WO2024100680A1 - Lithium-ion capacitor utilizing anode made from chemically pre-lithiated nitrogen doped reduced graphene oxide - Google Patents

Lithium-ion capacitor utilizing anode made from chemically pre-lithiated nitrogen doped reduced graphene oxide Download PDF

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Publication number
WO2024100680A1
WO2024100680A1 PCT/IN2023/051028 IN2023051028W WO2024100680A1 WO 2024100680 A1 WO2024100680 A1 WO 2024100680A1 IN 2023051028 W IN2023051028 W IN 2023051028W WO 2024100680 A1 WO2024100680 A1 WO 2024100680A1
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rgo
lithium
ion capacitor
lithiated
anode
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PCT/IN2023/051028
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French (fr)
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Milan Jana
Pushpendra Sing Gola
Anirban Maitra
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Godi India Pvt. Ltd.
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Publication of WO2024100680A1 publication Critical patent/WO2024100680A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • 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
    • 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
    • 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

Definitions

  • the present invention relates to energy storage devices, and specifically relates to lithium-ion capacitors.
  • Lithium-ion capacitors are energy storage elements having high energy density compared to supercapacitors and high power density compared to batteries, such as Lithium (Li)-ion batteries.
  • a lithium-ion battery consists of a Li-metal oxide (i.e. LiCo2O4, LiMn2O4, etc) cathode, a graphite anode, and a Li-salt (i.e. LiPFe) containing electrolyte.
  • Li + ions migrate from a cathode to an anode.
  • Li + ions migrate from the anode to the cathode.
  • loss of Li + ions during initial cycles can be compensated by Li present in the cathode.
  • a lithium-ion capacitor makes use of a battery type carbon material (i.e. graphite, or hard carbon) as an anode and a supercapacitor type activated carbon material as a cathode.
  • the activated carbon material used as the cathode does not contain Li + ions.
  • cations Li + ions migrate from an electrolyte to the anode and corresponding anions (i.e. PFe" ions) of the electrolyte migrate to the cathode.
  • Fig. 1A illustrates a voltage vs. specific capacity plot for conventional lithium-ion capacitors, in accordance with prior-art. Discharging and charging of a lithium-ion capacitor at first cycle is illustrated by curve 102, discharging and charging of the lithium-ion capacitor at second cycle are illustrated by curve 104, and charging and discharging of the lithium-ion capacitor at third cycle are illustrated by curve 106. As illustrated in Fig. 1A, a loss in specific capacity occurs during initial cycles (illustrated by arrow 108). For example, as illustrated in Fig. 1A, specific capacity for discharging at the second cycle (illustrated by curve 104) i.e.
  • the anode is electrochemically pre-lithiated by making a half-cell of carbon-based electrodes.
  • Fig. IB illustrates a current vs. voltage plot for an anode half cell made of carbon spheres, in accordance with prior-art.
  • Fig. 1C illustrates a current vs. voltage plot for a cathode half cell made of activated carbon, in accordance with prior-art. The cathode half-cell was tested at 5 mV s’ 1 . However, for pre-lithiation, assembling of the half-cell and again de-assembling of the half-cell to obtain the electrode add up extra steps in a cell manufacturing process.
  • a Li metal foil is deposited on an anode surface to compensate the loss of Li + ions during initial charging.
  • Fig. ID illustrates perspective view of a lithium-ion capacitor utilizing a Li metal foil 116 deposited on the anode surface, in accordance with prior-art.
  • this process is not industrially viable in terms of safety and for large-scale production.
  • Fig. IE illustrates a plot between specific capacitance and number of cycles when highly concentrated electrolytes are used in fabrication of a lithium-ion capacitor, in accordance with prior-art. It is difficult to find high concentrated electrolyte with required viscosity, conductivity, thermal stability, and electrochemical stability.
  • sacrificial Li-salt has been used at a cathode to fabricate a highly efficient version of lithium-ion capacitor.
  • Fig. IF illustrates a plot of current vs. potential for different cycles with usage of sacrificial Li-salt at the cathode, in accordance with prior-art.
  • curve 118 illustrates a graph for 1 st cycle
  • curve 120 illustrates a graph for 2 nd cycle
  • curve 122 illustrates a graph for 5 th cycle
  • curve 124 illustrates a graph for 10 th cycle.
  • a general objective of the present invention is to fabricate an anode for use in a lithium-ion capacitor.
  • Another objective of the present invention is to compensate initial loss of Li by irreversible reactions and solid electrolyte interphase (SEI) layer formation.
  • SEI solid electrolyte interphase
  • Another objective of the present invention is to provide high porosity to a material used in fabrication of the anode.
  • Another objective of the present invention is to provide enough diffusion paths for Li + ions, resulting in high-rate capability.
  • Yet another objective of the present invention is to provide a large surface area to a material used in fabrication of an anode, to accommodate a large number of Li + .
  • Still another objective of the present invention is to prevent an agglomeration of the material used in fabrication of the anode.
