EP4264722A1

EP4264722A1 - All-solid-state lithium-sulphur electrochemical element

Info

Publication number: EP4264722A1
Application number: EP21823307.0A
Authority: EP
Inventors: Florent FISCHER; Elodie Guerin; Thierry Hezeque; Christian Jordy
Original assignee: SAFT Societe des Accumulateurs Fixes et de Traction SA; Centre National dEtudes Spatiales CNES
Current assignee: SAFT Societe des Accumulateurs Fixes et de Traction SA; Centre National dEtudes Spatiales CNES
Priority date: 2020-12-18
Filing date: 2021-12-06
Publication date: 2023-10-25
Also published as: FR3118308B1; WO2022128566A1; FR3118308A1

Abstract

An all-solid-state lithium-sulphur electrochemical element comprising: a) at least one cathode comprising a cathode active material composition comprising: i) elemental sulphur, ii) carbon, iii) a solid electrolyte, the cathode comprising copper; b) at least one anode the active material of which is lithium or a lithium-based alloy, c) a solid electrolyte which is positioned between the at least one cathode and the at least one anode, and which is identical to or different from the solid electrolyte present in the cathode active material composition, the amount of copper in the cathode being less than or equal to 0.37 g per ampere-hour charged by the element, the ratio nCu/nLi in the element, when said element is in the charged state, being greater than or equal to 0.04 and less than 0.81, wherein nCu represents the mole number of copper and nLi represents the sum of the mole numbers of lithium in the solid electrolyte of the cathode and in the solid electrolyte positioned between the at least one cathode and the at least one anode.

Description

Title: ALL SOLID LITHIUM-SULFUR ELECTROCHEMICAL ELEMENT

Technical field of the invention

[0001] The technical field of the invention is that of all-solid lithium-sulphur electrochemical elements as well as that of methods for assembling such elements.

Background of the invention

[0002] The term "element" used in the following denotes an electrochemical element. The terms “element” and “electrochemical element” are used interchangeably in the following. Lithium/sulfur (Li/S) electrochemical elements comprising a liquid electrolyte are known from the state of the art. They typically comprise at least one positive electrode (cathode) of elemental sulfur, an organic liquid electrolyte and at least one negative electrode (anode) of lithium metal or lithium metal alloy. The cathode is usually composite, i.e. it is prepared from elemental sulfur and non-electrochemically active additives. As non-electrochemically active additives, mention may be made of an electronic conductor, such as carbon, making it possible to improve the electronic conductivity of the cathode because sulfur is an electronic insulator. Mention may also be made of one or more polymeric binders making it possible to ensure cohesion between the different materials of the cathode. Due to the low atomic mass of lithium and the moderate mass of sulfur, Li/S electrochemical elements are relatively light. They are a promising alternative to lithium-ion cells due to their higher energy density and low sulfur cost.

[0003] Starting from a cathode of elemental sulfur and an anode of lithium metal or a lithium alloy, the electrochemical element is initially in the charged state. In discharge, the elemental sulfur of the cathode is reduced to lithium sulphide Li2S and the metallic lithium or the metallic lithium alloy is oxidized at the anode. The following reactions take place at the electrodes:

Cathode: Ss + 16 e' — > 8 S ² '

Anode: Li — > Li ⁺ + e'

The overall cell discharge reaction is: 16 Li + Sx — > 8 Li2S

[0004] Unlike a lithium-ion electrochemical cell, a lithium/sulfur electrochemical cell typically comprises an electrolyte whose solvent is based on ethers. Ethers, such as 1,3-dioxolane or tetrahydrofuran have been used for several decades and allow significant solubilization of lithium polysulphides. Organic solvents of the glyme type with the general formula EI-fO-CEE-CEEJn-OEI, such as 1,2-dimethoxyethane (DME), are also frequently used as solvent for the electrolyte.

[0005] During the reduction of sulfur which occurs during the discharge of the element, the cyclic molecules of sulfur (in the form of octasulfur Ss) are reduced and form linear chains of lithium polysulphides, of general formula Li2S _n , n generally ranging from 2 to 8. The first compounds formed during the discharge of the element are the long-chain lithium polysulphides, such as Li2Ss or Li2Se. Long-chain lithium polysulfides are likely to migrate through the electrolyte and reach the lithium anode where they will be reduced to short-chain polysulfides during charging following cell discharge. The short-chain polysulfides return to the cathode where they are again reoxidized to long-chain polysulfides, and so on. This shuttle mechanism (“shuttle”) of the polysulphides between the anode and the cathode is the cause of a low coulombic efficiency of the element, that is to say a low ratio between the capacity discharged by the element and the capacitance charged in the element during the charge preceding the discharge. In addition, it leads to a high self-discharge, as well as a deterioration in the life of the element in cycling.

Furthermore, the liquid electrolyte of an Li/S electrochemical element can, in the event of thermal runaway of the element, react exothermically with the active materials of the negative and positive electrodes and in certain cases, the elements can catch fire, posing a safety risk to the user.

