ECO-ELECTRODE, DEVICE STORING ELECTRICAL ENERGY AND PROCESS FOR PREPARATION THEREOF

Abstract

The present invention relates to a composite electrode for a device storing electrical energy wherein said electrode comprises an electrode body and an electrode shell, wherein said body comprises at least one water-soluble polymer and wherein at least a part of said shell comprises a shell comprising at least one organic or organometallic material.

The present invention also relates to a device storing electrical energy comprising said composite electrode and a process for preparing said composite electrode.

Claims

1. A composite electrode for a device storing electrical energy wherein said electrode comprises an electrode body and an electrode shell, wherein said body comprises at least one water-soluble polymer and wherein at least a part of said shell comprises a shell comprising at least one organic or organometallic material.

2. The composite electrode according to claim 1, wherein said water-soluble polymer is selected from the group consisting of polysaccharides, Poly(ethylene glycol) (PEG), Polyoxyethylene (POE), Polyvinyl pyrrolidone (PVP), Polyvinyl alcohol (PVA), polylactic acid (PLA), Polyacrylic acid (PAA), Polyacrylamides, N-(2-Hydroxypropyl) methacrylamide (HPMA), Cellulose derivatives, in particular alkylcellulose, dialkylcellulose, hydroxyalkylcellulose, hydroxyalkylalkylcellulose, carboxyalkylcellulose, Pectins, Chitosan, Chitosan Derivatives, Dextran, Carrageenan, Guar gum, Guar gum derivatives, in particular chydroxypropyl guar, arboxyalkyl guar, Hyaluronic acid (HA), Starch or Starch Based Derivatives, polyethyloxazoline, and derivatives thereof.

3. The composite electrode according to claim 1, wherein said water-soluble polymer is selected from the group consisting of Hydroxypropylmethyl cellulose (HPMC), Hydroxypropyl cellulose (HPC), Hydroxyethyl cellulose (HEC), Carboxy methyl cellulose (CMC), in particular Sodium carboxy methyl cellulose (Na-CMC).

4. The composite electrode according to claim 1, wherein said organic or organometallic material is deposited by plasma treatment, for example said organometallic material is an organosilane or an organoalane or a mixture of an organic material with an organometallic material; for examples a precursor of an organometallic material is a siloxane, for example divinyltetramethyl disiloxane (DVTMDSO), octamethyl cyclotetrasiloxane (OMCATS hexamethyldisilazane (HMDSN), tetramethyldisiloxane, tetramethylcyclotetrasiloxane, Trimethylsilane, methyl- and methoxy-group organosilicon like tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMOS), dimethyldimethoxysilane (DMDMOS), trimethylmethoxysilane (TMMOS), or Hexamethyldisilane.

5. The composite electrode according to claim 1, wherein said organometallic material is deposited by plasma deposition, in particular Plasma-Enhanced Chemical Vapor Deposition (PECVD).

6. A process for preparing a composite electrode comprising a body comprising at least one water-soluble polymer, wherein said process comprises depositing by plasma deposition, in particular Plasma-Enhanced Chemical Vapor Deposition (PECVD) a material at least on a part of said body of said composite electrode.

7. The process according to claim 6, wherein said process comprises depositing by said plasma deposition at least one organic or organometallic material, thereby preparing a composite electrode.

8. The process according to claim 6, wherein said plasma deposition is performed under atmospheric pressure.

9. The process according to claim 6, wherein said plasma deposition is performed in the presence of a vapor phase comprising a precursor of organosilane or an organoalane bonds, for example said precursor is polyalkyldisiloxane, for example a disiloxane, for example Hexamethyldisiloxane (HMDSO), 2,4,6,8-Tetramethylcyclotetrasiloxane (TMCTS) or tetraethoxysilane (TEOS).

10. The process according to claim 6, wherein said plasma deposition is performed according to a roll-to-roll process.

11. A device storing electrical energy wherein said device comprises one or more composite electrodes according to claim 1.

12. The device according to claim 11, wherein said device comprises an aqueous solution in contact with said composite electrodes.

13. The device according to claim 11, wherein said device comprises at least one aqueous electrolyte.

14. The device according to claim 11, wherein said device comprises at least one organic electrolyte.

15. The device according to claim 11, wherein said device is a battery, for example a Li or Li-ion battery, a sodium or multivalent ion battery, such as for example Mg or Ca, a hybrid battery, for example a hybrid battery using Zn, Li or Na ions, or alkaline battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0101] FIG. 1. is a schematic representation of a configuration of the Plasma-Enhanced Chemical Vapor Deposition System (PECVD).

[0102] FIG. 2. Represents different morphologies of shell depending on the precursor of the organometallic shell: HMDSO (left), TMCTS (middle) or TEOS (right).

