CN108232195A - A kind of pole piece moulding method of the water system ion battery based on polytetrafluoroethylene (PTFE) binding agent - Google Patents

Abstract

The invention relates to a pole piece forming method of a water-based ion battery based on a polytetrafluoroethylene binder, comprising: step 1) using ceramic powder and an inorganic carbon source conductive agent as raw materials for the electrode of the water-based ion battery, and using water as the Solvent, add polytetrafluoroethylene as a binder, and ball mill to obtain a uniform slurry; step 2) filter the obtained slurry to obtain a filter cake, and further dry the obtained filter cake to obtain a dry powder; step 3) The obtained dry powder is granulated and sieved to obtain a granular powder with uniform particle size; Step 4) The obtained granular powder is prepared in batches for battery pole pieces by dry pressing. The present invention adopts the method of ball milling to make slurry and joint granulation, and the obtained powder is in the form of granules, which greatly improves the fluidity problem of the powder caused by the binder, and makes the forming of the pole piece easy to control, so it is suitable for dry pressing. Produce thick pole pieces.

Description

A method for forming pole pieces of water-based ion batteries based on polytetrafluoroethylene binder

technical field

The invention relates to a pole piece forming method based on polytetrafluoroethylene (PTFE) binder as a water-based ion battery, in particular to a method of mixing by ball milling, conventional drying and granulation, combined with automatic weighing by powder automatic tablet forming machine The system control and batch pole piece production process belong to the field of ceramic powder materials.

Background technique

Low-cost electric energy storage systems are currently being rapidly developed under the impetus of the new energy field. It is estimated that the global annual market demand for batteries is about 15 billion US dollars. In terms of industrial batteries, such as: for UPS, power quality regulation , Backup batteries, etc., the total market volume can reach 5 billion US dollars. In the United States, Europe and Asia, a group of high-performance storage battery companies are being established to produce power system energy storage. In recent years, various new types of storage batteries have been successfully developed and applied in power systems. UK-based Regenesys Technologies (www.regenesys.com.au/) is using PSB (Polysulfide Broe Flow Battery) batteries to build a 15MW/120MW h energy storage power station with a net efficiency of about 75%. Due to its high energy density and energy storage efficiency, lithium-ion batteries are currently developing rapidly. In recent years, lithium-ion batteries have occupied 50% of the market share of small mobile device power supplies. However, there are still some challenges in the production of large-capacity lithium-ion batteries. Challenging work to do, the main hurdle being its high cost, and partly due to the special packaging it requires and the necessary internal overcharge protection circuitry. Compared with other storage batteries, the main advantages of aqueous ion batteries are high energy storage efficiency (nearly 100%) and long service life (rechargeable 3000 times when each discharge does not exceed 80% of the energy storage). And it is expected to be the battery with the lowest cost, which is also a battery that is not harmful to the environment.

In the past, nickel-cadmium, nickel-metal hydride batteries, supercapacitors, etc. used organic electrolytes, and the electrode preparation generally adopted a coating process. In the coating process, the binder system has a great influence on the bonding effect of the electrode materials. influences. The binder system in the electrode is mainly to increase the bonding strength of the electrode and prevent the active material from falling off during the cycle charge and discharge process of the electrode. It is very difficult to choose a binder for the water-based ion battery designed with a thick pole piece. The binder must ensure the uniformity and safety of the active material during pulping, and play a role in bonding the active material particles. At the same time, it has good thermal stability and stability to electrolyte. Due to the thick pole piece design, the choice of PTFE as the binder has a series of advantages that other binders do not have, such as making the pole piece powder have a fiber network structure, high porosity, high compressibility, excellent It is resistant to acid and alkali corrosion, not aging, resistant to kneading and denaturation, not easy to drop powder, and has high tensile strength. However, it is very challenging to realize the industrialized mass production of pole pieces. PTFE is used as the binder system of water-based ion batteries, and 60% PTFE emulsion is commonly used as the electrode binder. The difficulty is that irreversible condensation usually occurs during the stirring and mixing process, resulting in poor fluidity of the slurry and poor mixing uniformity. , secondly, due to the poor fluidity of the powder caused by PTFE, it is difficult to solve the problem, which makes it difficult to adopt the dry pressing molding process for the production of thick pole pieces. It is difficult to accurately control the quality and thickness of the electrode sheet in rolling forming to prepare the negative electrode of sodium ion battery, and it is difficult to control the ratio of positive and negative electrodes of the battery, which has a great impact on battery performance and is difficult to guarantee the consistency of the battery. Therefore, there are few literature reports on the large-scale industrial production of thick battery pole piece design using PTFE as the binder of aqueous ion batteries.