[0007] Replacing a liquid electrolyte with a solid electrolyte offers a solution to the risk of thermal runaway. By using a solid electrolyte, the exothermic reaction between the active materials and the electrolyte is suppressed, which considerably improves safety for the user. In addition, leakage of liquid electrolyte from the cell container is prevented in the event of the container being opened, when the cell is placed under extreme conditions (shock to the cell, overpressure in the container caused by an increase in heat, etc.). Finally, the replacement of a liquid electrolyte by a solid electrolyte offers a solution to the problem of the shuttle movement of lithium polysulphides in the liquid electrolyte. The solid nature of the electrolyte in fact prevents the shuttle movement of the lithium polysulphides.

Document EP-A-3 012 887 describes an “all-solid” Li/S element comprising:

- a cathode comprising a composite layer,

- an anode, and

- a solid electrolyte, the composite layer of the cathode comprising a mixture of the following three compounds:

A) an ionically conductive material containing phosphorus in a mass ratio ranging from 0.2 to 0.55 relative to the mass of the ionically conductive material;

B) sulfur and/or a sulfur by-product produced by the discharge of the element; and

C) an electronically conductive material, such as carbon black, compound B) representing at least 40% by mass of the sum of the masses of compounds A), B) and C).

It is said that this element has a good capacity in charge and in discharge, that it is crossed as well by a low intensity current (for example from 0.5 to 1 mA/cm ² ) as by a high intensity current (for example more than 5 mA/cm ² ).

[0009] The article “High loading CuS-based cathodes for all-solid-state lithium sulfur batteries with enhanced volumetric capacity” SM Hosseini, A. Varzi, S. Ito, Y. Aihara, S. Passerini, published in Energy Storage Materials, https://doi.Org/10.1016/j.ensm.2020.01.022 describes the effect of the addition of copper sulphide-sulphur-carbon composites in the cathode of a Li/S element on the performance of such an element. This article gives no indication as to how much copper to add to the cathode to minimize the risk of short circuits occurring.

[0010] Document JP 6716324 describes an all-solid lithium-sulfur electrochemical element comprising: a) a cathode comprising an electrode active material containing a sulfur-carbon composite and a metal such as copper; b) an anode whose active material is lithium; c) a solid hydride electrolyte such as LiBbL.

In the cathode, sulfur, carbon and metal are mixed to obtain a mixture in which the metal is uniformly dispersed in the sulfur-carbon composite. The cathode can also contain LiBEL in a mass equal to the mass of the mixture. The amount of copper used is small. It corresponds to an nCu/nLi ratio of 0.00245 where nCu denotes the number of moles of copper and nLi denotes the sum of the numbers of moles of lithium in the solid electrolyte of the cathode and in the solid electrolyte inserted between the cathode and the anode. At such a low copper concentration, the improvement in the volumetric capacity of the element is not significant.

[0011] It is sought to improve the volume electrochemical capacity of a Li/S element comprising a solid electrolyte while minimizing the risk of observing a short-circuit of the element during its operation. We are looking for a Li/S cell with a capacity of at least 2000 mAh, preferably at least 2500 mAh, per gram of sulfur for discharge at room temperature. We are also looking for a Li/S element comprising a solid electrolyte with a low drop in capacity during cycling operation.

Summary of the invention

To this end, the invention provides an all-solid lithium-sulfur electrochemical element comprising: a) at least one cathode comprising a composition of cathodic active material comprising; i) elemental sulphur, ii) carbon, iii) a solid electrolyte, the cathode comprising copper, b) at least one anode whose active material is lithium or a lithium-based alloy, c) a solid electrolyte intercalated between said at least one cathode and said at least one anode, identical to or different from the solid electrolyte present in the cathodic active material composition, the amount of copper in the cathode being less than or equal to 0.37 g per ampere hour charged by the element, the nCu/nLi ratio in the element in the charged state being greater than or equal to 0.04 and less than 0.81 where nCu denotes the number of moles of copper and nLi denotes the sum of the numbers mole of lithium in the solid electrolyte of the cathode and in the solid electrolyte interposed between said at least one cathode and said at least one anode.

[0013] It was discovered that the presence of copper in the cathode made it possible to increase the electrochemical capacity of the element. The increase in electrochemical capacity of the element is reversible. Indeed, the element can be subjected to several cycles without experiencing a significant drop in its capacity. It was further discovered that the choice of a maximum quantity of copper of 0.37 g per charged ampere hour of the element associated with the choice of an nCu/nLi ratio greater than or equal to 0.04 and less than 0 .81 made it possible to minimize the risk of occurrence of a short circuit in the element, thus extending its life.

According to one embodiment, the copper is present in one or more of the following forms a, P and y: a) in the form of a metal collector serving as a current collector of the cathode, the metal collector being made of copper or a copper-based alloy or being made of a metal at least partially covered with a coating of copper or a copper-based alloy,

P) in the form of a copper powder incorporated into the composition of cathodic active material, y) IN the form of a chemical compound containing copper incorporated into the composition of cathodic active material.

According to one embodiment, the solid electrolyte of the cathodic active material composition and/or the solid electrolyte interposed between said at least one cathode and said at least one anode is a sulfur compound.

