US 10,026,995 B2  28  27  Example 2: Ni Foam and CVD Graphene  Foam-Based Conductive Porous Layers on Ni  Foam Templates  Example 4: Some Examples of Electrolytes Used  Example 4: Preparation of Graphene Oxide (GO)  and Reduced Graphene Oxide (RGO) Nano Sheets  from Natural Graphite Powder  The procedure for producing CVD graphene foam was  adapted from that disclosed in open literature: Chen, Z. et al.  "Three-dimensional flexible and conductive interconnected  graphene networks grown by chemical vapor deposition,"  Nature Materials, 10, 424-428 (2011 ). Nickel foam, a porous  structure with an interconnected 3D scaffold of nickel was  chosen as a template for the growth of graphene foam.  Briefly, carbon was introduced into a nickel foam by decom› posing CH$_{4 }$ at 1,000°  C. under ambient pressure, and gra› phene films were then deposited on the surface of the nickel  foam. Due to the difference in the thermal expansion coef› ficients between nickel and graphene, ripples and wrinkles  were formed on the graphene films. Four types of foams  made in this example were used as a current collector in the  presently invented lithium batteries: Ni foam, CVD gra› phene-coated Ni form, CVD graphene foam (Ni being  etched away), and conductive polymer bonded CVD gra- phene foam.  In order to recover (separate) graphene foam from the  supporting Ni foam, Ni frame was etched away. In the  procedure proposed by Chen, et al., before etching away the  nickel skeleton by a hot HCI ( or FeCl$_{3}$ )  solution, a thin layer  of poly (methyl methacrylate) (PMMA) was deposited on  the surface of the graphene films as a support to prevent the  graphene network from collapsing during nickel etching.  After the PMMA layer was carefully removed by hot  acetone, a fragile graphene foam sample was obtained. The  use of the PMMA support layer was considered critical to  preparing a free-standing film of graphene foam. Instead, we  used a conducting polymer as a binder resin to hold gra› phene together while Ni was etched away. It may be noted  that the CVD graphene foam used herein is intended as a  foamed current collector to accommodate a suspension of  active material dispersed in a liquid electrolyte. For instance,  liquid or gel slurry of hard carbon nano particles dispersed  in a liquid or gel electrolyte for the anode, and slurry of  graphene-supported NaFePO$_{4 }$ nano particles dispersed in a  liquid or gel electrolyte in the cathode.  Example 3: Graphitic Foam-Based Conductive  Porous Layers from Pitch-Based Carbon Foams  Pitch powder, granules, or pellets are placed in a alumi› num mold with the desired final shape of the foam. Mit› subishi ARA-24 mesa-phase pitch was utilized. The sample  is evacuated to less than 1 torr and then heated to a  temperature approximately 300° C. At this point, the  vacuum was released to a nitrogen blanket and then a  pressure ofup to 1,000 psi was applied. The temperature of  the system was then raised to 800°  C. This was performed  at a rate of 2 degree C./min. The temperature was held for  at least 15 minutes to achieve a soak and then the furnace  power was turned off and cooled to room temperature at a  rate of approximately 1.5 degree C./min with release of  pressure at a rate of approximately 2 psi/min. Final foam  temperatures were 630°  C. and 800°  C. During the cooling  cycle, pressure is released gradually to atmospheric condi› tions. The foam was then heat treated to 1050°  C. (carbon› ized) under a nitrogen blanket and then heat treated in  separate runs in a graphite crucible to 2500°  C. and 2800°  C.  (graphitized) in Argon.  