[0103] FIGS. 3A-3B represent contact angle measurements for a CMC electrode FIG. 3A uncoated and FIG. 3B after coating with a shell according to the invention.

[0104] FIGS. 3C-3E represent tests of mechanical stability of the electrode in an aqueous electrolyte. FIG. 3C for a CMC electrode 10s after hardening, FIG. 3D for a coated electrode 10s after hardening and FIG. 3E 6 months after hardening

[0105] FIG. 4 represent measurement of the deposition stability window in a LiTFSI electrolyte 1m in H.sub.2O

[0106] FIG. 5 represents galvanostatic curves for different surface organosilicon deposits in an electrolyte 1m LITFSI in H.sub.2O to C/10

[0107] FIG. 6 represents curves of the coulombic Efficiency in an electrolyte 1m LITFSI in H.sub.2O to C/10, as a function of the number of cycles for a LFP-CMC electrode having a shell obtained by HMDSO plasma deposition.

[0108] FIG. 7 is an infra-red spectrum of the surface of the body of a composite electrode with CMC as binder without a shell and of a shell obtained by HMDSO plasma deposition shell before cycling and after cycling.

[0109] FIG. 8 represents impedance curves in an electrolyte 1m LITFSI in H.sub.2O as a function of the number of cycles for a LFP-CMC electrode having a shell obtained by HMDSO plasma deposition

EXAMPLES

[0110] The following illustrative examples of the invention are directed to an electrode and a battery representing one kind of device storing electrical energy.

[0111] LiFePO.sub.4 (P2 from Johnson Matthey) was used as active material. LiFePO.sub.4 was also chemically oxidized into FePO.sub.4 using acetic acid and hydrogen peroxide method reported by Lepage et al. Note that other active materials, stable in the electrochemical stability window and in contact with aqueous electrolytes can be used.

[0112] The electrodes for electrochemical evaluation in aqueous electrolyte were fabricated by combining 84 wt % of active material (either LFP or FePO.sub.4), 9 wt % of carbon black Timcal C65, and 7 wt % of sodium carboxymethyl cellulose (CMC from Sigma Aldrich 419273, Mw=90,000 g/mol) binder previously dissolved in deionized water. The slurry was mixed for 20 min to get homogeneous by using a Kurabo Mazerustar KK-50S planetary mixer-deaerator and spread on a 30 μm thick stainless-steel foil using the doctor blade method. The use of stainless-steel current collector (8) avoids the typical corrosion issue observed in Al current collector in aqueous media with lithium salts. The coating was then dried at 70° C. under vacuum in an oven overnight. Discs of 8 mm for the LFP electrode and 12 mm for the FePO.sub.4 one were punched from the coating. The over-dimensioning of the anode allowed for balancing of the cathode capacity and ensured the limitations are only due to the working electrode.

[0113] The polymer was deposited in a plane-to-plane dielectric barrier discharge at atmospheric pressure. The experimental setup used in this work was described in previous papers (J Profili, O Levasseur, N Naudé, C Chaneac, L Stafford, N Gherardi, Influence of the voltage waveform during nanocomposite layer deposition by aerosol-assisted atmospheric pressure Townsend discharge, 2016 Aug. 7, Journal of Applied Physics, Volume 120, Issue 5, Pages 053302, AIP Publishing; Jacopo Profili, Olivier Levasseur, Jean-Bernard Blaisot, Anja Koronai, Luc Stafford, Nicolas Gherardi, Nebulization of nanocolloidal suspensions for the growth of nanocomposite coatings in dielectric barrier discharges, 2016 October, Plasma Processes and Polymers, Volume 13, Issue 10, Pages 981-989; Olivier Levasseur, Reetesh Kumar Gangwar, Jacopo Profili, Nicolas Naudé, Nicolas Gherardi, Luc Stafford, Influence of substrate outgassing on the plasma properties during wood treatment in He dielectric barrier discharges at atmospheric pressure, 2017 August, Plasma Processes and Polymers, Volume 14, Issue 8, Pages 1600172). Briefly, all experiments were conducted with helium (He, PURITY Praxair) as the carrier gas. The gas mixture (1) (4.5 SLM of He with 120 mg/h of HMDSO vapor) was continuously injected from one side of the DBD cell to the exit (5). The constant atmospheric pressure (1 bar) was achieved during the process through a gentle pumping of the vessel. The purity of the gases injected during the process was ensured by keeping the DBD cell in a sealed stainless-steel chamber under vacuum prior the experiments. The discharge cell consists of two dielectric plates (3) (Al.sub.2O.sub.3, 635 μm thick) separated by 1 mm gas gap. The electrodes (2) (silver-platinum paste, 3×3 cm2 in area) are spread on side of the alumina surfaces. The stainless-steel substrates within the electrode's disks were placed on the lower dielectric surface between the electrodes (8) at its surface in contact with the discharge area (4). To prevent any detachment of the substrate from the electrode the metal foil was attached to the lower surface with Kapton® tapes on four sides. Note that this geometrical configuration allows the treatment of foils and laminar substrates and can be easily adapted into a roll-to-roll configuration for the continuous treatment of electrodes foils.

