TW434930B - Processing of bipolar separator plates for electrochemical cells - Google Patents

Abstract

The present invention uses a thermoplastic fluorocarbon resin powder and a vermicular expanded graphite to prepare a composite material. The fluorocarbon resin powder is sieved first and then uniformly mixed with the vermicular expanded graphite at a suitable ratio. The mixture is placed in a mold and thermally compressed into a composite dividing plate for a fuel cell, etc. The pre-sieving of the fluorocarbon resin re-separates some coagulated powder and prevents the occurrence of a non-uniform mixing between the coagulated powder and the vermicular expanded graphite. The weight ratio of the vermicular expanded graphite in the composition is 98% to 25%. Tests indicate that the composite according to the present invention has a volume resistivity less than 1.52x10<SP>-3</SP> Ω-cm which is far better than a composite material of graphite powder and a fluorocarbon polymeric material which has a volume resistivity less than 8.9x10<SP>-2</SP> Ω-cm. The volume resistivity of the former is obviously 50 times less than that of the later.

Description

434930 ___ V. Description of the invention ("-(I) the prior art. And the red battery is a device that uses electricity in the hydrogen-containing fuel to generate electricity and heat directly through the electrochemical reaction. Because of its low pollution, high = ^ 'S clean power generation technology' can be applied to generator sets, vehicle power, and inter-type power, etc., so it has become the object of intense research and development and promotion in the United States, Japan, and Europe in recent years. Bipolar current collector- separator)

重要 Fuel cell (Fuel Cel 1) important components, the main function of the bipolar separator plate has five: (1) as a fuel gas (such as hydrogen H2) and oxidant (such as oxygen 02 or upper defects) milk separator '(2) There are gas diversion grooves on both surfaces of the bipolar separator plate as cloth gas diversion grooves, (3) as current conduction between the cathode and the anode of another battery (ce 1 1), ( 4) As a current collector, (5) a coolant deflector can also be added inside the bipolar separator plate to remove the battery heat. Therefore, the bipolar separator must have high gas impermeability to gas, high electrical conductivity, and good corrosion resistance. In addition, the bipolar separator must have sufficient bending strength to resist operating pressure and thermal cycling stability. It is also hoped that the bipolar separator plate can be made as thin as possible in the use design, so that the size of the fuel cell is reduced, and the electrical and thermal conductivity is improved so as to achieve a more economical and diversified fuel cell.

Commercially most bipolar separators use processable artificial graphite, which has strong corrosion resistance and good electrical conductivity (the volume resistivity of P0C0 EDM-3 is 2. 9 7 X 1 0 3 Ω -cm) and Metals are relatively light weight. But graphite material is quite brittle, so it is very difficult to process and graphite is a porous material (卩 0 (; 0 〖011-3 of 116, the air leakage rate is about 2 乂 10_31: 〇]:] ./ 56 ( ^), The gas will leak out from the micropores 'cannot reach the effect of air swimming' so it cannot be made here

Page 4 of 434930 V. Description of the invention (2)-a very thin air-tight double cymbal is used, most of which use a thick graphite bipolar separator plate to reduce gas leakage, which also causes a relatively low fuel cell stack Weight, low volume and low internal resistance cannot be achieved. Graphite materials for fuel cells include artificial graphite (such as Japan's Toyo Carbon IG-15 graphite, the U.S. graphite), graphite powder composite thermosetting polymer materials, and graphite powder composite thermoplastic polymer materials. For example, U.S. Patent Nos. 4,301,222; 4, 1 97 1 78 all mention the production of bipolar separator plates for fuel cells. '' In terms of carbon powder composite thermoplastic polymer materials, U.S. Patent Nos. 4,30,1,2 2 and 4,214,9 6 9 mention graphite powder composite fluorocarbon polymer composite materials and carbon fiber reinforced graphite powder composites. Fluorocarbon polymer composite materials, the volume resistivity of the two is 2. 54 ~ 8.9x1 〇_2Ω-cm, this volume resistivity is about 9 9 × χ 10 and the United States p〇c than the artificial graphite such as Japan Toyo Carbon IG15 graphite. Graphite is about 2.97x1 0_3 Ω-cm high. How to reduce the volume resistivity of this graphite composite frore polymer material is the main object of the present invention. Respiration is the same as the conductive graphite of the present invention, which uses vermicular expanded graphite. It uses scale-like natural graphite powder as a raw material, and is treated with acidification, and then washed and dried appropriately to obtain expandable graphite powder ( expandable graphite). The expandable graphite powder is heated instantly at a high temperature (700 ~ 1000), and an expanded worm-like graphite is obtained. Its expansion ratio can reach 100 ~ 500 times. Because the worm-like graphite comes from natural graphite, it has High degree of graphitization and electrical conductivity, and its shape is similar to sheet shape. After compression, the sheet and the sheet are bonded to each other, so that the whole has better conductivity.

