Process for metal-sulfur battery cathode containing humic acid-derived conductive foam

Abstract

Provided is a process for producing a sulfur cathode for a metal-sulfur battery. The process comprises: (a) Preparing a humic acid-derived foam or combined humic acid/graphene-derived foam composed of multiple pores and pore walls, wherein the pore walls contain one or a plurality of hexagonal carbon atomic planes; and (b) Impregnating the foam with sulfur or sulfide in a form of thin particles or coating, having a diameter or thickness less than 500 nm, which are lodged in the pores or deposited on the pore walls of the foam.

We claim: 
     
         1 . A roll-to-roll process for producing a continuous-length sheet of the humic acid-derived foam, said process comprising:
 (a) preparing a humic acid dispersion having humic acid molecules and optional graphene sheets dispersed in a liquid medium, wherein said dispersion contains a blowing agent, wherein said humic acid has a content of non-carbon elements less than 5% by weight;   (b) continuously or intermittently dispensing and depositing said humic acid dispersion onto a surface of a supporting substrate to form a wet layer of humic acid, wherein said supporting substrate is a continuous thin film supplied from a feeder roller and collected on a collector roller;   (c) partially or completely removing said liquid medium from the wet layer of humic acid to form a dried layer of humic acid in a heating zone or multiple heating zones; and   (d) heat treating the dried layer of humic acid in one of said heating zones containing a heating temperature from 80° C. to 500° C. at a desired heating rate sufficient to activate said blowing agent for producing said humic acid-derived foam, which is composed of multiple pores and pore walls, wherein said pore walls contain single-layer or few-layer humic acid-derived hexagonal carbon atomic planes, said few-layer hexagonal carbon atomic planes are chemically bonded to create electron-conducting pathways, have 2-10 layers of stacked hexagonal carbon atomic planes having an inter-plane spacing d 002  from 0.3354 nm to 0.60 nm as measured by X-ray diffraction, and contain 0.01% to 5% by weight of non-carbon elements.   
     
     
         2 . The process of  claim 1 , wherein said humic acid-derived foam has a density from 0.005 to 1.7 g/cm 3 , a specific surface area from 50 to 3,200 m 2 /g, a thermal conductivity of at least 100 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 500 S/cm per unit of specific gravity. 
     
     
         3 . A The process of  claim 1 , wherein said dispensing and depositing procedure includes subjecting said humic acid dispersion to an orientation-inducing stress. 
     
     
         4 . The process of  claim 1 , further including a step of heat-treating the humic acid-derived foam at a second heat treatment temperature higher than said first heat treatment temperature for a length of time sufficient for obtaining a graphitic foam wherein said pore walls contain stacked hexagonal carbon atomic planes having an inter-planar spacing d 002  from 0.3354 nm to 0.36 nm and a content of non-carbon elements less than 2% by weight. 
     
     
         5 . The process of  claim 4 , wherein said humic acid-derived foam has a density from 0.005 to 1.7 g/cm 3 , a specific surface area from 50 to 3,200 m 2 /g, a thermal conductivity of at least 100 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 500 S/cm per unit of specific gravity. 
     
     
         6 . The process of  claim 1 , wherein said blowing agent is a physical blowing agent, a chemical blowing agent, a mixture thereof, a dissolution-and-leaching agent, or a mechanically introduced blowing agent. 
     
     
         7 . The process of  claim 1 , wherein said first heat treatment temperature is from 100° C. to 1,500° C. 
     
     
         8 . The process of  claim 4 , wherein said second heat treatment temperature includes at least a temperature selected from (A) 300-1,500° C., (B) 1,500-2,100° C., and/or (C) 2,100-3,200° C. 
     
     
         9 . The process of  claim 4 , wherein said second heat treatment temperature includes a temperature in the range of 300-1,500° C. for at least 1 hour and then a temperature in the range of 1,500-3,200° C. for at least 1 hour. 
     
     
         10 . The process of  claim 4 , wherein said non-carbon elements include an element selected from the group consisting of oxygen, fluorine, chlorine, bromine, iodine, nitrogen, hydrogen, and boron. 
     
     
         11 . The process of  claim 4 , wherein said step (c) of heat treating the dried layer of humic acid at said first heat treatment temperature is conducted under a compressive stress. 
     
     
         12 . The process of  claim 1 , further comprising a compression step to reduce a thickness, a pore size, or a porosity level of said foam. 
     
     
         13 . The process of  claim 4 , wherein said first and/or second heat treatment temperature contains a temperature in the range of 300° C-1,500° C. and the foam has an oxygen content or non-carbon content less than 1%, and pore walls having an inter-planar spacing less than 0.35 nm, a thermal conductivity of at least 250 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 2,500 S/cm per unit of specific gravity. 
     
     
         14 . The process of  claim 4 , wherein said first and/or second heat treatment temperature contains a temperature in the range of 1,500° C.-2,100° C. and the foam has an oxygen content or non-carbon content less than 0.01%, pore walls having an inter-planar spacing less than 0.34 nm, a thermal conductivity of at least 300 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 3,000 S/cm per unit of specific gravity. 
     
     
         15 . The process of  claim 4 , wherein said first and/or second heat treatment temperature contains a temperature greater than 2,100° C. and the foam has an oxygen content or non-carbon content no greater than 0.001%, pore walls having an inter-planar spacing less than 0.336 nm, a mosaic spread value no greater than 0.7, a thermal conductivity of at least 350 W/mK per unit of specific gravity, and/or an electrical conductivity no less than 3,500 S/cm per unit of specific gravity. 
     
     
         16 . The process of  claim 4 , wherein said first and/or second heat treatment temperature contains a temperature no less than 2,500° C. and the foam has pore walls containing stacked hexagonal carbon planes having an inter-planar spacing less than 0.336 nm, a mosaic spread value no greater than 0.4, a thermal conductivity greater than 400 W/mK per unit of specific gravity, and/or an electrical conductivity greater than 4,000 S/cm per unit of specific gravity.