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
  • H01G11/84—Processes for the manufacture of hybrid or EDL capacitors, or components 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
  • H01G11/54—Electrolytes
  • H01G11/58—Liquid electrolytes
  • H01G11/62—Liquid electrolytes characterised by the solute, e.g. salts, anions or cations therein
• • 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 a method of assembling a hybrid electrochemical system.
• a hybrid supercapacitor combining the storage principles of a lithium-ion secondary battery and an electrochemical double-layer capacitor has a higher energy density. typically about 7 Wh.kg- 1 , a standard EDLC
• a symmetrical cell of a standard EDLC is composed of two identical capacitive electrodes The potential difference of such an unloaded cell is 0 V It increases linearly with time during the static galvanic charge of the cell, and during charging the potential of the positive electrode increases linearly and the potential of the negative electrode decreases linearly. the cell voltage decreases linearly
• the industrial symmetric EDLCs operating in an organic medium usually have a nominal voltage of the order of 2.7 V.
• the lithium battery-type electrode is characterized risen by an almost constant potential during the charging and discharging of the system.
• the main problems to solve in this type of hybrid supercapacitor are the formation of the passivation layer and the intercalation / insertion of lithium into the negative electrode.
• the passivation of the negative electrode enables the formation on this electrode of an intermediate layer during a first charge cycle.
• the lithium ions are desolvated before being inserted / inserted in the negative electrode.
• the presence of a well formed passivation layer makes it possible to avoid the exfoliation of the negative carbon electrode during the cycling of the system.
• Lithium is inserted / inserted into the negative electrode until a LL 0.5 C 6 composition is reached.
• the potential of the negative electrode remains relatively stable during successive charges / discharges of the hybrid supercapacitor.
• lithium metal is particularly expensive and industrially binding.
• lithium metal can give rise to a thermal runaway, and therefore pose security problems.
• the cells used are laboratory cells providing an electrolyte reservoir large enough that during the intercalation / insertion of lithium into the negative electrode, the conductivity and composition of the electrolyte remain unchanged.
• the volume of electrolyte is limited and the insertion / insertion of lithium in the negative electrode depletes the electrolyte, which causes a decrease in the performance of the system.
• the inventors have developed a hybrid supercapacitor to overcome the disadvantages of the state of the art.
• the disadvantages of the solutions proposed in the prior art are overcome, according to the process according to the present invention, by using, as in the last publication cited, the lithium salt of the electrolyte to perform the intercalation / insertion of lithium. to the negative electrode but strongly increasing the lithium ion concentration of the electrolyte and then accept depletion.
• the depletion of ions having an impact on the conductivity, the quantity and the concentration of electrolyte are chosen to allow to accept this depletion while maintaining a conductivity of the electrolyte compatible with a powerful system of energy storage.
• Part of the Li + ions contained in the electrolyte is used to form the passivation layer and the intercalation / insertion compound LL 0.5 C 6 to the negative electrode
• the subject of the present invention is therefore a process for producing a hybrid supercapacitor, said method comprising at least one step of assembling a negative electrode based on at least one non-porous carbon material and a positive electrode. based on at least one porous carbon material, said electrodes being separated from each other by means of a separator impregnated with a liquid electrolyte comprising at least one lithium salt in solution in at least one solvent, and then at least a first charging step, said method being characterized in that:
• the ionic lithium concentration in the liquid electrolyte before the first charging step is greater than or equal to 1.6 mol / L
• the lithium salt of the liquid electrolyte comprises at least 50% by weight of a salt chosen from lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and its derivatives such as lithium bis (fluorosulfonyl) imide (LiFSI) and lithium bis (pentafluoromethylsulfonyl) imide (LiBETI);
• a salt chosen from lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) and its derivatives such as lithium bis (fluorosulfonyl) imide (LiFSI) and lithium bis (pentafluoromethylsulfonyl) imide (LiBETI);
• the solvent of the liquid electrolyte comprises at least 80% by volume of a solvent chosen from cyclic alkylcarbonates, chosen in particular from ethylenecarbonate (EC) and propylenecarbonate (PC), and acyclic alkylcarbonates chosen especially from dimethylcarbonate ( DMC), diethylcarbonate (DEC) and methyl-isopropyl carbonate (MiPC), lactones (such as beta- and gamma-lactones and caprolactones), esters such as ethyl acetate and ethylbutyrate (EB ), oxalanes such as dimethoxyethane (DME), and mixtures thereof; it being understood that said solvent comprises at least 20% by volume of ethylenecarbonate;
• a solvent chosen from cyclic alkylcarbonates, chosen in particular from ethylenecarbonate (EC) and propylenecarbonate (PC), and acyclic alkylcarbonates chosen especially from dimethylcarbonate ( DMC), diethylcarbonate (D
• the porous carbon material of the positive electrode is chosen from materials in which the average pore size is greater than 0.7 nm and has a specific surface area greater than 700 m 2 / g, in particular ranging from 700 to 2000 m About 2 / g (BET method);
• the non-porous carbon material of the negative electrode is chosen from materials capable of interposing / inserting lithium ions and having a specific surface area of less than or equal to 150 m 2 / g; in particular 80 m 2 / g;
• the charge of said supercapacitor is performed in several successive charging steps up to a maximum voltage (U max ) of between 4 and 5 volts and at a current density of 10 mA / g at 400 mA / g; each charging step being separated from the next charging step by an intermediate step of self-discharge or discharge at a current less than 5 mA / g.