Contents of the invention

Aiming at the problems existing in the prior art, the object of the present invention is to provide a pole piece forming method based on polytetrafluoroethylene binder as an aqueous ion battery with short production cycle, cheap equipment, simple process, easy control and suitable for mass production .

Here, the present invention provides a kind of pole piece forming method based on polytetrafluoroethylene (PTFE) binding agent as aqueous ion battery, comprising:

Step 1) Using the ceramic powder used in the electrode of the water-based ion battery and the inorganic carbon source conductive agent as raw materials, using water as a solvent, adding polytetrafluoroethylene as a binder, and ball milling to obtain a uniform slurry;

Step 2) filtering the obtained slurry to obtain a filter cake, and further drying the obtained filter cake to obtain a dry powder;

Step 3) granulating and sieving the obtained dry powder to obtain a granular powder with uniform particle size;

Step 4) The obtained granular powder is prepared in batches into battery pole pieces by a method of dry pressing.

The present invention adopts the method of ball milling to make slurry and joint granulation, and the obtained powder is in the form of granules, which greatly improves the fluidity problem of the powder caused by the binder, and makes the forming of the pole piece easy to control, so it is suitable for dry pressing. Produce thick pole pieces. The thickness of the pole piece obtained by the present invention may be 0-3 mm.

In the present invention, the water-based ion battery may be a water-based sodium-ion battery or a water-based lithium-ion battery.

In the present invention, the pole piece can be a positive pole piece or a negative pole piece. Preferably, the ceramic powder of the positive pole piece is at least one of LiMn ₂ O ₄ , LiFePO ₄ , LiCoO ₂ , LiNiO ₂ , λ-MnO ₂ , and NaMnO ₂ . The ceramic powder of the negative pole piece is at least one of NaTi ₂ (PO4) ₃ and LiTi ₂ (PO4) ₃ .

Preferably, the conductive agent is an inorganic carbon source, preferably at least one of artificial graphite, natural graphite, activated carbon, graphene, carbon black, carbon fiber, and mesoporous carbon.

Preferably, in step 1), the content of the binder is 0-25wt.%, preferably 5-20wt.%, of the ceramic powder.

Preferably, in step 1), the solid content of the obtained slurry is 0-80wt.%, preferably 10-60wt.%.

Preferably, step 1) includes:

After pouring the ceramic powder, conductive agent, solvent and ball milling beads into the ball mill barrel according to a certain ratio, ball milling at a speed of 0 to 300 rpm for less than 5 hours to obtain the first slurry, in which zirconia is used as the ball milling beads. The ball ratio is 1: (3-6); and the binder polytetrafluoroethylene is added to the obtained first slurry, mixed and ball-milled at a speed of 0-300 rpm for less than 5 hours. The problem of poor fluidity can be solved by step-by-step ball milling.

Preferably, in step 2), the equipment used for filtration is a plate and frame filter press or centrifugal filter equipment, and a filter cloth with a pore size of 0-100 μm, preferably 0-50 μm is selected, and after dehydration to a certain humidity, the filter cloth is obtained. The solid on the cloth is further dried in an oven, preferably, the temperature of the oven is set at 80-150°C.

Preferably, in step 3), mechanical granulation is adopted, and the mesh is sieved with a mesh size of 0-5 mm, preferably 0-3 mm. Granulating the prepared powder can increase the fluidity of the powder, and it is easy to control the precision in the process of forming the pole piece, and it is easy to adopt the dry pressing forming process.

Preferably, in step 4), an automatic powder tableting machine is used for tableting. Preferably, an equal volume method is used for tablet compression.

