A method for preparing a continuously produced lithium thionyl chloride composite carbon electrode

Abstract

The present invention discloses a method for preparing a continuously produced lithium thionyl chloride composite carbon electrode, which relates to the field of battery production technology. The method comprises: pre-pressing acetylene black and uniformly mixing it with binder powder to form a powder; subjecting the powder to three steps of mixing, rolling to film formation, and rolling to film bonding at successively increasing temperatures between 80°C and 200°C to complete fiberization, thereby obtaining a lithium thionyl chloride composite carbon electrode. The preparation process of the present invention does not require a baking step, thus saving energy and reducing emissions by more than 50%. The production cycle is shortened from 3 days of wet film rolling or 2 days of semi-dry powder on-line to 1 day. There is no need to use first-level flammable and explosive organic solvents with poor production safety, thereby reducing safety risks and production costs. The growth suitability of the bonding strength of each section of fiberization is controlled through process design, so that the film can be bonded after film formation, and thick electrodes required for higher capacity can be prepared without adverse effects such as de-meshing and floating powder.

Description

Technical Field

[0001] The present invention relates to the technical field of battery production, in particular to a method for preparing a composite carbon electrode for a lithium thionyl chloride power battery. Background Art

[0002] There are currently two methods for preparing lithium thionyl chloride composite carbon electrodes. The first is the traditional wet film rolling method, and the second is the semi-dry powder screen preparation method.

[0003] The first method involves drying the powdered wet paste at 150°C, soaking it in isopropyl alcohol or ethanol, and pressing it into blocks. The blocks are then rolled repeatedly on a rolling mill and cut into thin wet films. After drying, the films shrink into dry films, which are then cut into the required size. The films are then bonded to both sides of the current collector with adhesive, and then flattened, plasticized at high temperatures, and shaped into composite carbon electrodes. This preparation method requires multiple drying cycles, which results in high energy consumption. The wet film absorbs a large amount of first-level flammable and explosive organic solvents through saturated immersion, which is unfriendly to the production environment and detrimental to safety management. After drying, the wet film has poor consistency in size, film density, and flatness, affecting the consistency of the discharge capacity. Multiple cuts produce a large amount of scrap, resulting in a raw material utilization rate of only 50% to 60%. The defects of this method in continuous production are as follows: 1) It requires repeated reversing and rolling to form a film, which is not conducive to continuous film formation; 2) The paste is dehydrated by using electric heating and air drying for 23 to 24 hours, and then hot-immersed in a first-class flammable and explosive organic solvent, and repeatedly reversing and rolling to form a membrane. The membrane is then dried for 10 to 13 hours using a vacuum and solvent recovery system to form a dry membrane. The dry membrane is then bonded to the collecting net with an adhesive, sintered at high temperature, and then pressed into shape. Therefore, the wet film rolling production cycle is as long as 3 days.

[0004] The second method involves passing the mixed semi-dry and wet materials through a 0.5-1.5mm mesh sieve to produce strips 1-2cm long. This material is then passed through a centrifugal pelletizer to produce pellets with a particle size of 0.5-1.5mm. This pellets are then dried and crushed into a fine powder, which is then uniformly mixed with an aqueous solvent to obtain a semi-dry powder. The powder is then placed on a mesh screen, dried, and then passed through a rolling mill to produce a composite carbon electrode of the desired thickness. This preparation method is not suitable for producing thicker composite carbon electrodes. As the mesh thickness increases, more surface powder accumulates, increasing self-discharge losses. Therefore, the thickness is generally not allowed to exceed 2mm. Above 2mm, the powder adheres poorly to the mesh screen, resulting in powder release and failure. The drawbacks of this method in terms of continuous production are: 1) the pellets are vacuum dried for 12-16 hours; 2) the dried pellets are crushed into a fine powder; the fine powder is uniformly mixed with an aqueous solvent to obtain a semi-dry powder; the semi-dry powder is vacuum dried on the mesh screen for 8-10 hours before being rolled into a semi-dry powder. Consequently, the production cycle for the semi-dry powder is as long as two days.