• U max maximum voltage
• the successive charging steps are also separated by self-discharge steps.
• the set of successive charging steps and self-discharge or low-current discharge stages (also called relaxation stages) of step f) is called the formation cycle.
• the formation cycle leads to the formation of the passivation layer and the intercalation / insertion of the lithium ions into the negative electrode.
• the successive charging steps lead to the consumption of the lithium ions contained in the electrolyte and to a decrease in its concentration.
• FIG. 1 represents the evolution of the conductivity (mS / cm) as a function of the concentration (mol / L) of a liquid electrolyte containing LiTFSI in a mixture EC / DMC (1/1, v / v) with during the process of storing energy in a supercapacitor according to the invention.
• This figure shows that the lithium ion concentration of the electrolyte is chosen as very high (point B) with respect to the optimal concentration (point A).
• the charge / relaxation cycles of step f) allow the formation of the passivation layer and insert / insert the lithium ions into the negative electrode. These cycles cause a decrease in the concentration of the electrolyte up to point A (optimal).
• the ionic lithium concentration in the liquid electrolyte before the first charging step is greater than or equal to about 2.0 mol / L.
• the liquid electrolyte is chosen from the following lithium salt / solvent (s): i) LiTFSI / EC / DMC mixture (1/1; v / v);
• the lithiated ionic compound (a compound which in a solvent dissociates to form Li + ions), and the solvent are chosen so that the electrolyte has a Walden product as high as possible at brought into contact (in particular 20 ° C to 25 ° C).
• Table 1 shows the Walden product for various LiTFSI-based liquid electrolytes that can be used according to the process of the invention, compared with that of a liquid electrolyte based on LiPF 6 alone in a mixture of solvents already known:
• NB In this table, the proportions of the solvents used in mixture are given in volume, for example EC / DMC means that the solvent consists of a mixture with equal volumes of EC and DMC.
• the values of the selected pairs are of the same order of magnitude as the usual electrolytes, which confirms their interest for the application.
• the liquid electrolyte that can be used according to the process according to the invention may additionally contain LiPF 6 to as additional lithium salt.
• the liquid electrolyte contains LiPF 6 as an additional lithium salt
• LiPF 6 as an additional lithium salt
• this quantity representing at least maximum of one quarter of the molar amount of lithium salts mentioned in point b), and preferably from 1 to 10% by weight relative to in relation to the mass of lithium salts referred to in point (b) above.
• This additional lithium salt is advantageous insofar as it makes it possible to passivate the aluminum collector of the positive electrode.
• the porous carbon material of the positive electrode is preferably selected from carbide-derived carbon (CDC), porous carbon nanotubes, porous carbon blacks, porous carbon fibers, carbon onions, carbons derived from carbon. coke (whose porosity is increased by charge).
• CDC carbide-derived carbon
• porous carbon nanotubes porous carbon nanotubes
• porous carbon blacks porous carbon fibers
• carbon onions carbons derived from carbon. coke (whose porosity is increased by charge).
• the specific surface area of the porous carbon material of the positive electrode varies from 1200 to 1800 m 2 / g approximately (BET method).
• the density of the porous carbon material of the positive electrode preferably ranges from 0.5 to 0.8 g / cm 3 .
• the oxygen content in the porous carbon material of the positive electrode is preferably less than 2% by weight.
• the positive electrode preferably has a thickness ranging from 70 to 120 ⁇ approximately.
• the non-porous carbon material of the negative electrode is chosen from among the materials allowing the intercalation / insertion of lithium.