P.5 434930 V. Description of the invention (3)

The purpose of the present invention is to produce a highly conductive fluorocarbon resin composite worm-like graphite material 'for use in a bipolar separator plate on a fuel cell. (III) Technical content The present invention is a method for manufacturing a bipolar separator for a fuel cell. Its main feature is to use thermoplastic fluorocarbon resin powder and worm-like graphite to make a composite material. The fluorocarbon resin powder is first sieved through a 60 ~ 100 mesh screen and uniform with the worm-like graphite at an appropriate ratio. After mixing, the two are stirred and mixed evenly and put into a mold, and then pressed into a flat plate of composite material or a unipolar separator plate with a groove on one side or a bipolar separator plate with a groove on both sides by a hot press. The fluorocarbon resin powder is first sieved to separate some powders with agglomeration phenomenon, to prevent large particles from condensing and mixing with snail-shaped graphite. The weight ratio of the worm-like graphite in the composition is 98% to 25%, and the weight ratio of the worm-like graphite is preferably 95% to 50%. According to the technology of the present invention, the thermoplastic fluorocarbon resin powder includes polyvinylidene fluoride (PVDF) polymer, vinylidene fluoride and hexa-propylene copolymer (vinylidene fluoride / hexafluoropropylene copolymer, VDF / HFP copolymer). ) And Teflon resin (polytetrafluoroethylene, PTFE), etc., the weight ratio is 2% to 75%, and the preferred fluorine blocking resin weight ratio is 5% to 50%. The feature of the present invention is that the volume resistivity of graphite composite fluorocarbon polymer materials can be made less than 1.52x1 Ο-3 Ω-cm, which is much better than the volume resistivity of graphite composite fluorine barrier polymer materials of the prior art is less than 8.

434930 V. Description of the invention (4) 9x1 0-2 Ω-cm, the volume resistivity of the present invention is significantly smaller than the volume resistivity of the prior art by more than 50 times. Example 4: A thermoplastic polyvinylidene fluoride resin powder (Solvay

Solef 1012 PVDF produced by Polymers, density 1.78g / cm3, particle size: 100 ~ 150, melting point: 174. 〇After sieving through 80 mesh sieve, mix with worm-like graphite uniformly at an appropriate ratio. After the two are evenly mixed and mixed, put them into the mold, and then press the hot press to make a composite flat plate or a single concave surface. Slotted monopolar separator plate or grooved bipolar separator plate, etc., pressure is 100 kg / cm2, temperature is 24 0 ° C, pressing time is 2 hours, take out the pressed composite material for measurement Density and volume resistivity measured with HP4338B. + Milliohmmeter. (Ω-cm) 'and leak rate measured with ASM 180t He gas leak detector from ALC TEL, France (1; 〇r r. 1 / sec) As shown in Table 1. Table 1. Properties of PVDF resin composite worm-like graphite materials. The volume resistivity and air leakage density of worm-like graphite (wt-cm) (Ω-cm) (t orr. 1 / sec) (g / cc) Example 1 95 7.96x10 4 5xl0-9 1.43 Example 2 90 8 · 32xl0-4 5x10 · 8 1.52 Example 3 75 1. 03xl0-3 6xl0-9 1.5 9 Example 4 50 1. 52x103 1.2xl0 -9 1. 75

43493 0 V. Description of the invention (5) Examples 5-9: The operation method is the same as that of Examples 1-4. The thermoplastic fluorocarbon resin powder is a copolymer powder of vinylidene fluoride and hexafluoropropylene produced by Changxing Chemical Industry Co., Ltd. (ETERFLON-420 1 VDF / HFP copolymer), the hot pressing conditions are a pressure of 100 kg / cm2, a temperature of 180 ° C, and a pressing time of 2 hours. The density, volume resistivity, and air leakage rate are shown in Table 2. Table 2. Properties of VDF / HFP copolymer composite worm-like graphite materials. Snail-like graphite, volume resistivity, air leakage rate, density (wt%) (Ω -cm) (torr. 1 / sec) (g / cc) Example 5 95 8. 59xl0-4 2x1 0-8 1.38 Example 6 9 0 8. 70x10 4 lxl0-8 1. 43 Example 7 85 9. 65x1 0-4 lxl 0-8 1.44, Example 8 80 1. ΙΤχΙΟ-3 9x1 O'9 1.45 Example 9 75 1. 17x10 3 3x1 O'8 1.4 7

Claims (1)

434930 VI. Scope of patent application 1. A method for manufacturing a battery bipolar separator plate. The process is to uniformly mix both thermoplastic fluorocarbon resin powder and worm-like graphite into a composite material by hot pressing. 2. For example, a method for manufacturing a battery bipolar separator in the scope of the patent application, wherein the thermoplastic fluorocarbon resin powder may be a polyvinylidene fluoride resin powder and a copolymer powder of vinylidene fluoride and hexafluoropropylene. 3. For the manufacturing method of the battery bipolar separator plate according to item 1 of the patent application, wherein the composite material can be a flat plate, a single-sided t-groove unipolar separator, and a double-sided bipolar separator with a groove. Board, etc. 4. The manufacturing method of the battery bipolar separator according to item 1 of the patent application, wherein the fluorocarbon resin powder is mixed with worm-shaped graphite and passed through a 60 to 100 mesh screen. 5. The manufacturing method of the battery bipolar separator according to item 1 of the patent application, wherein the weight ratio of worm-shaped graphite is 95 to 50%, and the weight ratio of fluorocarbon resin powder is 5% to 50%.