WO2013096931A1 - Dispositifs de stockage d'énergie - Google Patents
Dispositifs de stockage d'énergie Download PDFInfo
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- WO2013096931A1 WO2013096931A1 PCT/US2012/071529 US2012071529W WO2013096931A1 WO 2013096931 A1 WO2013096931 A1 WO 2013096931A1 US 2012071529 W US2012071529 W US 2012071529W WO 2013096931 A1 WO2013096931 A1 WO 2013096931A1
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- intercalation material
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- cnfs
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- intercalation
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- 238000004146 energy storage Methods 0.000 title claims description 16
- 239000002134 carbon nanofiber Substances 0.000 claims abstract description 237
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 154
- 238000009830 intercalation Methods 0.000 claims abstract description 59
- 230000002687 intercalation Effects 0.000 claims abstract description 59
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 45
- 238000000034 method Methods 0.000 claims abstract description 22
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 12
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- 239000002071 nanotube Substances 0.000 claims 1
- 238000000926 separation method Methods 0.000 claims 1
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- 229920000742 Cotton Polymers 0.000 description 1
- 229910013458 LiC6 Inorganic materials 0.000 description 1
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- -1 LiNi02 Inorganic materials 0.000 description 1
- XOJVVFBFDXDTEG-UHFFFAOYSA-N Norphytane Natural products CC(C)CCCC(C)CCCC(C)CCCC(C)C XOJVVFBFDXDTEG-UHFFFAOYSA-N 0.000 description 1
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- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
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- 229910052718 tin Inorganic materials 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
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Classifications
-
- 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
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
-
- 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
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- H—ELECTRICITY
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- 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
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- H—ELECTRICITY
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- H01M4/02—Electrodes composed of, or comprising, active material
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- H01M4/0402—Methods of deposition of the material
- H01M4/0421—Methods of deposition of the material involving vapour deposition
- H01M4/0423—Physical vapour deposition
- H01M4/0426—Sputtering
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- 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
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- 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
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- H01M4/134—Electrodes based on metals, Si or alloys
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
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- B82Y40/00—Manufacture or treatment of nanostructures
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- 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
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- 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
- H01M4/139—Processes of manufacture
- H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- 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
- 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
- Y02E60/13—Energy storage using capacitors
-
- 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
- the invention is in the field of energy storage devices, including but not limited to batteries, capacitors and fuel cells.
- Rechargeable lithium ion batteries are key electrical energy storage devices for power supply in portable electronics, power tools, and future electric vehicles. Improving the specific energy capacity, charging/discharging speed, and cycling lifetime is critical for their broader applications.
- a power storage device includes a hybrid core-shell NW (nano-wire) architecture in a high-performance Li-ion anode by incorporating an array of vertically aligned carbon nanofibers (VACNFs) coaxially coated with a layer of amorphous silicon.
- the vertically aligned CNFs include multiwalled carbon nanotubes (MWCNTs), which are optionally grown on a Cu substrate using a DC -biased plasma chemical vapor deposition (PECVD) process.
- PECVD DC -biased plasma chemical vapor deposition
- the carbon nanofibers (CNFs) grown by this method can have a unique interior morphology distinguishing them from the hollow structure of common MWCNTs and conventional solid carbon nanofibers.
- these CNFs optionally consist of a series of bamboo-like nodes across the mostly hollow central channel. This microstructure can be attributed to a stack of conical graphitic cups discussed further elsewhere herein.
- these PECVD-grown CNFs are typically uniformly aligned normal to the substrate surface and are well separated from each other. They may be without any entanglement or with minimal entanglement, and thus form a brush-like structure referred to as a VACNF array.
- the diameter of individual CNFs can be selected to provide desired mechanical strength so that the VACNF array is robust and can retain its integrity through Si deposition and wet electrochemical tests.
- Various embodiments of the invention include an energy storage system comprising a conductive substrate; a plurality of vertically aligned carbon nanofibers grown on the substrate, the carbon nanofibers including a plurality multi-walled carbon nanotubes; and an electrolyte including one or more charge carriers.
- Various embodiments of the invention include an energy storage system comprising a conductive substrate; a plurality of vertically aligned carbon nanofibers grown on the substrate; and a layer of intercalation material disposed on the plurality of vertically aligned carbon nanofibers and configured to have a lithium ion storage capacity of between approximately 1,500 and 4,000 mAh per gram of intercalation material.
