ELECTROCHEMICAL ELEMENT, AS WELL AS MODULES AND BATTERIES CONTAINING SAME

Abstract

This invention concerns an electrochemical element, in particular a sulphurous solid electrolyte element, comprising a protective casing, as well as modules and batteries comprising such elements.

Claims

1. An electrochemical element comprising at least one sulphurous electrolytic compound, wherein the element comprises a stack of two conductive electronic current collectors, wherein the stack comprises: a positive electrode; a negative electrode; and a layer comprising a solid electrolytic composition separating the positive electrode and the negative electrode; wherein the cell is characterised in that at least the lateral surface of the stack is at least partially covered with a chemical protection and/or mechanical reinforcement casing that is electrically insulating, and that the circumference of the casing is equal to: 2*k*bundle thickness+bundle circumference, such that k>0.1, and the bundle is the volume delimited by the plane defined by each of the electrodes, and the thickness of the bundle corresponding to the to the geometrical dimension perpendicular to the plane of the electrodes.

2. The element according to claim 1, such that the protective casing consists of an electronically non-conductive material.

3. The element according to claim 1, such that the casing comprises at least: one organic material and, optionally, one nanometre-sized inorganic material.

4. The element according to claim 1, such that the casing consists of a first chemical protection layer and a second mechanical reinforcement layer.

5. The element according to claim 1, such that the casing has a total thickness less than 100 μm and a grammage less than 5 mg/cm.sup.2.

6. The element according to claim 1, such that the casing comprises at least one material having a water permeability less than 0.1 g/m.sup.2/d/μm.

7. The element according to claim 1, such that the casing has an elongation at break greater than 150%.

8. The element according to claim 1, such that the casing contains one or more components selected from elastomers (e.g. natural or synthetic rubbers, etc.), dyMAT ClrPYE MONO (multilayered structure of Ultra protective coating/PET/primer (5 μm/175 μm/100 μm) marketed by COVEME), dyMAT HDPYE SPV L (PET/PET/Primer (50 μm/250 μm/50 μm) marketed by COVEME), Ultra Barrier Solar Film (Fluoropolymer/Black tape/Pressure sensitive adhesive/PET marketed by 3M), polyethylene terephtalate (PET), polyethylene (PE); poly(methyl methacrylate) (PMMA); polyvinylidene fluoride (PVDF); polypropylene (PP); polycarbonate (PC); poly(ethylene-co-tetrafluoroethylene) (ETFE); polyimide (PI); Polyisobutene (PIB), and derivatives and mixtures thereof.

9. A method for manufacturing an element according to claim 1, comprising: manufacturing the stack and depositing a casing as defined according to claim 1, in particular by atomic layer deposition (ALD), molecular layer deposition (MLD), spraying, and/or physical vapour deposition.

10. A electrochemical module comprising the stack of at least two elements according to claim 1, wherein each element is electrically connected to one or more other elements, and such that all or part of the module covered with a casing as defined according to claim 1.

11. A watertight module comprising a module according to claim 10 inside a watertight compartment.

12. A battery comprising one or more modules according to claim 10.

13. The battery comprising one or more watertight modules according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0119] FIGS. 1A-1C show an element according to the invention that is not protected FIG. 1A, protected by a casing according to the invention FIGS. 1B and 1C, wherein the envelope provides a chemical protection layer FIG. 1B or a mechanical reinforcement layer FIGS. 1C.

[0120] FIG. 2 shows a module comprising an assembly of elements according to the invention.

[0121] FIG. 3 shows the inhibition of H2S production by means of the casing according to the invention.

DETAILED DESCRIPTION

[0122] As shown in FIGS. 1A-1C, a stack suited for the invention consists of an elementary assembly of a positive electrode (1) and a negative electrode (2), separated by a catalytic layer (3). In one variant, the electrodes (1) and (2) may, of course, be reversed.

[0123] An element comprising a protective casing (4) according to the invention is shown in FIGS. 1B and 1C: In one variant, the casing (4) consists of a thin layer (4) that provides chemical production. In another variant, the casing (4) consists of a first layer (4) that provides chemical protection and a second layer (4′) that is thicker and provides mechanical reinforcement.

[0124] An illustrative module according to the invention is shown in FIG. 2. In this schematic representation, a module consists of three elements that are stacked. Each element consists of a positive electrode (1) and a negative electrode (2), which are separated by a catalytic layer (3). In the variant shown, the casing (4) covers the lateral surface of the module, as well as the lower and upper surfaces of the module, which are defined by the outer surfaces of the lower and rear electrode of the assembly.