• the non-porous carbon material of the negative electrode is preferably selected from graphite, low temperature carbons (hard or soft), carbon black, non-porous carbon nanotubes and non-porous carbon fibers.
• the density of the non-porous carbon material of the negative electrode preferably ranges from 1.0 to 1.9 g / cm 3 .
• the specific surface (BET method) of the non-porous carbon material of the negative electrode is preferably less than about 50 m 2 / g.
• the negative electrode preferably has a thickness varying from approximately 40 to 70 ⁇ .
• the ratio between the mass of the positive electrode and that of the negative electrode is greater than or equal to 1.
• This ratio M E + / M E- preferably varies from 1 to 5 inclusive.
• the ratio M E + / M E- is equal to 1 This ratio is preferably optimized so as to have the same number of charges at the level of the positive and negative electrodes.
• the positive and / or negative electrodes comprise generally at least one binder and optionally at least one agent conferring electronic conductivity.
• the binder can be chosen from organic binders conventionally known to those skilled in the art and electrochemically stable up to a potential of 5 V vs Li.
• organic binders conventionally known to those skilled in the art and electrochemically stable up to a potential of 5 V vs Li.
• these binders mention may be made in particular of:
• PVDF polyvinylidene fluoride
• the binder is preferably about 5 to about 15% by weight based on the total weight of the electrode.
• the agent conferring electronic conduction properties may be carbon, preferably selected from carbon blacks such as acetylene black, carbon blacks with a high surface area such as the products sold under the name Ketjenblack® EC. 600JD by the company AKZO NOBEL, carbon nanotubes, graphite, or mixtures of these materials. It may also be an aqueous dispersion of carbon black or graphite such as the product sold under the trade name Electrodag EB-012 by ACHESON. Other products can also be used.
• the material conferring electronic conduction properties is preferably from 1 to 10% by weight approximately with respect to the total mass of the electrode.
• the composite material constituting the electrodes is preferably deposited on a current collector, such as a copper current collector for the negative electrode and aluminum for the positive electrode.
• the temperature of implementation of the process according to the invention can be the ambient temperature but can also be a temperature higher than the ambient temperature (for example between 25 ° C and 70 ° C) to increase the solubility of the lithiated compound in the solvent used.
• the process according to the invention is carried out at a temperature greater than or equal to 35 ° C.
• the charge / relaxation cycles for forming the passivation layer and inserting / inserting the lithium in the negative electrode are made at a temperature greater than or equal to 35 ° C. This makes it possible to accelerate the formation of the passivation layer.
• the liquid electrolyte that can be used according to the process according to the invention may also contain one or more co-solvents intended to increase the ionic conductivity and to extend the temperature of use, such co-solvents being chosen from alkyl esters. such as ethyl acetate, methyl propanoate, ethyl propanoate, ethyl butyrate, methyl butyrate, etc. and mixtures thereof.
• the cosolvent (s) preferably represent from 20 to 80% by volume relative to the total mass of the liquid electrolyte. These co-solvents make it possible in particular to improve the cold performance of the supercapacitor.
• the duration of the relaxation steps between each of the successive charging steps of step f) varies from approximately 1 to 3 hours.
• step f) comprises the following sub-steps:
• a charging sub-step 1 at a current density of between 10 and 400 mA / g to a voltage U max of between 4.0 V and 5 V inclusive, followed by a relaxation period of a duration of 1 hour minimum. ;
• a charging sub-step 4 at a current density of between 10 and 400 mA / g to a voltage U max4 > U max and ⁇ 5 V, followed by a relaxation period of a duration of 1 hour minimum;
• the sub-step 5) of the formation cycle can be repeated until a stable potential close to 0 V is obtained at the negative electrode in the case of a 3-electrode cell where the potential of each electrode of the system can be followed.
• the training cycle is stopped either according to results obtained in 3-electrode cell, ie when the voltage at the end of the relaxation period is the same from one substep to the other, indicating a stabilization of the potential of the negative electrode.
• sub-step 5 can be repeated until a stable potential of the negative electrode close to 0.1V vs. V is reached. Li + / Li.
• step f) of the process according to the invention then makes it possible to form the intercalation compound LL 0.5 C 6 to the negative electrode.
• Charge / relaxation cycles may also include more or fewer steps than described herein, charging voltages may also vary.
• the product resulting from the process according to the invention comprises electrodes as described in points d) and e) of claim 1, an electrolyte comprising a lithium salt and a solvent as described in points b) and c)
• the lithium concentration in the electrolyte of the final product may be less than the threshold defined in the claim.
