Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/04—Hybrid capacitors
  • H01G11/06—Hybrid capacitors with one of the electrodes allowing ions to be reversibly doped thereinto, e.g. lithium ion capacitors [LIC]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/32—Carbon-based
  • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/54—Electrolytes
  • H01G11/56—Solid electrolytes, e.g. gels; Additives therein
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/54—Electrolytes
  • H01G11/58—Liquid electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/44—Methods for charging or discharging
  • H01M10/446—Initial charging measures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M16/00—Structural combinations of different types of electrochemical generators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
  • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

• This invention is based on the research results of a project sponsored by the US National Science Foundation SBIR-STTR Program.
• the present invention relates generally to the field of electrochemical energy storage devices and, more particularly, to a totally new lithium ion-exchanging energy storage device wherein both the anode and the cathode do not involve lithium diffusion in and out of the bulk of a solid electrode-active material (i.e., requiring no lithium intercalation or de- intercalation).
• the lithium storage mechanism in both the anode and the cathode is surface- controlled, obviating the need for solid-state diffusion (intercalation or de-intercalation) of lithium, which otherwise is very slow.
• This device has the high energy density of a lithium- ion battery and the high power density of a supercapacitor (usually even higher than the power densities of supercapacitors).
• This device is herein referred to as a surface-mediated, lithium ion-exchanging battery device.
• Supercapacitors are being considered for electric vehicle (EV), renewable energy storage, and modern grid applications.
• the high volumetric capacitance density of a supercapacitor derives from using porous electrodes to create a large surface area conducive to the formation of diffuse double layer charges.
• This electric double layer (EDL) of charges is formed in the electrolyte near the electrode surface when voltage is imposed.
• the required ions for this EDL mechanism near an electrode are pre-existing in the liquid electrolyte when the cell is made or in a discharged state, and mostly do not come from the opposite electrode.
• the required ions to be formed into an EDL near the surface of a negative electrode (anode) active material do not have to come from the positive electrode (cathode) ; i.e., not captured or stored in the surfaces or interiors of a cathode active material.
• the required ions to be formed into an EDL near the surface of a cathode active material do not have to come from the surface or interior of an anode active material.
• the ions both cations and anions
• the ions already in the liquid electrolyte are formed into EDLs near their respective local electrodes (typically via local molecular or ionic polarization of charges).
• the amount of charges that can be stored is dictated solely by the concentrations of cations and anions that are available in the electrolyte. These concentrations are typically very low (limited by the solubility of a salt in a solvent), resulting in a low energy density.
• lithium ions are usually not part of preferred or commonly used supercapacitor electrolytes.
• the stored energy is further augmented by pseudo- capacitance effects due to some electrochemical reactions (e.g., redox).
• redox electrochemical reactions
• the ions involved in a redox pair also pre-exist in the electrolyte. Again, there is no major exchange of ions between an anode active material and a cathode active material.
• EDL supercapacitor Since the formation of EDLs does not involve a chemical reaction or an exchange of ions between the two opposite electrodes, the charge or discharge process of an EDL supercapacitor can be very fast, typically in seconds, resulting in a very high power density (typically 5,000-10,000 W/Kg). Compared with batteries, supercapacitors offer a higher power density, require no maintenance, offer a much higher cycle-life, require a very simple charging circuit, and are generally much safer. Physical, rather than chemical, energy storage is the key reason for their safe operation and extraordinarily high cycle-life.
• supercapacitors possess very low energy densities when compared to batteries (e.g., 5-8 Wh/kg for commercial supercapacitors vs. 10-30 Wh/Kg for the lead acid battery and 50-100 Wh/kg for the NiMH battery).
• Lithium-ion batteries possess a much higher energy density, typically in the range of 100-180 Wh/kg, based on the cell weight.
• lithium-ion batteries Although possessing a much higher energy density, lithium-ion batteries deliver a very low power density (typically 100-500 W/Kg), requiring typically hours for re-charge. Conventional lithium-ion batteries also pose some safety concern.
• the low power density or long re-charge time of a lithium ion battery is due to the mechanism of shuttling lithium ions between the interior of an anode and the interior of a cathode, which requires lithium ions to enter or intercalate into the bulk of anode active material particles during re-charge, and into the bulk of cathode active material particles during discharge.
• Fig. 1 (A) in a most commonly used lithium- ion battery featuring graphite particles as an anode active material, lithium ions are required to diffuse into the inter-planar spaces of a graphite crystal at the anode during re-charge.
• lithium ions have to come all the way from the cathode side by diffusing out of the bulk of a cathode active particle, through the pores of a solid separator (pores being filled with a liquid electrolyte), and into the bulk of a graphite particle at the anode.
• lithium ions diffuse out of the anode active material (e.g. de- intercalate out of graphite particles), migrate through the liquid electrolyte phase, and then diffuse into the bulk of complex cathode crystals (e.g. intercalate into particles lithium cobalt oxide, lithium iron phosphate, or other lithium insertion compound).
• liquid electrolyte only reaches the external surface of a solid particle (e.g. graphite particle 10 ⁇ in diameter) and lithium ions swimming in the liquid electrolyte can only migrate (via fast liquid-state diffusion) to the graphite surface.
• the diffusion coefficients of lithium in solid particles of lithium metal oxide are typically 10 "16 -10 8 cm 2 /sec (more typically 10 "14 -10 10 cm 2 /sec), and those of lithium in liquid are approximately 10 "6 cm 2 /sec.
• CNTs multi-walled carbon nano-tubes
• LIC lithium-ion capacitor
• CNTs are known to contain a significant amount of impurity, particularly those
• transition metal or noble metal particles used as a catalyst required of a chemical vapor deposition process. These catalytic materials are highly undesirable in a battery electrode due to their high propensity to cause harmful reactions with electrolyte.
• CNTs tend to form a tangled mass resembling a hairball, which is difficult to work with during electrode fabrication (e.g., difficult to disperse in a liquid solvent or resin matrix).
• the thickness of the LBL electrodes produced by Lee, et al was limited to 3 ⁇ or less.
• CNTs have very limited amounts of suitable sites to accept a functional group without damaging the basal plane structure.
• a CNT has only one end that is readily functionalizable and this end is an extremely small proportion of the total CNT surface.
• cathode active materials used in the so-called “lithium super- battery” include a chemically functionalized nano graphene platelet (NGP) or a
• the functionalized disordered carbon or functionalized NGP is used in the cathode (not the anode) of the lithium super-battery.
• lithium ions in the liquid electrolyte only have to migrate to the edges or surfaces of graphene sheets (in the case of functionalized NGP cathode), or the edges/surfaces of the aromatic ring structures (small graphene sheets) in a disordered carbon matrix. No solid-state diffusion is required at the cathode.
• a functionalized graphene or carbon having functional groups thereon enables reversible storage of lithium on the surfaces (including edges), not the bulk, of the cathode material.
• Such a cathode material provides one type of lithium-storing or lithium-capturing surface.
• lithium ions In conventional lithium-ion batteries, lithium ions must diffuse into and out of the bulk of a cathode active material, such as lithium cobalt oxide (L1C0O 2 ) and lithium iron phosphate (LiFeP0 4 ). In these conventional lithium-ion batteries, lithium ions must also diffuse in and out of the inter-planar spaces in a graphite crystal serving as an anode active material. The lithium insertion or extraction procedures at both the cathode and the anode are very slow. Due to these slow processes of lithium diffusion in and out of these intercalation compounds (commonly referred to as solid-state diffusion or intercalation processes), the conventional lithium ion batteries do not exhibit a high power density and the batteries require a long re-charge time.
• a cathode active material such as lithium cobalt oxide (L1C0O 2 ) and lithium iron phosphate (LiFeP0 4 ).
• LiFeP0 4 lithium iron phosphate
• the anode comprises either particles of a lithium titanate-type anode active material (still requiring solid state diffusion), schematically illustrated in Fig.1(B), or a lithium foil alone (without a nano- structured material to support or capture lithium ions/atoms), illustrated in Fig.1(C).
• lithium has to deposit onto the front surface of an anode current collector alone (e.g. copper foil) when the battery is re-charged. Since the specific surface area of a current collector is very low (typically « 1 m 2 /gram), the over-all lithium re-deposition rate is relatively low (this issue is being overcome in the instant invention).
• Both the anode and the cathode have large amounts of surface areas to allow lithium ions to deposit thereon simultaneously, enabling dramatically higher charge and discharge rates and higher power densities.
• the uniform dispersion of these surfaces of a nano-structured material (e.g. graphene, CNT, disordered carbon, nano-wire, and nano-fiber) in an electrode also provides a more uniform electric field in the electrode in which lithium can more uniformly deposit without forming a dendrite.
• Such a nano-structure eliminates the potential formation of dendrites, which was a problem in conventional lithium metal batteries (commonly used in 1980s and early 1990s before being replaced by lithium-ion batteries).
• Such a device is herein referred to as a surface-controlled, lithium ion-exchanging battery.
• graphene surfaces are capable of capturing or trapping lithium atoms without the need for solid state diffusion. Regardless if the surfaces contain functional groups or not, graphene surfaces are capable of storing lithium atoms in a stable and reversible manner, provided these surfaces are accessible to lithium ion-containing electrolyte and are in direct contact with the electrolyte.
• the lithium storing capacity is in direct proportion to the total surface area that is directly exposed to the lithium ion-containing electrolyte, as indicated in FIG. 13. For instance, the data point with the highest specific capacity in FIG.
• the term "surface-mediated cell” does not include any lithium-air (lithium-oxygen) cell, lithium-sulfur cell, or any cell wherein the operation of the energy storage device involves the introduction of oxygen from outside of the device, or involves the formation of a metal oxide, metal sulfide, metal selenide, metal telluride, metal hydroxide, or metal-halogen compound at the cathode.