- Various embodiments of the invention include an energy storage system comprising a conductive substrate; a plurality of vertically aligned carbon nanofibers grown on the substrate; and a layer of intercalation material disposed on the plurality of vertically aligned carbon nanofibers and configured such that an ion storage capacity of the intercalation material is approximately the same at charging rates of 1C and 3C.
- Various embodiments of the invention include a method of producing an energy storage device, the method comprising providing a substrate; growing carbon nanofibers on the substrate, the carbon nonofibers having a stacked-cone structure; and applying intercalation material to the carbon nanofibers, the intercalation material being configured for intercalation of charge carriers.
- FIGs. 1A and IB illustrate a CNF array comprising a plurality of CNF grown on a substrate, according to various embodiments of the invention.
- FIGs. 2A-2C illustrate a plurality of vertically aligned CNFs in different states, according to various embodiments of the invention.
- FIGs. 3A-3C illustrate details of a CNF, according to various embodiments of the invention.
- FIG. 4 illustrates a schematic of the stacked-cone structure of a CNF, according to various embodiments of the invention.
- FIGs. 5A-5C illustrate an electrochemical characterization of ⁇ 3 ⁇ long CNFs, according to various embodiments of the invention.
- FIGs. 6A-6C illustrates scanning electron microscopy images of 3 ⁇ long CNFs, according to various embodiments of the invention.
- FIGs. 7A-7C illustrate results obtained using CNFs including a Si layer as Li-ion battery anodes, according to various embodiments of the invention.
- FIG. 8 illustrates how the capacity of a CNF array varies with charging rate, according to various embodiment of the invention.
- FIG. 9 A illustrates Raman spectra of CNF arrays, according to various embodiments of the invention.
- FIGs. 1 OA- 10C shows the variation of Li * insertion-extraction capacities and the coulombic efficiency over 15 charge-discharge cycles, according to various embodiments of the invention.
- FIGs. 1 1 A-l 1C show scanning electron microscopy images of freshly prepared CNF arrays, according to various embodiments of the invention.
- FIG. 1 ID shows a cross-section of a nano fiber/silicon complex including more than one CNF.
- FIG. 12 illustrates a carbon nano-fiber array including fibers of 10 um in length, according to various embodiments of the invention.
- FIG. 13 illustrates methods of producing CNF arrays, according to various embodiments of the invention.
- FIGs. 1 A and I B illustrate a CNF Array 100 comprising a plurality of CNF 1 10 grown on a conductive Substrate 105, according to various embodiments of the invention.
- the CNF Array 100 is shown in the Li extracted (discharged) state and in FIG. 1 B the CNF Array 100 is shown in the Li inserted (charged) state.
- the CNF 1 10 in these and other embodiments discussed herein are optionally vertically aligned.
- the CNF 1 10 are grown on a Substrate 105 of Cu using a DC-biased plasma chemical vapor deposition (PECVD) process.
- PECVD DC-biased plasma chemical vapor deposition
- the CNFs 1 10 grown by this method can have a unique morphology that includes a stack of conical graphitic structures similar to stacked cups or cones or a spiral. This creates a very fine structure that facilitates lithium intercalation. This structure is referred to here as the "stacked-cone" structure elsewhere herein.
- these CNFs 1 10 are typically uniformly aligned normal to the substrate surface and are well separated from each other. The diameter of individual CNFs can be selected to provide desired mechanical strength so that the CNF Array 100 is robust and can retain its integrity through Si deposition and wet electrochemical cycles.
- a seed layer is optionally employed for growing CNFs 1 10 on Substrate 105.
- the CNF Array 100 is placed in contact with an Electrolyte 125 including one or more charge carriers, such as a lithium ion.
- the CNFs 1 10 are configured such that some of Electrolyte 125 is disposed between CNFs 1 10 and/or can ready Substrate 105 via gaps between CNFs 110.
- the diameter of individual CNFs 1 10 illustrated in FIGs. 1A and IB are nominally between 100 and 200 nm, although diameters between 75 and 300 nm, or other ranges are possible. CNFs 1 10 are optionally tapered along their length.
- the open space between the CNFs 1 10 enables a Silicon Layer 1 15 to be deposited onto each CNFs to form a gradually thinned coaxial shell with a mass at a Tip 120 of the CNF 1 10.
- This design enables the whole Silicon Layer 1 15 to be electrically connected through the CNF 1 10 and to remain fully active during charge-discharge cycling.
- the expansion that occurs on alloying of lithium with Silicon Layer 1 15 can be easily accommodated in the radial direction, e.g.
- FIGs. 1A and IB are perspective views.