  • a lithium-ion capacitor may comprise an anode fabricated through deposition of nitrogen-doped reduced graphene oxide (N-rGO) lithiated by long alkyl chain- Lithium (Li), over a first current collector.
  • the long alkyl chain-Li may include n-butyl Li.
  • the lithium-ion capacitor may comprise a cathode fabricated through deposition of activated carbon over a second current collector.
  • the lithium-ion capacitor may further comprise an electrolyte for allowing ion exchange between the anode and the cathode.
  • the N-rGO may be synthesized from graphene oxide (GO) by simultaneously performing reduction and nitrogen doping operations at a high temperature, in presence of a nitrogen source.
  • GO graphene oxide
  • lithiation of the N-rGO may be optimized by changing a volume of a solution of the long alkyl chain-Li.
  • porosity of the N-rGO may be increased by one or more of steam activation and chemical activation.
  • the first current collector is made of copper and the second current collector is made of aluminium.
  • N-rGO nitrogen-doped reduced graphene oxide
  • GO graphene oxide
  • the N-rGO may be lithiated to obtain lithiated N-rGO by dispersion of the N-rGO in an organic solvent and gradually addition and mixing of a solution of long alkyl chain-Lithium (Li) into the N-rGO dispersed in the organic solvent.
  • Li long alkyl chain-Lithium
  • Hexane may be used as the organic solution
  • n-butyl Li may be used as the long alkyl chain-Li.
  • a precipitate may be prepared by heating the lithiated N-rGO at a predefined temperature.
  • the lithiation of the N-rGO may be performed in an inert atmosphere.
  • the precipitate may be coated on a first current collector, to result formation of the anode.
  • the first current collector is made of copper.
  • the lithiation of the N-rGO may be optimized by changing a volume of the solution of the long alkyl chain-Li.
  • porosity of the N-rGO may be increased by one or more of steam activation and chemical activation.
  • the precipitate may be coated on the first current collector at a relative humidity (RH) of less than or equal to 10.
  • the predefined temperature ranges from 45 °C to 55 °C.
  • Fig. 1A illustrates a voltage vs. specific capacity plot for conventional lithium-ion capacitors, in accordance with prior-art
  • Fig. IB illustrates a current vs. voltage plot for an anode half cell made of carbon spheres, in accordance with prior-art
  • Fig. 1C illustrates a current vs. voltage plot for a cathode half cell made of activated carbon, in accordance with prior-art
  • Fig. ID illustrates perspective view of a lithium-ion capacitor utilizing a Li metal foil deposited on the anode surface, in accordance with prior-art
  • Fig. IE illustrates a plot between specific capacitance and number of cycles when highly concentrated electrolytes are used in fabrication of a lithium-ion capacitor, in accordance with prior-art
  • Fig. IF illustrates a plot of current vs. potential for different cycles with usage of sacrificial Li- salt at the cathode, in accordance with prior-art
  • Fig. 2 illustrates an arrangement of components in a lithium-ion capacitor, in accordance with an embodiment of the present invention
  • Fig. 3 illustrates a flow chart of a method of fabrication of an anode for use in a lithium-ion capacitor, in accordance with an embodiment of the present invention
  • Fig. 4 illustrates an X-ray diffraction (XRD) pattern of N-rGO and lithiated-NrGO, in accordance with an embodiment of the present invention
  • Fig. 5A illustrates a plot between specific capacity and potential during charging/discharging of a lithiated N-rGO against Li/Li + , in accordance with an embodiment of the present invention
  • Fig. 5B illustrates a plot between specific capacity and potential during charging/discharging of an activated carbon against Li/Li + , in accordance with an embodiment of the present invention
  • Fig. 6A illustrates a plot between specific capacity and potential during charging/discharging of a lithium-ion capacitor utilizing the lithiated N-rGO at different rates, in accordance with an embodiment of the present invention.
  • Fig. 6B illustrates a plot between specific capacity retention and cycle number of the lithium- ion capacitor utilizing the lithiated N-rGO, in accordance with an embodiment of the present invention.
  • the present invention relates to fabrication of an anode for use in a lithium-ion capacitor.
  • Fig. 2 illustrates an arrangement of components in a lithium-ion capacitor 200, in accordance with an embodiment of the present invention.
  • the lithium-ion capacitor 200 comprises an anode 202, a cathode 204, and an electrolyte 206.
  • nitrogen-doped reduced graphene oxide (N-rGO) may be lithiated by long alkyl-Lithium (Li).
  • the N-rGO lithiated by the long alkyl-Li may be deposited on a first current collector 212, thereby obtaining the anode 202.
  • a method of fabrication of the anode 202 is described in detail with reference to Fig. 3.
  • the long alkyl chain-Li may be n-butyl Li.
  • the first current collector 212 may be made of copper.
  • the cathode 204 may be fabricated through deposition of activated carbon 210 over a second current collector 214. For example, a high surface area dis-ordered carbon may be deposited over the second current collector 214 for obtaining the cathode 204.
  • the second current collector 214 may be made of aluminium.
  • the N-rGO may be synthesized by simultaneously performing reduction and nitrogen doping operations on graphene oxide (GO).