[0125] The following examples are provided to illustrate the invention, without limiting its scope in any way.

EXAMPLES

Example 1

[0126] In order to validate the chemical protection of the casing according to the invention, an experiment was conducted with pouches of selected encapsulation materials.

[0127] An argyrodite sulphide electrolyte having the composition Li.sub.6PS.sub.5Cl was produced by mechanical synthesis (500 rpm, 20 h) from the precursors Li.sub.2S, P.sub.2S.sub.5, and LiCl in stoichiometric proportions. The ionic conductivity of this electrolyte was measured by impedance spectroscopy on a pellet compressed at 250 MPa in a pressurized cell, and reached 1 mS/cm at room temperature (RT).

[0128] On the other hand, the sulphide electrolyte powder obtained was compressed at 250 MPa to form a pellet 400 μm in thickness and 10 mm in diameter.

[0129] A casing (example #2) was made by arranging a sheet of dyMAT ClrPYE MONO (285 μm—marketed by COVEME) and a sheet of Ultra Barrier Solar Film (203 μm—marketed by 3M™) on either side of the sulphide electrolyte pellet. The edges of the casing thus formed, which go beyond the pellet, are then heat-sealed at 150° C. so as to contain the pellet without deterioration.

[0130] In a hermetic receptacle of a known volume filled with humid ambient air, the pellet thus enclosed was inserted and the H.sub.2S levels were measured using a specific sensor as a function of time.

[0131] Another casing (example #3) was produced according to the same procedure, but with sheets of dyMAT ClrPYE MONO (285 μm—COVEME) and dyMAT HDPYE SPV L (300 μm—COVEME) on either side of the pellet.

[0132] For comparative purposes, on the other hand, this measurement was taken using a sulphide electrolyte pellet without a casing.

[0133] As shown in FIG. 3, the unprotected material (comparative example) rapidly emits a substantial amount of H.sub.2S gas (10 cm.sup.3/g in less than 15 minutes), thus exceeding the limit provided by applicable regulations. With the moisture barrier protections tested, the H.sub.2S level remains below 1 ppm (detection limit of the sensor used) for over 30 minutes (#2) to more than 2 hours (#3), and remains low after 24 h. Thus, the sulphide material may be safely handled in ambient air.

Example 2

[0134] Given the sensitivity of the materials used to the ambient atmosphere, the following manipulations were carried out in environments having a dew point of less than −50° C., and can be carried out in an argon atmosphere.

[0135] Sulphide electrolyte powder (as produced in example 1) was cold-compressed (200 MPa) in a pellet mill to form a pellet approximately 400 μm in thickness (‘electrolytic layer’). Sulphide electrolyte powder was mixed with a mortar and pestle with powder of active positive material (NCA) in a mass ratio of NCA:SE 70:30 until a homogeneous distribution was reached. This mixture (which constitutes the positive electrode) was added to one side of the electrolytic layer in the pellet mill, and the assembly was then compressed again (200 MPa) to form a dense, solid pellet (with a thickness of the positive electrode near 100 μm). On the other side of the electrolytic layer, the negative electrode, consisting of graphite and solid electrolyte powder previously manually mixed by mortar and pestle (mass ratio electrolyte: graphite 40:60), was added. The entire stack was once again cold compressed (500 MPa) in a pellet mill an electrically insulating body so as to form the negative electrode layer with a thickness of approximately 100 μm. The masses of the positive and negative electrodes were balanced so as to give the negative electrode a slight excess capacity. The stack thus obtained was arranged between stainless steel current collectors.

[0136] The encapsulation according to the invention may be carried out on the stack thus produced. In this example, the casings described in example 1 were used for this encapsulation. The stack was introduced into one of these casings, the sides of which were then heat-sealed. Watertight current passengers (wires or clips used for the pouch cell assembly) ensure the electrical connection between the current collectors and the cycle cell without deterioration of the impermeability of the casing.

[0137] The stack thus encapsulated was then arranged in a cycle cell allowing for the application of a pressure (1-500 MPa) depending on the axis of symmetry of the pellet on both collectors without generating short circuits or deterioration of the casing.

[0138] To evaluate electrochemical performance, the cell thus assembled was then subjected to galvanostatic cycling between 2.8 and 4.1 V with a constant current such that the cell was totally charged in 20 h.