- from 0.01 up to 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 ⁇ (or more) nominal Si thickness can be deposited onto 3 ⁇ long CNFs 110 to form CNF Arrays 100 such as those illustrated in FIG.s 1A and IB.
- from 0.01 up 0.5, 1.0, 1.5, 2.5, 3.0, 4.0, 10, 20, 25 ⁇ (or more) nominal Si thickness can be deposited onto 10 ⁇ long CNFs 110 to form CNF Arrays 100.
- the nominal thickness of Si is between 0.01 ⁇ and the mean distance between CNFs 110.
- Li ion storage with up to -4,000 mAh/g mass-specific capacity at C/2 rate is achieved. This capacity is significantly higher than those obtained with Si nanowires alone or other Si-nanostructured carbon hybrids at the same power rate.
- the improved performance is attributed to the fully activated Si shell due to effective charge collection by CNFs 1 10 and short Li r path length in this hybrid architecture. Good cycling stability has been demonstrated in over 110 cycles.
- the storage capacity of Li ion storage of CNF Arrays 100 is approximately 750, 1500, 2000, 2500, 3000, 3500 or 4000 mAh per gram of Si, or within any range between these values.
- nominal thickness (of e.g., Si) is the amount of Si that would produce a flat layer of Si, of the said thickness, on Substrate 105.
- nominal thickness of Si of 1.0 ⁇ is an amount of Si that would result in a 1.0 ⁇ thick layer of Si if deposited directly on Substrate 105. Nominal thickness is reported because it can easily be measured by weight using methods know in the art.
- a nominal thickness of 1.0 ⁇ will result in a smaller thickness of Si Layer 115 on CNFs 110 because the Si is distributed over the greater area of the CNFs 1 10 surfaces.
- FIGs. 2A-2C illustrate CNF Array 100 having an average fiber length of approximately 3 ⁇ , according to various embodiments of the invention.
- FIGs. 2A-2C are scanning electron microscopy (SEM) images.
- FIG. 2A shows a plurality of vertically aligned CNFs 1 10 without Silicon Layer 1 15.
- FIG. 2B shows a plurality of vertically aligned CNFs 1 10 including Silicon Layer 1 15.
- FIG. 2C shows a plurality of vertically aligned CNFs 1 10 in the extracted (discharged) state after experiencing 100 lithium charge-discharge cycles.
- the CNFs 1 10 are firmly attached to a Cu Substrate 105 with essentially uniform vertical alignment and a random distribution on the surface of the substrate.
- the samples used in this study have an average areal density of l . l lxlO 9 CNFs/cm 2 (counted from top-view SEM images), corresponding to an average nearest-neighbor distance of -330 nm.
- the average length of the CNFs 1 10 in Figure 2 is -3.0 ⁇ with >90% of CNFs in the range of 2.5 to 3.5 ⁇ in length.
- the diameter spreads from -80 nm to 240 nm with an average of -147 nm.
- An inverse teardrop shaped Ni catalyst at Tip 120 presents at the tip of each CNF 110 capping the hollow channel at the center of the CNF, which promoted the tip growth of CNF 1 10 during the PECVD process.
- the size of the Ni catalyst nanoparticles defined the diameter of each CNFs 110. Longer CNFs 1 10, up to 10 ⁇ , were also employed in some studies to be discussed in later sections.
- the average nearest neighbor distance can vary between 200- 450nm, 275-385 nm, 300-360nm, or the like. Further, the average length of the CNFs 1 10 can be between approximately 2-20, 20-40, 40-60, 60-80, 80-100, 100-120, 120-250 ( ⁇ ), or more. Standard carbon nanofibers as long as a millimeter long are known in the art. In various embodiments, the average diameter can vary between approximately 50-125, 100- 200, 125-175 (nm), or other ranges. [0033] An amorphous Si Layer 115 was deposited onto the CNF Array 100 by magnetron sputtering.
- the open structure of brush-like CNF Arrays 100 made it possible for Si to reach deep down into the array and produce conformal structures between the CNFs 1 10. As a result, it formed a thick Si coating at the CNF tip followed by a gradually thinned coaxial Si shell around the lower portion of the CNF, presenting an interesting tapered core-shell structure similar to a cotton swab.
- the amount of Si deposition is characterized by the nominal thickness of Si films on a flat surface using a quartz crystal microbalance (QCM) during sputtering.
- QCM quartz crystal microbalance
- the Li + insertion/extraction capacities were normalized to the total Si mass derived from the nominal thickness.
- the Si-coated CNFs 1 10 were well-separated from each other, forming an open core-shell CNF array structure (shown in FIG. 2B). This structure allowed electrolyte to freely accessing the entire surface of the Si Layer 1 15.
