Ultrathin graphite felt and preparation method thereof

Abstract

The invention discloses an ultrathin graphite felt and a preparation method thereof. According to the preparation method, a spunlace and needling combined process is adopted, a pre-oxidized silk screen tire of 10-80 g / cm < 2 > is prepared through the spunlace process, then the pre-oxidized silk screen tire is stacked in a multi-layer mode, then water needle needling is further conducted, a spunlace felt of 120-320 g / cm < 2 > is formed through needling, the thickness is smaller than or equal to 1.5 mm, then needling is further conducted, the thickness is smaller than or equal to 1.2 mm, and finally carbonization and graphitization are conducted to prepare the ultrathin graphite felt. The graphite felt prepared by the invention is thin in thickness and short in proton transmission distance, and the prepared electrode material is higher in operation efficiency.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and in particular to an ultra-thin graphite felt and a preparation method thereof. Background Art

[0002] Currently, the electrode fabric used in flow batteries is primarily graphite felt that has been surface-treated to make it hydrophilic, typically with a thickness of 2.0mm or more. Traditional needle-punched fabrics below 2.0mm yield relatively poor uniformity, making them difficult to manufacture thinner. Furthermore, the electrode reaction depth in flow batteries is approximately 0.3mm. This means that if a 2.0mm electrode is used, the utilization rate is only 15%, with as much as 85% of the area wasted. Fuel cells and some PEM and AEM electrolyzers also use carbon electrodes, typically graphitized carbon paper and carbon cloth. The main drawback of carbon paper is its brittleness, while the main drawback of carbon cloth is its severe edge raveling and brittleness, making it prone to breakage and damage. This is especially true in PEM and AEM electrolyzers, where internal pressures exceed 2 MPa, which can easily crush carbon paper. In both flow batteries and fuel cells, carbon materials serve as electrodes. Thinner thickness reduces mass transfer distances, reduces internal resistance, and allows for significantly thinner battery structures, further increasing energy density.

[0003] Based on the above, the existing technology has the following problems: (1) The thickness of the uniform needle-punched felt made by the needle-punching process is limited. Generally, the thickness of the pre-oxidized wire felt is about 2.3mm, and the thickness after graphitization is about 2.0mm, which is still relatively thick; (2) The electrode felt with a thickness below 2.5mm has a low density, poor structural stability, and poor thickness and density uniformity; (3) The thickness of the electrode cloth can be made within 1mm, but its density is generally 0.45g / cm 3 The density is too high, which is not conducive to the diffusion and flow of the electrolyte. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an ultra-thin graphite felt and a preparation method thereof.

[0005] In a first aspect, the present invention provides a method for preparing ultrathin graphite felt, which is achieved through the following technical solutions.

[0006] A method for preparing ultrathin graphite felt comprises the following steps:

[0007] S1. Opening

[0008] The pre-oxidized silk fibers are chopped into short fibers, and then the fibers are crimped and opened, with an opening strength of ≤3.0m / s;

[0009] S2. Hydroentanglement stage

[0010] The opened fibers are laid into a pre-oxidized wire mesh with a CV value of ≤8%. The mesh is stacked and laid, and punctured with a water needle. The water needle puncture control parameters are as follows: water needle pressure: 40-60 bar in the pre-wetting area, 80-120 bar in the main reinforcement area; water flow rate per hole: 1.8-2.5 L / min·m; hydroentanglement density: 60-80 holes / cm 2 , double-sided spunlace;

[0011] After spunlace, pre-dry with hot air at 40-120℃ to reduce the moisture content to 15%-20%. At the same time, the surface density deviation of the spunlace is controlled to ≤±3%, and the thickness after spunlace is controlled to 0.5-2.0mm;

[0012] S3. Acupuncture stage

[0013] Needling pressure: 0.4-0.8MPa; needling is completed in three passes, with a total density of 150-180 needles / cm 2 , acupuncture speed: 2.0-2.5m / min; pre-puncture depth: 6-8mm, main puncture depth: 10-12mm; acupuncture compression ratio: 30%-45%;

[0014] S4. Carbonization and Graphitization

[0015] The pierced pre-oxidized thin fiber felt is carbonized and graphitized to produce ultra-thin graphite felt.