[0005] Both of the above methods require multiple drying steps in the middle, which cannot achieve continuous production of electrodes. Therefore, it is necessary to develop a preparation method for lithium thionyl chloride composite carbon electrodes that is simple in process, does not require solvents, is efficient and safe, and can be continuously produced. Summary of the Invention

[0006] The purpose of the present invention is to solve the shortcomings of the above-mentioned background technology and provide a method for preparing lithium thionyl chloride composite carbon electrode with simple process, no need for solvent, high efficiency and safety, and continuous production, that is, a method of pre-forming a dry powder film and then sandwiching the film.

[0007] The technical solution of the present invention is: a method for preparing a lithium thionyl chloride composite carbon electrode in a continuous production process, comprising:

[0008] Acetylene black is pre-pressed and evenly mixed with binder powder to form a powder. The powder is subjected to three steps of mixing, rolling film formation, and rolling film bonding at a temperature of 80 to 200°C, to complete fiberization, thereby obtaining a lithium thionyl chloride composite carbon electrode.

[0009] Preferably, the acetylene black is pre-pressed by a rolling mill to an apparent specific gravity of 5-7 ml / g, and the acetylene black is mixed with the binder powder for 20-40 minutes after pre-pressing.

[0010] Preferably, the adhesive powder is polytetrafluoroethylene (PTFE) powder with an average particle size of 0.5-10 μm. The mass percentage of the adhesive powder in the powder is 3-6%, and the rest is acetylene black.

[0011] Preferably, the mixing process includes: mixing the materials in a mixer at a temperature of 80-90° C. until the particle size is 0.1-0.5 mm in diameter, thereby achieving initial fiberization.

[0012] Preferably, the roll-forming film process includes: rolling the film at a temperature of 120-150° C. through a rolling mill to achieve mid-section fiberization.

[0013] Preferably, the roll-pressing film bonding process includes: taking two rolls of film with a mesh in between, and bonding the films at 180-200° C. through a rolling mill to achieve final fiberization, thereby obtaining a lithium thionyl chloride composite carbon electrode.

[0014] Preferably, the roller linear speed in the roll film forming and sandwich film closing processes ranges from 2 to 3 m / min.

[0015] Preferably, the temperature conditions of the three steps of mixing, rolling film forming and sandwiching film forming are 80°C, 120°C and 180°C respectively.

[0016] Preferably, the thickness h of the prepared lithium thionyl chloride composite carbon electrode satisfies 4 mm ≥ h ≥ 1 mm. More preferably, 4 mm ≥ h > 2 mm.

[0017] The present invention also provides a lithium thionyl chloride composite carbon electrode, which is prepared by any of the above methods for preparing a lithium thionyl chloride composite carbon electrode in continuous production.

[0018] The beneficial effects of the present invention are:

[0019] 1) The absence of a baking process allows the entire production process to be continuous, saving energy and reducing emissions by more than 50%. The production cycle is shortened from 3 days for wet rolling or 2 days for semi-dry powder to 1 day. There is no need to use Class I flammable and explosive organic solvents with poor production safety, reducing safety risks and production costs.

[0020] 2) Raw material utilization increased from 60% to 95%: The wet film forming process involves slitting and trimming; wet pressing requires reversing direction, requiring slitting after reaching a certain length (slitting results in unusable ends); multiple pressing cycles are required to achieve the required film size and density; repeated pressing in a single direction can damage the pore structure, resulting in a rough surface and cracking; and because continuous film formation is not possible, only wet films are produced one by one (the wet film shrinks after drying), requiring trimming to ensure that the dried film area exceeds the required area. Ultimately, raw material utilization is only 60%. The present invention, however, enables continuous film formation, resulting in stable film dimensions that directly meet the required size, without waste from slitting and trimming, and a 100% yield rate, saving energy and protecting the environment.

[0021] 3) The present invention eliminates the need for drying equipment and mucous membranes, which require a large area of ​​land. The land area required for lithium thionyl chloride composite carbon electrode production is reduced by 60% to 70%. The present invention reduces labor requirements by 70% to 80%. Through continuous film formation, the use of mucous membranes and wet film formation, which require a large number of workers, is eliminated.