• the negative electrode of the final product is a graphite electrode and that the intercalation compound formed is preferably close to the intercalation stage II, ie LL 0.5 C 6 .
• a hybrid supercapacitor was produced according to the following method, according to the invention:
• Negative electrode 91% by weight of graphite sold under the trade name SLP30 by TIMCAL, 8% by weight of PVDF, 1% by weight of carbon black. This composite electrode material was coated on a copper collector. Thickness of the coating: 50 ⁇ .
• Li + / Li reference electrode was added to monitor the evolution of the potentials of the positive and negative electrodes. Note that this electrode has been integrated in the assembly for the purpose of making measurements and is not an integral part of the invention.
• the system was loaded according to the training cycle according to the invention comprising chronopotentiometric loading steps followed by relaxation period of 2 hours as described in the appended FIG. 2 in which the voltage and the electrode potentials (in volts) are a function of time (in seconds). These are charge cycles (at 37.2mA / g) / self discharge. The system voltage at the end of the cycles was 4.2V.
• the characteristics of the negative electrode were chosen so that its potential was of the order of 0.1V vs Li + / Li after the end of the charge / self discharge cycles, corresponding approximately to stage II lithium intercalation in graphite.
• a static galvano cycle is a charge and discharge of the system.
• a symmetrical supercapacitor not according to the invention was produced according to the following mode:
• This composite electrode material was coated on an aluminum current collector having a thickness of 30 ⁇ . Thickness of the coating: 100 ⁇ .
• Li + / Li reference electrode was added to monitor the evolution of the potentials of the positive and negative electrodes.
• a symmetrical supercapacitor not according to the invention was produced according to the following mode, in accordance with that described in Comparative Example 1:
• This composite electrode material was coated on an aluminum current collector having a thickness of 30 ⁇ . Thickness of the coating: 100 ⁇ .
• Electrolyte used LiTFSI 2 mol / L in EC / DMC 1: 1 (v / v) mixture.
• a Li / Li reference electrode has been added to monitor the evolution of the potentials of the positive and negative electrodes.
• a hybrid supercapacitor not according to the invention was produced according to the following mode:
• Negative electrode 91% by weight of graphite sold under the trade name SLP30 by TIMCAL, 8% by weight of PVDF, 1% by weight of carbon black. This composite electrode material was coated on a copper collector. Thickness of the coating: 50 ⁇
• Electrolyte used LiTFSI 2 mol / L + 1% LiPF 6 in EC / DMC mixture 1: 1 (v / v)
• Li + / Li reference electrode was added to monitor the evolution of the potentials of the positive and negative electrodes.
• the formation cycle (not according to the invention, consisted of a direct charge up to 4.4 V followed by a self-discharge period of 2 hours.
• the evolution of the voltage and electrode potentials (in V) as a function of time (in seconds) during the formation cycle is shown in the attached FIG.
• a hybrid supercapacitor according to the invention was produced according to the following mode:
• Negative electrode 91% by weight of graphite sold under the trade name SLP30 by TIMCAL, 8% by weight of PVDF, 1% by weight of carbon black. This composite electrode material was coated on a copper collector. Thickness of the coating: 50 ⁇ .
• positive and negative electrodes are identical to those of example 1 and that, unlike in example 1, no reference electrode made of lithium metal is present in the system.
• Electrolyte used 2 mol / L LiTFSI + 1 mol% LiPF 6 in EC / DMC mixture 1: 1 (v / v)
• the system was loaded according to the training cycles according to the invention comprising chronopotentiometric charging steps followed by relaxation periods of 2 hours, as described in the appended FIG. 2 in which the voltage (in volts) is function of time (in sec). These are charge cycles (at 37.2mA / g) / self discharge. The maximum system voltage was 4.4V.
• FIG. 10 shows the evolution of the voltage (in V) as a function of time (in seconds) during the training cycles.
• Example 2 The initial capacity is higher in Example 2 than in Example 1 because the maximum voltage is also higher.
• the decrease in capacity is greater in the case of Example 2 during cycling, probably because of the corrosion of aluminum, despite a weak addition of LiPF 6 in the electrolyte.
• step f) makes it possible to ensure the stability of the supercapacitor over time (unlike other charging methods, as can be seen from Comparative Example 6) and to obtain both a supercapacitor having a high energy density and also reliable.
• the invention makes it possible to obtain a hybrid supercapacitor which makes it possible to increase the working voltage and thus to deliver a higher energy density than symmetrical supercapacitors of the state of the art.

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• 2012
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