• the present invention provides a surface-mediated, lithium ion-exchanging energy storage device (SMC) comprising: (a) a positive electrode (cathode) comprising a functionalized or non-functionalized cathode active material having a surface area to capture or store lithium thereon; (b) a negative electrode (anode) comprising a functionalized or non- functionalized anode active material having a surface area to capture or store lithium thereon; (c) a porous separator disposed between the two electrodes; and (d) a lithium- containing electrolyte in physical contact with the two electrodes.
• SMC surface-mediated, lithium ion-exchanging energy storage device
• the anode active material and/or the cathode active material has a specific surface area of no less than 100 m 2 /g being in direct physical contact with the electrolyte to receive lithium ions therefrom or to provide lithium ions thereto.
• At least one of the two electrodes contains therein a lithium source prior to a first charge or a first discharge cycle of the energy storage device, and at least the cathode active material is not a functionalized material (i.e. this material bears no functional group capable of redox reaction with Li).
• the lithium source may be preferably in a form of solid lithium foil, lithium chip, lithium powder, or surface-stabilized lithium particles.
• the lithium source may be a layer of lithium thin film pre-loaded on surfaces of an anode active material.
• the surfaces of an SMC electrode material e.g., pristine graphene containing essentially > 99% carbon
• the electrolyte comprises liquid electrolyte (e.g. organic liquid or ionic liquid) or gel electrolyte in which lithium ions have a high diffusion coefficient.
• Solid electrolyte is normally not desirable, but some thin layer of solid electrolyte may be used if it exhibits a relatively high diffusion rate.
• a lithium source e.g. small pieces of lithium foil
• a nano-structured anode e.g. comprising non-functionalized graphene sheets
• a porous polymer separator when the battery device is made
• a nano- structured cathode comprises non-functionalized graphene sheets surrounded by
• interconnected pores that are preferably meso-scaled (2 nm - 50 nm), but can be smaller than 2 nm.
• lithium foil is ionized to generate lithium ions in the liquid electrolyte.
• Lithium ions rapidly migrate through the pores of the polymer separator into the cathode side. Since the cathode is also meso-porous having interconnected pores to accommodate liquid electrolyte therein, lithium ions basically just have to sail through liquid to reach an active site on the cathode.
• the active site is a functional group in another embodiment it may be the edge or surface of a graphene sheet.
• the subsequent surface redox reaction between a lithium ion and a surface-borne functional group is fast and reversible; in the latter case, the graphene surface is in direct contact with electrolyte and readily accepts lithium ions from the electrolyte.
• the graphene surface is in direct contact with electrolyte and readily accepts lithium ions from the electrolyte.
• Both embodiments enable fast discharging of the SMC and a high power density. This is in stark contrast to the conventional lithium-ion battery wherein lithium ions are required to diffuse into the bulk of a solid cathode particle (e.g., micron-sized lithium cobalt oxide) during discharge, which is a very slow process.
• a solid cathode particle e.g., micron-sized lithium cobalt oxide
• the discharge process continues until either the lithium foil is completely ionized or the active sites on the cathode active material are occupied by lithium atoms.
• lithium ions are released from the massive surfaces of the cathode active material, diffuse through liquid electrolyte, and get captured by surface-borne functional groups in one embodiment or by the surfaces of an anode active material (e.g. simply get electrochemically deposited on a surface of the nano-structured anode material) in the non-functional group embodiment.
• no solid-state diffusion is required and, hence, the whole process is very fast, requiring a short re-charge time. This is contrasted with the required solid-state diffusion of lithium ions into the bulk of graphite particles at the anode of a conventional lithium-ion battery.
• the battery or energy storage device provides a very unique platform of exchanging lithium ions between the massive surfaces of an anode and the massive surfaces of a cathode that requires no solid-state diffusion in both electrodes.
• the process is substantially dictated by the surface-capturing of lithium, plus the liquid-phase diffusion (all being very fast).
• the device is herein referred to as a surface-mediated, lithium ion- exchanging battery.
• This is a totally different and patently distinct class of energy storage device than the conventional lithium-ion battery, wherein solid-state diffusion of lithium (intercalation and de-intercalation) is required at both the anode and the cathode during both the charge and discharge cycles.
• This surface-mediated, lithium ion-exchanging battery device is also patently distinct from the conventional supercapacitor based on the electric double layer (EDL) mechanism or pseudo-capacitance mechanism.
• EDL electric double layer
• no lithium ions are exchanged between the two electrodes (since lithium is not stored in the bulk or surfaces of the electrode; instead, they are stored in the electric double layers near the electrode surfaces).
• a supercapacitor is re-charged, the electric double layers are formed near the activated carbon surfaces at both the anode and the cathode sides.
• Each and every EDL is composed of a layer of negatively charged species and a layer of positively charged species in the electrolyte (in addition to the charges on surfaces of the electrode material (e.g.
• the charge storage capacitance of a supercapacitor (even when using a Li-containing electrolyte) is limited by the amounts of cations and anions that participate in the formation of EDL charges. These amounts are dictated by the original concentration of Li + ions and their counter ions (anions) from a lithium salt, which are in turn dictated by the solubility limits of these ions in the electrolyte solvent.
• the amounts of lithium ions that can be shuttled between the anode surface and the cathode surface of a SMC are not limited by the chemical solubility of lithium salt in this same solvent. Assume that an identical 5 mL of solvent (containing 5 moles of Li + ions, as described above for a supercapacitor) is used in the SMC. Since the solvent is already fully saturated with the lithium salt, one would expect that this solvent cannot and will not accept any more Li + ions from an extra lithium source (5 moles being the maximum).
• the amount of lithium capable of contributing to the charge storage is controlled (limited) by the amount of surface active sites of a cathode capable of capturing lithium ions from the electrolyte. This is so even when this amount of surface active sites far exceeds the amount of Li + ions that the solvent can hold at one time (e.g. 5 moles in the present discussion), provided that the implemented lithium source can provide the extra amount lithium ions.
• these active sites can be functional groups in one embodiment or they can be the surface defects of graphene, or the benzene ring centers on a graphene plane (FIG. 3(D) and (E)).
• lithium atoms are found to be capable of strongly and reversibly bonding to the individual centers of benzene rings (hexagons of carbon atoms) that constitute a graphene sheet, or of being reversibly trapped by graphene surface defect sites.
• the surface-mediated, lithium ion-exchanging battery device is also patently distinct from the super-battery as disclosed in two of our earlier applications (US Application No. 12/806,679 and No. 12/924,21 1), which does not have an anode active material at the anode (The anode side only contains an anode current collector).
• the anode side only contains an anode current collector.
• the cathode not only the cathode but also the anode has large amounts of surface areas to allow lithium ions to deposit thereon simultaneously, enabling dramatically higher charge and discharge rates and higher power densities.
• the anode current collector e.g. Cu foil
• the large specific surface area of a nano-structured anode and optionally functionalized material is capable of accommodating a large amount of lithium ions at the same time.
• the uniform dispersion of these surfaces of a nano material e.g.
• graphene or CNT in an electrode also provides a more uniform electric field in the electrode in which lithium can more uniformly deposit without forming a dendrite. More surface areas also mean more deposition spots and each spot only has a small quantity of lithium, insufficient to form a dangerous dendrite. Such a nano-structure eliminates the potential formation of dendrites, which was the most serious problem in conventional lithium metal batteries.
• At least the cathode of the two electrodes has an active material that is not a functionalized material (i.e., having no functional group attached to its surface that is exposed to electrolyte).
• the term "functionalized material” means a material having a functional group (e.g., carbonyl) that is capable of reacting with a lithium atom or ion to form a redox pair.
• the cathode active material has a high specific surface area (> 100 m 2 /g) that is in direct contact with the electrolyte (e.g.
• both of the two electrodes have a high specific surface area (> 100 m 2 /g) that is in direct contact with the electrolyte and capable of capturing/storing lithium atoms/ions in their surface active sites.
• At least one of the two electrodes has a nano-structured non-functional material having a high specific surface area no less than 500 m 2 /gram (preferably > 1,000 m 2 /gram, more preferably > 1,500 m 2 /gram, and most preferably > 2,000 m 2 /gram) to store or support lithium ions or atoms thereon.
• 500 m 2 /gram preferably > 1,000 m 2 /gram, more preferably > 1,500 m 2 /gram, and most preferably > 2,000 m 2 /gram
• the lithium source comprises a lithium chip, lithium foil, lithium powder, surface-passivated or stabilized lithium particles, or a combination thereof.
• the lithium source may be implemented at the anode side before the first discharge procedure is carried out on this battery device.
• the lithium source may be implemented at the cathode side before the first charge procedure is carried out on this battery device.
• both the cathode and the anode may be fabricated to contain some lithium source during the battery manufacturing process. It is important to note that this solid lithium source provides the majority of the lithium ions that are to be exchanged between the anode surfaces and the cathode surfaces during the charge-discharge cycles.
• any symmetric supercapacitor even if containing Li-based electrolyte, does not exhibit a high energy density.
• At least one of the anode active material and the cathode active material is (are) selected from the following:
• polymeric carbon or carbonized resin meso-phase carbon, coke, carbonized pitch, carbon black, activated carbon, or partially graphitized carbon
• graphene graphene, graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, or chemically or thermally reduced graphene oxide;
• meso-porous carbon e.g. obtained by template-assisted synthesis or chemical
• a carbon nanotube selected from a single-walled carbon nanotube or multi-walled carbon nanotube;
• CNTs are not preferred nano-structured materials due to the high costs and other technical issues, CNTs (alone or in combination with another nano-structured material) can still be used in the presently invented surface-controlled lithium ion-exchanging battery.
• PTCDA perylenetetracarboxylicacid-dianhydride
• NTCDA 1,4,5,8- n
• R is a hydrocarbon radical (e.g., 1 to 6 carbon atoms).
• These organic or polymeric materials possess functional groups (e.g. carbonyl group) capable of undergoing a reversible and fast redox reaction with lithium.
• These functional materials tend to have a relatively low electronic conductivity and, hence, preferably the functional material selected from this group is combined with (e.g.