[0022] 4) This method improves the adhesiveness of the fully fiberized binder without destroying its structure. Through process design, the growth of adhesive strength at each stage of fiberization is controlled to achieve the desired level of film bonding after film formation. This solves the challenges of existing lithium-thionyl chloride power-type composite carbon electrodes, which cannot be bonded or bonded continuously. Furthermore, it enables the production of thicker electrodes required for higher capacity, without the negative impacts of debonding or floating powder on product quality.

[0023] 5) By pre-pressing acetylene black to a volume specific gravity of 5~7ml / g, the volume is reduced, and the amount of adhesive can be reduced while film formation is achieved. Reducing the amount of adhesive can reduce impedance and enhance the catalytic effect of acetylene black, thereby increasing the load voltage level and high current capacity.

[0024] 6) The present invention realizes a composite film preparation method of pre-filming and then sandwiching the mesh, which solves the problem that dry powder mesh cannot be used to prepare composite carbon electrodes larger than 2mm. This is because as the thickness of the mesh increases, more powder will float on the surface, which will increase the self-discharge loss; and when the adhesion to the mesh is insufficient, it will fall off the mesh, causing an increase in internal resistance, thereby reducing the discharge voltage level and increasing energy internal consumption.

[0025] 7) Although wet film preparation can produce composite carbon electrodes larger than 2mm, it is not easy to achieve continuous production and requires multiple drying times with high energy consumption; multiple cuttings produce a lot of scraps, resulting in a raw material utilization rate of only 50%~60%; the wet film uses a saturated immersion method to absorb a large amount of first-level flammable and explosive organic solvents, which is not friendly to the production environment and is not conducive to safety control. After drying, the wet film has poor consistency in size, film density, and flatness, which affects the consistency of the discharge capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the discharge curve of the ER26M lithium primary battery at 700mA constant current discharge to 2V. DETAILED DESCRIPTION

[0027] The following will be clearly and completely described with reference to the embodiments of the present invention and the technical effects produced, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without paying creative work all fall within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased commercially.

[0028] The present invention provides a method for preparing a lithium thionyl chloride composite carbon electrode for continuous lithium production, comprising:

[0029] Acetylene black is pre-pressed and evenly mixed with binder powder to form a powder. The powder is subjected to three steps of mixing, rolling and film forming, and sandwiching the film at a temperature of 80 to 200°C, to complete fiberization, thereby obtaining a lithium thionyl chloride composite carbon electrode.

[0030] In some optional embodiments, acetylene black is pre-pressed to an apparent specific gravity of 5-7 ml / g and then mixed with a binder powder for 20-40 minutes to form a powder. The binder powder is polytetrafluoroethylene (PTFE) powder with an average particle size of 0.5-10 μm. The binder powder comprises 3-6% by weight of the powder, with the remainder being acetylene black.

[0031] In some optional embodiments, the mixing step includes: mixing the materials in a mixer at a temperature of 80-90° C. to a particle size of 0.1-0.5 mm to achieve initial fiberization.

[0032] In some optional embodiments, the roll-to-film forming process includes: rolling the film at a temperature of 120-150° C. using a rolling mill, with a roller linear speed ranging from 2-3 m / min, to achieve mid-section fiberization.

[0033] In some optional embodiments, the mesh-sandwiching film-closing process includes: taking two rolls of film and sandwiching a mesh in the middle, and combining the films at a temperature of 180-200° C. through a rolling mill to achieve final fiberization to obtain a lithium thionyl chloride composite carbon electrode.

[0034] The linear speed range of rollers for film forming and film clamping is 2~3m / min.

[0035] The thickness h of the lithium thionyl chloride composite carbon electrode prepared above satisfies 4 mm ≥ h ≥ 1 mm. In some optional embodiments, 4 mm ≥ h > 2 mm.