The key point of the present invention is that it is different from the traditional PTFE binder to prepare water-based ionic electrode pole piece coating molding method. It is designed for thick pole piece and adopts the method of ball milling to make slurry and joint granulation, and the obtained powder becomes granular. Greatly improve the fluidity of the powder due to the binder, making the pole piece forming easy to control, combined with the precise weighing system in the powder forming process, the mass error of the pole piece can be controlled within 2%. Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. Through ball mill dispersion and adding binder PTFE, carbon coating of graphite and other active materials can be realized, the porosity of the pole piece can be increased, the specific surface area can be increased, the conductivity of the material can be improved, and the electrochemical performance of the material can be greatly improved;

2. Through mechanical granulation, particles with uniform size distribution can be obtained, which is conducive to improving the flow performance of the powder and creating conditions for powder compression molding;

3. Powder automatic molding equipment, combined with an accurate weighing system, can effectively control the quality of the pole piece and ensure the consistency of the pole piece. In addition, the use of dry pressing molding equipment can ensure that the pressure of the pole piece is adjustable, the thickness is controllable, and the pole piece is extremely stable. All parameters of sheet porosity can be adjusted. Pole piece molding yield is high, suitable for mass production;

4. The invention has short production cycle, cheap equipment, simple process and easy control, and has remarkable practical value and good application prospect.

Description of drawings

Fig. 1 is the flow chart of the batch production water system ion battery pole piece of an example of the present invention;

Fig. 2 is the SEM image of the powder particles obtained after granulation in Example 1;

Fig. 3 is the physical figure of the ceramic pole piece of embodiment 1 batch production, and wherein the left figure is the thickness of test pole piece, and the right figure is the size of test pole piece;

FIG. 4 is a charge-discharge curve diagram of a single battery assembled from pole pieces prepared in batches in Example 1. FIG.

Detailed ways

The present invention will be further described below in conjunction with the drawings and the following embodiments. It should be understood that the drawings and the following embodiments are only used to illustrate the present invention rather than limit the present invention. In addition, the lower limit value of the range value mentioned in the present invention is 0, preferably excluding 0.

The invention provides a method for forming pole pieces based on polytetrafluoroethylene (PTFE) binder as an aqueous ion battery. In the present invention, the water-based ion battery refers to an ion battery with a water-based electrolyte, such as a water-based sodium-ion battery, a water-based lithium-ion battery, and the like. The battery pole piece can be a positive pole piece or a negative pole piece. The present invention is especially suitable for the preparation of thick pole pieces, for example, the thickness can be 0-3mm.

The invention uses several specific raw materials, and obtains slurry with certain viscosity and particle size through a stepwise ball milling method. Through further drying of the slurry, combined with the granulation process, a uniformly mixed and fluid powder is obtained, and the pole pieces are mass-produced under a specific tableting process. Fig. 1 is a flow chart of mass production of pole pieces of aqueous ion batteries according to an example of the present invention. The present invention will be described below with reference to FIG. 1 .

First, mixing is carried out to obtain a slurry. Specifically, active material powders such as ceramic powders and conductive agents (such as carbon sources) used in the positive and negative electrodes of water-based ion batteries are used as raw material powders, water is used as a solvent, and a binder polytetrafluoroethylene (PTFE) is added. , ball milled to obtain a uniform slurry.

The positive electrode ceramic powder can be made of materials commonly used in this field that can intercalate and deintercalate sodium (or lithium) ions, such as LiMn ₂ O ₄ , LiFePO ₄ , LiCoO ₂ , LiNiO ₂ , λ- One or more of MnO ₂ and NaMnO ₂ . The negative electrode ceramic powder can be made of a material with a relatively low intercalation/extraction potential platform that can intercalate and deintercalate sodium (or lithium) ions, such as one or more of NaTi ₂ (PO4) ₃ and LiTi ₂ (PO4) ₃ . The purity of the raw ceramic powder can be industrial grade, and can be synthesized by oneself or purchased commercially.

The carbon source can be an inorganic carbon source, preferably any one or several of artificial graphite, natural graphite, activated carbon, graphene, carbon black, carbon fiber, and mesoporous carbon. The mass ratio of the ceramic powder and the conductive agent may be (50-95): (50-5).

