Classifications

• • 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
  • H01G11/34—Carbon-based characterised by carbonisation or activation of carbon
• • 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
  • H01G11/14—Arrangements or processes for adjusting or protecting hybrid or EDL capacitors
• • 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
  • H01G11/38—Carbon pastes or blends; Binders or additives therein
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/22—Electrodes
  • H01G11/30—Electrodes characterised by their material
  • H01G11/50—Electrodes characterised by their material specially adapted for lithium-ion capacitors, e.g. for lithium-doping or for intercalation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
  • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components thereof
  • H01G11/86—Processes for the manufacture of hybrid or EDL capacitors, or components thereof specially adapted for electrodes
• • 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
• • 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 the field of electrochemical energy storage and more particularly to a metal ion capacitor (MIC) that exhibits both high energy and high power densities.
• MIC metal ion capacitor
• prelithiation is even more critical for LIC because any additional source of Li+ ions should be large enough to not only address SEI formation but also to lithiate (on charge) the negative electrode.
• prelithiation of carbons in LICs remain a major technological barrier. Therefore, commercial LICs are so far based on anodes made of graphite, that, despite its sluggish kinetics, presents lower first cycle irreversibility than other carbonaceous materials such as hard carbon and enables easier prelithiation solutions.
• electrochemical prelithiation can be done in a separate cell.
• the electrochemical prelithiation process often requires a re-assembling step of the prelithiated negative electrode into the LIC cell under inert atmosphere, which is cost-increasing and reduces the possibility to use this method in a commercial way.
• Lithiated metal oxides are incorporated to the positive electrode and combined with the activated carbon as an irreversible source of lithium.
• Metal oxides such as U2M0O3, LisFeOe or U2RUO3 have been proposed achieving full prelithiation degree of graphite electrodes. Still, this approach presents some drawbacks that should be addressed for its implementation as a viable solution for prelithiation. Firstly, lithium extraction potential of most of these metal oxides is above 4.7 V vs. Li/Li + promoting electrolyte decomposition that negatively affects posterior LIC cyclability.
• the present invention tackles the limitations of the prior art by providing a metal ion capacitor (MIC) based on a hard carbon anode with outstanding power capabilities.
• a metal ion capacitor based on a hard carbon anode with outstanding power capabilities.
• the inventors have found that sacrificial salts may be added as source of metal ions to activated carbon (AC) in the positive electrode to efficiently compensate the high irreversible capacity of hard carbon (HC) anodes, allowing for a 1:1 and superior mass balances between anode and cathode.
• AC activated carbon
• HC hard carbon
• the extraordinary performance of this approach has been successfully demonstrated not only in lithium ion capacitors (LICs) but also in other metal ion capacitors such as sodium and potassium ion capacitors.
• the MIC described herein is compatible with an industrial and easily scalable fabrication process that enables the use of HCs as negative electrode in MICs, increasing the energy and allowing targeting for higher power than that of graphite-based capacitors.
• the present invention is directed to a metal ion capacitor comprising: a negative electrode which comprises a hard carbon, a positive electrode which comprises an activated carbon and a sacrificial salt, and a separator positioned between the two electrodes; wherein the sacrificial salt is selected from the group consisting of squarate, oxalate, ketomalonate and di-ketosuccinate or a combination thereof.
• an electrolytic solution can be incorporated throughout cathode, anode and separator.
• the electrolytic solution comprises an electrolyte material (solute) dissolved in a solvent.
• the present invention is directed to a process for manufacturing the metal ion capacitor as described herein, said process comprising the preparation of the negative hard carbon electrode and/or the activated carbon of the positive electrode from biomass waste.
• the present invention is directed to the use of a sacrificial salt as a source of metal ions for pre-doping a negative electrode of a metal ion capacitor and to compensate for the need of metal ions to form the solid electrolyte interphase (SEI) on the negative electrode, wherein said sacrificial salt is combined with activated carbon in the positive electrode, said sacrificial salt being selected from the group consisting of squarate, oxalate, ketomalonate and di-ketosuccinate or a combination thereof, and wherein said negative electrode comprises a hard carbon.