[0036] The present application will be further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application. Example 1

[0037] This embodiment provides a method for preparing a lithium thionyl chloride composite carbon electrode in a continuous production process, and the steps are as follows:

[0038] 1) Acetylene black pretreatment: First, pre-press the acetylene black to a volume specific gravity of 5-7 ml / g (specifically 5 ml / g in this embodiment);

[0039] 2) Mixing powder: Using a mixer, add a binder (polytetrafluoroethylene (PTFE) powder, average particle size 0.5-10 μm) to acetylene black and mix uniformly for 20-40 minutes to form a powder. The binder powder content in the powder is 3% by weight (specifically 3% in this embodiment);

[0040] 3) Initial fiberization: Heat the mixer to 80°C and continue mixing until the particle size is 0.1-0.5 mm.

[0041] 4) Intermediate fiberization and film making: The powder particles after the initial fiberization are pre-pressed into a thick film through a rolling mill at a temperature of 120°C, and then thinned into a composite carbon electrode membrane of the required size through continuous roller pressing, wherein the roller linear speed is specifically 3m / min;

[0042] 5) Final fiber composite membrane: Take 2 rolls of composite carbon electrode membrane, sandwich a mesh in the middle (the mesh material can generally be nickel mesh), and pass the membrane through a rolling mill at a temperature of 180°C to form a composite carbon electrode of the required size, where the roller linear speed is specifically 3m / min. Example 2

[0043] This embodiment provides a method for preparing a lithium thionyl chloride composite carbon electrode in a continuous production process, and the steps are as follows:

[0044] 1) Acetylene black pretreatment: First, pre-press the acetylene black to a volume specific gravity of 5-7 ml / g (specifically 7 ml / g in this embodiment);

[0045] 2) Mixing powder: Use a mixer to add binder (polytetrafluoroethylene (PTFE) powder, average particle size 0.5-10 μm) to acetylene black and mix evenly for 20-40 minutes to form a powder. The binder powder content in the powder is 6% by mass.

[0046] 3) Initial fiberization: Heat the mixer to 90°C and continue mixing until the particle size is 0.1-0.5 mm.

[0047] 4) Intermediate fiberization and film making: The powder particles after the initial fiberization are pre-pressed into a thick film through a rolling mill at a temperature of 150°C, and then thinned into a composite carbon electrode membrane of the required size through continuous rolling, wherein the roller linear speed is specifically 2m / min;

[0048] 5) Final fiber composite membrane: Take 2 rolls of composite carbon electrode membrane, sandwich a mesh in the middle (the mesh material can generally be nickel stretched mesh), and pass the membrane through a rolling mill at a temperature of 200°C to form a composite carbon electrode of the required size, wherein the roller linear speed is specifically 2m / min. Example 3

[0049] This embodiment provides a method for preparing a lithium thionyl chloride composite carbon electrode in a continuous production process, and the steps are as follows:

[0050] 1) Acetylene black pretreatment: First, pre-press the acetylene black to a volume specific gravity of 5-7 ml / g (specifically 6 ml / g in this embodiment);

[0051] 2) Mixed powder: Use a mixer to add binder (polytetrafluoroethylene (PTFE) powder, average particle size 0.5-10 μm) to acetylene black and mix evenly for 20-40 minutes to form a powder. The binder powder content in the powder is 4.5% by mass.

[0052] 3) Initial fiberization: Heat the mixer to 85°C and continue mixing until the particle size is 0.1-0.5 mm in diameter;

[0053] 4) Intermediate fiberization and film making: The powder particles after the initial fiberization are pre-pressed into a thick film through a rolling mill at a temperature of 135°C, and then thinned into a composite carbon electrode membrane of the required size through continuous roller pressing, wherein the roller linear speed is specifically 2.5m / min;

[0054] 5) Final fiber composite membrane: Take 2 rolls of composite carbon electrode membrane, sandwich a mesh in the middle (the mesh material can generally be nickel mesh), and pass the membrane through a rolling mill at a temperature of 190°C to form a composite carbon electrode of the required size, where the roller linear speed is specifically 2.5m / min. Example 4

[0055] This embodiment provides a method for preparing a lithium thionyl chloride composite carbon electrode in a continuous production process, and the steps are as follows:

[0056] 1) Acetylene black pretreatment: First, pre-press the acetylene black to a volume specific gravity of 5-7 ml / g (specifically 5.5 ml / g in this embodiment);

[0057] 2) Mixing powder: Use a mixer to add binder (polytetrafluoroethylene (PTFE) powder, average particle size 0.5-10 μm) to acetylene black and mix evenly for 20-40 minutes to form a powder. The binder powder content in the powder is 3% by weight.