• nano-structured material such as nano graphene, carbon nanotube, disordered carbon, nano graphite, material selected from nano graphene, carbon nanotube, disordered carbon, nano graphite, metal nanowire, conductive nano-wire, carbon nano-fiber, and polymeric nano-fiber).
• a disordered carbon soft carbon, hard carbon, activated carbon, carbon black, etc
• functional groups that can react with the matting functional groups on the aforementioned functional materials (e.g. the hydroxyl group on Tetrahydroxy-p- benzoquinone).
• a nano-structured carbon material such as non-functionalized nano graphene, carbon nanotube, disordered carbon, or nano graphite, may simply provide a surface upon which lithium atoms can be deposited, e.g. via defect site trapping or benzene ring center capturing.
• the disordered carbon material may be formed of two phases with a first phase being graphite crystals or stacks of graphene planes and a second phase being non-crystalline carbon and wherein the first phase is dispersed in the second phase or bonded by the second phase.
• the disordered carbon material may contain less than 90% by volume of graphite crystals and at least 10% by volume of non-crystalline carbon.
• the anode or cathode active materials of a SMC may comprise non-functionalized nano graphene selected from a single-layer graphene sheet or a multi-layer graphene platelet.
• the active materials may comprise single-walled or multi-walled carbon nanotube.
• the anode active material and/or the cathode active material of a SMC is a non-functionalized graphene material selected from a single-layer sheet or multi-layer platelet of graphene, graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, doped graphene, or chemically or thermally reduced graphene oxide.
• the anode active material and/or the cathode active material is a non-functionalized single- walled or multi-walled carbon nanotube (CNT), oxidized CNT, fluorinated CNT, hydrogenated CNT, nitrogenated CNT, boron-doped CNT, nitrogen-doped CNT, or doped CNT.
• CNT carbon nanotube
• the lithium source may be selected from lithium metal (e.g., in a thin foil or powder form, preferably stabilized or surface-passivated), a lithium metal alloy, a mixture of lithium metal or lithium alloy with a lithium intercalation compound, a lithiated compound, lithiated titanium dioxide, lithium titanate, lithium manganate, a lithium transition metal oxide, Li 4 Ti 5 0i 2 , or a combination thereof.
• the lithium intercalation compound or lithiated compound may be selected from the following groups of materials:
• the electrolyte may be selected from any of the electrolytes used in conventional lithium ion batteries or lithium metal batteries.
• the electrolyte is preferably liquid electrolyte or gel electrolyte.
• the electrolyte may comprise a lithium salt-doped ionic liquid.
• the positive electrode preferably has a thickness greater than 5 ⁇ , preferably greater than 50 ⁇ , and more preferably greater than 100 ⁇ .
• At least 90% of the lithium is stored on surfaces of the anode active material (lithium being in direct physical contact with anode surfaces) when the device is in a charged state, or at least 90% of the lithium is stored on surfaces of the cathode active material (lithium being in direct physical contact with cathode surfaces) when the device is in a discharged state.
• the SMC typically operates in a voltage range of from 1.0 volts to 4.5 volts, but can be prescribed to operate in a subset of this range (e.g. from 1.5 volts to 4.0 volts or from 2.0 volts to 3.9 volts, etc). It is also possible to operate above 4.5 volts, or slightly below 1.0 volts (not preferred). It may be noted that a symmetric supercapacitor featuring an organic electrolyte can only operates up to 3.0 volts and typically operates from 0 to 2.7 volts. In contrast, a SMC using exactly the same organic electrolyte typically operates from 1.5 volts to 4.5 volts. This is another piece of evidence that the SMC and the supercapacitor are two fundamentally distinct classes of energy storage devices, operating on different mechanisms and principles.
• the charge and/or discharge operation of the SMC does not involve lithium intercalation or solid state diffusion. This is usually the case even if multi-layer graphene platelets are used in either the anode or the cathode. Lithium intercalation into interstitial spaces between two graphene planes typically occur in a voltage below 1.5 volts (relative to Li/Li + ), mostly below 0.3 volts.
• the presently invented lithium ion-exchanging cell involves shuttling lithium ions between the surfaces of an anode and surfaces of a cathode, which operates on the range of 1.5 volts to 4.5 volts.
• the SMC device provides an energy density typically of no less than 150 Wh/kg and power density no lower than 25 Kw/kg, all based on the total electrode weight. More typically, the battery device provides an energy density of greater than 300 Wh/kg and power density greater than 20 Kw/kg. In many cases, the battery device provides an energy density greater than 400 Wh/kg and power density greater than 10 Kw/kg. Most typically, the battery device provides an energy density greater than 300 Wh/kg or a power density greater than 100 Kw/kg. In some cases, the power density is significantly higher than 200 Kw/kg, or even higher than 400 Kw/kg, which is 1-3 orders of magnitude higher than the power densities (1-10 Kw/kg) of conventional supercapacitors.
• the positive electrode preferably has a thickness greater than 5 ⁇ , more preferably greater than 50 ⁇ , and most preferably greater than 100 ⁇ .
• the present invention also provides a method of operating the energy storage device (SMC).
• the method includes implementing a lithium source at the anode and ionizing the lithium source to release lithium ions into the electrolyte during the first discharge cycle of the device.
• the method further includes electrochemically driving the released lithium ions onto the cathode where the released lithium ions are captured by the cathode active material surfaces, e.g., by interacting with a functional group or interacting with graphene.
• the method can further include a step of releasing lithium ions from said cathode surfaces during a re-charge cycle of said device, electrically driving said released lithium ions to said anode active material surfaces using an external battery charging device.
• the method may include implementing a lithium source at the cathode and operating the lithium source to release lithium ions into the electrolyte during the first charge cycle of the device.
• the invention further provides a method of operating a surface-mediated energy storage device, which method includes: (a) providing a surface-mediated cell comprising an anode, a lithium source, a porous separator, liquid or gel electrolyte, and a cathode, wherein in one embodiment, the anode and/or the cathode are functionalized and in a second embodiment the anode and/or the cathode are non-functionalized materials having lithium- capturing surfaces; (b) releasing lithium ions from the lithium source during the first discharge of the device; (c) exchanging lithium ions between the lithium-capturing surfaces of the anode and the lithium-capturing surfaces of the cathode during a subsequent charge or discharge.
• both the charge and discharge of the device do not involve lithium intercalation or solid state diffusion.
• the instant application discloses another method of operating a surface-mediated energy storage device.
• the method includes: (a) providing a surface-mediated cell comprising an anode, a lithium source, a porous separator, electrolyte (having an initial amount of lithium ions), and a cathode, wherein both the anode and the cathode have a material having lithium-capturing surfaces in contact with the electrolyte; (b) releasing lithium ions from the lithium source into the electrolyte during the first discharge of this device; (c) operating the cathode to capture lithium ions from the electrolyte and store the captured lithium on cathode surfaces (preferably having a specific surface area of greater than 100 m 2 /g, more preferably greater than 1,000 m 2 /g, and most preferably greater than2,000 m 2 /g); and (d) exchanging an amount of lithium ions (greater than the initial amount) between the lithium-capturing surfaces of the anode and the lithium-capturing surfaces of the cathode
• FIG. 1 (A) a prior art lithium-ion battery cell using graphite, Si, or lithium titanate as an anode active material and lithium iron phosphate (or lithium cobalt oxide, etc) as a cathode active material; (B) a prior art lithium super-battery cell with a lithium titanate as an anode active material and a cathode made of a functional material (e.g., functionalized nano graphene, CNT, or disordered carbon powder); (C) a prior art lithium super-battery cell with a lithium foil anode (but no nano-structured functional material) and a cathode made of functionalized graphene, CNT, or disordered carbon; (D) an example of a surface-mediated, lithium ion-exchanging battery device in accordance with one embodiment of the invention, which contains a nano-structured material (with or without a functional group capable of reacting with lithium ions or atoms) at the anode, a lithium source (
• FIG. 2 (A) The structure of a surface-mediated, lithium ion-exchanging battery device when it is made (prior to the first discharge or charge cycle), containing a nano- structured material at the anode, a lithium source (e.g.
• lithium foil or surface-stabilized lithium powder a porous separator, liquid electrolyte, a nano-structured non-functionalized material at the cathode;
• B The structure of this battery device after its first discharge operation (lithium is ionized with the lithium ions diffusing through liquid electrolyte to reach the surfaces of (functionalized or not-functionalized) nano-structured cathode and get rapidly captured by these surfaces);
• C The structure of this battery device after being recharged (lithium ions are released from the cathode surfaces, diffusing through liquid electrolyte to reach the surfaces of the (functionalized or not-functionalized) nano-structured anode and get rapidly plated onto these surfaces).
• the huge surface areas can serve as a supporting substrate onto which massive amounts of lithium ions can electro-deposit concurrently. Such a massive, simultaneous deposition cannot be accomplished with the anode current collector alone which has a low specific surface area.
• FIG. 3 (A) Schematic of a lithium storage mechanism wherein functional groups attached to an edge or surface of an aromatic ring or graphene sheet can readily react with a lithium ion to form a redox pair; (B) Theoretical formation of electric double layers as a minor or negligible mechanism of charge storage; (C) Lithium captured at a benzene ring center of a graphene plane; (D) Llithium atoms trapped in a graphene surface defect.
• FIG. 4 Examples of disordered carbon that can be used as a nano-structured material having high surface areas (in direct contact with electrolyte) at the anode and/or the cathode:
• A Schematic of a soft carbon, wherein neighboring stacks of graphene sheets or small aromatic rings are favorably oriented with respect to each other at a small angle that is conducive to the growth or merging (graphitizable);
• B hard carbon (non-graphitizable);
• C carbon black, having a large number of small aromatic ring domains arranged to form a nano- scaled spherical particle.
• an individual carbon black particle is activated to open up small gates that enable liquid electrolyte to access the edge- or surface-borne functional groups inside a particle, as illustrated in (D).
• FIG. 5 (A) A SEM image of curved nano graphene sheets. ; (B) A SEM image of another graphene morphology. These graphene morphologies can provide very high specific surface area (typically from 300 to 2,000 m 2 /g).
