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EP-4739737-A1 - HIGHLY ELECTRICALLY CONDUCTIVE COMPOUNDS CONTAINING HDPE AND CARBON NANOTUBES FOR BATTERY ELECTRODE PLATES

EP4739737A1EP 4739737 A1EP4739737 A1EP 4739737A1EP-4739737-A1

Abstract

Thermoplastic compositions include: from about 35 wt% to about 70 wt% of a polymer resin, wherein the polymer resin comprises at least two polymer resins, wherein at least one of the polymer resins includes a high density polyethylene (HDPE) polymer having a degree of crystallinity of at least 47% as measured by differential scanning calorimetry (DSC); from about 10 wt% to about 40 wt% synthetic graphite; from about 5 wt% to about 15 wt% carbon nanotubes (CNTs); and from about 3 wt% to about 15 wt% conductive carbon black powder.

Inventors

  • SILVI, NORBERTO
  • THOMPSON, WALTER

Assignees

  • SHPP Global Technologies B.V.

Dates

Publication Date
20260513
Application Date
20240801

Claims (15)

  1. 1. A thermoplastic composition comprising: from about 35 wt% to about 70 wt% of a polymer resin, wherein the polymer resin comprises at least two polymer resins, wherein at least one of the polymer resins comprises a high density polyethylene (HDPE) polymer having a degree of crystallinity of at least 47% as measured by differential scanning calorimetry (DSC); from about 10 wt% to about 40 wt% synthetic graphite; from about 5 wt% to about 15 wt% carbon nanotubes (CNTs); and from about 3 wt% to about 15 wt% conductive carbon black powder, wherein the combined weight percent value of all components does not exceed 100 wt%, and all weight percent values are based on the total weight of the composition.
  2. 2. The thermoplastic composition according to claim 1, wherein the HDPE has a degree of crystallinity of at least 55% as measured by differential scanning calorimetry (DSC).
  3. 3. The thermoplastic composition according to claim 1 or 2, wherein the HDPE has a density of at least 0.939 g/cm 3 as determined according to ASTM D1505.
  4. 4. The thermoplastic composition according to any of claims 1 to 3, wherein the synthetic graphite comprises at least 50% particles having a particle diameter of from 4 micron (pm) to 75 pm as determined by laser diffraction.
  5. 5. The thermoplastic composition according to any of claims 1 to 4, wherein the synthetic graphite has a specific surface area of from greater than 5 m 2 /g to less than 26 m 2 /g as determined according to a Brunauer, Emmett and Teller (BET) analysis.
  6. 6. The thermoplastic composition according to any of claims 1 to 5, wherein the synthetic graphite has a purity level of at least 99.5 wt%.
  7. 7. The thermoplastic composition according to any of claims 1 to 6, wherein the composition comprises less than 49 wt% carbon filler, wherein the carbon filler comprises the synthetic graphite, the CNTs and the conductive carbon black powder.
  8. 8. The thermoplastic composition according to any of claims 1 to 7, wherein the composition has a volume resistivity of less than 0.45 Ohm.cm as measured according to ASTM D991.
  9. 9. The thermoplastic composition according to any of claims 1 to 8, wherein the composition has improved chemical resistance against zinc bromide corrosion as compared to a comparative composition that includes a polyethylene polymer having a degree of crystallinity of less than 47% instead of the HDPE polymer having a degree of crystallinity of at least 47%.
  10. 10. The thermoplastic composition according to any of claims 1 to 9, wherein the composition is extrudable into sheets having a width of at least 7 in and a thickness of 1 mm or lower using conventional melt extrusion methods.
  11. 11. The thermoplastic composition according to any of claims 1 to 10, wherein the composition comprises from about 5 wt% to about 30 wt% of the high density polyethylene (HDPE) polymer having a degree of crystallinity of at least 47%.
  12. 12. The thermoplastic composition according to any of claims 1 to 11, wherein the composition comprises: from about 10 wt% to about 20 wt% of the HDPE polymer having a degree of crystallinity of at least 47%; from about 25 wt% to about 40 wt% of the synthetic graphite; and from about 5 wt% to about 10 wt% CNTs.
  13. 13. The thermoplastic composition according to any of claims 1 to 12, wherein the composition has: a modulus of elasticity of at least 4000 MPa as measured according to ASTM D638; a tensile stress at break of at least 30.5 MPa as measured according to ASTM D638; a flexural modulus of at least 2600 MPa as measured according to ASTM D790; a flexural stress at break of at least 45 MPa as measured according to ASTM D790; or a specific gravity of at least 1.24 as measured according to ASTM D792.
  14. 14. An article comprising the composition according to any of claims 1 to 13,
  15. 15. The article according to claim 14, wherein the article is a sheet having a thickness of 1 mm or lower, or wherein the article is a battery electrode plate, a bipolar plate of a fuel cell, or a sheet of a plate heat exchanger.