According to one embodiment, the quantity of copper present in the cathode is less than or equal to 0.12 g per ampere hour charged by the element, preferably equal to 0.06 ± 0.03 g per ampere hour. .

According to one embodiment, the nCu/nLi ratio is less than 0.5, preferably less than 0.3.

According to one embodiment, the solid electrolyte used in the cathode or interposed between the anode and the cathode during assembly of the element is in the form of a powder, the powder being covered with copper or of a compound containing copper.

According to one embodiment, the solid electrolyte of the cathodic active material composition and the solid electrolyte interposed between said at least one cathode and said at least one anode are chosen from the group consisting of:

- Li _x PSy where 1.4 <x < 1.6 and 3 <y < 3.5, likely to be obtained from Li ₂ S and P ₂ S ₅ precursors,

- a compound of formula (l-y)Li3PS4.yLiX where X denotes a halogen atom with 0.05 < Y < 0.40,

- a compound of formula (Li ₂ S) _a (P ₂ S5)b(LiX) _c (Li ₂ O)d with a+b+c+d=l, - LiePSsX where X denotes a halogen atom, which can be obtained from the precursors I 2S, P2S5 and LiX,

- a mixture of LiePSsX with a solid solution of LiX-LiBFL where X is a halogen,

- an argyrodite compound optionally substituted by borohydride, having the formula Li ₇ -xPS6-xX _x .z(BH ₄ )z in which X is chosen from the group consisting of Cl, Br, I, F and CN; 0<x<2 and 0<z<0.50, and

- a mixture of Li2S/P2S/LiCl/LiBr/LiX compounds, X designates one or more halogen atoms from Cl, Br and I after heat treatment of the mixture.

According to one embodiment, the solid electrolyte has the formula Li7-xPS6-xXx-z(BH4) _z in which X is I; x=1 and 0.1<z<0.35.

According to one embodiment, the solid electrolyte is chosen from LiePSsI, LiePSsCl, LiePS5lo,9o(BH4)o,io, LiePS5lo,83(BH4)o,i7, Li6PSsIo,67(BH4)o,33, LiePS5lo,5o(BH4)o,5o and LiePS5Clo,83(BH4)o,i7.

According to one embodiment, the solid electrolyte of the cathodic active material composition has the formula Li _x PS _y where 1.4 <x <1.6 and 3 <y <3.5 and the solid electrolyte inserted between said at least one cathode and said at least one anode is chosen from:

- a compound of formula Li7-xPS6-xXx-z(BH4) _z wherein X is selected from the group consisting of Cl, Br, I, F and CN; 0<x<2 and 0<z<0.50, and

- a mixture of Li2S/P2S/LiCl/LiBr/LiX compounds, X denotes one or more halogen atoms from Cl, Br and I followed by heat treatment of the mixture.

According to one embodiment, the solid electrolyte interposed between said at least one cathode and said at least one anode has the formula LiePSsL/e BFLji/e.

According to one embodiment, the alloy is an alloy of lithium and one or more chemical elements chosen from the group consisting of indium, silicon, tin and carbon.

Brief description of figures

[0025] [Fig. 1] is a schematic sectional view of the lithium-sulfur element according to the invention.

[0026] [Fig. 2] represents the charge and discharge curves of the comparative element 1 and of the element 1 according to the invention. Charging and discharging were carried out at room temperature at a charging rate of C/50 and D/50.

[0027] [Fig. 3] represents the variation in discharge capacity per gram of sulfur during cycling of element 1 according to the invention at room temperature. The charge phases are carried out at a rate of C/10 up to a voltage of 2.3 V. The discharge phases are carried out at a discharge rate of D/5 up to a stop voltage.

[0028] [Fig. 4] represents the charge and discharge curves of comparative element 2 and of element 2 outside the invention over two cycles. Charge at C/50 rate and discharge at D/50 rate.

[0029] [Fig. 5] represents the charging and discharging voltage curves of the comparative element 3 and of the element 3 according to the invention as a function of the discharged capacity (mAh). Charge at C/20 rate and discharge at D/20 rate. [0030] [Fig. 6] represents the charging and discharging voltage curves of the element 3 according to the invention at cycles 3, 4, 5 and 6 as a function of the capacitance of the element per gram of sulfur in the composite SC. Charge at C/20 rate and discharge at D/20 rate.

[0031] [Fig. 7] represents the charge and discharge voltage curves of element 3 compared to cycles 1 and 8 as a function of the capacity of the element per gram of sulfur in the S-C composite. Charge at C/20 rate and discharge at D/20 rate.

Description of embodiments of the invention

The invention is based on the discovery of the existence of an interaction between copper and the constituents of the cathode. This interaction leads to an increase in the electrochemical capacity of the element. The amount of copper in the cathode must be less than or equal to 0.37 g per ampere hour charged by the element. In addition, the nCu/nLi ratio in the element in the charged state must be greater than or equal to 0.04 and less than 0.81 where nCu denotes the number of moles of copper and nLi denotes the sum of the numbers of moles of lithium in the solid electrolyte of the cathode and in the solid electrolyte interposed between said at least one cathode and said at least one anode. The nCu/nLi ratio in the cell in the charged state may be greater than or equal to 0.09 or greater than or equal to 0.11 or greater than or equal to 0.29 or greater than or equal to 0.40 or greater or equal to 0.50 or greater than or equal to 0.70. It can be less than or equal to 0.09 or less than or equal to 0.11 or less than or equal to 0.29 or less than or equal to 0.40 or less than or equal to 0.50 or less than or equal to 0.70 .