• FIG. 6 (A) Ragone plot of five types of cells: two surface-mediated, lithium ion- exchanging battery cells (one with functional groups in both electrode active materials and the other with non-functionalized active materials), a prior art lithium super-battery (formed of a Li metal anode and a functionalized disordered carbon cathode), a prior art symmetric supercapacitor composed of two functionalized disordered carbon electrodes (no lithium foil as a lithium source), and a symmetric supercapacitor based on LBL-CNTs (the data for CNT- based supercapacitor were read off a figure of Lee, et al).
• FIG. 7 (A) Ragone plots of a functionalized NGP -based lithium super-battery and two corresponding surface-mediated, lithium ion-exchanging battery devices (one with functional groups and one without a functional group). These data further demonstrate that the surface-mediated devices perform better than the super-battery, particularly when at the higher densities (higher power density region). (B) Long-term cycling stability of a SMC in accordance with one embodiment of the instant application vs. that of a SMC (with functional groups in its electrodes) of an earlier application.
• the discharge current density is 1 A/g
• FIG. 9 Cyclic voltammetry (CV) diagrams of a graphene-based symmetric supercapacitor (left curve) and a corresponding surface-mediated cell of the present invention having a lithium source implemented at the anode (right curve).
• FIG. 10 The Ragone plots of graphene surface-enabled Li ion-exchanging cells with different electrode thicknesses: The energy density and power density values were calculated based on total cell weight (A) and based on cathode weight only (B).
• FIG. 1 Cycle performance of several SMCs: Cell N (chemically reduced graphene- based), Cell AC (activated carbon), and Cell M (exfoliated graphite from artificial graphite).
• FIG. 12 Specific capacity plotted as a function of the electrode specific surface area for several cells.
• the electrodes were prepared from different graphene related materials.
• This invention provides an electrochemical energy storage device that is herein referred to as a surface-mediated, lithium ion-exchanging cell (or simply surface-mediated cell, SMC).
• this SMC device can provide a power density
• This device can exhibit an energy density comparable to that of a battery, and significantly higher than conventional supercapacitors.
• the surface-mediated, ion-exchanging battery is composed of a positive electrode containing a functionalized or non-functionalized material having a lithium-storing or lithium-capturing surface (the functionalized or non-functionalized material being preferably nano-structured with nano-scaled or meso-scaled pores and great amounts of surface areas), a negative electrode containing a high surface area material having a lithium-storing or lithium- capturing surface (preferably nano-structured with nano-scaled or meso-scaled pores), a porous separator disposed between the two electrodes, a lithium-containing electrolyte in physical contact with the two electrodes, and a lithium ion source implemented at the anode or the cathode.
• electrolyte types include organic liquid electrolyte, gel electrolyte, and ionic liquid electrolyte (preferably containing lithium ions), or a combination thereof, although one may choose to use aqueous or solid electrolytes.
• the lithium ion source can be selected from a lithium chip, lithium foil, lithium powder, surface stabilized lithium particles, lithium film coated on a surface of an anode or cathode active material, or a combination thereof.
• the anode active material is prelithiated, or pre-coated or pre-plated with lithium.
• the lithium source may be selected from a lithium metal alloy, a mixture of lithium metal or lithium alloy with a lithium intercalation compound, a lithiated compound, lithiated titanium dioxide, lithium titanate, lithium manganate, a lithium transition metal oxide, I ⁇ TisO ⁇ , or a combination thereof.
• the lithium intercalation compound or lithiated compound may be selected from the following groups of materials: (a) Lithiated silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), cobalt (Co), nickel (Ni), manganese (Mn), cadmium (Cd), and mixtures thereof; (b) Lithiated alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Co, Ni, Mn, Cd, and their mixtures; (c) Lithiated oxides, carbides, nitrides, sulfides, phosphides, selenides, tellurides, or antimonides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, Ti, Co, Ni, Mn, Cd, and mixtures or composites thereof, or (d) Lithiated salt
• the positive electrode preferably has a thickness greater than 5 ⁇ , more preferably greater than 50 ⁇ , and most preferably greater than 100 ⁇ .
• a surface-mediated, ion-exchanging battery device is given in FIG. 1(D) and FIG.2.
• FIG. 1(A) The internal structure of a conventional lithium-ion battery may be schematically shown in Fig. 1(A).
• the lithium ions move in the opposite direction, but must travel
• the operation of a conventional lithium-ion battery involves de- intercalation of lithium ions from the bulk (not the surface) of an electrode active material particle in one electrode (e.g., anode, during discharge) and intercalation of lithium ions into the bulk of an electrode active material particle in the opposite electrode (e.g. cathode).
• an electrode active material particle in one electrode e.g., anode, during discharge
• intercalation of lithium ions into the bulk of an electrode active material particle in the opposite electrode e.g. cathode
• diffusion through a liquid electrolyte is fast, but diffusion through a solid is dramatically slower (by 3-8 orders of magnitude).
• SMC surface-mediated cell
• the SMC is essentially intercalation- free, with most of the lithium being stored on the massive surface areas of the electrode active materials. Typically > 90% of lithium atoms are captured on graphene surfaces, and more typically less than 1% of lithium could accidentally enter the interior of a multi-layer graphene structure.
• the charge/discharge time of a SMC is limited only by the migration of lithium ions through liquid electrolyte (organic or ionic liquid), which is very fast and results in ultra-high power densities unmatched even by the supercapacitors (which are noted for their high power densities). This is further explained in what follows:
• the required diffusion time can be approximated as t ⁇ x 2 /D, according to a well-known kinetics equation.
• the total required time scale for a lithium ion to complete a charge or discharge process may be estimated as:
• t total (£a/2) 2 / electrolyte + (d 2flD a + (Lsf/D s + (Zc/2) 2 / e lectrolyte + ⁇ dJl lD c ( 1 )
• i3 ⁇ 4iectroiyte Li ion diffusion coefficient in electrolyte
• D a Li ion diffusion coefficient in an anode active material particle
• D s Li ion diffusion coefficient through a porous separator
• D c Li ion diffusion coefficient in a cathode active material particle.
• Li + in or through various liquid mediums or solid membrane or particles are given below (based on open literature data): liquid electrolyte (2 x 10 "6 cm 2 /s); separator (7.5 xlO "7 cm 2 /s); LiFeP0 4 cathode (10 ⁇ 13 cm 2 /s); Li 3 V 2 (P0 4 ) 3 cathode (10 13 to 10 ⁇ 9 cm 2 /s); nano-Si anode (10 " 12 cm 2 /s); graphite anode (1-4 x 10 "10 cm 2 /s); and Li 4 TisOi2 anode (1.3 x 10 "11 cm 2 /s).
• Li ions do not have to diffuse through a solid-state cathode particle and, hence, are not subject to the limitation by a low solid-state diffusion coefficient at the cathode (e.g. 10 "13 cm 2 /s in a LiFeP0 4 particle).
• the cathode active materials are highly porous, allowing liquid electrolyte to reach the interior of the pores where the functional groups are present to readily and reversibly react with lithium ions that diffuse into these pores through a liquid medium (not a solid medium) with a high diffusion coefficient (e.g., 2 x 10 "6 cm 2 /s).
• a liquid medium not a solid medium
• a high diffusion coefficient e.g. 2 x 10 "6 cm 2 /s.
• the final term, (d c /2) 2 /D c in Eq. (1) is practically non-existing.
• the required total diffusion time is now dictated by the thicknesses of the electrodes and the separator.
• the above discussion is based on the premise that the reversible reaction between a functional group and a lithium ion in the electrolyte is fast, and the whole charge-discharge process is not reaction-controlled.
• the cathode is a meso-porous structure of a nano carbon material (e.g., activated carbon), but lithium titanate or graphite particles constitute the anode (schematically illustrated in Fig. 1(B)).
• a cell discharge situation lithium ions must diffuse out of lithium titanate particles or graphite particles (a slow de- intercalation step), and then migrate in liquid electrolyte across the anode thickness.
• lithium ions must move (in liquid electrolyte) across a porous separator, diffuse across part of the cathode thickness in liquid electrolyte to reach a location close to a surface area of a nano-structured cathode active material.
• solid-state diffusion There is no need for solid-state diffusion at the cathode side. The whole process is essentially dictated by the solid-state diffusion at the anode.
• this LIC should exhibit a slower kinetic process (hence, a lower power density) as compared to the super-battery (partially surface-mediated) and the fully surface mediated cell (SMC) herein disclosed.
• the first group is a conventional lithium-ion battery with a graphite particle anode and lithium iron phosphate cathode (Gr/LiFeP0 4 ).
• the second and third groups are both
• LIC Li 4 Ti 5 0i2/f-CNM
• the anode is composed of Li 4 Ti 5 0i2 particles and the cathode is functionalized carbon nano material (f-CNM), such as CNT or activated carbon (AC).
• f-CNM carbon nano material
• AC activated carbon
• the fifth group is a partially surface-mediated cell (Li foil/f-CNM) where the anode is a lithium
• CNTs carbon nanotubes
• NGPs nano graphene platelets
• Gr/LiFeP0 4 1.00E-06 200 20 2.00E-10 100 7.50E-07 200 1 1.0E-13 3.02E+04
• Nano-Si/LiFeP0 4 1.00E-06 200 0.1 1.00E-12 100 7.50E-07 200 0.1 1.0E-13 5.08E+02
• Li foil/f-CNM 1.00E-06 10 0 1.30E-11 10 7.50E-07 0.3 0.1 1.0E-6 5.84E-01
• Li foil/f-CNM 1.00E-06 10 0 1.30E-1 1 10 7.50E-07 3 0.1 1.0E-6 6.06E-01
• Li foil/f-CNM 1.00E-06 30 0 1.30E-1 1 10 7.50E-07 30 0.1 1.0E-6 4.83E+00
• Table 1(b) The required diffusion time to reach a particle in the anode (t La ),
• conventional lithium ion batteries exhibit very low power densities (typically 100-500 W/Kg) and very long re-charge times.