The present invention uses polytetrafluoroethylene (PTFE) as a binder, which can make the pole piece powder have a fiber network structure, high porosity, high compressibility, excellent acid and alkali corrosion resistance, no aging, and Kneading denatured, not easy to drop powder, with high tensile strength and other characteristics. The binder content can be 0-25wt.%, preferably 5-20wt.%, of the raw material powder (including ceramic powder and conductive agent). By changing the amount of the binder, the porosity of the obtained pole piece can be adjusted. For example, within the above range, as the amount of binder increases, the porosity of the pole piece also increases.

For ball milling, zirconia can be used as ball milling beads, and the material-to-ball ratio can be 1:(3-6). The solid content of the obtained slurry is 0-80wt.%, preferably 10-60wt.%. The viscosity of the slurry can be 0-1000Pa.s.

In one example, the slurry with certain viscosity and particle size is obtained by step ball milling method. Specifically, after pouring the powder, solvent, and ball milling beads into a ball mill barrel according to a certain ratio, ball milling at a speed of 0 to 300 rpm for 0 to 5 hours to obtain the first slurry; and in the obtained first slurry Then add the binder PTFE, mix and ball mill for 0-5 hours at a speed of 0-300 rpm. Compared with one-step ball milling, step-by-step ball milling can be evenly milled and effectively disperse PTFE binder.

Next, the slurry is dried. The slurry is first filtered to obtain a filter cake to reduce energy consumption for further powder drying, and then the obtained filter cake is further dried in an oven. The slurry contains a binder, which can control the pores of the filter cloth to control the filtration and dehydration of the slurry. Plate and frame filter press equipment or centrifugal filter equipment can be used. The pores of the filter cloth can be 0-100 μm. After dehydration to a certain humidity, the solid on the filter cloth is obtained, and further dried in an oven to obtain a dry powder. During the drying process, preferably, the temperature of the drying oven is set at 80-150° C. (solvent volatilization temperature). The drying time may range from 0 to 48 hours.

The dry powder is granulated, shaken and sieved to obtain a granular powder. It can be sieved with a mesh of 0-3mm. In this way, powder particles with better fluidity can be obtained, which is convenient for further pole piece forming. Fig. 2 shows the SEM of the granulated powder in an example of the present invention, it can be seen that the powder is in the form of granules.

The obtained granular powder is further compressed into tablets to obtain pole pieces. In the present invention, the method of dry pressing can be adopted, and the positive and negative pole pieces of the battery can be prepared in batches automatically with a powder forming tablet press. Thus, the thickness and strength of the pole pieces can be effectively controlled, and pole pieces with uniform quality can be obtained in batches. When compressing tablets, a self-made specific mold can be used to meet the size required for production. Adjust the pressure of the two-way punch to control the forming thickness and mechanical strength of the pole piece. The porosity of pole piece can be adjusted by the amount of binder. For example, the pressure can be controlled at 0-300MPa. The thickness of the obtained pole piece can be 0-3mm, and its strength can be 0-10Mpa. The porosity of pole piece can be adjusted in the range of 10-70%.

The invention has the advantages of simple process, low cost, uniform ball milling and good powder dispersion. The humidity of the powder obtained by filter press or centrifugal drying is controllable, which reduces energy consumption for further powder drying and is conducive to large-scale production and preparation at low cost. Moreover, the prepared powder adopts the step-by-step ball milling combined granulation method to solve the problem of poor fluidity of the powder due to the binder, which lays the foundation for the mass production of the pole piece, and also provides a guarantee for the performance of the battery, making the commercialization of the battery application can be achieved.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1

Use 60g of positive electrode ceramic powder λ-MnO ₂ , 10g of carbon black as an inorganic carbon source, 15g of activated carbon, and 10g of natural graphite powder as raw materials, use deionized water as a solvent, and control the solid content of the powder to 30wt.%. Zirconium is used as ball milling beads, the ratio of material to ball is 1:5, and the coarse mill is milled at a high speed of 120 rpm/min for 2 hours to obtain a uniform slurry. Continue to add 5wt.% PTFE binder (different amounts of binder added have different effects on pores, see Table 1), further ball mill at 300 rpm for 5 hours, and then pour out the slurry. Filter the obtained slurry with plate-and-frame filter press equipment to obtain a filter cake, and further oven-dry the obtained filter cake, set the temperature at 110°C, and place it for 12 hours to obtain a dry block material, and dry the obtained filter cake The material is mechanically granulated, and sieved by vibration with a 3mm mesh to obtain a granular powder with uniform particle size, which is convenient for further electrode sheet forming. The obtained granular powder is further automatically prepared in batches for battery positive electrodes using a powder forming tablet press. , the pressure is 200MPa.