  • the reduction and nitrogen doping operations may be simultaneously performed at a high temperature in presence of a nitrogen source.
  • a plurality of different nitrogen sources may be used for the synthesis of the N-rGO.
  • Lithiation of the N-rGO, for obtaining the lithiated N-rGO 208, may be optimized by changing a volume of a solution of the long alkyl chain-Li.
  • an amount of Li to be added on the N-rGO may be optimized by changing the volume of the solution of the long alkyl chain-Li.
  • porosity of the lithiated N-rGO 208 may be increased by one or more of steam activation and chemical activation techniques.
  • steam activation technique steam may be passed through a powder material in an inert atmosphere at a temperature ranging from 600 °C to 800 °C for 1 to 2 h. Small water particle may react with carbon and release as carbon dioxide or carbon monoxide. Further, number of pores in the surface of N-rGO may be increased by removal of carbon from its surface.
  • the powder material may be mixed with KOH or NaOH followed by heating at a temperature ranging from 600 °C to 800 °C for 1 to 2 h. Further, the powder material may be washed to make it pH free.
  • the lithiated N-rGO 208 may be coated on a copper foil for obtaining the anode 202 for use in the lithium-ion capacitor 200.
  • the anode 202 and the cathode 204 may be inserted into the electrolyte 206.
  • the electrolyte 206 may contain a Li-salt.
  • the electrolyte 206 may consist of Lithium hexafluorophosphate (LiPFe) as the Li-salt.
  • LiPFe Lithium hexafluorophosphate
  • During charging LiPFe may get divided into Li + ions and PFe" ions.
  • the Li + ions may migrate towards the anode 202 and the PFe" ions may migrate towards the cathode 204 during charging of the lithium-ion capacitor 200.
  • N-reduced Graphene Oxide may be prepared by simultaneously performing reduction and nitrogen-doping operations on Graphene Oxide (GO).
  • the reduction and nitrogen-doping operations may be performed at a high temperature in presence of a nitrogen source.
  • the N-rGO may be prepared by thermal treatment of GO in presence of different nitrogen sources.
  • the N-rGO has a high surface area to accommodate a large number of Li + ions. Porosity of the N-rGO may be increased by one or more of steam activation and chemical activation.
  • lithiation of the N-rGO may be performed.
  • the N-rGO may be lithiated by long alkyl chain-Li.
  • the process of lithiation of the N-rGO is described in detail with reference to sub-steps 304a, 304b, 304c, and 304d.
  • the N-rGO may be dispersed into an organic solvent, for example Hexane.
  • a solution of long alkyl chain-Li may be gradually added and mixed with the N-rGO dispersed in the organic solvent. Lithiation of the N-rGO may be optimized by changing a volume of the solution of the long alkyl chain-Li.
  • n-butyl Li may be used as the long alkyl chain-Li.
  • the solution of the n-butyl Li may be added to the N-rGO in dropwise manner. Further, the solution may be continuously stirred such that the n-butyl Li gets scattered evenly in the N- rGO.
  • the lithiation of the N-rGO may be performed in an inert atmosphere, for obtaining lithiated N-rGO.
  • a precipitate may be prepared by heating the lithiated N-rGO at a predefined temperature.
  • the lithiated N-rGO may be heated at a predefined temperature to prepare the precipitate.
  • the predefined temperature may range from 45 °C to 55 °C.
  • the precipitate may be collected by filtration followed by washing with alkaline organic solvent in an inert atmosphere.
  • the precipitate may be coated on a first current collector to obtain the anode.
  • the precipitate may be coated on the first current collector at a relative humidity (RH) of less than or equal to 10.
  • X-ray diffraction (XRD) test of N-rGO and Lithiated N-rGO was performed and results of the XRD test were plotted, as illustrated through Fig. 4. It was observed from plot 402, a 29 peak for N-rGO appears at around 24.5 0 and confirms reduction of graphene oxide. Further, the 29 peak was shifted to a lower value of 21.5 0 in case of lithiated N-rGO as observed from plot 404. Thus, interlayer spacing due to the lithium intercalation is increased in N-rGO.
  • N-rGO coated electrode may be considered while fabricating the lithiated N-rGO coated electrode as the anode.
  • specific negative to positive charge ratios (N/P ratios) of N-rGO and activated carbon may be established to demonstrate the lithium-ion capacitor for longer cycle stability, high energy and power density.
  • Fig. 5A illustrates a plot between specific capacity and potential during charging/discharging of a lithiated N-rGO against Li/Li + , in accordance with an embodiment of the present invention.
  • Curve 502 illustrates a graph for 1 st discharge of lithiated N-rGO at 0.1 A g 1
  • curve 504 illustrates a graph for 1 st charge of the lithiated N-rGO
  • curve 506 illustrates a graph for 2 nd discharge of the lithiated N-rGO. It was observed that there is no such capacity difference is present between 1 st charge and 2 nd discharge of the lithiated N-rGO.
  • Fig. 5B illustrates a plot between specific capacity and potential during charging/discharging of an activated carbon against Li/Li + , in accordance with an embodiment of the present invention.