• SEI solid electrolyte interphase
• Figure 1 shows the X-ray pattern of as synthetized squarates (experimental): U2C4O4, N 3 2 0 4 0 4 and K2C4O4 .
• ICDS inorganic crystal structure database
• Figure 2 shows 1 st , 2 nd and 5 th cyclic voltammetry (CV) and charge/discharge cycles for U2C4O4, Na2C4C>4 and K2C4O4 mixed with Super C65 in a 60:30 ratio as described in examples 3-5, showing their decomposition potentials and the high irreversibility shown by all the squarates in view of the negligible current remaining in the 5 th cycle.
• CV cyclic voltammetry
• Figure 3 shows 1 st , 2 nd , 5 th and 10 th CV and charge/discharge cycles for U2C4O4, Na2C4C>4 and K2C4O4 mixed with activated carbon in a 40:50 ratio with 5:5 for C65 conducting carbon and PVDF binder, as described in examples 3-5. After the first cycle, the remaining capacity is only owing to the AC contribution.
• Figure 4 shows rate capability test together with the coulombic efficiency for an olive pit derived hard carbon vs. Li/Li + , as described in example 3.
• Figure 5 shows rate capability test together with the coulombic efficiency an olive pit derived hard carbon compared to commercially available graphite vs. Li/Li + , as described in example 3.
• Figure 6 shows capacity comparison for an olive pit derived hard carbon and activated carbon mixed with lithium squarate in order to select the best mass balance possible, as described in example 3.
• Figure 7 shows first charge for a LIC carried out at C/10 together with the potential swing of the HC and AC+ salt, as described in example 3.
• LIC was assembled using a 1 to 1 mass balance and charge was carried out at C/10.
• Figure 8 shows voltage profiles for a LIC operated between 2-4 V at different applied currents accounting for different discharge times ranging from several minutes to few seconds, as described in example 3. Potential swing for HC and AC+ salt is also shown.
• Figure 9 shows Ragone Plot comparing a herein reported LIC with an EDLC based on symmetric olive pit derived ACs for comparison, as described in example 3.
• Figure 10 shows capacity comparison for an olive pit derived hard carbon and activated carbon mixed with sodium squarate in order to select the best mass balance possible, as described in example 4.
• Figure 11 shows the first charge for a NIC carried out at C/10 together with the potential swing of the HC and AC+ salt, as described in example 4.
• Figure 12 shows voltage profiles for a NIC operated between 2-4 V at different applied currents accounting for different discharge times ranging from several minutes to few seconds, as described in example 4. Potential swing for HC and AC+ salt is also shown.
• Figure 13 shows a Ragone Plot comparing a herein reported NIC with an EDLC based on symmetric olive pit derived ACs for comparison purposes, as described in example 4.
• Figure 14 shows capacity comparison for an olive pit derived hard carbon and activated carbon mixed with potassium squarate in order to select the best mass balance possible, as described in example 5.
• Figure 15 shows the first charge for a KIC carried out at C/10 together with the potential swing of the HC and AC+ salt, as described in example 5.
• LIC lithium ion capacitor
• LIBs lithium ion batteries
• the positive electrode is not a lithium source and all the lithium must come from the prelithiation source.
• graphite is used as the negative electrode owing to its low irreversible capacity being only about 5%, therefore minimizing the lithium amount needed in the prelithiation step.
• the sluggish kinetics of graphite limits LIC technology in terms of power and the use of more powerful materials in the negative electrode is highly desirable.
• the technology should be applicable not only to LICs but also to other metal ion capacitors such as sodium ion and potassium ion capacitors.
• the solution provided in this invention is a metal ion capacitor which comprises: at least one anode comprising a hard carbon (HC), at least one cathode comprising an activated carbon (AC) and a sacrificial salt selected from the group consisting of squarate, oxalate, ketomalonate and di- ketosuccinate or a combination thereof, and a separator interposed between the two electrodes.
• HC hard carbon
• AC activated carbon
• sacrificial salt selected from the group consisting of squarate, oxalate, ketomalonate and di- ketosuccinate or a combination thereof
• the electrodes, anode and cathode are preferably immersed or otherwise positioned in an electrolytic solution with the separator interposed between them.