- the average tip diameter was -457 nm in comparison with the -147 nm average diameter of the CNFs 1 10 prior to application of the Si Layer 1 15.
- the average radial Si thickness at the Tip 120 was estimated to be -155 nm. This was apparently much smaller than the 0.50 ⁇ nominal Si thickness since most Si spread along the full length of CNFs.
- the stacked-cone of CNFs 1 10 provides additional fine structure to the Si Layer 1 15.
- the stacked-cone structure is optionally the result of a spiral growth pattern that produces the stacked-cone structure when viewed in cross-section.
- FIGs. 3A - 3C The transmission electron microscopy (TEM) images in FIGs. 3A - 3C further illustrate the structural details of Si-coated CNFs 1 10.
- a Si Layer 1 15 of -390 nm Si was produced directly above the Tip 120 of a -210 nm diameter CNF 110.
- the largest portion of the cotton-swab-shaped Si Layer 1 15 was -430 nm in diameter which appeared near the very end of the Tip 120.
- the coaxial Si Layer 1 15 around the CNF 1 10 showed a feather-like texture with modulated contrast, clearly different from the uniform Si deposits above the tip (see FIG. 3A). This is likely a result of the stacked-cone microstructure of the PECVD-grown CNFs 110.
- CNFs 1 10 include unevenly stacked cuplike graphitic structures along the CNF 1 10 center axis.
- the use of such variations in the diameter of CNFs 1 10 was previously disclosed in commonly owned U.S. Patent Application Ser. No. 12/904, 1 13 filed Oct. 13, 2010.
- the stacked-cone structure consists of more than ten cup-like graphitic layers that can be clearly seen in FIG. 3B as indicated by the dashed lines.
- the resolution and contrast of FIGs. 3B and 3C are limited since the electron beam needs to penetrate through hundreds of nanometer thick CNF or Si-CNF hybrid, but the structural characteristics are consistent with the high-resolution TEM studies using smaller CNFs in literature.
- This unique structure generated clusters of broken graphitic edges along the CNF sidewall which cause varied nucleation rates during Si deposition and thus modulate the density of the Si Layer 1 15 on the CNF 110 sidewall.
- the modulated density results in the ultra-high surface area Si structures indicated by a (100 nm square) Box 310 in FIG 3 A.
- the feather like Si structures of Si Layer 115 provide an excellent Li ion interface that results in very high Li capacity and also fast electron transfer to CNF 1 10.
- the dark area at Tip 120 is Nickel catalyst for growth of the CNFs. Other catalysts can also be used.
- FIGs. 3B and 3C are images recorded before (3B) and after (3C) lithium
- the sample in 3C was in the dlithiated (discharged) state when it was taken out of an electrochemical cell.
- the dashed lines in FIG. 3B are visual guidance of the stacked-cone graphic layers inside the CNFs 110.
- the long dashed lines in FIG. 3C represent the sidewall surface of the CNF 110.
- the stacked-cone structure of CNFs 1 10 is drastically different from commonly used carbon nanotubes (CNTs) or graphite.
- the stacked-cone structure results in improved Li insertion, even without the addition of Si Layer 1 15, relative to standard carbon nanotubes or nanowires.
- the stacked-cone graphitic structure of CNFs 1 10 allows Li intercalation into the graphitic layers through the sidewall of CNFs 1 10 (rather than merely at the ends).
- the Li+ transport path across the wall of each of CNFs 1 10 is very short (with D -290 nm in some embodiments), quite different from the long path from the open ends in commonly used seamless carbon nanotubes (CNTs).
- CNF radius T C NF 74 nm
- CNF wall thickness t w -50 nm
- graphitic cone angle ⁇ 10°
- FIGs. 5A-5C illustrate an electrochemical characterization of -3 ⁇ long CNFs 1 10. This characterization illustrates the phenomenon described in relation to FIG 4.
- FIG. 5A shows cyclic voltammograms (CV) from 1.5 V to 0.001 V versus a Li/Li reference electrode at 0.1, 0.5 and 1.0 mV/s scan rates. A lithium disk was used as the counter electrode. Data were taken from the second cycle and normalized to the exposed geometric surface area.
- FIG. 5A shows cyclic voltammograms (CV) from 1.5 V to 0.001 V versus a Li/Li reference electrode at 0.1, 0.5 and 1.0 mV/s scan rates. A lithium disk was used as the counter electrode. Data were taken from the second cycle and normalized to the exposed geometric surface area.