  • Curve 508 illustrates the charging of the activated carbon and curve 510 illustrates the discharging of the activated carbon.
  • Fig. 6A illustrates a plot between specific capacity and potential during charging/discharging of a lithium-ion capacitor utilizing the lithiated N-rGO at different rates, in accordance with an embodiment of the present invention.
  • the lithium-ion capacitor utilizes lithiated N-rGO as anode and activated carbon as cathode.
  • Curve 602 illustrates a plot between the specific capacity and the potential at 0.01 A g 1
  • curve 604 illustrates a plot between the specific capacity and the potential at 0.1 A g 1
  • curve 606 illustrates a plot between the specific capacity and the potential at 0.5 A g 1
  • curve 608 illustrates a plot between the specific capacity and the potential at 1 A g 1
  • curve 610 illustrates a plot between the specific capacity and the potential at 2 A g’ 1 .
  • Fig. 6B illustrates a plot between specific capacity retention and cycle number of the lithium- ion capacitor utilizing the lithiated N-rGO, in accordance with an embodiment of the present invention.
  • the lithium-ion capacitor was tested at a current density of 0.25 A g 1 .
  • Curve 612 illustrates a stability curve of a lithium ion capacitor having lithiated NrGO as anode and curve 614 illustrates the stability curve of a lithium ion capacitor with only NrGO as anode. It was observed that the stability is significantly improved after lithiation of anode.
  • high porosity of the N-rGO provides enough diffusion path for Li + and eventually provides high-rate capability.
  • the high surface area of N-rGO with efficient ion transport path may accommodate large number of Li + ions which results in high power or energy density.
  • the nitrogen-doping may prevent the agglomeration of rGO layer during several charge-discharge process.
  • lithium-ion capacitor Although the details provided above are referenced to a lithium-ion capacitor, it must be noted that the described arrangement of components, materials used, and other essential principles could be utilised in other lithium-ion capacitors of different designs.

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Abstract

The present invention relates to a lithium-ion capacitor (200) A method to fabricate an anode (202) of the lithium-ion capacitor (200) includes preparing nitrogen-doped reduced graphene oxide (N-rGO) from graphene oxide (GO) by simultaneously performing reduction and nitrogen-doping operations at a high temperature in presence of a nitrogen source. The N-rGO is lithiated, for obtaining lithiated N-rGO (208), by dispersion of the N-rGO in an organic solvent and gradually adding and mixing a solution of long alkyl chain-Li into the N-rGO at a predefined temperature. A precipitate is prepared by heating the lithiated N-rGO (208) at a predefined temperature. The precipitate is coated on a first current collector (212), thereby obtaining the anode (202).

Description

LITHIUM-ION CAPACITOR UTILIZING ANODE MADE FROM CHEMICALLY PRE-LITHIATED NITROGEN DOPED REDUCED GRAPHENE OXIDE
FIELD OF INVENTION
The present invention relates to energy storage devices, and specifically relates to lithium-ion capacitors.
BACKGROUND
Lithium-ion capacitors are energy storage elements having high energy density compared to supercapacitors and high power density compared to batteries, such as Lithium (Li)-ion batteries. A lithium-ion battery consists of a Li-metal oxide (i.e. LiCo2O4, LiMn2O4, etc) cathode, a graphite anode, and a Li-salt (i.e. LiPFe) containing electrolyte. During charging, Li+ ions migrate from a cathode to an anode. During discharging, Li+ ions migrate from the anode to the cathode. Hence, loss of Li+ ions during initial cycles can be compensated by Li present in the cathode. In contrast, a lithium-ion capacitor makes use of a battery type carbon material (i.e. graphite, or hard carbon) as an anode and a supercapacitor type activated carbon material as a cathode. The activated carbon material used as the cathode does not contain Li+ ions. During charging, cations (Li+ ions) migrate from an electrolyte to the anode and corresponding anions (i.e. PFe" ions) of the electrolyte migrate to the cathode. Thus, irreversible loss of Li+ ions due to solid electrolyte interphase (SEI) layer formation and irreversible electrochemical processes in initial cycles is not compensated by the cathode as the cathode of lithium-ion capacitors does not contain Li+ ions. Eventually, loss of Li+ ions results in capacity fading, decay in ionic conductivity of electrolyte, change in viscosity of electrolyte, and low working potential of the lithium-ion capacitor, with subsequent cycles.