[0033] The introduction of copper into the cathode can be achieved in three different ways:

1) by the use of a metal collector made of copper or a copper-based alloy or by the use of a collector made of a metal at least partially covered with a copper or alloy coating copper-based,

2) by adding copper powder to the cathodic active material composition,

3) by adding a chemical compound containing copper to the cathodic active material composition.

The introduction of copper can be done in one or more of these three ways. The structure of the element according to the invention is represented schematically in FIG. 1. The element comprises a cathode (1), an anode (2) and a solid electrolyte (3) inserted between the anode and the cathode. Figure 1 shows a single stack of a cathode, a layer of solid electrolyte acting as a separator and an anode. However, the invention is not limited to this schematic representation. The electrochemical bundle may consist of several stacks.

Cathode

The cathode (1) comprises a current collector (4) preferably in the form of a copper strip or a strip of a copper-based alloy. The strap can be solid or perforated. The current collector can also be a metal strip covered on at least one of its faces with a copper or copper-based alloy coating. The current collector can also be a copper foam, an expanded copper or a copper felt. Alternatively, the current collector can be a solid or perforated strip made of a metal other than copper, for example aluminum, and copper is brought to the cathode either in the form of a copper powder incorporated into the composition of cathodic active material, or in the form of a chemical compound containing copper.

The cathodic active material composition deposited on at least one of the faces of the current collector comprises the following constituents:

- a composite (5) prepared from elemental solid sulfur and carbon.

- a solid electrolyte (7), and

- generally one or more binder(s) and at least one electronically conductive compound (6).

Elemental solid sulfur exists in different molecular forms. The preferred form is sulfur alpha Sa, of formula Sx corresponding to cyclooctasulfur, which is the thermodynamically most stable form. Preferably, the cathode does not contain transition metal sulfides such as TiS2, TiSs, TiS4, NiS, N1S2, CuS, FeS2, and MOS3. According to one embodiment, it does not contain Li2S when mounting the element. Preferably, the cathode contains no other electrochemically active species than elemental sulfur and copper introduced in the forms presented above.

The carbon used in the composite has a porous structure. It can have mesoporosity, i.e. pores having an average diameter greater than 2 nm and less than 50 nm or have microporosity, i.e. pores having an average diameter less than 2 nm . The average pore diameter can be between 0.5 and 2 nm. The pores of the porous structure house the elemental sulfur particles.

The solid electrolyte (7) of the cathode is an ionically conductive compound, mainly conductive of Lit II ions is preferably an inorganic sulfur compound which can be chosen from:

- a compound of formula Li _x PS _y where 1.4<x<1.6 and 3<y<3.5, capable of being obtained from the precursors Li2S and P2S5. A preferred compound is Lii _; 5PS3.3. A typical precursor composition comprises 60 mole % Li2S and 40 mole % P2S5;

- a compound of formula (l-y)Li3PS4.yLiX where X denotes a halogen atom (y being between 0.05 and 0.40);

- a compound of formula (Li2S) _a (P2S5)b(LiX) _c (Li2O)d with a+b+c+d=1;

- a compound of formula LiePSsX of argyrodite type where X denotes a halogen atom, capable of being obtained from the precursors Li2S, P2S5 and LiX, for example LiePSsI or Li ₆ PS ₅ Cl;

- a mixture of LiePSsX with a solid solution of LiX-LiBFL where X is a halogen,

- an argyrodite compound optionally substituted by borohydride, having the formula Li7-xPS6-xX _x -z(BH4)z in which X is chosen from the group consisting of Cl, Br, I, F and CN; 0<x<2 and 0<z<0.50. x can be equal to 1. X is preferably I or Cl; 0.1<z<0.35 or

0.1<z<0.20 or even 0.15<z<0.20. This compound can be chosen from

- a compound resulting from the mixture of Li2S/P2S/LiCl/LiBr/LiX, X denotes one or more halogen atoms from Cl, Br and I and followed by a treatment, for example prepared by mechanical grinding followed by a heat treatment.

The binder can be chosen from polyvinylidene fluoride (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC) , poly(vinyl formal), polyester, block polyetheramides, polymers of acrylic acid, methacrylic acid, acrylamide, itaconic acid, sulfonic acid, elastomer and cellulosic compounds. The elastomer or elastomers that can be used as binder can be chosen from styrene-butadiene (SBR), butadiene-acrylonitrile (NBR), hydrogenated butadiene-acrylonitrile (HNBR), and a mixture of several of these.

[0040] The electronically conductive compound is generally carbon black.