• the anode is made of hard carbon.
• the HC material preferably has a specific surface area less than about 500 m 2 /g, e.g., less than about 100 m 2 /g.
• the HC material used to form the anode is non-graphitizable and may preferably have an average particle size of less than about 100 microns, e.g., less than about 100, about 10, about 5 or less than or equal to about 1 microns.
• the HC material has an average particle size is in the range from about 0.1 to about 5 microns, e.g., from about 0.5 to about 2 microns, or more specifically about 1 microns. Unexpectedly, even with low particle size good performance may be achieved.
• a thickness of the anode containing HC can range, for example, from about 25 to about 600 microns.
• the cathode is made of a composite material that comprises activated carbon and a sacrificial salt.
• the AC material preferably has a specific surface area greater than about 500 m 2 /g.
• the AC material used to form the cathode may preferably have an average particle size of less than 100 microns, e.g., less than about 100, about 10 or about 5 microns.
• a thickness of the cathode containing AC/sacrificial salt can range, for example, from about 25 to about 600 microns.
• the HC and AC that act respectively as anode and cathode can be synthetized from a wide variety of precursors, such as sucrose, cellulose, polyvinyl (PVC), furfuryl alcohol or even better, from sustainable resources like recycled biomass.
• these carbon materials are prepared from biomass waste such as coconut shells, peanut shells, fruit peels, olive pits, etc.
• biomass waste such as coconut shells, peanut shells, fruit peels, olive pits, etc.
• HC and AC are synthesized from recycled olive pits.
• the preparation of HC comprises heating the carbon precursor at high temperature, normally about 600 °C or more (e.g. about 600-1800 °C, about 650-1500 °C, about 700-1200 °C, or about 750-1000 °C) for at least about 30 min (e.g. about 30- 240 min) under atmosphere inert (e.g. Ar flow) so as to pyrolyze said precursor. If solid, the carbon precursor may be crushed prior to the pyrolysis. In certain instances, the temperature is increased gradually (e.g. ramp rate of about 2-10 °C min 1 ) until reaching the pyrolysis temperature.
• HC is prepared from biomass waste (e.g. olive pits) by a process comprising heating the biomass waste, preferably previously crushed, at a ramp rate of about 3-8 °C min 1 to a predefined temperature ranging from about 600-1800 °C (e.g. about 750-1000 °C) and further holding it for about 1.5-2.5 h.
• biomass waste is crushed and loaded in a furnace (e.g. a tubular furnace) for the pyrolysis process by heating under an Ar flow (e.g. of about 50-250 ml min 1 ) at a ramp rate of about 4-6 °C min 1 to a predefined temperature ranging from about 750-1000 °C (e.g. about 800 °C) and further holding it for about 1.5- 2.5 h.
• the HC may be then mechanically ground and milled.
• the HC is then manually coarse-ground in a mortar/pestle, before being ball- milled in a planetary mill. Milling may be performed for about 60-120 minutes.
• the Activated Carbon (AC) may be prepared from the previously obtained Hard Carbon (HC) (without being mechanically ground and milled).
• the previously obtained Hard Carbon (HC) without the ground and ball milling step
• an hydroxide such as potassium hydroxide in different mass ratios, normally about 1:1 or more (e.g. about 1:10, about 1:8, about 1:6, about 1:4 or about 1:2).
• the HC mixed with hydroxide may be then activated by heating up to a temperature between about 600-800 °C (e.g, about 650 °C, about 700 °C, about 750 °C) under atmosphere inert (e.g. Ar flow).
• the materials mixture is placed in a boat and activated by heating up to a temperature between about 600-800 °C (e.g, about 650 °C, about 700 °C, about 750 °C) under atmosphere inert (e.g. Ar flow between about 50-250 ml min 1 ), preferably inside a horizontal stainless steel tube, within a furnace (e.g. a tubular furnace).
• atmosphere inert e.g. Ar flow between about 50-250 ml min 1
• a furnace e.g. a tubular furnace.