Fig. 1A illustrates a voltage vs. specific capacity plot for conventional lithium-ion capacitors, in accordance with prior-art. Discharging and charging of a lithium-ion capacitor at first cycle is illustrated by curve 102, discharging and charging of the lithium-ion capacitor at second cycle are illustrated by curve 104, and charging and discharging of the lithium-ion capacitor at third cycle are illustrated by curve 106. As illustrated in Fig. 1A, a loss in specific capacity occurs during initial cycles (illustrated by arrow 108). For example, as illustrated in Fig. 1A, specific capacity for discharging at the second cycle (illustrated by curve 104) i.e. around 580 mA h g 1 is less than the specific capacity for discharging at the first cycle (illustrated by curve 102) i.e. around 1500 mA h g 1. Conventionally, several strategies have been adopted to overcome the irreversible loss of Li+ ions in the initial cycles of charging and discharging of the lithium-ion capacitor, as described henceforth with reference to Figs. IB through IF. In one approach, the anode is electrochemically pre-lithiated by making a half-cell of carbon-based electrodes. Fig. IB illustrates a current vs. voltage plot for an anode half cell made of carbon spheres, in accordance with prior-art. Charging of the lithium-ion capacitor at 1st cycle is illustrated by curve 110, charging of the lithium-ion capacitor at 5th cycle is illustrated by curve 112, and charging of the lithium-ion capacitor at 10th cycle is illustrated by curve 114. Fig. 1C illustrates a current vs. voltage plot for a cathode half cell made of activated carbon, in accordance with prior-art. The cathode half-cell was tested at 5 mV s’1. However, for pre-lithiation, assembling of the half-cell and again de-assembling of the half-cell to obtain the electrode add up extra steps in a cell manufacturing process.
In another approach, a Li metal foil is deposited on an anode surface to compensate the loss of Li+ ions during initial charging. Fig. ID illustrates perspective view of a lithium-ion capacitor utilizing a Li metal foil 116 deposited on the anode surface, in accordance with prior-art. However, this process is not industrially viable in terms of safety and for large-scale production.
In yet another approach, highly concentrated electrolytes have been used to compensate the initial irreversible loss of Li+ ions. Fig. IE illustrates a plot between specific capacitance and number of cycles when highly concentrated electrolytes are used in fabrication of a lithium-ion capacitor, in accordance with prior-art. It is difficult to find high concentrated electrolyte with required viscosity, conductivity, thermal stability, and electrochemical stability.
In another approach, sacrificial Li-salt has been used at a cathode to fabricate a highly efficient version of lithium-ion capacitor. Fig. IF illustrates a plot of current vs. potential for different cycles with usage of sacrificial Li-salt at the cathode, in accordance with prior-art. For example, curve 118 illustrates a graph for 1st cycle, curve 120 illustrates a graph for 2nd cycle, curve 122 illustrates a graph for 5th cycle, and curve 124 illustrates a graph for 10th cycle. Energy density of such lithium-ion capacitor is limited by specific capacity of the cathode, as the presence of 30-40% sacrificial Li-salt results in low capacity as well as low energy density. Thus, there remains a need to compensate solid electrolyte interphase (SEI) layer formation and to compensate irreversible loss of Li+ ions in initial charging and discharging cycles of lithium-ion capacitors.
OBJECTS OF THE INVENTION
A general objective of the present invention is to fabricate an anode for use in a lithium-ion capacitor.
Another objective of the present invention is to compensate initial loss of Li by irreversible reactions and solid electrolyte interphase (SEI) layer formation.
Another objective of the present invention is to provide high porosity to a material used in fabrication of the anode.
Another objective of the present invention is to provide enough diffusion paths for Li+ ions, resulting in high-rate capability.
Yet another objective of the present invention is to provide a large surface area to a material used in fabrication of an anode, to accommodate a large number of Li+.
Still another objective of the present invention is to prevent an agglomeration of the material used in fabrication of the anode.
SUMMARY OF THE INVENTION
The summary is provided to introduce aspects related to fabrication of anode for usage in a lithium-ion capacitor, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
In one embodiment, a lithium-ion capacitor may comprise an anode fabricated through deposition of nitrogen-doped reduced graphene oxide (N-rGO) lithiated by long alkyl chain- Lithium (Li), over a first current collector. In one implementation, the long alkyl chain-Li may include n-butyl Li. The lithium-ion capacitor may comprise a cathode fabricated through deposition of activated carbon over a second current collector. The lithium-ion capacitor may further comprise an electrolyte for allowing ion exchange between the anode and the cathode.
In one aspect, the N-rGO may be synthesized from graphene oxide (GO) by simultaneously performing reduction and nitrogen doping operations at a high temperature, in presence of a nitrogen source.
In one aspect, lithiation of the N-rGO may be optimized by changing a volume of a solution of the long alkyl chain-Li.
In one aspect, porosity of the N-rGO may be increased by one or more of steam activation and chemical activation.
In one aspect, the first current collector is made of copper and the second current collector is made of aluminium.
In one embodiment, to fabricate an anode for use in a lithium-ion capacitor, nitrogen-doped reduced graphene oxide (N-rGO) may be prepared from graphene oxide (GO) by simultaneously performing reduction and nitrogen-doping operations at a high temperature, in presence of a nitrogen source. The N-rGO may be lithiated to obtain lithiated N-rGO by dispersion of the N-rGO in an organic solvent and gradually addition and mixing of a solution of long alkyl chain-Lithium (Li) into the N-rGO dispersed in the organic solvent. In one implementation, Hexane may be used as the organic solution n-butyl Li may be used as the long alkyl chain-Li. A precipitate may be prepared by heating the lithiated N-rGO at a predefined temperature. The lithiation of the N-rGO may be performed in an inert atmosphere. The precipitate may be coated on a first current collector, to result formation of the anode. The first current collector is made of copper.