A possible process for the preparation of the composition of cathodic active material is as follows:

[0042] In a first step, the solid electrolyte of the cathode is synthesized by mechanosynthesis, that is to say high-energy mechanical-chemical grinding, by grinding a mixture of precursors of the solid electrolyte. For example, the high-energy mechanical-chemical grinding of the Li2S and P2S5 precursors leads to the compound of formula Li _x PS _y where 1.4<x<1.6 and 3<y<3.5. The solid electrolyte is obtained in the form of a powder.

In a second step, a powder is prepared from a mixture comprising a composite of elemental solid sulfur and carbon and generally one or more binder(s) and at least one electronically conductive compound.

[0044] The particles of elemental sulfur are incorporated into the pores of the porous structure of the carbon. This is done by mixing porous carbon with solid elemental sulfur. Typically, the mass of solid elemental sulfur is 30-90% or 55-65% of the sum of the masses of solid elemental sulfur and carbon. The mass of carbon is typically 70 to 10% or 45 to 35% of the sum of the masses of solid elemental sulfur and carbon. The mixture is preferably heated to a temperature close to 155° C. for about 5 hours, under vacuum, to allow the sulfur molecules to penetrate into the open pores of the carbon. Around 155°C, sulfur in the liquid state has its lowest viscosity. The mixture is then heated under inert gas at a temperature between 200°C and 350°C for about 30 minutes, which has the effect of sublimating the sulfur and eliminating the excess. The product obtained is then generally mixed with at least one binder and at least one good electronic conductor compound. A powder comprising the composite S-C is obtained.

The solid electrolyte powder is mixed with the powder comprising the SC composite, for example using a planetary grinder. The mixture may for example comprise from 30% to 60%, preferably approximately 50% by mass of the solid electrolyte powder and from 70% to 40%, preferably approximately 50% by mass of the powder comprising the composite S- C. A composition of cathodic active material is thus obtained. By placing this composition in a tablet mold and by applying to this composition a compression force of the order of several tons per cm ² , it is possible to make this composition compact and to give it the form of a pellet, which is easier to handle than a composition in powder form.

Anode

The anode may consist of lithium or of an alloy based on lithium and a chemical element chosen from among Mg, Al, B, Zn, Ag, Si, Sn, In and C, preferably In. The anode may also consist of a layer of lithium metal on which is deposited an indium layer, the indium layer being in contact with the solid electrolyte layer. These two layers form an alloy of lithium and indium. A current collector, for example made of copper, can be attached to the layer of lithium metal or of the lithium alloy. FIG. 1 represents an anode (2) comprising a layer made up of lithium or of an alloy of lithium and indium (8) joined to a current collector (9). The anode can also consist only of a sheet of lithium.

Solid electrolyte between anode and cathode

The solid electrolyte (10) intended to separate the anode from the cathode can be identical to or different from that used in the manufacture of the composition of cathodic active material. It acts as a separator between the anode and the cathode, preventing the anode from coming into contact with the cathode but nevertheless allowing the transport of the l.i ions. Its thickness can vary between 10 μm and 1 mm. Preferably, the thickness of the separator is less than or equal to 100 μm. More preferably, it ranges from 10 μm to 50 μm. A thickness greater than 100 μm can penalize the mass capacity of the element.

Element manufacturing process

The cathode active material composition is deposited on a current collector, preferably made of copper, and the assembly is compressed to a pressure of the order of several tons per cm ² , which allows the material composition active cathode from adhering to the current collector.

It is also possible - before putting the powder of cathodic active material composition in contact with the current collector - to put this powder in contact with a powder of the solid electrolyte intended to separate the anode from the cathode, then compact the two powders by compression. A pellet is then obtained consisting of the joining of the composition of cathodic active material with the solid electrolyte. Then the current collector of the cathode is fixed by compression on one face of the pellet made of the composition of cathodic active material.

Finally, an anode is attached to the free surface of the pellet consisting of the solid electrolyte powder. The anode is fixed by compression. It is not necessary to insert a separator between the anode and the cathode because the solid electrolyte fulfills this role.

In the case where the supply of copper to the cathode is carried out by the use of a copper current collector, the essential steps of the method for manufacturing an element according to the invention are as follows: a ) provision of a first powder of a solid electrolyte, b) provision of a second powder of a carbon-sulfur composite, which powder optionally comprises an electronic conductor and one or more binders, c) mixing the first powder with the second powder to obtain a cathodic active material composition, e) compressing the cathodic active material composition, f) bringing the compressed cathodic active material composition into contact with a solid electrolyte, identical or different from the solid electrolyte present in the composition of cathodic active material and compression of the assembly obtained, g) bringing the composition of cathodic active material obtained in step f) into contact with a sheet of copper or consisting of an alloy based on copper or consisting of a metal other than copper, the metal being at least partially covered with a coating of copper or a copper-based alloy, then compression of the assembly obtained, h ) bringing a free surface of the assembly obtained in step g) into contact with a lithium metal or lithium-based alloy anode, i) compression of the assembly obtained in step h).

According to a variant, the positioning of the cathode strip in step g) can be carried out before step f) of compression of the composition of cathode active material with the solid electrolyte.