- FIG. 5A shows cyclic voltammograms (CV) from 1.5 V to 0.001 V versus a Li/Li reference electrode at 0.1, 0.5 and 1.0 mV/s scan rates. A
- FIG. 5B shows the galvanostatic charge-discharge profiles at C/0.5, CI and C/2 power rates, corresponding to current densities of 647, 323 and 162 mA/g (normalized to estimated carbon mass) or 71.0, 35.5 and 17.8 ⁇ / ⁇ 2 (normalized to the geometric surface area), respectively.
- a freshly assembled half-cell typically showed the open circuit potential (OCP) of the uncoated CNFs 1 10 anode was -2.50 to 3.00 V vs. Li/Lf reference electrode.
- OCP open circuit potential
- electropotential is below 1.20 V.
- the first cycle from OCP to 0.001 V involved the formation of a necessary protective layer, i.e. the solid electrolyte interphase (SEI), by the SEI
- CNF arrays 100 were somewhat different from those of staged intercalation into graphite and slow Li + diffusion into the hollow channel of CNTs.
- Li-ion insertion into CNFs 1 10 is likely through intercalation between graphitic layers from the sidewall due to its unique structure.
- the TEM image in FIG. 3C indicates that the graphitic stacks in the stacked-cones inside the CNF 110 are somewhat disrupted during Li + intercalation-extraction cycles, likely due to the large volume change that occurs on Li + intercalation. Some debris and nanoparticles are observed as white objects inside CNFs 1 10 as well as at the exterior surface.
- the Li " intercalation and extraction capacities were normalized to the estimated mass or the CNFs 1 10 (1.1 x 10 4 g/cm 2 ) that was calculated based on a hollow vertically aligned CNF structure with the following average parameters: length (3.0 um), density (1.1 x 10 9 CNFs per cm"), outer diameter (147 nm), and hollow inner diameter (49 nm, -1/3 of the outer diameter).
- the density of the solid graphitic wall of the CNFs 1 10 was assumed to be the same as graphite (2.2 g/cm ).
- the intercalation capacity was 430 mA h g " and the extraction capacity is 390 mA h g " , both of which are slightly higher than the theoretical value of 372 mA h g ⁇ ' for graphite, which may be attributed to SEI formation and the irreversible Li + insertion into the hollow compartments inside the CNFs 1 10.
- the extraction capacities were found to be more than 90% of the intercalation values at all power rates and both the intercalation and extraction capacities decreased by ⁇ 9% as the power rate increased from C/2 to C/l and by -20% from C/l to C/0.5, comparable to graphite anodes.
- the SEI serves as a sheath to increase the mechanical strength of the CNFs 1 10, preventing them from collapsing into microbundles by the cohesive capillary force of a solvent as observed in the study with other polymer coatings.
- FIGs. 6A-6C illustrates scanning electron microscopy images of 3 ⁇ long CNFs 1 10, according to various embodiments of the invention.
- FIG. 6 A shows CNFs 1 10 in delithiated (discharged) state after intercalation extraction cycles.
- FIG. 6B shows CNFs 1 10 including Si Layer 1 15 after 100 cycles in the delithiated state.
- FIG. 6C shows CNFs 110 including Si Layer 115 after 100 cycles in the lithiated state. These images are 45 degree perspective views.
- FIGs. 7A-7C illustrate results obtained using CNFs 1 10 including a Si Layer 1 15 as Li-ion battery anodes. These results were obtained using a nominal Si thickness of 0.50 ⁇ .
- FIG. 6 A shows CNFs 1 10 in delithiated (discharged) state after intercalation extraction cycles.
- FIG. 6B shows CNFs 1 10 including Si Layer 1 15 after 100 cycles in the delithiated state.
- FIG. 6C shows CNFs 110 including Si Layer 115
- FIG. 7A shows cyclic voltammograms between 1.5 V and 0.05 V versus Li/Li * at 0.10, 0.50 and 1.0 mV s " ' scan rates. The measurements were made after the sample going through 150 charge-discharge cycles and the data of the second cycle at each scan rate are shown.
- FIG. 7B shows galvanostatic charge- discharge profiles at C/0.5, C/l and C/2 power rates with the sample at 120 cycles. All profiles were taken from the second cycle at each rate.
- FIG. 7C shows insertion and extraction capacities (to the left vertical axis) and coulombic efficiency (to the right vertical axis) of two CNF Arrays 100 (used as electrodes) versus the charge- discharge cycle number.