In one aspect, the lithiation of the N-rGO may be optimized by changing a volume of the solution of the long alkyl chain-Li.
In one aspect, porosity of the N-rGO may be increased by one or more of steam activation and chemical activation. In one aspect, the precipitate may be coated on the first current collector at a relative humidity (RH) of less than or equal to 10.
In one aspect, the predefined temperature ranges from 45 °C to 55 °C.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention which are used to describe the principles of the present invention. The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this invention are not necessarily to the same embodiment, and they mean at least one. In the drawings:
Fig. 1A illustrates a voltage vs. specific capacity plot for conventional lithium-ion capacitors, in accordance with prior-art;
Fig. IB illustrates a current vs. voltage plot for an anode half cell made of carbon spheres, in accordance with prior-art;
Fig. 1C illustrates a current vs. voltage plot for a cathode half cell made of activated carbon, in accordance with prior-art;
Fig. ID illustrates perspective view of a lithium-ion capacitor utilizing a Li metal foil deposited on the anode surface, in accordance with prior-art;
Fig. IE illustrates a plot between specific capacitance and number of cycles when highly concentrated electrolytes are used in fabrication of a lithium-ion capacitor, in accordance with prior-art; Fig. IF illustrates a plot of current vs. potential for different cycles with usage of sacrificial Li- salt at the cathode, in accordance with prior-art;
Fig. 2 illustrates an arrangement of components in a lithium-ion capacitor, in accordance with an embodiment of the present invention;
Fig. 3 illustrates a flow chart of a method of fabrication of an anode for use in a lithium-ion capacitor, in accordance with an embodiment of the present invention;
Fig. 4 illustrates an X-ray diffraction (XRD) pattern of N-rGO and lithiated-NrGO, in accordance with an embodiment of the present invention;
Fig. 5A illustrates a plot between specific capacity and potential during charging/discharging of a lithiated N-rGO against Li/Li+, in accordance with an embodiment of the present invention;
Fig. 5B illustrates a plot between specific capacity and potential during charging/discharging of an activated carbon against Li/Li+, in accordance with an embodiment of the present invention;
Fig. 6A illustrates a plot between specific capacity and potential during charging/discharging of a lithium-ion capacitor utilizing the lithiated N-rGO at different rates, in accordance with an embodiment of the present invention; and
Fig. 6B illustrates a plot between specific capacity retention and cycle number of the lithium- ion capacitor utilizing the lithiated N-rGO, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The present invention relates to fabrication of an anode for use in a lithium-ion capacitor. Fig. 2 illustrates an arrangement of components in a lithium-ion capacitor 200, in accordance with an embodiment of the present invention. As illustrated in Fig. 2, the lithium-ion capacitor 200 comprises an anode 202, a cathode 204, and an electrolyte 206. For fabrication of the anode 202, nitrogen-doped reduced graphene oxide (N-rGO) may be lithiated by long alkyl-Lithium (Li). Further, the N-rGO lithiated by the long alkyl-Li (alternatively referred as lithiated N- rGO 208) may be deposited on a first current collector 212, thereby obtaining the anode 202. A method of fabrication of the anode 202 is described in detail with reference to Fig. 3. In one implementation, the long alkyl chain-Li may be n-butyl Li. The first current collector 212 may be made of copper. The cathode 204 may be fabricated through deposition of activated carbon 210 over a second current collector 214. For example, a high surface area dis-ordered carbon may be deposited over the second current collector 214 for obtaining the cathode 204. In one implementation, the second current collector 214 may be made of aluminium.
In one implementation, the N-rGO may be synthesized by simultaneously performing reduction and nitrogen doping operations on graphene oxide (GO). The reduction and nitrogen doping operations may be simultaneously performed at a high temperature in presence of a nitrogen source. In one scenario, a plurality of different nitrogen sources may be used for the synthesis of the N-rGO. Lithiation of the N-rGO, for obtaining the lithiated N-rGO 208, may be optimized by changing a volume of a solution of the long alkyl chain-Li. For example, an amount of Li to be added on the N-rGO may be optimized by changing the volume of the solution of the long alkyl chain-Li. Further, porosity of the lithiated N-rGO 208 may be increased by one or more of steam activation and chemical activation techniques. Within the steam activation technique, steam may be passed through a powder material in an inert atmosphere at a temperature ranging from 600 °C to 800 °C for 1 to 2 h. Small water particle may react with carbon and release as carbon dioxide or carbon monoxide. Further, number of pores in the surface of N-rGO may be increased by removal of carbon from its surface. In the chemical activation, the powder material may be mixed with KOH or NaOH followed by heating at a temperature ranging from 600 °C to 800 °C for 1 to 2 h. Further, the powder material may be washed to make it pH free. The lithiated N-rGO 208 may be coated on a copper foil for obtaining the anode 202 for use in the lithium-ion capacitor 200.