Fig. 2 is an SEM image of the powder particles obtained after granulation in Example 1. It can be seen that the powder is in the form of granules, and the particle size is relatively uniform. Fig. 3 is a physical picture of the ceramic pole piece mass-produced in Example 1. It can be seen that the surface of the pole piece is smooth and flat, and the thickness is consistent. After testing, the pole piece has a thickness of 2.486mm and a strength of 5.2Mpa.

Table 1 shows the porosity of the pole piece obtained by changing the amount of binder used in Example 1. It can be seen that different amounts of binder added have different effects on the pores;

Table 1 Porosity of pole piece corresponding to different PTFE contents

Referring to Example 1, the pole pieces prepared in batches were assembled into a single battery for testing. The test result was: at a rate of 0.1C, the normal discharge capacity of the battery reached 30Ah (see FIG. 4 ), meeting the performance requirements of the water-based ion battery.

Example 2

70g positive electrode ceramic powder LiMn ₂ O ₄ , inorganic carbon source 5g carbon black, 5g activated carbon, and 10g artificial graphite powder were used as raw materials, deionized water was used as a solvent, and the solid content of the powder was controlled to 30wt.%. Zirconium is used as ball milling beads, the ratio of material to ball is 1:6, and the coarse mill is milled at a high speed of 200 rpm/min for 4 hours to obtain a uniform slurry. Continue to add 10wt.% PTFE binder, further ball mill at 250 rpm for 3 hours, and pour out the slurry. Filter the obtained slurry with plate-and-frame filter press equipment to obtain a filter cake, and further oven-dry the obtained filter cake, set the temperature at 110°C, and place it for 12 hours to obtain a dry block material, and dry the obtained The material is granulated by a swinging granulator, vibrating and sieved with a 1mm mesh to obtain a granular powder with uniform particle size, which is convenient for further electrode sheet forming, and the obtained granular powder is further automatically prepared in batches by a powder forming tablet press machine. Positive pole piece, molding pressure is 300MPa.

After testing, the pole piece has a thickness of 2.512mm, a strength of 8.6Mpa, and a porosity of 35.86%.

Example 3

With 60g of negative electrode ceramic powder NaTi ₂ (PO4) ₃ , 10g of carbon black as an inorganic carbon source, and 15g of natural graphite powder as raw materials, use deionized water as a solvent, control the solid content of the powder to 60wt.%, and use zirconia as Ball milling beads, the ratio of material to ball is 1:3, and the coarse mill is milled at a high speed of 100 rpm/min for 5 hours to obtain a uniform slurry. Continue to add 15wt.% PTFE binder, further ball mill at 300 rpm for 2 hours, and pour out the slurry. Filter the obtained slurry with plate-and-frame filter press equipment to obtain a filter cake, and further oven-dry the obtained filter cake, set the temperature at 110°C, and place it for 12 hours to obtain a dry block material, and dry the obtained filter cake The material is mechanically granulated, and sieved by vibration with a 2mm mesh to obtain a granular powder with uniform particle size, which is convenient for further electrode sheet forming. The obtained granular powder is further automatically prepared in batches for battery negative electrodes using a powder forming tablet press. , the pressure is 300MPa.

After testing, the pole piece has a thickness of 2.623mm, a strength of 8.4Mpa, and a porosity of 40.5%.