- the first CNF Array 100 was first conditioned with one cycle at the C/10 rate, one cycle at the C/5 rate, and two cycles at the C/2 rate. It was then tested at the C/2 insertion rate and C/5 extraction rate for the rest of the 96 cycles. The filled and open squares represent the insertion and extraction capacities, respectively.
- the second electrode was first conditioned with two cycles each at C/10, C/5, C/2, C/l , C/0.5 and C/0.2 rates. It was subsequently tested at the C/l rate for the next 88 cycles.
- the columbic efficiencies of both electrodes are represented by filled ( 1 st electrode) and open (2nd electrode) diamonds, which mostly overlap at 99%.
- both the cathodic wave for Lf insertion and the anodic wave for Li " extraction shift to lower values (below -0.5 and 0.7 V, respectively).
- the peak current density increases by 10 to 30 times after application of Si Layer 1 15 and is directly proportional to the scan rate.
- alloy-forming Lf insertion into Si is much faster than intercalation into uncoated CNFs, which was limited by the slow diffusion of Li + between graphitic layers.
- the cathodic peak at -0.28 V was not observed in previous studies on pure Si nanowires.
- the three anodic peaks representing the transformation of the Li-Si alloy into amorphous Si are similar to those with Si nanowires despite shifting to lower potentials by 100 to 200 mV.
- the total Li * storage capacity of CNF Arrays 100 including Si Layer 115 was about 10 times greater than CNF Arrays 100 that lacked Si Layer 1 1 . This occurred even though the low potential limit for the charging cycle was increased from 0.001 V to 0.050 V. As a result, the amount of Li + intercalation into the CNF core appears to have been negligible.
- the specific capacity was calculated by dividing only the mass of Si that was calculated from the measured nominal thickness and a bulk density of 2.33 g cm°. This method was chosen as an appropriate metric to compare the specific capacity of the Si Layer 1 15 to the theoretical value of bulk Si.
- FIG. 8 illustrates how the capacity of CNF Array 100 varies with charging rate, according to various embodiments of the invention. Data is shown for several numbers of cycles.
- FIG. 8 shows average specific discharge capacity for a group of cycles with identical current rates versus the charge rate (C-rate) required to achieve full capacity in set hours (C/'h e.g., full Capacity/hours). Vertical Lines are focused on C/4, 1 C, 3C and 8C.
- the CNF Array 100 was first conditioned with two cycles each at C/8, C/4, C/2, C/1 , C/0.8, C/0.4, and C/0.16 rates symmetrically, and subsequently tested at a C/1 symmetric rate for the next 88 cycles. This was repeated from cycle 101 to cycle 200.
- the electrode was cycled for five cycles at each of C/4, C/3, C/2, C/1 , C/0.75, C/0.66, C/0.50, C/0.33, C/0.25, C/0.20 and C/0.15 rates symmetrically and subsequently tested at a C/1 symmetric rate for the next 45 cycles. This was repeated from cycle 301 to cycle 400 and from cycle 401 to cycle 500.
- the change in capacity is small ( ⁇ 16%) while the C-rate is varied by 32 fold.
- the electrode after 100 cycles showed increased capacity when the C-rate is changed from 3C to 8C. Thus, faster charge rates resulted in improved capacity.
- High capacity >2,700 mAh/g
- Capacity at rates above 3C increase as C-rate increased. The drop in specific capacity with the number of cycles is due to known, correctable, factors.
- the insertion capacity only dropped by 8.3% from 3643 mA h g "1 at the 5th cycle to 3341 mA h g " 1 at the 100th cycle. Even at the C/1 charge -discharge rate, the insertion capacity only drops by 1 1 % from 3096 mA h g " 1 at the 13 th cycle to 2752 mA h g " 1 at the 100 th cycle.
- the difference in the Li + capacity between these two sets of data was mostly attributable to the initial conditioning parameters and small sample-to-sample variations. This was indicated by the similar values of insertion-extraction capacity during the first few conditioning cycles in FIG. 7C at C/10 and C/5 rates.
- the specific capacity disclosed herein is significantly higher than those reported using other nanostructured Si materials at similar power rates, including -2500 mA h g "1 at the C/2 rate and -2200 mA h g "1 at the C/l rate with Si NWs, and -800 mA h g "1 at the C/l rate with randomly oriented carbon nanofiber-Si core-shell NWs.
- the coaxial core-shell NW structure on well- separated CNFs 1 10 such as included in various embodiments of the invention, provides an enhanced charge-discharge rate, nearly full Lf storage capacity of Si, and a long cycle life, relative to the prior art.