In the case where the supply of copper to the cathode is carried out by the addition of a metallic copper powder or by the use of a copper-based compound, the essential steps of the manufacturing process of an element according to the invention are as follows: a) provision of a first powder of a solid electrolyte, b) provision of a second powder of a carbon-sulfur composite, which powder optionally comprises a electronic conductor and one or more binders, c) provision of a third powder consisting of copper or of a chemical compound containing copper, d) mixing of the three powders to obtain a composition of cathodic active material, e) compression of the cathodic active material composition, f) bringing the compressed cathodic active material composition into contact with a solid electrolyte, identical to or different from the solid electrolyte present in the cathodic active material composition and compressing the assembly o bheld, g) bringing the assembly obtained in step f) into contact with a strip and compressing the assembly obtained, h) bringing a free surface of the assembly obtained in step g) into contact with a lithium metal or lithium-based alloy anode, i) compression of the assembly obtained in step h).

According to a variant, the positioning of the strip of step g) can be carried out before step f) of compression of the composition of cathodic active material with the solid electrolyte.

The quantity of the element copper present in the cathode is less than or equal to 0.37 grams of copper per ampere. time charged by the item. The quantity of copper per charged ampere hour is known to the operator who manufactures the element. Indeed, on the one hand, the operator knows the quantity of copper introduced into the element, whether the copper is introduced in the form of a metal collector or of a copper powder or of a compound chemical containing copper. If it is introduced in the form of a copper-based compound, knowing the molecular molar mass of this compound makes it possible to know the number of moles of the compound and to deduce the equivalent copper mass therefrom. The number of ampere hours charged can be obtained from knowledge of the mass of sulfur used in the element and the theoretical mass capacity of sulfur which is 1670 mAh per gram of sulfur. (Generally, the electrochemical capacity of elemental sulfur of the cathode is lower than that of lithium of the anode. The capacity of elemental sulfur limits the capacity of the element). The number of ampere-hours charged can also be determined by slowly charging the element at ambient temperature, for example at a rate of C/50 or slower, as carried out in the examples of figures 2 and 4.

The nCu/nLi ratio must be greater than or equal to 0.04 and less than 0.81, preferably less than 0.5. If the quantity of copper in the cathode is greater than 0.37 g per ampere hour charged by the element or if the nCu/nLi ratio is greater than or equal to 0.81, the quantity of Cu ⁺ or Cu ²⁺ ions formed in the electrolyte during charging will be too great and may migrate towards the anode and be reduced there to Cu metal. The formation of Cu metal in the vicinity of the anode could lead to the formation of copper dendrites liable to be the cause of an internal short circuit between the anode and the cathode. The number of moles of copper nCu can be obtained by dividing the mass of copper used by the molar mass of copper or by dividing the mass of the copper-based compound used by its molecular molar mass. The number of moles of lithium nLi can be calculated from knowledge of the mass of the lithium-based compound used in the element and the molecular molar mass of this compound.

The electrochemical element according to the invention offers the following advantages:

- it has a high gravimetric capacity. A gravimetric capacity of at least about 2000 mAh per gram of sulfur in the S-C composite can be achieved for discharge at room temperature, preferably at least about 2500 mAh/g.

- it can be cycled for a significant number of cycles reducing the risk of dendrites. Indeed, the replacement of a liquid electrolyte by a solid electrolyte makes it possible to reduce the risk of the appearance of a short circuit between the anode and the cathode. Dendrites are less likely to form in the case of a solid electrolyte than a liquid electrolyte.

- it has a good cycle life.

- copper being a good electronic conductor element, it contributes to the increase of the electronic conductivity of the cathode and allows a discharge of the cathode at higher discharge rates.

The electrochemical element according to the invention can be advantageously used in fields in which electrochemical elements having a higher specific energy than that of lithium-ion elements are sought. Mention may be made of the space domain (satellites) and the aeronautical domain. Examples 1 to 3

Two electrochemical elements differing in the nature of the current collector of their cathode have been manufactured. Their constituents are described in Table 1 below. Element 1 according to the invention differs from comparative element 1 by the nature of the strip of the cathode which is made of copper instead of aluminum for the strip of comparative element 1.

[Table 1]

* Elemental solid sulfur available from Sigma-Aldrich, under reference 215198.

** Carbon Black

*** obtained from a mixture of precursor Li2S and P2S5 at a molar ratio of 60:40

**** obtained by following the procedure described in WO 2019/057840

The elements have undergone a charge-discharge cycle. The elements have been tested under a pressure of 100 MPa. The variation of the voltage as a function of the charged or discharged capacitance is represented in FIG. 2. It can be seen that the charged and discharged capacitances of the element 1 according to the invention comprising a copper current collector are greater than those of the element 1 comparative comprising an aluminum current collector. The discharge capacity of the element 1 according to the invention is 2500 mAh per gram of sulfur in the S-C composite, whereas that of the comparative element 1 is only about 1350 mAh per gram of sulfur in the S-C composite. This represents a significant capacity increase of approximately 85%.