[0058] 3) Initial fiberization: Heat the mixer to 85°C and continue mixing until the particle size is 0.1-0.5 mm in diameter;

[0059] 4) Intermediate fiberization and film making: The powder particles after the initial fiberization are pre-pressed into a thick film through a rolling mill at a temperature of 150°C, and then thinned into a composite carbon electrode membrane of the required size through continuous rolling, wherein the roller linear speed is specifically 2.5m / min;

[0060] 5) Final fiber composite membrane: Take 2 rolls of composite carbon electrode membrane, sandwich a mesh in the middle (the mesh material can generally be nickel mesh), and pass the membrane through a rolling mill at a temperature of 190°C to form a composite carbon electrode of the required size, where the roller linear speed is specifically 2.5m / min.

[0061] Comparative Example (Wet)

[0062] This comparative example adopts the wet method to prepare the carbon positive electrode, and the steps are as follows:

[0063] 1) Powder pretreatment: Mix 1000g acetylene black, 30g anhydrous alcohol, 60g positive electrode conductive copper powder, 70g polytetrafluoroethylene emulsion binder, and 7000g pure water to form a wet material and stir evenly; place the wet material in a 150℃ electric heating blast drying oven for 23~24h to form a paste;

[0064] 2) Wet rolling: the obtained paste is soaked in alcohol for 10 minutes and then rolled into a wet film; the wet film is placed in a vacuum drying oven at 120℃ and dried for 10 hours to form a dry film;

[0065] 3) Adhesive film: Use adhesive to bond the dry film collector mesh together and place it in a 240℃ oven for 15 minutes to sinter;

[0066] 4) Positive electrode forming: The sintered positive electrode is shaped by a finishing mill, cut and spot welded to form the positive electrode cover assembly.

[0067] Comparative example (semi-wet)

[0068] This comparative example adopts the semi-wet method to prepare the carbon positive electrode, and the steps are as follows:

[0069] 1) Powder pretreatment: 1000g of acetylene black, 6g of anhydrous alcohol, 60g of copper powder as a cathode conductive agent, 70g of polytetrafluoroethylene emulsion binder, and 3000g of pure water were mixed to form a wet material and stirred evenly. The wet material was extruded into strips with a 0.5mm mesh size through an extruder to obtain strips with a length of 1-2cm. The strips were then passed through a centrifugal pelletizing machine to obtain fine pellets with a particle size of 0.5mm. The fine pellets were then dried in a vacuum drying oven at 100°C for 12 hours.

[0070] 2) Powder screen: The obtained dried fine pellets are crushed into fine powder with a particle size of 0.1-0.2 μm; the powder is evenly mixed with a 50% alcohol aqueous solution at a mass ratio of 1:2.2 to form a semi-dry powder; the semi-dry powder is evenly sprinkled onto both sides of the nickel mesh through an impeller feeder, and the powder is bonded to the nickel mesh through a rolling mill; the nickel mesh with the semi-dry powder is placed in a vacuum drying oven at 120°C for 8 hours; the positive nickel mesh is placed in a 240°C oven for 15 minutes to maintain heat and fiberize;

[0071] 3) Positive electrode forming: The fibrous positive electrode nickel mesh is rolled by a finishing mill for shaping, cut and cleaned, and then the positive electrode cover assembly is spot welded to form the positive electrode.

[0072] Performance Testing

[0073] The carbon electrodes prepared in Example 1 and the comparative example were assembled into ER26M lithium primary batteries, and performance tests were conducted using a constant current discharge of 700 mA to 2 V. The capacity (mAh) was used as an indicator. The results are shown in Table 1, and the corresponding discharge curves are shown in Table 2. Figure 1 .