[0114] The discharge area (4) is starting at a distance (7) of about 10 mm from the beginning of the substrate (6)

[0115] The discharge is then ignited in the discharge area (4) by applying a sinusoidal voltage (2 kV, 20 kHz) to the electrodes. Treatment was carried out in these conditions for 10 minutes. The applied voltage and the current were measured by a high voltage probe (TEKTRONIX P6015A) and a wide-band current coil (LILCO Ltd. 13W5000), respectively. The oscilloscope (Tektronix DPO5204B) was used to record all the voltage and current waveforms as well as calculated the dissipate power during the deposition.

[0116] The morphology of the electrode was observed using a Tabletop Electronic Microscope HITACHI TM3030Plus and the cross section was investigated using a JEOL FE-SEM 7600 Field Emission Gun (FEG) Scanning Electron Microscopy (SEM), with a 10 kV accelerating voltage, a working distance of ≈4 mm, and a magnification from 5 k to 50 k. Chemical mapping was performed using X-Ray Energy Dispersive Spectroscopy (EDS) to investigate the elemental distribution in the electrode before and after plasma treatment. The quality of the deposited film was characterized by ATR-FTIR (Vertex 70 (Bruker®) equipped with an attenuated total reflectance (ATR) module). X-Ray Diffraction (XRD) patterns of the electrode before and after deposition was performed using a Bruker D8 Advance with a Cu Kα radiation (λ=1.5406 Å) with steps of 0.02° in a 2θ range of 10-60° in order to characterize the structural modifications that occurred upon plasma treatment. The wetting behavior of the different surfaces was measured by using a contact angle goniometer (OneAttension Theta, Biolin Scientific). Each surface was characterized by studying the contact angle (sessile drop method) of the droplet (deionized water, 2 μL in volume) gently dropped on the surface of the material. The results were recorded with a video-camera system after stabilization of the volume (typically around 7 seconds) and during 300 s (not affected by the evaporation of the liquid).

[0117] Aqueous electrolytes were prepared under air and then degassed from O.sub.2 using N.sub.2 before storage in a N.sub.2-filled glovebox. Precise amount of LiTFSI (3M) was weighed in an Ar-filled glovebox. LiTFSI was then dissolved in the corresponding volume of deionized water in order to reach 1 m concentration. The same procedure was used for sulfate salts (Li.sub.2SO.sub.4, Na.sub.2SO.sub.4 and ZnSO.sub.4 (Alfa Aesar)) solutions (1 m).

[0118] All the cells were assembled in a N.sub.2-filled glovebox. Attention was taken to assemble the batteries in the absence of O.sub.2 as it is detrimental to the battery cycle life.sup.18. Film electrochemical stability was measured using a three electrode Swagelok cell. The working electrode was a 10 mm disc of stainless steel with 500 nm thick HMDSO film, the counter electrode and reference electrode were respectively a 10 mm disc of stainless steel and an Ag/AgCl electrode (BaSi inc). For the sake of comparison, the same configuration was used with a bare stainless-steel disc as working electrode. Cyclic voltammetry was undertaken between −0.75 to 1.25 V vs. Ag/AgCl, i.e. 2.51 to 4.51 vs. Li.sup.+/Li, with a sweep rate of 0.5 mV/s in the case of LiTFSI electrolyte. With sulfate electrolytes, the stability window was measured from −0.50 to 1.00 V vs. Li.sup.+/Li.

[0119] Two-electrode Swagelok cells were used for the cycling tests. A GF/D borosilicate glassfiber sheet from Whatman was used as a separator. The electrochemical performances were determined on the cells between −0.6 V and 0.6 V vs. LiFePO.sub.4/FePO.sub.4 (i.e. 2.8 V and 4.0 V vs. Li.sup.+/Li) at different current rates. All the electrochemical measurements were performed using a VMP electrochemical station (Biologic, France) at room temperature. For each sample, 2 cells were assembled to insure reproducibility. Capacity variations lower than 1 mAh/g were found for every 2-cell sets. For impedance measurement, three-electrode cells were used in the same configuration with Ag/AgCl reference electrode.

[0120] The plasma treatment according to the invention uses only non-toxic gases and a small amount of non-toxic precursor (typically 1-1000 ppm) for the manufacture of the shell. The plasma treatment according to the invention can be generated at atmospheric pressure, which greatly reduces the costs associated with pumping and gas control systems. The process according to the invention is therefore economical and green.

[0121] The process is very suitable for processing substrates in the form of flexible and configurable sheets with different power supplies. It is simple to make and is very compatible with serial industrial processes.