Description

HIGHLY ELECTRICALLY CONDUCTIVE COMPOUNDS CONTAINING HDPE AND CARBON NANOTUBES FOR BATTERY ELECTRODE PLATES FIELD OF THE DISCLOSURE [0001] The present disclosure relates to thermoplastic compositions including high density polyethylene and several forms of carbon fdler that have good volume electrical resistivity and mechanical properties. BACKGROUND OF THE DISCLOSURE [0002] Zinc-bromine batteries were conceived in the late 1800’s - see, e.g., U.S. Patent 312,812 (granted in 1885 to Bradley). Development of commercial zinc-bromine batteries has lagged due to: (1) the tendency of zinc to form dendrites upon deposition, which may short circuit the cell; and (2) the high solubility of bromine in the aqueous zinc bromide electrolyte, which allows diffusion and direct reaction with the zinc electrode, resulting in self-discharge of the cell. It is important to control the pH of the electrolyte to reduce zinc corrosion rate and mossy zinc deposits. These problems are discussed in “Zinc/Bromine Batteries,” Paul C. Butler et al., Report No. SAND2000-0893, pp. 37-1, 3, 6 (2000). [0003] The search for carbon-plastic electrode composites to use as electrode plates in zinc bromide batteries started in the late 1970s. U.S. Patent 4,169,816 (‘816 Patent) by Exxon Research & Engineering, for example, describes a homogeneous blend of a crystalline polypropylene-ethylene copolymer, an electrically conductive carbon black, a small quantity of silica, and a fiber-reinforcing agent selected from carbon fibers and mixtures of carbon and glass fibers. The composition was reported to have excellent strength, good extrudability, excellent volume resistivity (1 Ohm.cm), and good impermeability. This patent suggests that to impart electrical conductivity, the composition should contain at least 15 parts by weight of a finely divided conductive carbon powder per hundred parts (pph) of the copolymer. It also states that 35 pph of the conductive carbon should not be employed; otherwise, the composition is too brittle and also less easily extrudable into thin nonporous sheets. Also, increasing the amount of carbon to about 35 pph tends to increase the permeability of the thin sheets manufactured from such compositions to liquids such as bromine, as an example. It is preferred that the finely divided conductive carbon black has a surface area greater than about 500 m2/g, such as those manufactured under the tradename Ketjen Black EC. [0004] Johnson Controls began research into plastic-carbon electrodes in the 1990s, reporting at the time that the polypropylene -ethylene copolymer based electrodes developed by Exxon were susceptible to oxidative attack, swelling and warpage. They explained that the mechanism behind the bromide attack was the vulnerability of tertiary hydrogens in the backbone of the propylene chain. To circumvent this problem Johnson Controls selected high density polyethylene (HDPE) homopolymer, which eliminates most, if not all, tertiary hydrogens on the backbone chain. Johnson Controls reported positive results in aging studies with the base polymer substitution; HDPE was superior to EP Copolymer. [0005] Globe-Union Inc. (a Johnson Controls subsidiary) patented an HDPE-based carbon-plastic electrodes in December 1992. U.S. Patent 5,173,362 (‘362 Patent) describes compositions for electrode systems, particularly those to be used for bipolar electrodes in zinc-bromine batteries. These compositions preferably include carbon-black as a conductive fdler in a polymeric matrix, with reinforcing materials such as glass fibers. The warpage of the zinc-bromine electrodes experienced in the prior art, and which was believed to be caused by physical expansion of the electrodes due to bromine absorption by the material of the electrode, was substantially eliminated in the compositions and fabrication processes described in this patent. In this patent, materials were prepared using a lamination process, known as glass-mat reinforced thermoplastics technology or, in a different embodiment, the substrate is made using a slurry process. Bromination, unlike chlorination, is extremely selective to the chemistry of the polymer matrix used, and the tertiary hydrogens of polypropylene systems react approximately twenty thousand times faster with bromine than the secondary hydrogens in polyethylene. Three carbon blacks were used in the described compositions, but the Ketjenblack EC-300J grade offered the best combination of electrical conductivity and processability/extrudability properties for the amount of carbon used. [0006] The ‘362 Patent broadly describes carbon black and fiber loading ranges of from 5-40 wt% and 10-70 wt%, respectively. However, the exemplified compositions (Table 5) describe carbon loadings of 18 wt% (identical to the Exxon ‘816 Patent), so it is believed that the carbon and fiber loadings used in the ‘362 Patent are close to those described in the ‘816 Patent. [0007] International (PCT) Publication WO 2022/195511,