-10 ℃, and the stirring and mixing speed is 50r/min-100 r/min; wherein, the powder, the PTFE adhesive and the auxiliary agent are 2 to 5 percent of PTFE, 0.05 to 0.1 percent of auxiliary agent and 94.9 to 97.5 percent of powder according to weight percentage.

And step 3: and (3) carrying out heat treatment on the premixed electrode material obtained in the step (2) at the temperature of 80-200 ℃ for 60-100min to obtain premixed heat-insulating electrode powder.

And 4, step 4: and (4) shearing the premixed heat-insulating electrode powder material obtained in the step (3) at a high speed to obtain the uniformly mixed highly fibrous electrode material, wherein the shearing time is 5-20min, the shearing temperature is 80-200 ℃, and the shearing speed is 10000r/min-20000r/min.

And 5: and (5) transferring the highly fibrous electrode material obtained in the step (4) to a continuous rolling device for hot-pressing film forming to obtain the electrode piece.

2. The dry process for preparing a fiberized electrode according to claim 1, wherein the PTFE binder is a modified PTFE binder powder having a standard relative density (SSG) of 2.14 to 2.18, a tensile strength of 3.5 to 4.5MPa, an elongation of 300% to 500%, and an average particle size of 3 to 10 μm.

3. The dry-process fiberization electrode preparation method according to claim 1, wherein the auxiliary agent is a mixture of one or more of silicon oxide, titanium oxide, graphene, and ceramic powder.

4. The dry-process method for preparing the fiberized electrode according to claim 1, wherein the conductive agent is one or more of conductive carbon black, ketjen black, conductive graphite, carbon fiber, carbon nanotube, graphene and superconducting carbon black.

Further, the electrode material is one or a mixture of more of lithium iron phosphate, nickel cobalt manganese ternary material-523 type, 811 type, 622 type, lithium cobaltate, lithium manganate and graphite.

5. The dry process fiberizing electrode process of claim 1, wherein the shear mixing device is one of a single screw extruder, a twin screw extruder, a supersonic jet mill.

6. The dry-process fiberization electrode preparation method according to claim 1, wherein the continuous rolling film-forming process is carried out under a pressure of 5-200T and at a heating temperature of 100-300 ℃, and the thickness of the electrode sheet is 50-3000 μm.

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