The capacity obtained is greater than the theoretical capacity of the sulfur present in the carbon-sulfur composite. The additional capacity observed is reversible because it is maintained over several cycles. Figure 3 represents the variation of the capacity of the element 1 according to the invention per gram of sulfur in the composite S-C according to the number of cycles carried out. Capacity loss is approximately 25% after 40 cycles.

[0062] Two other elements were manufactured. Their constituents are described in Tables 2 and 3 below. In both elements, the pores of the porous carbon are free of elemental sulfur, so that the measured discharged capacitance cannot be attributed to the electrochemical activity of elemental sulfur. Element 2 outside the invention differs from comparative element 2 by the nature of the strip of the cathode which is made of copper instead of aluminum for the strip of comparative element 2. Variation curves voltage of these two elements during the first two cycles are shown in Figure 4.

[Table 2]

* available from Akzo Nobel under the trade name “Ketjen Black®” ECP600J

** obtained from a mixture of precursor I 2S and P2S5 at a molar ratio of 60:40.

Table 3] The elements being assembled in the charged state, the first cycling phase is a discharge phase. It can be seen that after the initial phase of discharge (dchi in FIG. 4), the two elements have similar discharged capacities (0.31 mAh for element 2 outside the invention and 0.40 mAh for comparative element 2) .

During the charge (chi) following the initial discharge, the charged capacity of element 2 outside the invention is 3.5 mAh. That of the comparative element 2 is only 0.39 mAh. During the second discharge (dch2), the capacity of element 2 outside the invention is 3.2 mAh. That of the comparative element 2 is only 0.45 mAh. These results confirm the existence of an interaction between the copper of the cathode and the other constituents of the cathode.

[0065] Two other elements were manufactured. Their constituents are described in Table 4 below. Element 3 according to the invention differs from comparative element 3 by the nature of the strip of the cathode which is made of copper instead of being aluminum for the strip of comparative element 3.

[Table 4]

* elemental solid sulfur available from Sigma-Aldrich, under reference 215198.

** carbon black

FIG. 5 represents the charging and discharging voltage curves of the comparative element 3 and of the element 3 according to the invention as a function of the discharged capacity (mAh). It can be seen that the charged and discharged capacities of the element 3 according to the invention comprising a copper current collector are greater than those of the comparative element 3 comprising an aluminum current collector. The discharge capacity of the element 3 according to the invention is 2.5 mAh whereas that of the comparative element 3 is only about 0.35 mAh per gram of sulfur in the S-C composite, i.e. a multiplication by 7 of the capacity.

FIG. 6 represents the charging and discharging voltage curves of the element 3 according to the invention at cycles no. 3, 4, 5 and 6 as a function of the capacity of the element per gram of sulfur in the SC-composite. The discharged capacity is between 8000 and 9000 mAh per gram of sulfur in the SC composite. The capacitance discharged by comparative element 3 is much lower as shown in FIG. 7 which represents the charging and discharging voltage curves of comparative element 3 at cycles n° 1 and 8 as a function of the capacity of the element per gram of sulfur in the composite SC. The discharged capacity is only about 1200 mAh per gram of sulfur in the SC composite.

[0069] Other examples:

Table 5] comparative example * a mass of 2 mg corresponds to a thickness of 25 μm. a mass of 40 mg corresponds to a thickness of 500 μm.

Measurement of nCu/nLi and mCu ratios in g/Ah:

The electrochemical element is charged to a voltage of 2.7V. The element, made up of a positive and negative electrode surface S, is disassembled and then placed in a sealed container of known volume (V) equipped with a septum and a pressure and temperature sensor. A quantity of water, mEEO, equal to 5 times the mass of the element, is introduced into the container using a needle to react all the lithium metal which is transformed into hydrogen. The number of moles of hydrogen formed can be calculated from the variation in pressure, dP, the dead volume of the cell, Vm, (corresponding to the volume of the container corrected for the volume of the element analyzed and the volume of water added) and container temperature (T); nH2= dP*Vm/(R*T). The quantity of lithium in the reduced state is equal to Nu reduced=nH2/2.

The container is then opened, then the collector of the negative electrode is extracted before carrying out the following steps. The rest of the element is then placed in a beaker. A solution of KMnCU at 1 mol/L is then added to the container so as to oxidize the sulphide ions of the electrolyte, giving VK the volume of this solution. This step then makes it possible to attack the entire element with a concentrated acid solution having the effect of dissolving all the constituents while avoiding the formation of FUS, i.e. V _ac the volume of acid making it possible to reach a pH of the solution after etching equal to 1. The concentrations of lithium Cu and copper Cc _u can then be measured by ICP The total number of moles of lithium NLitotai= CLi*(V _water +VK+V _ac ) and Ncu = Ccu *(V _water +VK+V _ac );

The number of moles of lithium in the electrolyte is equal to the number of total moles of Li subtracted from the number of moles of lithium in the reduced state: Nu= (total Nu - reduced Nu);

The nCu/nLi ratio of the electrolyte is equal to the ratio of the quantities Ncu and Nu previously calculated divided by the surface area S of the electrode.