• the temperature is increased gradually (e.g. ramp rate of about 2-10 °C min -1 ).
• the holding time at the defined temperature may be normally set between about 30 min and about 5 h (e.g, between about 1-2h, about 2-3h, about 3-4h, about 4- 5h).
• the microporous AC may be washed off until neutral pH and dried.
• the microporous AC may be washed off with a diluted solution of acid and water until neutral pH is reached and then dried at about 100-150 °C, preferably under vacuum.
• AC is prepared by physically mixing previously obtained HC with potassium hydroxide in about a 1:5 to 1:7 mass ratio.
• Mixed materials are placed in a boat (e.g. an Inconel ⁇ boat) and activated by heating up to about 650-750 °C under an Ar flow of about 50-250 ml_ min 1 inside a horizontal stainless steel tube within a tubular furnace.
• the temperature is increased gradually at a ramp rate of about 3-8 °C min 1 and the holding time at the defined temperature is set at about 1.5-2.5 h.
• the microporous AC is washed off with a diluted solution of hydrochloric acid and water until neutral pH was reached and then dried at about 120°C under vacuum.
• the AC is combined with a sacrificial salt in the cathode of the metal ion capacitor of the present invention.
• the sacrificial salt acts as a source of metal ions for pre-doping the negative electrode and to compensate for the need of metal ions to form the solid electrolyte interphase (SEI) on the negative electrode.
• SEI solid electrolyte interphase
• the term “sacrificial salt” refers to a metal salt that is able to decompose releasing metal ions during the first charge(s) so that the metal ions may be charged into the negative electrode and the loss of active metal ions due to SEI formation is compensated.
• the sacrificial salt is capable of supplying metal ions into the structure of HC as well as compensating its high irreversible capacity by providing the metal ions necessary for the formation of the passivation layer at the surface of the negative electrode.
• Sacrificial salts useful in the present invention include squarates, oxalates, ketomalonates and di-ketosuccinates or a combination thereof.
• the metal of the sacrificial salt is preferably selected from a metal ion of +1 charge such as an alkali metal.
• the chemical formula of these salts for metal ions of +1 charge such as alkali metal ions (e.g.
• Li, Na, and K are as follows: squarate (M2C4O4), oxalate (M2C2O4), ketomalonate (M2C3O5) and di-ketosuccinate (M2C4O6), wherein M is a metal ion of +1 charge. All these salts convert into the gaseous products of CO and CO2, which produce no residues and, thus, could be removed after cell formation cycles.
• the sacrificial salt is selected from the group consisting of squarate, and ketomalonate or a combination thereof .
• the sacrificial salt is a squarate of formula M2C4O4 wherein M is selected from Li, Na and K.
• M is selected from Li, Na and K.
• the chemical structure of U2C4O4, Na 2 C 4 0 4 and K2C4O4 and their decomposition reaction are depicted below.
• the composite cathode can be formed from a mixture of sacrificial salt and activated carbon in a suitable ratio.
• the amount of sacrificial salt in the composite electrode can range from about 10 wt.% to about 60 wt.% (e.g., about 10, about 20, about 30, about 40, about 50 or about 60 weight %). In a more particular embodiment, the amount of sacrificial salt in the composite electrode is about 40 wt.%. In embodiments, the amount of AC in the composite electrode can range from about 10 wt.% to about 60 wt.% (e.g., about 10, about 20, about 30, about 40, about 50 or about 60 weight %). In a more particular embodiment, the amount of AC in the composite electrode is about 50 wt.%. In a even more particular embodiment, the composite cathode comprises about 40 wt.% of sacrificial salt and about 50 wt.% of AC.
• the cathode as well as the anode may be formed by casting (e.g., tape casting) a slurry mixture of the associated components.
• a cathode slurry may comprise activated carbon and an optional binder, and an anode slurry may comprise hard carbon, an optional binder and an optional source of conductive carbon such as graphite or carbon black.
• Example binders include, but are not limited to, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
• PVDF polyvinylidene fluoride
• PTFE polytetrafluoroethylene
• Specific examples of conductive carbon include, but are not limited to, super C45 and super C65.