The anode 202 and the cathode 204 may be inserted into the electrolyte 206. The electrolyte 206 may contain a Li-salt. For example, the electrolyte 206 may consist of Lithium hexafluorophosphate (LiPFe) as the Li-salt. During charging, LiPFe may get divided into Li+ ions and PFe" ions. The Li+ ions may migrate towards the anode 202 and the PFe" ions may migrate towards the cathode 204 during charging of the lithium-ion capacitor 200.
A method of fabrication of an anode for use in a lithium-ion capacitor is now described with reference to Fig. 3. At step 302, N-reduced Graphene Oxide (N-rGO) may be prepared by simultaneously performing reduction and nitrogen-doping operations on Graphene Oxide (GO). The reduction and nitrogen-doping operations may be performed at a high temperature in presence of a nitrogen source. For example, the N-rGO may be prepared by thermal treatment of GO in presence of different nitrogen sources. The N-rGO has a high surface area to accommodate a large number of Li+ ions. Porosity of the N-rGO may be increased by one or more of steam activation and chemical activation.
At step 304, lithiation of the N-rGO may be performed. In one implementation, the N-rGO may be lithiated by long alkyl chain-Li. The process of lithiation of the N-rGO is described in detail with reference to sub-steps 304a, 304b, 304c, and 304d. At sub-step 304a, the N-rGO may be dispersed into an organic solvent, for example Hexane. At sub-step 304b, a solution of long alkyl chain-Li may be gradually added and mixed with the N-rGO dispersed in the organic solvent. Lithiation of the N-rGO may be optimized by changing a volume of the solution of the long alkyl chain-Li. In one implementation, n-butyl Li may be used as the long alkyl chain-Li. The solution of the n-butyl Li may be added to the N-rGO in dropwise manner. Further, the solution may be continuously stirred such that the n-butyl Li gets scattered evenly in the N- rGO. The lithiation of the N-rGO may be performed in an inert atmosphere, for obtaining lithiated N-rGO.
At sub step 304c, a precipitate may be prepared by heating the lithiated N-rGO at a predefined temperature. For example, the lithiated N-rGO may be heated at a predefined temperature to prepare the precipitate. The predefined temperature may range from 45 °C to 55 °C. At sub step 304d, the precipitate may be collected by filtration followed by washing with alkaline organic solvent in an inert atmosphere. At step 306, the precipitate may be coated on a first current collector to obtain the anode. In one implementation, the precipitate may be coated on the first current collector at a relative humidity (RH) of less than or equal to 10.
X-ray diffraction (XRD) test of N-rGO and Lithiated N-rGO was performed and results of the XRD test were plotted, as illustrated through Fig. 4. It was observed from plot 402, a 29 peak for N-rGO appears at around 24.5 0 and confirms reduction of graphene oxide. Further, the 29 peak was shifted to a lower value of 21.5 0 in case of lithiated N-rGO as observed from plot 404. Thus, interlayer spacing due to the lithium intercalation is increased in N-rGO. In case of lithiated N-rGO, it was observed from plot 404, 29 peaks corresponding to LiCe appear at 23° and 35° as shown by * in XRD plot, 29 peaks corresponding to LiCn appear at 45° and 25° as shown by • in the XRD plot. 29 peak corresponding to LiC2 appears at 32° as shown by ® in the XRD plot.
In one implementation, industrial parameters such as material loading, peel strength may be considered while fabricating the lithiated N-rGO coated electrode as the anode. In one implementation, specific negative to positive charge ratios (N/P ratios) of N-rGO and activated carbon may be established to demonstrate the lithium-ion capacitor for longer cycle stability, high energy and power density.
In one implementation, the lithium-ion capacitor as disclosed in the present invention was tested. It was observed that the lithium-ion capacitor, fabricated through the above-mentioned method, compensates initial loss of Li+ by irreversible reactions and SEI layer formation. Fig. 5A illustrates a plot between specific capacity and potential during charging/discharging of a lithiated N-rGO against Li/Li+, in accordance with an embodiment of the present invention. Curve 502 illustrates a graph for 1st discharge of lithiated N-rGO at 0.1 A g 1, curve 504 illustrates a graph for 1st charge of the lithiated N-rGO, and curve 506 illustrates a graph for 2nd discharge of the lithiated N-rGO. It was observed that there is no such capacity difference is present between 1st charge and 2nd discharge of the lithiated N-rGO. Fig. 5B illustrates a plot between specific capacity and potential during charging/discharging of an activated carbon against Li/Li+, in accordance with an embodiment of the present invention. Curve 508 illustrates the charging of the activated carbon and curve 510 illustrates the discharging of the activated carbon. Fig. 6A illustrates a plot between specific capacity and potential during charging/discharging of a lithium-ion capacitor utilizing the lithiated N-rGO at different rates, in accordance with an embodiment of the present invention. The lithium-ion capacitor utilizes lithiated N-rGO as anode and activated carbon as cathode. Curve 602 illustrates a plot between the specific capacity and the potential at 0.01 A g 1, curve 604 illustrates a plot between the specific capacity and the potential at 0.1 A g 1, curve 606 illustrates a plot between the specific capacity and the potential at 0.5 A g 1, curve 608 illustrates a plot between the specific capacity and the potential at 1 A g 1, and curve 610 illustrates a plot between the specific capacity and the potential at 2 A g’1.