Example 4

With 50g of negative electrode ceramic powder LiTi ₂ (PO4) ₃ , 20g of carbon black as an inorganic carbon source, and 10g of natural graphite powder as raw materials, use deionized water as a solvent, control the solid content of the powder to 50wt.%, and use zirconia as Ball mill the beads, the ratio of material to ball is 1:5, and the high speed of the coarse mill is 150 rpm/min for 3 hours to obtain a uniform slurry. Continue to add 20wt.% PTFE binder, further ball mill at 200 rpm for 3 hours, and pour out the slurry. Filter the obtained slurry with plate-and-frame filter press equipment to obtain a filter cake, and further oven-dry the obtained filter cake, set the temperature at 100°C, and place it for 24 hours to obtain a dry block material, and dry the obtained filter cake The material is mechanically granulated, and sieved by vibration with a 2mm mesh to obtain a granular powder with uniform particle size, which is convenient for further electrode sheet forming. The obtained granular powder is further automatically prepared in batches for battery negative electrodes using a powder forming tablet press. , The molding pressure is 100MPa.

After testing, the pole piece has a thickness of 2.684mm, a strength of 4.5Mpa and a porosity of 57.6%.

Industrial Applicability: The method of the present invention reduces the production difficulty and production cost of using PTFE binder as the pole piece forming process of the water-based ion battery, improves the electrochemical performance of the produced pole piece, and lays the foundation for the commercial production of the water-based ion battery .

Claims (10)

1. A pole piece forming method of a water-based ion battery based on polytetrafluoroethylene binder, characterized in that, comprising: Step 1) Use the ceramic powder and inorganic carbon source conductive agent used in the electrode of the water-based ion battery as raw materials, use water as the solvent, add polytetrafluoroethylene as the binder, and ball mill to obtain a uniform slurry; Step 2) Filter the obtained slurry to obtain a filter cake, and further dry the obtained filter cake to obtain a dry powder; Step 3) Granulating and sieving the obtained dry powder to obtain a granular powder with uniform particle size; Step 4) Prepare battery pole pieces in batches from the obtained granular powder by dry pressing. 2. The method according to claim 1, wherein the water-based ion battery is a water-based sodium-ion battery or a water-based lithium-ion battery. 3. The method according to claim 1 or 2, wherein the pole piece is a positive pole piece or a negative pole piece; the ceramic powder of the positive pole piece is LiMn ₂ O ₄ , LiFePO ₄ , LiCoO ₂ , LiNiO _2. At least one of λ-MnO ₂ , NaMnO ₂ ; the ceramic powder of the negative plate is at least one of NaTi ₂ (PO4) ₃ , LiTi ₂ (PO4) ₃ . 4. The method according to any one of claims 1 to 3, wherein the conductive agent is an inorganic carbon source, preferably artificial graphite, natural graphite, activated carbon, graphene, carbon black, carbon fiber, mesoporous at least one of carbon. 5. The method according to any one of claims 1 to 4, characterized in that in step 1), polytetrafluoroethylene (PTFE) is used as the binder, and the content of the binder is 0% of the ceramic powder. ~25wt.%. 6. The method according to any one of claims 1-5, characterized in that, in step 1), the solid content of the obtained slurry is 0-80 wt.%. 7. The method according to any one of claims 1 to 6, wherein step 1) comprises: After pouring the ceramic powder, conductive agent, solvent and ball milling beads into the ball mill barrel according to a certain ratio, ball milling at a speed of 0 to 300 rpm for less than 5 hours to obtain the first slurry, in which zirconia is used as the ball milling beads. The ball ratio is 1: (3-6); and the binder polytetrafluoroethylene is added to the obtained first slurry, mixed and ball-milled at a speed of 0-300 rpm for less than 5 hours. 8. The method according to any one of claims 1 to 7, characterized in that, in step 2), the equipment used for filtration is a plate and frame filter press or centrifugal filter equipment, and the selection is 0-100 μm, The filter cloth with pores of 0-50 μm is preferred. After dehydration to a certain humidity, the solid on the filter cloth is obtained, and further dried in an oven. Preferably, the oven is set at a temperature of 80-150°C. 9 . The method according to any one of claims 1 to 8 , characterized in that, in step 3), mechanical granulation is adopted and sieved with a mesh of 0-5 mm. 10. The method according to any one of claims 1 to 9, characterized in that, in step 4), an automatic powder tableting machine is used for tableting; preferably, an equal volume method is used for tableting.