[0016] Furthermore, in step S1, pre-oxidized silk fibers with a limiting oxygen index of 38-45% and a diameter of 1.5-2.4 Dtex are selected, chopped into short fibers of 30-120 mm, and then the fibers are curled with a curl of 3-5 per cm; environmental control: humidity 40-70%, temperature 15-35°C, to prevent static electricity.

[0017] Furthermore, in step S2, the opened fibers are laid into a pre-oxidized wire mesh of 10-80 g / cm2, using a fork laying and random laying method; 10-25 layers of the mesh are stacked and laid for water needle puncture.

[0018] Furthermore, in step S2, the water needle nozzle is made of sapphire material with an aperture of 0.10-0.12 mm; the production line speed is 4-6 m / min; and the water spunlace power is 0.8-1.2 kWh / kg.

[0019] Furthermore, in step S3, the pre-puncture needle selects a conical tooth needle with a size parameter of 15mm×18mm, a needle specification of 36Gauge×38mm, and a needle density of 600-1000 needles / m; the main puncture needle selects a micro-tooth needle with a size parameter of 40mm×40mm, a needle specification of 40Gauge×40mm, and a needle density of 1000-1500 needles / m.

[0020] Furthermore, in step S3, the needle plate is arranged in a "herringbone" pattern.

[0021] Furthermore, in step S3, the acupuncture pressure is increased in stages, and the acupuncture pressure is increased from the lowest set pressure to the highest set pressure for multiple times.

[0022] Furthermore, in step S4, the punctured pre-oxidized filament felt is unwound into a continuous carbonization graphitization furnace, and nitrogen or argon is introduced for ventilation for 4-6 hours, and the pressure in the furnace is maintained at 0.2-0.5 MPa. The material enters the furnace at a speed of 200-500 mm / min. There are 20 temperature zones in the furnace, and the temperature of the carbonization temperature zone is maintained at 1200°C and the temperature of the graphitization temperature zone is maintained at 2200°C.

[0023] In a second aspect, the present invention provides an ultra-thin graphite felt, which is achieved through the following technical solutions.

[0024] An ultra-thin graphite felt prepared by the above preparation method.

[0025] This application has the following beneficial effects.

[0026] 1. The graphite felt of the present invention has uniform thickness and density; 2. The graphite felt of the present invention has high density, and the conventional density exceeds 30% of the fully needled felt with a thickness of about 2.0 mm. It has a compact structure, high mechanical stability, high strength, compact fiber overlap, and lower internal resistance; 3. Due to its high surface density and uniform surface, the graphite felt of the present invention has more complete contact with the bipolar plate and the proton membrane, resulting in lower contact resistance; 4. The graphite felt of the present invention is thin, the proton transmission distance is short, and the electrode material produced has higher operating efficiency; 5. The high density and compact structure make the graphite felt of the present invention resistant to electrolyte impact The brushing capacity is improved, so the service life of the entire battery stack or electrolytic cell is further increased; 6. The graphite felt of the present invention has a compact structure and close fiber overlap, which is not easy to de-fiber and delaminate, solving the problem of fiber loosening and shedding when using carbon cloth electrodes; 7. The present invention first hydroentangles and then needle-punches, which causes less damage to the fibers than direct needle-punching and spinning and weaving. Hydroentanglement can gently achieve fiber surface entanglement and reduce the mechanical damage of subsequent needle-punching to the brittle pre-oxidized yarn; the stepped pressure design takes into account the low-strength characteristics of the pre-oxidized yarn; the composite process significantly improves the strength of the felt body - hydroentanglement provides lateral bonding force, and needle-punching enhances longitudinal density. DETAILED DESCRIPTION

[0027] The present invention uses a combination of spunlace and needle punching processes. First, a pre-oxidized wire mesh of 10-80 g / cm2 is made by the spunlace process. The mesh is then stacked in multiple layers and further needle punched to form a spunlace felt of 120-320 g / cm2 with a thickness of ≤1.5 mm. Further needle punching is then performed to make its thickness ≤1.2 mm. Finally, carbonization and graphitization are performed to form an ultra-thin graphite felt.