• the amount of binder incorporated into the electrode may range from about 0 wt.% to about 20 wt.%, e.g., about 5 wt.% to about 10 wt.% of the overall electrode composition.
• the amount of conductive carbon incorporated into the electrode may range from about 0 wt.% to about 10 wt.%, e.g., about 5 wt.% of the overall anode composition.
• the composite cathode comprises about 40 wt% sacrificial salt, about 50 wt% AC, about 5 wt% C65 and about 5 wt% PVDF.
• the composite cathode which comprises activated carbon mixed with a sacrificial salt
• the anode of hard carbon may be porous or non-porous and may, for example, be impermeable to liquids including solvents used to form an electrolytic solution.
• the cathode and anode may be attached to respective positive and negative current collectors.
• the current collectors may comprise a metal foil such as aluminum foil of copper foil.
• the cathode, anode, separator and current collectors when assembled may collectively be referred to as an electrode set.
• the electrode set may consist essentially of cathode, anode, and separator, or consist essentially of a cathode, anode, separator and respective current collectors.
• a liquid electrolytic solution may be incorporated between the cathode and anode such that the electrolytic solution permeates the separator.
• the electrolytic solution may comprise an electrolyte material (solute) dissolved in a suitable solvent.
• the electrolyte material may be any material capable of functioning in an electrochemical device.
• the invention refers to a lithium ion capacitor wherein the electrolyte material is a lithium salt, i.e., a complex lithium salt such as LiPF 6 , L1BF 4 , LiCICU, LiAsF 6 , UF 3 SO 3 , Li[(CF 3 SC> 2 ) 2 N] or Li[(FSC> 2 ) 2 N] as well as mixtures thereof.
• the invention refers to a sodium ion capacitor wherein the electrolyte material is a sodium salt, i.e., a complex sodium salt such as NaPF 6 , NaBF 4 , NaCICL, NaAsFe, NaF 3 SC> 3 , Na[(CF3SC>2)2N] or Na[(FSC>2)2N] as well as mixtures thereof.
• a sodium salt i.e., a complex sodium salt such as NaPF 6 , NaBF 4 , NaCICL, NaAsFe, NaF 3 SC> 3 , Na[(CF3SC>2)2N] or Na[(FSC>2)2N] as well as mixtures thereof.
• the invention refers to a potassium ion capacitor
• the electrolyte material is a potassium salt, i.e., a complex potassium salt such as KPF 6 , KBF 4 , KCIO 4 , KAsF 6 , KF 3 SO 3 , K[(CF 3 S0 2 ) N] or K[(FSC> 2 ) 2 N] as well as mixtures thereof.
• Example solvents for forming an electrolyte solution include organic solvents or mixtures of organic solvents such as dimethyl carbonate (DMC), methyl propionate (MP), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl-methyl carbonate (EMC) or mixtures thereof as well as other solvents suitable for use in an electrolyte where the charge carrier is an alkaline metal ion such as lithium, sodium or potassium ion.
• the solvent may be capable of dissolving the electrolyte material.
• a complex salt such as a complex lithium, sodium or potassium salt is any ionic compound comprising a metal such as lithium, sodium or potassium and an additional metal, metalloid or non-metal atom that does not itself ionize and which is soluble in an organic solvent.
• LiPF 6 contains lithium and phosphorus as metal atoms, but the phosphorus does not ionize by itself. Rather, phosphorus ionizes as the PF 6 ion.
• UBF4 contains lithium metal and the metalloid boron. Although lithium ionizes (Li + ), boron does not ionize by itself, but as the BF4 ion.
• LiCICU contains lithium metal and the non-metal atoms chlorine and oxygen.
• the non-metal atoms ionize as the perchlorate ion (CIOT) ⁇
• the solvent may be any suitable solvent for use in an electrochemical energy storage device.
• the electrolytic solution is a solution of MPF 6 , wherein M is preferably Li, Na or K, in EC: PC.
• the invention refers to an alkali ion capacitor comprising an alkali metal sacrificial salt as positive electrode additive and an electrolyte based on an alkali metal salt.
