FR3112029A1 - SURFACE TREATED ELECTRODE, THE ELEMENTS, MODULES AND BATTERIES INCLUDING IT - Google Patents

Abstract

SURFACE-TREATED ELECTRODE, ELEMENTS, MODULES AND BATTERIES COMPRISING IT The invention also relates to an element, a module and an electrochemical battery comprising an electrode according to the invention. Figure for abstract: None

Description

SURFACE-TREATED ELECTRODE, ELEMENTS, MODULES AND BATTERIES COMPRISING IT

The present invention relates to the field of energy storage, and more specifically accumulators, in particular of the lithium type.

Rechargeable lithium-ion batteries indeed offer excellent energy and volume densities and today occupy a prominent place in the market for portable electronics, electric and hybrid vehicles and even stationary energy storage systems.

Their operation is based on the reversible exchange of the lithium ion between a positive electrode and a negative electrode, separated by an electrolyte.

The electrode, negative or positive, generally consists of a conductive support used as a current collector coated with a layer containing an active material and generally also a binder and an electronic conductive material.

Solid electrolytes also offer a significant improvement in terms of safety as they present a much lower risk of flammability than liquid electrolytes.

In particular, solid sulphide electrolytes have reached sufficient maturity to consider their industrial use. Their high values of ionic conductivity associated with their ductility and their limited density make them serious candidates for new generations of all-solid-state batteries that can compete with the energy densities of current Li-ion accumulators with liquid electrolytes.

Solid sulfide electrolytes, however, cause problems with electrode deterioration. Very reactive, the sulphide electrolytes react with the materials constituting the electrodes, in particular with the active material and the carbonaceous material. This deterioration of the electrodes then has the consequence of reducing the performance of the electrochemical cell as it operates.

It is therefore necessary to develop solutions to protect the electrodes from the electrolyte, in order to extend their life.

In order to overcome this problem, it has been proposed to protect the active material of the electrode by depositing a layer of lithium oxide.

US 9,912,014 and JP 2010/07539 teach in this sense to cover the surface of the active material of one of the electrodes, in particular of the cathode, with a thin layer of lithium niobate LiNbO ₃ .

However, only the active material of the electrode is protected. The other constituents of the electrode, in particular the electronically conductive material, are always in direct contact with the electrolyte and continue to deteriorate during the operation of the electrochemical cell.

None of these documents teaches a solution making it possible to protect the active material and the conductive material.

It therefore remains to provide effective protection making it possible to protect both the active material and the conductive material present in an electrode from electrolytic materials based on sulphides. Furthermore, a solution should be found which does not affect the electrochemical performance of the cell.

Thus, one of the aims of the invention is to solve these objectives by proposing an electrode covered, over all or part of its surface, with a coating layer of an electronic insulating and ion-conductive material.

The layer of electronic insulating material and ion conductor makes it possible to limit and/or prevent the reactions likely to occur between the materials of the electrode and the sulphide electrolyte, while allowing good electrochemical performance to be maintained.

The Applicant has also discovered that the presence of a layer of electronic insulating material and ionic conductor makes it possible to widen the window of accessible potential. Applied to the surface of the positive electrode (cathode), the layer of electronic insulating material and ion conductor makes it possible to lower the value of the accessible potentials. Applied to the surface of the negative electrode (anode), the layer of electronic insulating material and ion conductor makes it possible to increase the value of the accessible potentials.

The invention relates first of all to an electrode which can be used in an energy storage device comprising at least one active material and at least one carbonaceous electronic material, said electrode being covered, over all or part of its surface, with a layer coating in an electronic insulating and ion-conductive material, said electrode being such that A1 < 6 and A2 > 10,
with :

Or :
e represents the thickness of the coating layer (in m),
i represents the ionic conductivity of the electronic insulating material and ionic conductor (in Sm ^-1 ),
S(mat. act) represents the ratio of the surface developed by the active material to the total surface of the electrode (in m² of active material per cm² of electrode),
e represents the electronic conductivity of the electronic insulating material and ionic conductor (in Sm ^-1 ), and
S(cond.) represents the ratio of the surface of active material and of carbonaceous electronic material to the total surface of the electrode (in m ² per cm ² of electrode).

Preferably, the electronic insulating material and ionic conductor has an electronic conductivity less than or equal to 10 ^-10 Sm ^-1 , preferably less than or equal to 10 ^-12 Sm ^-1 .

Advantageously, the electronic insulating material and ionic conductor has an ionic conductivity greater than or equal to 10 ^-8 Sm ^-1 , preferably greater than or equal to 10 ^-6 Sm ^-1 .

According to one embodiment, the electronic insulating material and ionic conductor is chosen from halides, oxides, phosphates, sulphides, polymers and any one of their mixtures.

Preferably, the thickness of the coating layer ranges from 2 to 50nm, preferably from 5 to 10nm

Advantageously, the coating layer covers at least 50% of the surface of the electrode, preferably at least 75%, more preferably at least 90%, even more preferably at least 95%.

According to a preferred embodiment, the electrode is porous and at least a part of the pores of the electrode is at least partially filled with a solid electrolytic material, preferably a solid sulfur electrolytic material.

The invention also relates to a method for manufacturing an electrode as defined above, and in detail below, this method comprising:

(a) the provision of an electrode,

b) the deposition on all or part of the surface of the electrode of a coating layer as defined above, and in detail below,

c) optionally, the deposition by infiltration in at least part of the pores of the coating layer of a solid electrolytic material, preferably of a solid sulfur-containing electrolytic material, and

d) optionally, a treatment allowing the solidification of the electrolyte, in particular by heat treatment or by ultraviolet radiation.