[0028] The invention is further described below with reference to the following examples. Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials, reagents, etc. used in the following preparation examples and examples are all commercially available unless otherwise specified.

[0029] Example 1

[0030] A method for preparing ultrathin graphite felt comprises the following steps:

[0031] 1. Opening:

[0032] Select pre-oxidized filaments with a limiting oxygen index of 42% and a diameter of 2.2 Dtex and chop them into 53mm staple fibers. Then, crimp the fibers to a crimp density of 3 per centimeter. Open the fibers at a speed of 2.0 m / s to minimize fiber damage. Environmental control: Humidity 60% ± 5%, temperature 25°C ± 2°C, and prevent static electricity.

[0033] 2. Spunlace stage:

[0034] The mesh laying machine lays the mesh into a 15g / cm2 pre-oxidized wire mesh. The mesh is laid using a fork-laying and random meshing method, with a CV value (uniformity) of 5% to ensure uniformity. Then, 15 layers of mesh are stacked and laid, and punctured with a water needle. The water needle pressure is 45 bar in the pre-wetting area and 90 bar in the main reinforcement area. The water needle nozzle is made of sapphire and has a pore size of 0.12mm. The water flow rate per hole is 2.2L / min·m. The hydroentanglement density is 80 holes / cm 2 (Double-sided spunlace). Line speed 4m / min. Spunlace power 1.2kWh / kg.

[0035] 3. Acupuncture stage:

[0036] Needling pressure: 0.4-0.55MPa (increased in stages, three times of needling, with needling pressures of 0.4Mpa, 0.45Mpa, and 0.55Mpa respectively). Pre-needling needles are conical tooth needles (15×18), needle specifications are 36Gauge×38mm, and the needling density is 700 needles / m. Main needling needles are micro-tooth needles (40×40), needle specifications are 40Gauge×40mm, and the needling density is 1000 needles / m. Needling density: total density is 160 needles / cm 2 Needling speed: 2.0 m / min (completed in three passes) to avoid excessive fiber damage. Pre-needling depth: 6 mm to initially bind the fiber web. Main needle depth: 10 mm to increase felt density. Needle board arrangement: A herringbone pattern is used to enhance fiber disorder.

[0037] 4. Key process linkage control:

[0038] Transition from hydroentanglement to needlepunching:

[0039] (1) Pre-dry with hot air at 80°C after hydroentanglement (moisture content reduced to 20%) to avoid wet needle puncture and damage to the fiber;

[0040] (2) The surface density deviation of spunlace is controlled to ≤±2% to ensure the uniformity of needle punching.

[0041] Thickness control strategy:

[0042] (1) Thickness after hydroentanglement: 1.0 mm;

[0043] (2) Needle compression ratio: 40% (final 1.0 ± 0.05 mm);

[0044] (3) Real-time monitoring by online thickness gauge (laser sensor accuracy ±0.01mm).

[0045] 5. Carbonization and graphitization

[0046] Using a continuous carbonization and graphitization furnace, the pre-oxidized filament felt is unwound and placed into the furnace. Nitrogen is introduced for four hours, and the air is driven out. The furnace pressure is maintained at 0.3 MPa, and the material is fed into the furnace at a speed of 400 mm / min. The furnace has 20 temperature zones, each 2 meters long. Zones 1-3 operate at 200°C, 600°C, and 1000°C; zones 4-8 operate at 1200°C; zones 9-11 operate at 1400°C, 1700°C, and 2000°C; zones 12-16 operate at 2200°C; and zones 17-20 operate at 2000°C, 1600°C, 1200°C, and 800°C. A graphite felt with a thickness of 0.8 mm is produced.

[0047] 6. Testing:

[0048] (1) Square resistance test: The square resistance value was measured at five locations on the hardened and reactivated hard fabric electrode using a probe square resistance tester. The average square resistance was ≤0.5Ω.