• the required diffusion times are between 235 sec ( ⁇ 4 minutes) for a cathode thickness of 200 ⁇ and 1.96 sec for an ultra-thin cathode (e.g., 0.3 ⁇ LBL f-CNT as prepared by the layer-by-layer method of the MIT research group [S. W. Lee, et al, Nature Nanotechnology , 5 (2010) 531 - 537]).
• an ultra-thin electrode 0.3-3 ⁇
• the electrode thickness is a dominating factor.
• the total diffusion time can be as short as ⁇ 0.6 sec (when the cathode thickness is 0.3 ⁇ or 3 ⁇ ), which increases to 103 sec (still less than 2 minutes) when the cathode thickness is 200 ⁇ .
• our graphene-based surface-mediated cells (typically having an electrode thickness of 100-300 ⁇ ) perform better than the thin electrode-based LBL f- CNT cell (partially surface mediated).
• the above calculations for the super-batteries containing a lithium foil as the anode are applicable to the instant surface -mediated energy storage device as well, with the exception that the lithium foil thickness may be replaced by the thickness of a nano-structured anode.
• the lithium source lithium particles or pieces of lithium foil
• the lithium foil may be compressed against the nano- structured anode, or the lithium particles may be incorporated in the nano-structured anode when the battery device is made.
• the nano-structured anode e.g. NGP or CNT-based mat
• Li foil/f-CNM lithium super-battery
• d a particle diameter
• Li foil is electrochemically ionized to release ions.
• this surface-controlled reaction was assumed to be fast and not rate-limiting. In reality, this surface reaction can become rate- limiting when a high discharge rate is required (i.e. when the external circuit or load demands a high current density). This limitation may not be controlled by the surface ionization rate itself, but instead by the limited amount of surface area of the lithium foil during the first discharge cycle. In other words, at a given moment of time during the first discharge, there is only so much surface area from which lithium ions can be released simultaneously.
• This nano-structured anode is preferably composed of a nano carbon material having a high specific surface area
• nano graphene platelet GP, collectively referring to both single-layer and multi-layer versions of graphene, graphene oxide, graphene fluoride, doped graphene, etc), carbon nano-tube (single-walled or multi-walled), carbon nano-fiber (vapor-grown, electro-spun polymer derived, etc), disordered carbon, metal nano- wire, conductive nano-wire, etc.
• the nano-structured anode preferably has a specific surface area greater than 100 m 2 /g, more preferably greater than 500 m 2 /g, further preferably greater than 1,000 m 2 /g, even more preferably greater than 1,500 m 2 /g, and most preferably greater than 2,000 m 2 /g. These surfaces are preferably in direct contact with electrolyte (preferably organic liquid electrolyte) to capture lithium ions directly therefrom or to release lithium ions directly thereto.
• electrolyte preferably organic liquid electrolyte
• the lithium foil or lithium particles get ionized, releasing lithium ions at the anode which travel into the cathode side and get captured by the graphene surfaces of the cathode.
• these lithium ions Upon re-charging, these lithium ions return to the anode and uniformly deposit onto the massive surfaces of the nano-structured anode, forming an ultra-thin coating of lithium thereon.
• Such a huge surface area of lithium-decorated surfaces enables simultaneous release of great amounts of lithium ions during subsequent discharge cycles.
• This concurrent, massive releasing of lithium ions had not been feasible in a battery with an anode current collector alone whose specific surface area is normally much less than 1 m 2 /g.
• the high specific surface area of the nano-structured anode, » 100 m 2 /g enables both fast charging and fast discharging, achieving a high power density.
• the surface-mediated, lithium ion-exchanging battery device is also patently distinct from the conventional supercapacitor in the following aspects: (1) The conventional or prior art supercapacitors do not have a lithium ion source implemented at the anode when the cell is made.
• the electrolytes used in these prior art supercapacitors are mostly lithium-free or non- lithium-based. Even when a lithium salt is used in a supercapacitor electrolyte, the solubility of lithium salt in a solvent essentially sets an upper limit on the amount of lithium ions that can participate in the formation of electric double layers of charges inside the electrolyte phase (near but not on an electrode material surface, as illustrated in FIG. 3(B)). As a consequence, the specific capacitance and energy density of the resulting supercapacitor are relatively low (e.g. typically ⁇ 6 Wh/kg based on total cell weight), as opposed to, for instance, 160 Wh/kg (based on total cell weight) of the presently invented surface-mediated cells.
• the prior art supercapacitors are based on either the electric double layer (EDL) mechanism or the pseudo-capacitance mechanism to store their charges. In both mechanisms, no massive lithium ions are exchanged between the two electrodes (even when a lithium salt is used in electrolyte). In the EDL mechanism, for instance, the cations and anions in the electrolyte pair up to form electric double layers of charges near the surfaces of an electrode active material (but not on the surface). The cations are not captured or stored in or on the surfaces of the electrode active material.
• EDL electric double layer
• pseudo-capacitance mechanism to store their charges. In both mechanisms, no massive lithium ions are exchanged between the two electrodes (even when a lithium salt is used in electrolyte). In the EDL mechanism, for instance, the cations and anions in the electrolyte pair up to form electric double layers of charges near the surfaces of an electrode active material (but not on the surface). The cations are not captured or stored in or on the surfaces of the electrode active material.
• lithium atoms can be captured or trapped at the defect sites, graphene edges, benzene ring centers of a graphene plane, or functional groups on graphene surfaces.
• both the cations and anions co-exist in both the anode and the cathode when the supercapacitor is in a charged state.
• negative charges are present on the surfaces of activated carbon particles, which attract the positively charged species to form one layer of positive charges near these surfaces.
• negatively charged species that are attracted by these positive charges to form a layer of negative charges nearby.
• the opposite electrode of the supercapacitor has a similar arrangement, but the charges are opposite in polarity. This is the well-known concept of Helmholtz diffuse charge layers in electrochemistry.
• the charges on activated carbon particle surfaces are used or disappear and, consequently, the negatively charged species and the positively charged species of the salt become randomized and stay inside the electrolyte phase (not on the activated carbon particle surfaces).
• the SMC is in a charged state, the majority of lithium ions are attracted to attach or electro-plate on the graphene surfaces at the anode and the cathode side is essentially free of any lithium. After discharge, essentially all the lithium atoms are captured by the cathode active material surfaces with no or little lithium staying inside the electrolyte.
• the prior art symmetric supercapacitors (EDL supercapacitors) using a lithium salt- based organic electrolyte operate only in the range of 0 - 3 volts. They cannot operate above 3 volts; there is no additional charge storing capability beyond 3 volts and actually the organic electrolyte typically begins to break down at 2.7 volts.
• the surface-mediated cells of the present invention operate typically in the range of 1.0 - 4.5 volts, most typically in the range of 1.5-4.5 volts (e.g. please see FIG. 9), but preferably in the range of 1.5-4.0 volts.
• These two ranges of operating voltage are reflections of totally distinct charge storage mechanisms. Even though, on the paper, there appears to be an overlap of 1.5 - 3.0 volts between these two voltage ranges (range of 1-3 and range of 1.5-4.5 volts), this overlap is artificial, coincidental, and not scientifically meaningful because the charge storage mechanisms are
• the prior art EDL supercapacitors typically have an open-circuit voltage of 0-0.3 volts.
• the SMC typically has an open-circuit voltage of > 0.6 volts, more commonly > 0.8 volts, and most commonly > 1.0 volts (some > 1.2 volts or even > 1.5 volts, depending on the type and amount of the anode active material relative to the cathode, and the amount of the lithium source).
• FIG. 1 1 show the cycle performance of several SMCs: Cell N (graphene-based), Cell AC (activated carbon), and Cell M (exfoliated graphite from artificial graphite).
• Cell N graphene-based
• Cell AC activate carbon
• Cell M exfoliated graphite from artificial graphite
• the specific capacity of an electrode in a Li-ion exchanging, surface-mediated cell appears to be governed by the number of active sites on graphene surfaces of a nano-structured carbon material that are capable of capturing lithium ions therein or thereon.
• the nano-structured carbon material may be selected from activated carbon (AC), carbon black (CB), hard carbon, soft carbon, exfoliated graphite (EG), and isolated graphene sheets (nano graphene platelet or NGP) from natural graphite or artificial graphite. These carbon materials have a common building block - graphene or graphene-like aromatic ring structure.
• Mechanism 1 The geometric center of a benzene ring in a graphene plane is an active site for a lithium atom to adsorb onto;
• Mechanism 2 The defect site on a graphene sheet is capable of trapping a lithium ion;
• Mechanism 3 The cations (Li + ) and anions (from a Li salt) in the liquid electrolyte are capable of forming electric double layers of charges near the electrode material surfaces;
• Mechanism 4 A functional group on a graphene surface/edge can form a redox pair with a lithium ion.
• Mechanism 1 Lithium atoms are capable of forming stable interactions with C atoms on a graphene plane when electrolyte is not present to compete for lithium.
• the Li-C bond in such a layer would not result in an sp 2 to an sp 3 transition of carbon orbitals.
• Energy calculations have indicated the possible stability of such Li atom-adsorbed graphene layers (with lithium atoms bonded to the centers of benzene rings of a graphene plane) without the presence of electrolyte.
• the Li-adsorbed graphene layer (FIG. 3(D)) can be spontaneously formed in the presence of electrolyte.
• lithium ions have excellent chemical compatibility with other ingredients in the electrolyte (this is why they naturally exist in the electrolyte) and these ingredients (e.g. solvent) would compete against the graphene surface for trying to keep the lithium ions in the solvent phase, as opposed to being "high-jacked” by graphene surface .
• the bonding between lithium atoms and graphene surface has been most surprisingly strong.
• the SMC electrolyte is typically composed of a lithium ion salt dissolved in a solvent.