Fig. 6B illustrates a plot between specific capacity retention and cycle number of the lithium- ion capacitor utilizing the lithiated N-rGO, in accordance with an embodiment of the present invention. The lithium-ion capacitor was tested at a current density of 0.25 A g 1. Curve 612 illustrates a stability curve of a lithium ion capacitor having lithiated NrGO as anode and curve 614 illustrates the stability curve of a lithium ion capacitor with only NrGO as anode. It was observed that the stability is significantly improved after lithiation of anode.
Further, high porosity of the N-rGO provides enough diffusion path for Li+ and eventually provides high-rate capability. Further, the high surface area of N-rGO with efficient ion transport path may accommodate large number of Li+ ions which results in high power or energy density. Furthermore, the nitrogen-doping may prevent the agglomeration of rGO layer during several charge-discharge process.
Although the details provided above are referenced to a lithium-ion capacitor, it must be noted that the described arrangement of components, materials used, and other essential principles could be utilised in other lithium-ion capacitors of different designs.

Claims

WE CLAIM:
1. A lithium-ion capacitor (200) comprising: an anode (202) fabricated through deposition of nitrogen-doped reduced graphene oxide (N-rGO) lithiated by long alkyl chain-Lithium (Li), over a first current collector (212); a cathode (204) fabricated through deposition of activated carbon (210) over a second current collector (214); and an electrolyte (206) for allowing ion exchange between the anode (202) and the cathode (204).
2. The lithium-ion capacitor (200) as claimed in claim 1, wherein the N-rGO is synthesized from graphene oxide (GO) by simultaneously performing reduction and nitrogen doping operations at a high temperature in presence of a nitrogen source.
3. The lithium-ion capacitor (200) as claimed in claim 1, wherein lithiation of the N-rGO is optimized by changing a volume of a solution of the long alkyl chain-Li.
4. The lithium-ion capacitor (200) as claimed in claim 3, wherein the long alkyl chain-Li is n-butyl Li.
5. The lithium-ion capacitor (200) as claim in claim 1, wherein a porosity of the N-rGO is increased by one or more of steam activation or chemical activation.
6. The lithium-ion capacitor (200) as claimed in claim 1, wherein the first current collector (212) is made of copper and the second current collector (214) is made of aluminium.
7. A method of fabrication of an anode (202) for use in a lithium-ion capacitor (200), the method comprising: preparing nitrogen-doped reduced graphene oxide (N-rGO) from graphene oxide (GO) by simultaneously performing reduction and nitrogen -doping operations at a high temperature in presence of a nitrogen source; performing lithiation of the N-rGO, to obtain lithiated N-rGO (208), by: dispersing the N-rGO in an organic solvent; and gradually adding and mixing a solution of long alkyl chain-Lithium (Li) into the N-rGO dispersed in the organic solvent; preparing a precipitate by heating the lithiated N-rGO (208) at a predefined temperature; and coating the precipitate on a first current collector (212), thereby obtaining the anode (202).
8. The method as claimed in claim 7, wherein the lithiation of the N-rGO is optimized by changing a volume of the solution of the long alkyl chain-Li.
9. The method as claimed in claim 8, wherein the long alkyl chain-Li is n-butyl Li.
10. The method as claimed in claim 7, wherein a porosity of the N-rGO is increased by one or more of steam activation and chemical activation.
11. The method as claimed in claim 7, wherein the lithiation of the N-rGO is performed in an inert atmosphere.
12. The method as claimed in claim 7, wherein the precipitate is coated on the first current collector (212) at a relative humidity (RH) of less than or equal to 10.
13. The method as claimed in claim 7, wherein the organic solvent is Hexane.
14. The method as claimed in claim 7, wherein the first current collector (212) is made of copper.
15. The method as claimed in claim 7, wherein the predefined temperature ranges from 45 °C to 55 °C.
PCT/IN2023/051028 2022-11-07 2023-11-07 Lithium-ion capacitor utilizing anode made from chemically pre-lithiated nitrogen doped reduced graphene oxide WO2024100680A1 (en)

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140293507A1 (en) * 2013-03-28 2014-10-02 Kishor Purushottam Gadkaree Composite electrode for lithium ion capacitor

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Publication number Priority date Publication date Assignee Title
US20140293507A1 (en) * 2013-03-28 2014-10-02 Kishor Purushottam Gadkaree Composite electrode for lithium ion capacitor

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DENIS LOUIS CAMPÉON, YOSHIKAWA YUMI; TERANISHI TAKASHI; NISHINA YUTA: "Sophisticated rGO synthesis and pre-lithiation unlocking full-cell lithium-ion battery high-rate performances", ELECTROCHIMICA ACTA, ELSEVIER, AMSTERDAM, NL, vol. 363, 1 December 2020 (2020-12-01), AMSTERDAM, NL , pages 137257, XP093172334, ISSN: 0013-4686, DOI: 10.1016/j.electacta.2020.137257 *
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