[0049] (2) Thickness detection: Use Shanghai Kaifa thickness gauge (model JD 400So) to measure the thickness of 0.8mm±7.5%;

[0050] (3) Strength test: The breaking strength of the electrode felt is ≥10N according to the national standard GB / T 3923.2-2013.

[0051] Example 2

[0052] A method for preparing ultrathin graphite felt comprises the following steps:

[0053] 1. Opening:

[0054] Pre-oxidized fiber with limited oxygen index of 45% and diameter of 1.5Dtex is cut into 62mm staple. Then the fiber is crimped with crimp degree of 5 / cm. The fiber is opened with opening intensity of 3m / s at low speed to avoid fiber damage. Environmental control: humidity 50%±5%, temperature 25℃±2℃, and static electricity is prevented.

[0055] 2. Spunlace stage:

[0056] The pre-oxidized fiber web with a weight of 20g / m2 is prepared by a laying machine. Fork laying and random laying are used in the laying process, and the CV value (uniformity) is 6% to ensure uniformity. Then 13 layers of web are stacked and punctured by water needles. Water needle pressure: 50bar in pre-wetting area and 100bar in main reinforcement area. The water needle nozzle is made of sapphire material with a pore size of 0.12mm. The water flow rate is 2.0L / min·m. Spunlace density: 80 holes / cm 2 (double-sided spunlace). Production line speed: 6m / min. Spunlace power: 1.2kWh / kg.

[0057] 3. Needle punching stage:

[0058] Needle punching pressure: 0.45-0.6MPa (increased in stages, three times of needle punching, with needle punching pressure of 0.45Mpa, 0.5Mpa and 0.6Mpa respectively). Pre-punching needle: conical tooth needle (15×18), needle gauge: 36Gauge×38mm, needle density: 800 needles / m. Main punching: micro-tooth needle (40×40), needle gauge: 40Gauge×40mm, needle density: 1200 needles / m. Needle punching density: total density 180 needles / cm 2 (completed in 3 stages), needle punching speed: 2.5m / min, to avoid excessive damage to the fiber. Pre-punching depth: 8mm, to preliminarily hold the web. Main punching depth: 12mm, to improve the density of the felt. Needle plate arrangement: "herringbone" needle arrangement is used to enhance the randomness of the fiber.

[0059] 4. Key process linkage control:

[0060] Transition from spunlace to needle punching:

[0061] (1) After spunlace, hot air pre-drying at 80℃ (moisture content reduced to 15%) to avoid wet needle punching and fiber damage;

[0062] (2) Spunlace surface density deviation control ≤±3%, to ensure uniformity of needle punching.

[0063] Thickness control strategy:

[0064] (1) Thickness after spunlace: 1.2mm;

[0065] (2) Needle punching compression ratio: 45% (final thickness: 1.2±0.06mm).

[0066] (3) Real-time monitoring by online thickness gauge (laser sensor accuracy ±0.01mm).

[0067] 5. Carbonization and graphitization

[0068] Using a continuous carbonization and graphitization furnace, the pre-oxidized filament felt is unwound and placed into the furnace. Argon gas is introduced for 5 hours, air is expelled, and the furnace pressure is maintained at 0.25 MPa. The material enters the furnace at a speed of 350 mm / min. The furnace has 20 temperature zones, each 2 meters long. Zones 1-3 operate at 200°C, 500°C, and 800°C; zones 4-8 operate at 1000°C; zones 9-11 operate at 1300°C, 1600°C, and 1900°C; zones 12-16 operate at 2000°C; and zones 17-20 operate at 1800°C, 1500°C, 1200°C, and 800°C. A graphite felt with a thickness of 0.72 mm is produced.

[0069] 6. Testing:

[0070] (1) Square resistance test: The square resistance value was measured at five locations on the hardened and reactivated hard fabric electrode using a probe square resistance tester. The average square resistance was ≤0.5Ω.