[0074] Table 1 700mA constant current discharge to 2V capacity (mAh) performance comparison

[0075]

[0076] As can be seen from the table above, the simplest formula is used. The carbon electrode prepared by the preparation method of the present invention is assembled into an ER26M lithium primary battery, and its high current capacity is increased by 10% to 15%.

[0077] The carbon electrodes prepared in Example 1 and the comparative example were assembled into ER42M lithium primary batteries, and performance tests were performed using constant current discharge to 2V capacity (mAh) as an indicator. The results are shown in Tables 2 and 3. The capacity retention rate was tested at 70°C for 90 days, and the results are shown in Table 4.

[0078] Table 2 Performance comparison of 400mA constant current discharge to 2V capacity (mAh)

[0079]

[0080] As can be seen from Table 2, compared with the comparative example, the advantages of assembling the ER42M lithium primary battery using the carbon electrode prepared by the preparation method of the present invention are as follows: the capacity value of the present invention is optimal in electrode designs of different thicknesses; and a higher capacity value can be obtained as the electrode thickness increases.

[0081] Table 3 100mA constant current discharge to 2V capacity (mAh) performance comparison

[0082]

[0083] It can be seen from the data in Table 3 that, compared with the comparative example, the carbon electrode prepared by the preparation method of the present invention and assembled into an ER42M lithium primary battery has the following advantages: the capacity value of the present invention is optimal in electrode designs of different thicknesses; and a higher capacity value can be obtained as the electrode thickness increases.

[0084] Table 4 100mA constant current discharge to 2V capacity (mAh) performance comparison

[0085]

[0086] It can be seen from the data in Table 4 that, compared with the comparative example, the carbon electrode prepared by the preparation method of the present invention and assembled into the ER42M lithium primary battery has the following advantages: after storage at 70°C for 90 days (equivalent to storage at 23°C for 10 years), the capacity retention rate is as high as 96%, which is much better than the comparative example.

Claims

1. A method for preparing a lithium thionyl chloride composite carbon electrode for continuous production, characterized in that: include: The acetylene black is pre-pressed to an apparent specific gravity of 5-7 ml / g by a rolling mill and then uniformly mixed with a binder powder to form a powder. The mixing time is 20-40 minutes. The binder powder is polytetrafluoroethylene (PTFE) powder with an average particle size of 0.5-10 μm. The binder powder in the powder has a mass percentage of 3-6%, and the rest is acetylene black. The powder is subjected to three steps of mixing, rolling film formation, and sandwiching and film closing at a temperature condition increasing in sequence between 80 and 200°C to complete fiberization. The mixing step includes: mixing the powder by a mixer at a temperature condition of 80 to 90°C to a particle size diameter of 0.1 to 0.5 mm, thereby achieving initial fiberization; the rolling film forming step includes: rolling film formation by a rolling mill at a temperature condition of 120 to 150°C, thereby achieving middle fiberization; the sandwiching and film closing step includes: taking two rolls of film and sandwiching a mesh in the middle, and closing the film by a rolling mill at a temperature condition of 180 to 200°C to achieve final fiberization, thereby obtaining a lithium thionyl chloride composite carbon electrode, wherein the thickness h of the lithium thionyl chloride composite carbon electrode satisfies 4mm≥h≥1mm.

2. The method for preparing a lithium thionyl chloride composite carbon electrode for continuous production according to claim 1, wherein: The roller linear speed range in the roller pressing film forming and the clamping film closing process is 2-3 m / min.

3. The method for preparing a lithium thionyl chloride composite carbon electrode for continuous production according to claim 1, wherein: The temperature conditions of the three processes of mixing, rolling to form a film, and sandwiching and closing the film are 80° C., 120° C., and 180° C. respectively.

4. A lithium thionyl chloride composite carbon electrode, characterized in that The lithium thionyl chloride composite carbon electrode is prepared by the preparation method of any one of claims 1 to 3 for continuous production.

Images