- the extra insertion capacity can be attributed to the combination of three irreversible reactions: (1 ) the formation of a thin SEI (surface electrolyte interphase) layer (of tens of nanometers); (2) reactions of Li with SiO x presented on the Si surface (SiO x + 2xLi - Si + ,xLi20); and (3) the conversion of the starting crystalline Si coating with a higher theoretical capacity (-4200 mA h g "1 ) into amorphous Si with lower capacity ( ⁇ 3800 mA h g *1 ).
- the Si has interacted with electrolyte to produce SEI that fills the gaps between the feather-like structures.
- the interaction can include mixing, chemical reactions, charge coupling, encapsulation, and/or the like.
- the Si Layer 1 15, therefore, looks more uniform in FIG. 3B.
- the Si Layer 1 15 now comprises interleaved layers of Si (the feather-like structures) and SEI. Each of these interleaved layers can be on the order of a few 10s of nanometers.
- the SEI layer can be an ion permeable material that is a product of interaction between the electrolyte and Si Layer 1 15 (or other electrode material).
- the original Si Layer 1 15 likely consisted of nanocrystals embedded in an amorphous matrix associated with the feather-like TEM image in FIG. 3A. After initial cycles, the Si nanocrystals were converted into amorphous Si, consistent with the TEM images after the cycling test (see FIGs. 3B and 3C). However, the Si Layer 1 15 apparently did not slide along the CNF, in contrast to the large longitudinal expansion (by up to 100%) in pure Si NWs. Si Layer 1 15 was, thus, securely attached to CNFs 1 10 for over 120 cycles. The volume change of the Si shell during Li + insertion was dominated by radial expansion, while the CNF-Si interface remained intact.
- Various embodiments of the invention include CNFs 1 10 having different lengths and silicon shell thickness.
- One factor that can be controlled when CNFs 1 10 are generated is the open space between each CNF 1 10, e.g., the mean distance between CNFs 1 10 within CNF Array 100. This space allows Si Layer 1 15 to expand radially when charging and, thus in some embodiments provides stability. Because an optimum electrode structure depends on both the length of CNFs 1 10 and the thickness of Si Layer 1 15, it is sometimes desirable to use longer CNFs 1 10 and thicker Si Layers 1 15 in order to obtain higher total Li storage capacity. Longer CNFs 1 10 do correlate with greater storage capacity.
- FIGs 1 OA- I OC shows the variation of Li insertion-extraction capacities and the coulombic efficiency over 15 charge-discharge cycles with three 10 ⁇ long CNF 1 10 samples deposited with Si Layer 1 15 at a nominal thickness of 0.50, 1 .5 and 4.0 ⁇ , respectively.
- asymmetric rates C/2 for insertion and C/5 for extraction
- This protocol provided nearly 100% coulombic efficiency and minimum degradation over the cycles.
- the nominal thickness was measured in situ with a quartz crystal microbalance during sputtering.
- FIGs. 1 1 A- 1 1C show scanning electron microscopy images of freshly prepared CNF Arrays 100 (on -10 ⁇ long CNFs 1 10).
- the Si Layer 1 15 was generated using a nominal Si thickness of (a) 0.50 ⁇ , (b) 1.5 ⁇ , and c) 4.0 ⁇ , which were measured in-situ using a quartz crystal microbalance during deposition. All images are 45° perspective views.
- the average tip diameter was found to be -388 nm on the 10 ⁇ long CNFs, much smaller than the -457 nm average diameter on the 3.0 ⁇ long CNFs 1 10.
- the Si Layer 1 15 was thinner but more uniformly spread along the 10 ⁇ long CNFs 1 10.
- FIGs. 1 1 A and 1 IB each include roughly the same number of CNFs 110, however, in FIG. 1 IB has substantially fewer visible Tips 120.
- Si Layer 115 can form a nanofiber/silicon complex that includes a single CNF 1 10 (a cross-section of which is shown in FIG. 1A).
- Si Layer 1 15 can form a nanofiber/silicon complex that includes two, three or more CNF 1 10 under a single cover of silicon. This occurs when two or more CNFs 1 10 come together during the Si Layer 1 15 deposition process.
- a nanofiber/silicon complex is a structure that includes a continuous Si Layer 1 15 that envelops one or more CNF 1 10.
- FIG. 1 I D A cross-section of a nanofiber/silicon complex that includes two CNF 1 10 is illustrated in FIG. 1 I D.
- at least 1 %, 5% or 10% of nanofiber/silicon complexes include more than one CNF 1 10.