• the invention refers to a lithium ion capacitor comprising a lithium sacrificial salt as positive electrode additive and an electrolyte based on a lithium salt.
• the invention refers to a sodium ion capacitor comprising a sodium sacrificial salt as positive electrode additive and an electrolyte based on a sodium salt.
• the invention refers to a potassium ion capacitor comprising a potassium sacrificial salt as positive electrode additive and an electrolyte based on a potassium salt.
• a separator or ion conducting membrane, may be interposed between anode and cathode.
• the separator provides ionic conductivity while ensuring effective separation between the opposite electrodes.
• two types of separators can be used: either porous ones, wherein a solution of an electrolyte in a suitable solvent fills the porosity of the separator, or non-porous ones, which are generally either pure solid polymer electrolytes (i.e. electrolytes dissolved in a high molecular weight polyether host, like PEO and PPO, which acts as solid solvent) or gelled polymer electrolyte systems, which incorporates into a polymer matrix a plasticizer or solvent capable of forming a stable gel within the polymer host matrix and an electrolyte.
• a plasticizer or solvent capable of forming a stable gel within the polymer host matrix and an electrolyte.
• the separator is made from fiber glass material.
• One method of forming a metal-ion capacitor comprises assembling an electrode set comprising a composite cathode, an anode, and a separator disposed between the anode and the cathode, and then adding an electrolytic solution to the assembly.
• the positive electrode(s) and the negative electrode(s) are laminated or wound.
• the metal ion capacitor of the present invention may find practical application as a driving or auxiliary storage device for electronic automobiles, hybrid electronic automobiles, etc. Further, it is suitable as a storage device for various energy generation systems such as solar energy generation and wind power generation, and as a storage device for domestic electronic equipment, etc.
• a value of 3.5 preferably has an error margin of 3.45 to 3.54 and a range of 2% to 10% preferably covers a range of 1.5% to 10.4%.
• Said variations of a specified value are understood by the skilled person and are within the context of the present invention. Further, to provide a more concise description, some of the quantitative expressions given herein are not qualified with the term “about”. It is understood that, whether the term “about” is used explicitly or not, every quantity given herein is meant to refer to the actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including equivalents and approximations due to the experimental and/or measurement conditions for such given value.
• the sacrificial salts di-lithium squarate (U 2 C 4 O 4 ), squarate di-sodium squarate (Na 2 C 4 C> 4 ) and di-potassium squarate (K 2 C 4 O 4 ) were synthesized using 4-dihydroxy-3- cyclobutene-1,2-dione and the respective metal carbonates (i.e. U 2 CO 3 Na 2 CC> 3 or K 2 CO 3 ) as starting materials.
• a 1:1 mixture was taken and dissolved in deionized water followed by overnight stirring. The deionized water was removed by using a Buchi ® Rotavapor and dried under vacuum at 50°C for 12 hours prior to use.
• Figure 1 depicts the XRD patterns of the sacrificial salts.
• Olive pits were crushed and loaded in a tubular furnace for the pyrolysis process by heating under an Ar flow of 100 ml min 1 at a ramp rate of 5 °C min-1 to a predefined temperature of 800 °C and further holding it for 2 h (the activation yield is -25%) to obtain hard carbons.
• the HC was then manually coarse-ground in a hard porcelain mortar/pestle, before being ball-milled using ajar and balls made of zirconia with a 1:30 HC:ball mass ratio in a Pulverisette 5 (Fritsch International, Germany). Milling was performed for 90 minutes.
• the previously obtained Hard Carbon (HC) (without the ground and the ball milling step) is physically mixed with potassium hydroxide in a 1/6 mass ratio.
• the materials mixed with KOH are placed in an Inconel ⁇ boat and activated by heating up to a temperature between 700 °C under an Ar flow (100 ml min -1 ) inside a horizontal stainless steel tube within a tubular furnace.
• the heating ramp rate was 5 °C min 1 and the holding time at the defined temperature was 2 h.
• the microporous AC was washed off with a diluted solution of hydrochloric acid and water until neutral pH was reached and then dried at 120°C under vacuum (the activation yield is -75%).