[0071] (2) Thickness detection: Use Shanghai Kaifa thickness gauge (model JD 400So) to measure the thickness of 1.0mm±7.5%;

[0072] (3) Strength test: The breaking strength of the electrode felt is ≥10N according to the national standard GB / T 3923.2-2013.

[0073] The embodiments of this specific implementation method are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing ultrathin graphite felt, characterized in that: The following steps are involved: S1. Opening The pre-oxidized silk fibers are chopped into short fibers, and then the fibers are crimped and opened, with an opening strength of ≤3.0m / s; S2. Hydroentanglement stage The opened fibers are laid into a pre-oxidized wire mesh with a CV value of ≤8%. The mesh is stacked and laid, and punctured with a water needle. The water needle puncture control parameters are as follows: water needle pressure: 40-60 bar in the pre-wetting area, 80-120 bar in the main reinforcement area; water flow rate per hole: 1.8-2.5 L / min·m; hydroentanglement density: 60-80 holes / cm 2 , double-sided spunlace; After spunlace, pre-dry with hot air at 40-120℃ to reduce the moisture content to 15%-20%. At the same time, the surface density deviation of the spunlace is controlled to ≤±3%, and the thickness after spunlace is controlled to 0.5-2.0mm; S3. Acupuncture stage Needling pressure: 0.4-0.8MPa; needling is completed in three passes, with a total density of 150-180 needles / cm 2 , acupuncture speed: 2.0-2.5m / min; pre-puncture depth: 6-8mm, main puncture depth: 10-12mm; acupuncture compression ratio: 30%-45%; S4. Carbonization and Graphitization The pierced pre-oxidized thin fiber felt is carbonized and graphitized to produce ultra-thin graphite felt.

2. The method for preparing an ultrathin graphite felt according to claim 1, wherein: In step S1, pre-oxidized silk fibers with a limiting oxygen index of 38-45% and a diameter of 1.5-2.4 Dtex are selected, chopped into staple fibers of 30-120 mm, and then curled with a curl of 3-5 per cm; environmental control: humidity 40-70%, temperature 15-35°C, and static electricity prevention.

3. The method for preparing an ultrathin graphite felt according to claim 1, wherein: In step S2, the opened fibers are laid into a pre-oxidized wire mesh of 10-80 g / cm2, using a fork laying and random laying method; 10-25 layers of the mesh are stacked and laid for water needle puncture.

4. The method for preparing an ultrathin graphite felt according to claim 1, wherein: In step S2, the water needle nozzle is made of sapphire with an aperture of 0.10-0.12 mm; the production line speed is 4-6 m / min; and the water spunlace power is 0.8-1.2 kWh / kg.

5. The method for preparing an ultra-thin graphite felt according to claim 1, wherein: In step S3, the pre-needle is a conical tooth needle with a size parameter of 15mm×18mm, a needle specification of 36Gauge×38mm, and a needle density of 600-1000 needles / m; the main needle is a micro-tooth needle with a size parameter of 40mm×40mm, a needle specification of 40Gauge×40mm, and a needle density of 1000-1500 needles / m.

6. The method for preparing an ultrathin graphite felt according to claim 1, wherein: In step S3, the needle plate is arranged in a "herringbone" pattern.

7. The method for preparing an ultrathin graphite felt according to claim 1, wherein: In step S3, the acupuncture pressure is increased in stages, and the acupuncture pressure is increased from the lowest set pressure to the highest set pressure for multiple times.

8. The method for preparing an ultrathin graphite felt according to claim 1, wherein: In step S4, the punctured pre-oxidized filament felt is unwound into a continuous carbonization graphitization furnace, and nitrogen or argon is introduced for ventilation for 4-6 hours, and the pressure in the furnace is maintained at 0.2-0.5 MPa. The material enters the furnace at a speed of 200-500 mm / min. There are 20 temperature zones in the furnace, and the temperature of the carbonization temperature zone is maintained at 1200°C and the temperature of the graphitization temperature zone is maintained at 2200°C.

9. An ultrathin graphite felt prepared by the preparation method according to any one of claims 1 to 8.