- instances of CNF Arrays 100 having 0.50 and 1.5 ⁇ nominal Si thicknesses have comparable mass-specific capacities of 3208 ⁇ 343 and 3212 ⁇ 234 mA h g "1 , respectively.
- the samples with a 4.0 ⁇ nominal Si thickness give much lower capacity at 2072 ⁇ 298 mA h g "1 .
- the thinner Si coatings are fully activated and provide the maximum Li insertion capacity that amorphous Si could afford.
- the area- specific capacity increases proportionally with the Si thickness from 0.373 ⁇ 0.040 mA h cm “ " at 0.50 ⁇ Si to 1.12 ⁇ 0.08 mA h cm “" at 1.5 ⁇ Si thickness, but drops off from the linear curve to give 1.93 ⁇ 0.28 mA h cm " at 4.0 ⁇ nominal Si thickness.
- the thickness of 4.0 ⁇ is greater than the mean distance between CNFs 1 10.
- the structure of CNF Array 100 includes an Si Layer of approximately 200 to 300 rtm radial thickness on CNFs 1 10 having a length of approximately 30-40, 40-75, 75-125 microns (or more or combinations thereof) and diameters on the order of -50 nm.
- these CNF Array 100 are grown on conductive foils having a thickness within the ranges of -10 microns, -10-20 microns, -10- 50 microns, or more.
- Si (equivalent to 1.5 ⁇ nominal thickness on a flat surface) is deposited onto 10 ⁇ long CNFs 100 to form CNF Arrays 100.
- nanostructured architecture enables effective electrical connection with bulk quantities of Si material while maintaining a short Li+ insertion extraction path.
- high capacity near the theoretical limit is possible for over 120 charge-discharge cycle.
- the high capacity at significantly improved charging and power rates and the extraordinary cycle stability make this novel structure a choice anode material for high-performance Li-ion batteries.
- the same core-shell concept may be applied to cathode materials by replacing the Si shell with Ti0 2 , LiCo0 2 , LiNi0 2 , LiMn 2 0 4 , LiFeP0 4 , or the like.
- FIG. 13 illustrates methods of producing the CNF Arrays 100 disclosed herein.
- a Substrate 105 suitable for growth of CNFs 1 10 is provided.
- Substrate 105 may include a variety of materials, for example Cu.
- Substrate 105 is optionally a conductive foil having a thickness described elsewhere herein.
- nucleation cites for the growth of CNFs 1 10 are provided on Substrate 105.
- a variety of nucleation materials, such as Ni particles, are known in the art.
- the nucleation cites are optionally provided at a density so as to produce mean distances between CNFs 1 10, such as those taught elsewhere herein.
- Provide Nucleation Sites Step 1320 is optional in embodiments in which nucleation is not required for growth of CNFs 1 10, or similar structures.
- CNFs 1 10 are grown on Substrate 105.
- the CNFs 1 10 are optionally grown to produce the stacked-cone structure taught elsewhere herein, or a similarly variable structure.
- the CNFs 1 10 can be grown to any of the lengths taught elsewhere herein. Growth is optionally accomplished using PECVD processes such as those taught or cited in "A high-performance lithium-ion battery anode based on the core-shell heterostructure of silicon-coated vertically aligned carbon nanofibers" lankowski et al. J.
- an intercalation material such as Si Layer 1 15 is applied to the grown CNFs 1 10.
- the applied material may have any of the nominal thicknesses taught elsewhere herein so as to produce a Si Layer 1 15 thickness of tens or hundreds of nanometers.
- the CNF Array 100 produced using Steps 1310-1340 is conditioned using one or more lithium intercalation cycles.
- Si Layer 1 15 is optionally formed of intercalation materials in addition to or as an alternative to silicon.
- tin, germanium, carbon, silicon, or combinations thereof could be used as intercalation material.
- Ti0 2 (titanium oxide) or boron nitride nano-fibers can be used in place of the carbon nano-fibers.
- the electrodes taught herein may be included in a wide variety of energy storage devices including capacitors, batteries and hybrids thereof. These energy storage devices will be used in, for example, load balancing devices, communication devices, backup power supplies, vehicles and computing devices.
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Also Published As
Publication number | Publication date |
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KR20140128298A (ko) | 2014-11-05 |
GB201411191D0 (en) | 2014-08-06 |
GB2512230B (en) | 2019-08-28 |
GB2512230A (en) | 2014-09-24 |
CN104145355B (zh) | 2016-09-28 |
CN104145355A (zh) | 2014-11-12 |
KR102036196B1 (ko) | 2019-10-24 |
CN106910869A (zh) | 2017-06-30 |
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