• the electrolytic salts can be selected from lithium perchlorate (LiC10 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium borofluoride (LiBF 4 ), lithium hexafluoroarsenide (LiAsF 6 ), and lithium trifluoro-metasulfonate
• EDL electric double layers
• cations e.g. Li +
• counter ions e.g. PF 6 " and BF 4 " anions
• the maximum contribution of Mechanism 3 to the overall charge storage capacity is dictated by the concentration of cations or anions.
• the EDL mechanism typically contributes to less than approximately 10% (more typically ⁇ 5%) of the total lithium ion storage capacity of a SMC, explained below:
• FIG. 9 are CV diagrams of a graphene-based supercapacitor and the corresponding SMC. In both cells, the electrolyte is 1M
• Both un-separated graphite worms (exfoliated graphite) and the separated graphene sheets (NGPs) can have surface- or edge- borne functional groups.
• the SMC in the instant application is based mainly upon Mechanisms 1 and 2.
• the electric double layer mechanism contributes to less than 10% (mostly less than 5%) of the charge storage capacity of a SMC.
• the anode or the cathode contains some multi-layer graphene platelets, there might be some intercalation of lithium into the bulk of an active material if the SMC operating voltage goes below 1.5 volts. Even in this case, no more than 20% of the lithium is stored in the bulk of an anode active material when the device is in a charged state, or no more than 20% of the lithium is stored in the bulk of the cathode active material when the device is in a discharged state.
• no more than 10% of the lithium is stored in the bulk of the anode active material when the device is in a charged state, or no more than 10% of the lithium is stored in the bulk of the cathode active material when the device is in a discharged state.
• Nano-structured materials for use in the anode or cathode of the instant invention may preferably contain nano graphene platelet (NGP), carbon nano-tube (CNT), or disordered carbon.
• NGP nano graphene platelet
• CNT carbon nano-tube
• disordered carbon can be used as a supporting substrate for other organic or polymeric functional materials that have useful functional groups (e.g., carbonyl) but are not electrically conducting.
• the CNT is a better known material in the nano material industry and, hence, will not be further discussed herein. What follows is a description of NGP and nano-structured disordered carbon:
• Nano Graphene Platelet [0098] The applicant's research group has been actively developing applications for single- layer graphene [B. Z. Jang and W. C. Huang, "Nano-scaled Graphene Plates," US Patent Application No. 10/274,473 (10/21/2002); now U.S. Pat. No. 7,071,258 (07/04/2006)] including the use of graphene for supercapacitor [L. Song, A. Zhamu, J. Guo, and B. Z. Jang "Nano-scaled Graphene Plate Nanocomposites for Supercapacitor Electrodes” US Patent Appl. No. 11/499,861 (08/07/2006), now US Pat. No.
• Single-layer graphene or the graphene plane (a layer of carbon atoms forming a hexagonal or honeycomb-like structure) is a common building block of a wide array of graphitic materials, including natural graphite, artificial graphite, soft carbon, hard carbon, coke, activated carbon, carbon black, etc.
• graphitic materials typically multiple graphene sheets are stacked along the graphene thickness direction to form an ordered domain or crystallite of graphene planes. Multiple crystallites of domains are then connected with disordered or amorphous carbon species.
• nano graphene platelets or "graphene materials” collectively refer to single-layer and multi-layer versions of graphene, graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, doped graphene, etc.
• the NGP is described as having a length (the largest dimension), a width (the second largest dimension), and a thickness.
• the thickness is the smallest dimension, which is no greater than 100 nm and, in the present application, no greater than 10 nm (preferably no greater than 5 nm).
• the NGP may be single-layer graphene.
• the length and width are referred to as diameter.
• there is no limitation on the length and width but they are preferably smaller than 10 ⁇ and more preferably smaller than ⁇ ⁇ . We have been able to produce NGPs with length smaller than 100 nm or larger than 10 ⁇ .
• the NGP can be pristine graphene (with essentially 0% oxygen content, typically ⁇ 2% oxygen) or graphene oxide (typically from 10 up to approximately 45% by weight oxygen).
• Graphene oxide can be thermally or chemically reduced to become reduced graphene oxide (typically with an oxygen content of 1-20%, mostly below 5% by weight).
• the oxygen content was preferably in the range of 5% to 30% by weight, and more preferably in the range of 10% to 30% by weight.
• the SMC electrode typically has less than 5% oxygen (hence, essentially functional group-free) and, in many cases, less than 2%.
• the specific surface area accessible to liquid electrolyte is the single most important parameter in dictating the energy and power densities of a SMC.
• FIG.5(A) shows a graphene that is herein referred to as the curved graphene platelet or sheet.
• Curved NGPs are capable of forming a meso-porous structure having a desired pore size range (e.g. slightly > 2 nm) when they were stacked together to form an electrode. This size range appears to be conducive to being accessible by the commonly used lithium-containing electrolytes.
• the curved NGPs may be produced by:
• a laminar graphite material e.g., natural graphite powder
• an oxidant e.g., concentrated sulfuric acid and nitric acid, respectively
• GIC graphite intercalation compound
• GO graphite oxide
• a functionalizing agent e.g., an oxidizing agent such as sulfuric acid, nitric acid, hydrogen peroxide or, preferably, carboxylic acid, formic acid, etc., which is a source of-COOH group
• oxidizing agent such as sulfuric acid, nitric acid, hydrogen peroxide or, preferably, carboxylic acid, formic acid, etc., which is a source of-COOH group
• Stirring, mechanical shearing, or ultrasonication, and/or temperature can be used to break up graphite worms to form separated/isolated NGPs and/or to help attach desired functional groups to the oxidized NGPs, resulting in the formation of functionalized NGPs to obtain a graphene-liquid suspension;
• steps (a) to (b) are the most commonly used steps to obtain exfoliated graphite (FIG. 5B) and graphene oxide platelets in the field.
• Oxidized NGPs or GO platelets may be chemically reduced to recover conductivity properties using hydrazine as a reducing agent, before, during, or after chemical functionalization.
• the carboxylic acids being environmentally benign, are particularly desirable functionalizing agents for imparting carbonyl or carboxylic groups to NGPs in one embodiment.
• the carboxylic acid may be selected from the group consisting of aromatic carboxylic acid, aliphatic or cycloaliphatic carboxylic acid, straight chain or branched chain carboxylic acid, saturated and unsaturated monocarboxylic acids, dicarboxylic acids and polycarboxylic acids that have 1-10 carbon atoms, alkyl esters thereof, and combinations thereof.
• the carboxylic acid is selected from the group consisting of saturated aliphatic carboxylic acids of the formula H(CH2)nCOOH, wherein n is a number of from 0 to 5, including formic, acetic, propionic, butyric, pentanoic, and hexanoic acids, anydrides thereof, reactive carboxylic acid derivatives thereof, and combinations thereof.
• the most preferred carboxylic acids are formic acid and acetic acid.
• NGPs may be subjected to the following treatments, separately or in combination, before or after the functionalization operation:
• activation treatment analogous to activation of carbon black materials
• the activation treatment can be accomplished through C02 physical activation, KOH chemical activation, or exposure to nitric acid, fluorine, or ammonia plasma.
• a alternative way to impart functional groups to NGPs in a more controlled manner involves producing pristine NGPs without going through the conventional chemical intercalation/ oxidation procedure.
• the produced non-oxidized graphene naturally having edge surfaces being more chemically active
• Functional groups were attached to the edge surfaces first and essentially exhaust the active sites at the edge surfaces before any significant amount of functional groups began to attach themselves to the basal planes.
• the graphite has never been intercalated or oxidized and, hence, requires no subsequent chemical reduction. This method is fast, environmentally benign, and can be readily scaled up, paving the way to the mass production of pristine nano graphene materials. The same method was later studied by others and now more commonly referred to as the "liquid phase production.”
• the material may then be exposed to an oxidation or functionalization treatment using, for example, a gaseous-phase or liquid acid or acid mixture.
• the pristine NGPs may also be immersed in carboxylic acids at a desired temperature for a period of time to obtain NGPs with a desired level of functionalization.
• the oxidation treatment comprises subjecting the pristine NGP material to an oxidizing agent preferably selected from ozone, sulfonic (S03) vapor, an oxygen-containing gas, hydrogen peroxide vapor, nitric acid vapor, or a combination thereof.
• the treatment comprises subjecting the pristine NGP material to an oxidizing agent in a hydrogen-containing environment.
• oxidation treatment can be conducted by immersing NGPs in a liquid acid and/or oxidizer environment, such a procedure requires a subsequent water-rinsing and purification step (such a rinsing procedure is not as tedious as required in the case of conventional sulfuric acid-intercalation graphite, nevertheless).
• a gaseous treatment requiring no post-treatment rinsing is preferred.
• Conductive functionalized NGPs can be produced with an oxygen content no greater than 25% by weight, preferably between 5% and 25% by weight. Presumably, a majority of the functional groups are located at the edge surfaces of NGPs since the electrical conductivity would not be significantly reduced. Beyond 25% of over-all oxygen content, functional groups begin to appear on graphene plane surfaces, interrupting electron- conducting paths. The oxygen contents were determined using chemical elemental analysis and X-ray photoelectron spectroscopy (XPS).
• the partially oxidized NGP can be further functionalized by carrying out an additional step of contacting the partially oxidized NGPs with a reactant so that a functional group is added to a surface or edge of the nano graphene platelet.
• the functional group may contain alkyl or aryl silane, alkyl or aralkyl group, hydroxyl group, amine group,
• the disordered carbon material may be selected from a broad array of
• a disordered carbon material is typically formed of two phases wherein a first phase is small graphite crystal(s) or small stack(s) of graphite planes (with typically up to 10 graphite planes or aromatic ring structures overlapped together to form a small ordered domain) and a second phase is non-crystalline carbon, and wherein the first phase is dispersed in the second phase or bonded by the second phase.
• the second phase is made up of mostly smaller molecules, smaller aromatic rings, defects, and amorphous carbon.
• the optional desired functional groups are attached to an edge or plane surface of a aromatic ring structure.
• the disordered carbon is highly porous (e.g., activated carbon) or present in an ultra-fine powder form (e.g. carbon black) having nano-scaled features (hence, a high specific surface area).