• AC was mixed with each of the sacrificial salts of example 1 (U2C4O4, Na2C4C>4, and K2C4O4) and conducting carbon (C65) and binder (PVDF) so as to prepare three composite materials that were used as cathode in the following examples along with the synthesized HC that acted as anode.
• FIG. 1a depicts XRD patterns of the lithium sacrificial salt synthetized (experimental, up) and registered in the inorganic crystal structure database (ICDS, down).
• Figure 2 depicts the electrochemical performance of the synthesized salts in a half cell configuration in order to determine the decomposition potential and the experimental capacity. Since the salts are by themselves non-conducting organic compounds, they are mixed with a conducting carbon (Super C65 , Imerys Graphite & Carbon) to obtain a carbon coating on the salt in order to enable its decomposition. The potential window was set between 2 and 5 volts respect the corresponding M/M + to ensure full decomposition of the salt.
• Figure 2a shows the case for the lithium squarate in 1M LiFP 6 EC:DMC electrolyte. The first CV cycle shows a broad peak between 3.8 - 4.5 V vs. Li+/Li with a maxima centered at 4.2 V.
• the Galvanostatic (GA) charge/discharge measurement were carried out between 2 and 4.2 V, potential window determined from the CV.
• the specific capacity vs. Li7Li potential is shown in the Figure 2d.
• the first charge at C/10 up to 4.2 V (being C the theoretical capacity of U2C4O4 corresponding to 425.48 mAh g _1 ) shows a large plateau between 3.8 - 4 V vs. Li7Li from which an irreversible specific capacity of 375 mAh g _1 is obtained, whereas in the next cycles the capacity is almost negligible, corresponding to super C65.
• Figure 3 shows the different sacrificial salt combined with AC for the development of the positive electrode, hereafter named as “AC+salt”.
• Figure 3a shows U2C4O4 mixed with AC, conducting carbon (C65) and binder (PVDF) in weight ratio of 40 wt%, 50 wt%, 5 wt% and 5 wt% respectively.
• CVs show voltammograms recorded at 0.1 mV s 1 between 2 - 4.2 V vs. Li7Li. The upper potential was limited owing to the instability of the electrolyte beyond that potential. In the first anodic sweep, a broad peak between 3.8 V and 4.2 V vs. Li7Li describes the irreversible oxidation reaction of the salt.
• Figure 4 shows rate capability test performed to the hard carbon material to be used on the assembly of the LIC.
• GA charge/discharge measurement at different C-rates is shown where C corresponds to the theoretical capacity of UC 6 being 372 mAh g _1 .
• the HC delivers 1063 mAh g-1 from which 461 mAh g-1 are reversible, showing a CE of 43.4%.
• the high irreversible capacity observed for the HC is ascribed to its lower particle size and disordered nature that increases the electrode area. After 5 cycles capacity stabilizes in 394 mAh g _1 .
• Figure 5 shows rate capability test performed to the hard carbon material to be used on the assembly of the LIC compared to a similar graphite electrode. While rate capability is very similar up to 2C charge discharge rate, at 5C differences start to arise while at 10C it is already obvious that the HC outperform its graphite counterpart by at least a factor of 2.5 while this difference increases while the applied C rate increases. Thus, the convenience of using HC over graphite for powerful LICs is demonstrated. On the other hand the first CE for the HC is 42% while for the graphite is 72%.
• specific capacities of both electrodes are compared at different current densities. Accordingly, a 1:1 (HC:AC+salt) mass ratio was selected for the development of the LICs.
• Figure 7 shows the first galvanostatic lithiation of HC-based LICs.
• LIC HC:AC+salt
• Li + was extracted from the positive electrode and inserted into the microstructure of the HC allowing to reach 330 mV vs. Li + /Li.
• FIG. 1b depicts XRD patterns of the sodium sacrificial salt synthetized (experimental, up) and registered in the inorganic crystal structure database (ICDS, down).
• Figure 2 depicts the electrochemical performance of the synthesized salts in a half cell configuration in order to determine the decomposition potential and the experimental capacity.