Preferred non-lithium alkali metal salts include: sodium  perchlorate (NaCIO$_{4}$ ),  potassium perchlorate (KCIO$_{4}$ ),  sodium hexafluorophosphate (NaPF $_{6}$ ),  potassium hexafluo› rophosphate (KPF $_{6}$ ), sodium borofluoride (NaBF  4 ), potas› sium borofluoride (KBF  4 ),  sodium hexafluoroarsenide,  potassium hexafluoroarsenide, sodium trifluoro-metasul› fonate  (NaCF $_{3}$SO$_{3}$ ),  potassium  trifluoro-metasulfonate  (KCF$_{3}$ SO$_{3}$), bis-trifluoromethyl sulfonylimide sodium (NaN  (CF $_{3}$ SO$_{2}$ ) 2 ), and bis-trifluoromethyl sulfonylimide potas› sium [KN(CF$_{3}$SO$_{2}$) 2 ].  For aqueous electrolyte, sodium salt or potassium salt is  preferably selected from Na$_{2}$ SO$_{4}$ ,  K$_{2}$ SO$_{4}$ ,  a mixture thereof,  NaOH, KOH, NaCl, KC!, NaF, KF, NaBr, KBr, NaI, KI, or  a mixture thereof. The salt concentrations used in the present  study were from 0.3M to 3.0 M (most often 0.5M to 2.0M).  A wide range oflithium salts can be added as a second salt  (a modifier additive) dissolved in an organic liquid solvent  ( alone or in a mixture with another organic liquid or an ionic  liquid), if so desired. The following are good choices for  lithium salts that tend to be dissolved well in selected  organic or ionic liquid solvents: lithium borofluoride  (LiBF  4 ),  lithium  trifluoro-metasulfonate  (LiCF$_{3}$ SO$_{3}$),  lithium bis-trifluoromethyl sulfonylimide (LiN(CF$_{3}$SO$_{2}$ ) $_{2 }$or  LITFSI),  lithium bis( oxalato )borate  (LiBOB),  lithium  oxalyldifluoroborate (LiBF $_{2}$C$_{2}$O$_{4}$ ), and lithium bisperfluo› roethy-sulfonylimide (LiBETI). A good electrolyte additive  for helping to stabilize Li metal is LiNO$_{3}$ •  Particularly useful  ionic liquid-based lithium salts include: lithium bis(trifluoro  methanesulfonyl)imide (LiTFSI).  Preferred organic liquid solvents include: ethylene car› bonate (EC), dimethyl carbonate (DMC), methylethyl car› bonate (MEC), diethyl carbonate (DEC), propylene carbon› ate (PC), acetonitrile (AN), vinylene carbonate (VC), ally!  ethyl carbonate (AEC), 1,3-dioxolane (DOL), 1,2-dime› thoxyethane (DME), tetraethylene glycol dimethylether  (TEGDME),  Poly(ethylene  glycol)  dimethyl  ether  (PEGDME), diethylene glycol dibutyl ether (DEGDBE),  2-ethoxyethyl ether (EEE), hydrofloroether ( e.g. TPTP),  sulfone, and sulfolane.  Preferred ionic liquid solvents may be selected from a  room temperature ionic liquid (RTIL) having a cation  selected  from  tetraalkylammonium,  alkylpyridinium,  dialkyl-pyrrolidinium, or dialkylpiperidinium. The counter  anion is preferably selected from BF  4 -, B(CN) 4 -, CF $_{3}$CO$_{2 }$ -,  CF$_{3}$SO$_{3}$-,  N(SO$_{2}$CF$_{3}$ ) 2 -,  N(COCF$_{3}$)(SO$_{2}$CF$_{3}$ t,  or N  (SO$_{2}$F)$_{2 }$- . Particularly useful ionic liquid-based solvents  include N-n-butyl-N-ethylpyrrolidinium bis(trifluorometh› ane sulfonyl)imide (BEPyTFSI), N-methyl-N-propylpiperi› dinium bis(trifluoromethyl sulfonyl)imide (PP $_{13 }$TFSI), and  N,N-diethyl-N-methyl-N-(2-methoxyethyl) anrmonium bis  ( trifluoromethy lsulfonyl )imide.  Natural graphite from Huadong Graphite Co. (Qingdao,  China) was used as the starting material. GO was obtained  by following the well-known modified Hummers method,  which involved two oxidation stages. In a typical procedure,  the first oxidation was achieved in the following conditions:  1100 mg of graphite was placed in a 1000 mL boiling flask.  Then, 20 g of K$_{2}$S$_{2}$O$_{8}$ ,  20 g of P$_{2}$O$_{5}$ ,  and 400 mL of a  concentrated aqueous solution ofH$_{2}$ SO$_{4 }$ (96%) were added  in the flask. The mixture was heated under reflux for 6 hours  and then let without disturbing for 20 hours at room tem- perature. Oxidized graphite was filtered and rinsed with  abundant distilled water until neutral pH. A wet cake-like  material was recovered at the end of this first oxidation. 