• Soft carbon refers to a carbonaceous material composed of small graphite crystals wherein the orientations of these graphite crystals or stacks of graphene sheets are conducive to further merging of neighboring graphene sheets or further growth of these graphite crystals or graphene stacks (FIG. 4(A)) using a high-temperature heat treatment (graphitization). Hence, soft carbon is said to be graphitizable.
• Hard carbon refers to a carbonaceous material composed of small graphite crystals wherein these graphite crystals or stacks of graphene sheets are not oriented in a favorable directions (e.g. nearly perpendicular to each other) and, hence, are not conducive to further merging of neighboring graphene sheets or further growth of these graphite crystals or graphene stacks (i.e., not graphitizable).
• Carbon black (CB), acetylene black (AB), and activated carbon (AC) are typically composed of domains of aromatic rings or small graphene sheets, wherein aromatic rings or graphene sheets in adjoining domains are somehow connected through some chemical bonds in the disordered phase (matrix).
• These carbon materials are commonly obtained from thermal decomposition (heat treatment, pyrolyzation, or burning) of hydrocarbon gases or liquids, or natural products (wood, coconut shells, etc).
• polymeric carbons by simple pyrolysis of polymers or petroleum/coal tar pitch materials has been known for approximately three decades.
• polymers such as polyacrylonitrile (PAN), rayon, cellulose and phenol formaldehyde were heated above 300°C in an inert atmosphere they gradually lost most of their non-carbon contents.
• the resulting structure is generally referred to as a polymeric carbon.
• polymeric carbons can be made to be insulating, semi-conducting, or conducting with the electric conductivity range covering approximately 12 orders of magnitude. This wide scope of conductivity values can be further extended by doping the polymeric carbon with electron donors or acceptors.
• Polymeric carbons can assume an essentially amorphous structure, or have multiple graphite crystals or stacks of graphene planes dispersed in an amorphous carbon matrix. Depending upon the HTT used, various proportions and sizes of graphite crystals and defects are dispersed in an amorphous matrix. Various amounts of two-dimensional condensed aromatic rings or hexagons (precursors to graphene planes) can be found inside the microstructure of a heat treated polymer such as a PAN fiber. An appreciable amount of small-sized graphene sheets are believed to exist in PAN-based polymeric carbons treated at 300-l,000°C.
• the first class includes semi-crystalline PAN in a fiber form. As compared to phenolic resin, the pyrolized PAN fiber has a higher tendency to develop small crystallites that are dispersed in a disordered matrix.
• the second class represented by phenol formaldehyde, is a more isotropic, essentially amorphous and highly cross-linked polymer.
• the third class includes petroleum and coal tar pitch materials in bulk or fiber forms.
• the precursor material composition, heat treatment temperature (HTT), and heat treatment time (Htt) are three parameters that govern the length, width, thickness (number of graphene planes in a graphite crystal), and chemical composition of the resulting disordered carbon materials.
• PAN fibers were subjected to oxidation at 200-350°C while under a tension, and then partial or complete carbonization at 350-1, 500°C to obtain polymeric carbons with various nano-crystalline graphite structures (graphite crystallites). Selected samples of these polymeric carbons were further heat-treated at a temperature in the range of 1,500-2,000°C to partially graphitize the materials, but still retaining a desired amount of amorphous carbon (no less than 10%). Phenol formaldehyde resin and petroleum and coal tar pitch materials were subjected to similar heat treatments in a temperature range of 500 to 1,500°C.
• the disordered carbon materials obtained from PAN fibers or phenolic resins are preferably subjected to activation using a process commonly used to produce activated carbon (e.g., treated in a KOH melt at 900°C for 1-5 hours).
• This activation treatment is intended for making the disordered carbon meso-porous, enabling liquid electrolyte to reach the edges or surfaces of the constituent aromatic rings SMC device is made.
• Such an arrangement enables the lithium ions in the liquid to readily deposit onto graphene surfaces without having to undergo solid-state diffusion.
• Certain grades of petroleum pitch or coal tar pitch may be heat-treated (typically at 250-500°C) to obtain a liquid crystal-type, optically anisotropic structure commonly referred to as meso-phase.
• This meso-phase material can be extracted out of the liquid component of the mixture to produce meso-phase particles or spheres.
• these meso-phase particles or spheres may be subjected to further heat treatments for graphitization.
• Physical or chemical activation may be conducted on all kinds of disordered carbon (e.g. a soft carbon, hard carbon, polymeric carbon or carbonized resin, meso-phase carbon, coke, carbonized pitch, carbon black, activated carbon, or partially graphitized carbon) to obtain activated disordered carbon.
• disordered carbon e.g. a soft carbon, hard carbon, polymeric carbon or carbonized resin, meso-phase carbon, coke, carbonized pitch, carbon black, activated carbon, or partially graphitized carbon
• the activation treatment can be accomplished through oxidizing, CO 2 physical activation, KOH or NaOH chemical activation, or exposure to nitric acid, fluorine, or ammonia plasma (for the purpose of creating electrolyte-accessible pores, not for functionalization).
• organic- or polymer-based functional materials may contain pendant functional groups that are capable of rapidly and reversibly reacting with lithium ions in liquid or gel electrolyte.
• any of these non-conducting functional materials may be preferably combined with (e.g. chemically bonded or attached to) a nano-structured material, such as the NGP, CNT, disordered carbon, nanowire, and nano-fiber.
• a nano-structured material such as the NGP, CNT, disordered carbon, nanowire, and nano-fiber.
• both graphene and the constituent aromatic rings of a disordered carbon can have, on their edges or surfaces, functional groups that can react with the matting functional groups on the aforementioned functional materials (e.g. the hydroxyl group on Tetrahydroxy-p-benzoquinone).
• these organic or polymeric functional materials may be simply supported on a surface of a nano-structured material (e.g., graphene or nano-wire surface).
• the nano-structure material e.g. graphene and disordered carbon
• the cathode active material and/or the anode active material of the presently invented SMC may be selected from (a) a porous disordered carbon material selected from a soft carbon, hard carbon, polymeric carbon or carbonized resin, meso-phase carbon, coke, carbonized pitch, carbon black, activated carbon, or partially graphitized carbon; (b) a graphene material selected from a single-layer sheet or multi-layer platelet of graphene, graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene, functionalized graphene, or reduced graphene oxide; (c) exfoliated graphite; (d) meso-porous carbon; (e) a carbon nanotube selected from a single-walled carbon nanotube or multi-walled carbon nanotube; (f) a carbon nano-fiber, metal nano-wire, metal oxide nano-wire or fiber, or conductive polymer
• EXAMPLE 1 Functionalized and Non-functionalized Soft Carbon (One Type of Disordered Carbon), Soft Carbon-Based Super-Battery and Surface-Mediated Cells
• Non-functionalized and functionalized soft carbon materials were prepared from a liquid crystalline aromatic resin.
• the resin was ground with a mortar, and calcined at 900°C for 2 h in a 2 atmosphere to prepare the graphitizable carbon or soft carbon.
• the resulting soft carbon was mixed with small tablets of KOH (four- fold weight) in an alumina melting pot. Subsequently, the soft carbon containing KOH was heated at 750°C for 2 h in N 2 . Upon cooling, the alkali-rich residual carbon was washed with hot water until the outlet water reached a pH value of 7. The resulting material is activated, but non-functionalized soft carbon.
• the electrolyte solution was 1 M LiPF 6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a 3 :7 volume ratio.
• the separator was wetted by a minimum amount of electrolyte to reduce the background current.
• Cyclic voltammetry and galvanostatic measurements of the lithium cells were conducted using an Arbin 32-channel supercapacitor-battery tester at room temperature (in some cases, at a temperature as low as -40°C and as high as 60°C).
• sample- 1-CA As a reference sample (Sample- 1-CA), similar coin cells, containing a piece of lithium foil at the anode but without a nano-structured carbon layer, were also made and tested. This is a prior art lithium super-battery. Additionally, a symmetric supercapacitor with both electrodes being composed of a functionalized soft carbon material, but containing no additional lithium source than what is available in the liquid electrolyte, was also fabricated and evaluated (Sample- 1-CB). The data was compared to the data of the prior art symmetric supercapacitor (f-LBL-CNT/f-LBL-CNT) of Lee, et al.
• the power density of a known supercapacitor is typically of 5,000-10,000 W/Kg, but that of a lithium-ion battery is 100-500 W/kg. This implies that the surface-mediated lithium ion-exchanging cells have an energy density comparable to that of a modern battery, which is 5-16 times higher than the energy density of conventional supercapacitors.
• the SMCs also exhibit a power density (or charge-discharge rates) significantly higher than the power density of conventional electrochemical supercapacitors.
• the non-functionalized surface-mediated cells exhibit much better cycle stability as compared to the functional material-based cell.
• the non-functionalized surface cell maintains a high energy density even after 2500 charge/discharge cycles.
• the functionalized surface-controlled cell suffers a faster decay with repeated charges/discharges.
• the cells of Sample- 1 and Samples- 1-CA work on the redox reactions of lithium ions with select functional groups on the surfaces/edges of aromatic rings at the cathode side (Sample- 1 -CA) and at both the cathode and the anode (Sample- 1).
• These functional groups attached to both the edge and plane surfaces of aromatic rings (small graphene sheets), are capable of rapidly and reversibly react with lithium.
• the SMCs based on non- functionalized surfaces perform even better.
• the surface-mediated lithium ion-exchanging battery of the present invention is a revolutionary new energy storage device that fundamentally differs from a supercapacitor and a lithium-ion battery. In terms of both energy density and power density, neither conventional device even comes close.
• EXAMPLE 2 NGPs from sulfuric acid intercalation and exfoliation of MCMBs
• MCMB 2528 microbeads (Osaka Gas Chemical Company, Japan) have a density of about 2.24 g/cm 3 ; a median size of about 22.5 microns, and an inter-planar distance of about 0.336 nm.