• Figure 2b shows the case for the sodium squarate in 1M NaPF 6 EC: PC.
• the first cycle shows a broad peak between 3.5 - 4.15 V vs. Na7Na in which the decomposition of Na2C4C>4 occurs.
• the second cycle shows a broad but much less intense peak ascribed to the salt remaining in the electrode after the first cycle. Even so, the absence of peaks in the following cycles shows that all the salt has been irreversibly decomposed.
• Figure 2e shows the GA charge/discharge measurement carried out within the 2 - 4.2 V vs. Na7Na potential window.
• the first charge at C/10 up to 4.2 V (being C the theoretical capacity of Na2C4C>4 corresponding to 339.268 mAh g 1 shows a sloppy profile between 3.7 - 4.2 V vs. Na+/Na from which an irreversible specific capacity of 275 mAh g -1 is obtained. In the next cycles the capacity is almost null, corresponding to super C65.
• Figure 3b shows Na2C4C>4 mixed with AC, conducting carbon (C65) and binder (PVDF) in weight ratio of 40 wt%, 50 wt%, 5 wt% and 5 wt% respectively.
• CVs show voltammograms recorded at 0.1 mV s 1 between 2 - 4.2 V vs.
• Figure 3e shows the first charge step of the composite at C/10 (being C the theoretical specific capacity of Na2C4C>4), showing an irreversible specific capacity of 350 mAh g _1 respect the mass of the salt. This higher capacity than observed for the one measured for the reference salt is ascribed to the contribution of the AC.
• Figure 11 shows the first charge step up to a fixed 4.2 V at C/10 respect the mass of the HC.
• the sodium-based sacrificial salt of the positive electrode is oxidized in the potential of 3.5 - 4 V vs. Na + /Na, while the extracted Na + is inserted into the microstructure of the HC and a cut-off potential of 180 mV is achieved.
• Figure 1c depicts XRD pattern of the potassium sacrificial salt.
• Figure 2 depicts the electrochemical performance of the synthesized salts in a half cell configuration in order to determine the decomposition potential and the experimental capacity.
• Figure 2c shows the case for the potassium squarates in 1M KPF 6 EC:DMC.
• the first cycle shows a broad peak between 3.5 - 4.5 V vs. K7K in which the decomposition of K2C4O4 occurs. Further increase on the current is ascribed to the electrolyte decomposition.
• the peak between 3.5 - 4.5 V disappears but peaks above 4.5 V confirms electrolyte decomposition.
• Figure 2f shows the GA charge/discharge measurement carried out within the 2 - 4.5 V vs. K7K potential window.
• the first charge at C/10 up to 4.5 V (being C the theoretical capacity of K2C4O4 corresponding to 282 mAh g _1 shows a sloppy profile between 3.6 - 4.5 V vs. K7K from which an irreversible specific capacity of 225 mAh g _1 is obtained. In the next cycles the capacity is almost null, corresponding only to super C65.
• Figure 3c shows K2C4O4 mixed with AC, conducting carbon (C65) and binder (PVDF) in weight ratio of 40 wt%, 50 wt%, 5 wt% and 5 wt% respectively.
• CVs show voltammograms recorded at 0.1 mV s 1 between 2 - 4.2 V vs. Li7Li. The upper potential was limited owing to the instability of the electrolyte beyond that potential.
• a broad peak between 3.6 V and 4.2 V vs. Li7Li describes the irreversible oxidation reaction of the salt. In the following cycle less intense peak appears owing to the salt remaining in the electrode.
• Figure 3f shows the first charge step of the composite at C/10 (being C the theoretical specific capacity of K2C4O4), showing an irreversible specific capacity of 250 mAh g _1 respect the mass of the salt. This higher capacity than observed for the one measured for the reference salt is ascribed to the contribution of the AC.
• Figure 15 shows the first charge step up to a fixed 4.2 V at C/10 respect the mass of the HC.
• the potassium-based sacrificial salt of the positive electrode is oxidized in the potential of 3.5 - 4.2 V vs. K7K, while the extracted K + is inserted into the microstructure of the HC and a cut-off potential of 600 mV is achieved.

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