The examples in Table 5 allow the following lessons to be drawn:

- The element in example 1 differs from the reference example in that it contains copper in its cathode. The volume capacity changes from 3000 mAh/cc (Cu+S) for the element of the reference example to 3106 mAh/cc (Cu+S) for the element of example 1. no short circuit.

- The elements of examples 9 to 15 are comparative. They have a high copper content and have short circuits. These elements are characterized either by a mass of copper per Ah of sulfur greater than 0.37 g/Ah (Examples 9 to 14), or by an nCu/nLi ratio greater than 0.81 (Example 15).

- The elements of examples 3 and 4 contain 40 mg of solid electrolyte between the anode and the cathode. This high quantity of solid electrolyte strongly penalizes the mass capacity because it is only 551 and 452 mAh/g (Cu+S).

Claims

[Claim 1] An all-solid lithium-sulfur electrochemical cell comprising: a) at least one cathode comprising a cathodic active material composition comprising: i) elemental sulfur, ii) carbon, iii) a solid electrolyte, the cathode comprising copper , b) at least one anode whose active material is lithium or a lithium-based alloy, c) a solid electrolyte interposed between said at least one cathode and said at least one anode, identical to or different from the solid electrolyte present in the composition of cathode active material, the amount of copper in the cathode being less than or equal to 0.37 g per ampere hour charged by the element, the nCu/nLi ratio in the element in the charged state being greater than or equal to 0.04 and less than 0.81 where nCu denotes the number of moles of copper and nLi denotes the sum of the numbers of moles of lithium in the solid electrolyte of the cathode and in the solid electrolyte interposed between said at least a cathode and t said at least one anode.

[Claim 2] An electrochemical cell according to claim 1, wherein the copper is present in one or more of the following forms a, P and y: a) in the form of a metallic collector serving as the current collector of the cathode , the metal collector being made of copper or a copper-based alloy or being made of a metal at least partially covered with a coating of copper or a copper-based alloy,

[Claim 3] An electrochemical cell according to claim 1 or 2, wherein the solid electrolyte of the cathodic active material composition and/or the solid electrolyte interposed between said at least one cathode and said at least one anode is a sulfur compound .

[Claim 4] Electrochemical element according to one of the preceding claims, in which the quantity of copper present in the cathode is less than or equal to 0.12 g per ampere hour charged by the element, preferably equal to 0.06 ± 0.03 g per ampere hour. [Claim 5] Electrochemical cell according to one of the preceding claims, in which the nCu/nLi ratio is less than 0,

5, preferably less than 0.3.

[Claim 6] Electrochemical element according to one of the preceding claims, in which the solid electrolyte used in the cathode or interposed between the anode and the cathode during assembly of the element is in the form of a powder, the powder being coated with copper or a compound containing copper.

[Claim 7] All-solid lithium-sulfur electrochemical cell according to one of the preceding claims, in which the solid electrolyte of the cathode active material composition and the solid electrolyte interposed between the said at least one cathode and the said at least one anode are selected from the group consisting of:

- Li _x PSy where 1.4 <x < 1.6 and 3 <y < 3.5, likely to be obtained from Li2S and P2S5 precursors,

- a compound of formula (Li2S)a(P2S5)b(LiX) _c (Li2O)d with a+b+c+d=l,

- LiePSsX where X denotes a halogen atom, which can be obtained from the precursors Li2S, P2S5 and LiX,

- a mixture of LiePSsX with a solid solution of LiX-LiBEU where X is a halogen,

- an argyrodite compound optionally substituted by borohydride, having the formula Li7-xPS6-xX _x -z(BH4)z in which X is chosen from the group consisting of Cl, Br, I, F and CN; 0<x<2 and 0<z<0.50, and

- a mixture of Li2S/P2S/LiCl/LiBr/LiX compounds, X denotes one or more halogen atoms from Cl, Br and I after heat treatment of the mixture.

[Claim 8] An all-solid lithium-sulfur electrochemical cell according to claim 7, wherein the solid electrolyte has the formula Li7-xPS6-xXx-z(BH4) _z wherein X is I; x=1 and 0.1<z<0.35.

[Claim 9] All-solid lithium-sulfur electrochemical cell according to claim 7, in which the solid electrolyte is selected from among LiePSsI, LiePSsCl,

[Claim 10] Electrochemical cell according to one of the preceding claims, in which:

- the solid electrolyte of the cathodic active material composition has the formula Li _x PS _y where 1.4 <x <1.6 and 3 <y <3.5 and

- the solid electrolyte interposed between said at least one cathode and said at least one anode is chosen from:

- a compound of formula Li7-xPS6-xXx-z(BH4) _z in which X is chosen from the group consisting of Cl, Br, I, F and CN; 0<x<2 and 0<z<0.50, and

[Claim 11] Electrochemical element according to claim 10, in which the solid electrolyte interposed between the said at least one cathode and the said at least one anode has the formula LiePSsE/e BEL^i/e.

[Claim 12] All-solid lithium-sulfur electrochemical cell according to one of the preceding claims, in which the alloy is an alloy of lithium and one or more chemical elements selected from the group consisting of indium, silicon, tin and carbon.