• the sample was then washed repeatedly with deionized water until the pH of the filtrate was neutral.
• the slurry was dried and stored in a vacuum oven at 60°C for 24 hours.
• the dried powder sample was placed in a quartz tube and inserted into a horizontal tube furnace pre-set at a desired temperature, 600°C for 30 seconds to obtain exfoliated graphite.
• the exfoliated MCMB sample was subjected to further functionalization in formic acid at 25°C for 30 minutes in an ultrasonication bath to obtain functionalized graphene (f- NGP).
• Non- functionalized NGPs were also obtained via ultrasonication of exfoliated MCMBs in water without any functionalizing agent.
• NGPs were used as both a cathode material and as an anode material.
• a lithium foil was added between the anode and the separator.
• the anode is a lithium foil (no nano-structured NGP) and the cathode is f-NGP.
• the Ragone plot for these three types of cells is shown in FIG. 7.
• Both of the NGP -based, surface-mediated, lithium ion-exchanging battery devices exhibit significantly higher energy densities and power densities than those of the corresponding super-battery, particularly at relatively high current densities (higher power density data points in the plot).
• the non-functionalized surface-mediated cell performs better than the functionalized surface-controlled cell in terms of energy density and power density. Also quite significantly and surprisingly, as compared with the functionalized surface- mediated cell, the non-functionalized surface-mediated cell exhibits a much better long-term stability as repeated charges/discharges continue (FIG. 8).
• EXAMPLE 3 Organic 3,4,9, lO-perylenetetracarboxylicacid-dianhydride
• PTCDA PTCDA sulfide polymer
• Enolation is an important reaction of carbonyl double bonds, which can be stabilized by conjugated structures. Enolation makes it possible for Li ions to be captured or released reversibly at the positions of oxygen atoms when the carbonyl groups are reduced or oxidized, implying that it could be used as a novel organic energy-storage system in Li-ion batteries.
• each carbonyl group can receive one electron and capture one Li ion to form lithium enolate, and the Li ions can be released in the reverse oxidation process.
• the first type was a simple mixture of PTCDA and carbon black (approximately 20% by weight), bonded by PVDF (Sample 3 -A).
• the second type was a similar mixture of PTCDA sulfide polymer again with carbon black as a conductive filler.
• the PTCDA sulfide polymer was synthesized by using PTCDA (bright red) and sublimed sulfur as starting materials, which were fully mixed by grinding with a mass ratio of 1 : 1. The mixtures were reacted at 500°C in a flowing argon atmosphere for 3 h to obtain black-red powders of PTCDA sulfide polymer.
• This synthesis route was originally proposed by X. Y. Han, et al. ["Aromatic carbonyl derivative polymers as high-performance Li-ion storage materials," Adv. Material, 19, 1616-1621 (2007)].
• EXAMPLE 4 SMCs based on graphene materials (NGPs) from natural graphite, carbon fibers, and artificial graphite and based on carbon black (CB) and treated CB
• Oxidized NGP or graphene oxide (GO) was prepared with a modified Hummers' method that involved exposing the starting graphitic materials to a mixture of sulfuric acid, sodium nitrate, and potassium permanganate at a ratio of 4: 1 :0.1 for 72 hours. The resulting GO was then thoroughly rinsed with water to obtain GO suspension, which was followed by two different routes of material preparation. One route involved subjecting the GO suspension to ultrasonication to obtain isolated graphene oxide sheets suspended in water (for Cell-N). The other route involved spray-drying GO suspension to obtain graphite
• intercalation compound GIC
• GO powder GO powder
• the GIC or GO powder was then thermally exfoliated at 1,050°C for 45 seconds to obtain exfoliated graphite or graphite worms (Cell- G).
• Exfoliated graphite worms from artificial graphite and carbon fibers were then subjected to ultrasonication to separate or isolate oxidized graphene sheets (Cell-M and Cell-C, respectively).
• Carbon black (CB) was subjected to a chemical treatment similar to the Hummers' method to open up nano-gates, enabling electrolyte access to the interior (Cell t- CB).
• Each electrode composed of 85% graphene, 5% Super-P (AB-based conductive additive), and 10% PTFE, was coated on Al foil.
• the thickness of the electrode was typically around 150-200 ⁇ , but an additional series of samples with thicknesses of approximately 80, 100, 150 ⁇ was prepared to evaluate the effect of electrode size on the power and energy densities of the resulting supercapacitor-battery cells. Electrodes as thin as 20 ⁇ were also made for comparison. The electrode was dried in a vacuum oven at 120°C for 12 hours before use. The negative electrode was Li metal supportd on a layer of graphene sheets. Coin-size cells were assembled in a glove box using 1M LiPF ⁇ EC+DMC as electrolyte.
• EXAMPLE 5 Functionalized and Non-functionalized Activated Carbon
• Activated carbon (AC, from Ashbury Carbon Co.) was treated with an acid solution (sulfuric acid, nitric acid, and potassium permanganate at a ratio of 4: 1 :0.05) for 24 hours. Upon completion of the reaction, the mixture was poured into deionized water and filtered. The treated AC was repeatedly washed in a 5% solution of HC1 to remove most of the sulphate ions. The sample was then washed repeatedly with deionized water until the pH of the filtrate was neutral. The slurry was subjected to further functionalization in formic acid at 25°C for 30 minutes in an ultrasonication bath.
• AC Activated carbon
• f-AC chemically functionalized activated carbon
• the NGP-mediated electrodes provide the cells (e.g. Cell M) with a specific capacitance of 127 mAh/g at a current density of 1 A/g, reaching a cell-level energy density of 85 Wh/kg Ce ii ( Figure 8(C)) at a current density of 0.1 A/g, which is 17 times higher than the typically 5 Wh/kg ce ii of commercial AC-based symmetric supercapacitors.
• Another graphene surface-mediated cell exhibits an even higher energy density of 160 Wh/kg ce u, comparable to that of a lithium-ion battery.
• the energy density of Cell-N maintains a value over 5 1 .2 Wh/kg ce ii even at a current density as high as 10 A/g, delivering a power density of 4.55 kW/kg ce ii.
• the power density of commercial AC-based symmetric supercapacitors is typically in the range of 1 - 10 kW/kg ce ii at an energy density of 5 Wh/kg ce u, This implies that, compared with a conventional supercapacitor at the same power density, the surface-mediated devices can deliver > 10 times the energy density.
• the power density is 25.6 kW/kg ce ii at 50 A/g with an energy density of 24 Wh/kgceii.
• the power density increases to 93.7 kW/kg ce ii at 200 A/g with an energy density of 12 Wh/kg C eii ( Figure 8(D)).
• This power density is one order of magnitude higher than that of conventional supercapacitors that are noted for their high power densities, and 2-3 orders of magnitude higher than those (typically 0. 1 - 1 .0 kW/kg ce ii) of conventional lithium-ion batteries.
• Figure 8(B) contains a comparison of CV data showing that the carbon fiber- derived graphene has slightly better performance than graphite-derived graphene as an electrode active material. This is likely due to the more curved or wrinkled shapes of fiber- derived graphene, which avoid complete face-to-face re-stacking of graphene sheets during electrode preparation.
• the lower energy density and power density of the exfoliated graphite- based cell (Cell-G) relative to the fully separated NGP -based (Cells M and C) might be ascribed to a lower specific surface area of EG (typically 200-300 m 2 /g based on BET measurements), as opposed to the typically 600-900 m 2 /g of mostly isolated single-layer graphene sheets.
• Figure 8(D) indicates that the energy density and power density values of carbon black (CB) can be significantly increased by subjecting CB to an activation/functionalization treatment that involves an exposure to a mixture of sulfuric acid, sodium nitrate, and potassium permanganate for 24 hours.
• the BET surface area was found to increase from approximately 60 m 2 /g to approximately 300 m 2 /g, resulting in a capacity increase from 8.47 mAh/g to 46.63 mAh/g).
• the cell with treated carbon black electrodes exhibits power and energy densities comparable to those of activated carbon electrode.
• FIG. 10 shows the Ragone plots of graphene surface-enabled Li ion-exchanging cells with different electrode thicknesses.
• the energy density and power density values were calculated based on total cell weight in FIG. 10(A) and based on the cathode weight only in FIG. 10(B).
• These data show that the electrode thickness plays a critical role in dictating the energy density and power density of a SMC.
• SMCs having thick electrodes can perform very well, without having to use expensive and slow processes (such as layer-by-layer, LBL, proposed by Lee, et al) to make ultra-thin electrodes for use in CNT -based super-batteries.
• FIG. 10 has also clearly demonstrated that the surface-mediated cells are a class of energy storage cells by itself, distinct from both supercapacitors and lithium-ion batteries.
• FIG. 12 indicates that the specific surface area of the electrode is the single most important parameter in dictating the lithium storage capacity.
• the data point having the highest specific capacity in this plot is obtained from a chemically reduced graphene oxide.
• Our chemical analysis data indicate that this heavily reduced graphene material has an oxygen content less than 2.0%, suggesting that essentially no functional group exists.
• Heavily oxidized graphene, upon chemical or thermal reduction, is known to have a fair amount of surface defect sites. This and other several data points confirm the significance of the surface trapping mechanism.
• Four data points (denoted by "x") are for pristine graphene electrodes wherein the graphene material was obtained from direct ultrasonication of pure graphite (> 99.9% carbon). These data points show that pure graphene surfaces (with benzene ring centers, and without surface defect or functional group) are equally capable of capturing lithium ions from electrolyte and storing comparable amounts of lithium on a per unit surface area basis.
• the instant invention provides an energy storage device that has the features of both a supercapacitor and a lithium ion battery.
• These fully surface-enabled, lithium ion-exchanging cells are already capable of storing an energy density of at least 160 Wh/kg ce ii, which is substantially higher than that of conventional electric double layer (EDL) supercapacitors.
• the power density of at least 100 kW/kg ce ii is substantially higher than that of conventional EDL supercapacitors and much higher than that of conventional lithium-ion batteries.
• EDL electric double layer

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