The invention also relates to an electrochemical element comprising a stack between two electronically conductive current collectors, said stack comprising:

- a positive electrode;

- a negative electrode;

- a layer comprising a solid electrolytic composition separating said positive electrode and said negative electrode, the electrolytic composition comprising at least one solid electrolytic compound, preferably chosen from solid sulfur-containing electrolytic compounds and polymers;

Said element being characterized in that at least one of said positive electrode and of said negative electrode is as defined above, and in detail below.

Preferably, in the electrochemical element according to the invention, both said positive electrode and said negative electrode are covered, over all or part of their surface, with a coating layer, identical or different, as defined below. above and in detail below.

The invention further relates to a method for manufacturing an electrochemical element as defined above and in detail below, this method comprising:

i) supplying a positive electrode and a negative electrode, at least one of said positive electrode and said negative electrode according to the invention or having been obtained by implementing a method according to invention, and

ii) the formation, between said positive electrode and said negative electrode, of a layer comprising a solid electrolytic composition.

The invention further relates to an electrochemical module comprising the stacking of at least two elements as defined above and in detail below, each element being electrically connected with one or more other element(s) .

The invention finally relates to a battery comprising one or more module(s) as defined above and in detail below.

Detailed description of the invention

The invention relates first of all to an electrode that can be used in an energy storage device, said electrode being covered, over all or part of its surface, with a coating layer of an electronic insulating and ion-conductive material.

The electrode according to the invention can be a positive electrode (also called cathode) or a negative electrode (also called anode).

The term positive electrode designates the electrode where the electrons enter, and where the cations (Li ⁺ ) arrive in discharge.

The term negative electrode designates the electrode from which the electrons leave, and from which the cations (Li ⁺ ) are released in discharge

Preferably, the electrode according to the invention is a negative electrode.

In the context of the present invention, the positive electrode can be of any known type. The cathode typically consists of a conductive support used as a current collector on which is deposited the cathodic active material and a carbonaceous electronic material. A binder can also be incorporated into the mixture.

The cathodic active material is not particularly limited. It can be chosen from the following groups or mixtures thereof:

- a compound (a) of formula Li _x M _1-yzw M' _y M'' _z M''' _w O ₂ (LMO ₂ ) where M, M', M'' and M''' are chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, W and Mo provided that at least M or M 'or M'' or M''' is chosen from Mn, Co, Ni, or Fe; M, M', M'' and M''' being different from each other; and 0.8≤x≤1.4; 0≤y≤0.5; 0≤z≤0.5; 0≤w≤0.2 and x+y+z+w<2.1;

- a compound (b) of formula Li _x Mn _2-yz M' _y M'' _z O ₄ (LMO), where M' and M" are chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; M' and M" being different from each other, and 1≤x≤1.4; 0≤y≤0.6; 0≤z≤0.2;

- a compound (c) of formula Li _x Fe _1-y M _y PO ₄ (LFMP) where M is chosen from the group consisting of B, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo; and 0.8≤x≤1.2; 0≤y≤0.6;

- a compound (d) of formula Li _x Mn _1-yz M' _y M'' _z PO ₄ (LMP), where M' and M'' are different from each other and are chosen from the group consisting of in B, Mg, Al, Si, Ca, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb and Mo, with 0.8≤x≤1.2; 0≤y≤0.6; 0≤z≤0.2;

- a compound (e) of formula xLi ₂ MnO ₃ ; (1-x)LiMO ₂ where M is at least one element chosen from Ni, Co and Mn and x≤1.

- a compound (f) of formula Li _1+x MO _2-y F _y of cubic structure where M represents at least one element chosen from the group consisting of Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd and Sm and where 0 ≤ x ≤ 0.5 and 0 ≤ y ≤ 1.

- a compound (g) of the LiVPO ₄ F (LVPF) type.

The current collector is preferably a two-dimensional conductive support such as a solid or perforated strip, based on carbon or metal, for example nickel, steel, stainless steel or aluminum, preferably aluminum. The current collector can be coated on one or both sides with a layer of carbon.

In the context of the present invention, the negative electrode can be of any known type. The anode typically consists of a conductive support used as a current collector on which is deposited the anode active material and a carbonaceous electronic material. A binder can also be incorporated into the mixture.

It is understood that in "anode free" systems, a negative electrode is also present (generally limited initially to the current collector alone).

The anodic active material is not particularly limited. It can be chosen from the following groups and their mixtures:

- Metallic lithium or metallic lithium alloy

- Graphite

- Silicon

- Anode-free type

- a titanium and niobium oxide TNO having the formula:

Li _x Ti _ay M _y Nb _{b- z} M' _z O _{( (x+4a+5b)/2)-c- d} X _c

Or :

0 ≤ x ≤ 5; 0 ≤ y ≤ 1; 0 ≤ z ≤ 2; 1 ≤ a ≤ 5; 1 ≤ b ≤ 25; 0.25≤a/b≤2; 0 ≤ c ≤ 2 and 0 ≤ d ≤ 2; a-y > 0; b-z > 0;

M and M′ each represent at least one element chosen from the group consisting of Li, Na, K, Mg, Ca, B, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Y, Zr, Nb, Mo, Ru, Ag, Sn, Sb, Ta, W, Bi, La, Pr, Eu, Nd and Sm;

X represents at least one element selected from the group consisting of S, F, Cl and Br.

The subscript d represents an oxygen deficiency. The index d can be less than or equal to 0.5.

Said at least one titanium and niobium oxide can be chosen from TiNb ₂ O ₇ , Ti ₂ Nb ₂ O _{7 ,} Ti ₂ Nb ₂ O ₉ and Ti ₂ Nb ₁₀ O ₂₉ .

- a lithiated titanium oxide or a titanium oxide capable of being lithiated. The lithiated titanium oxide is chosen from the following oxides:

i) Li _xa M _a Ti _yb M' _b O _4-cd X _c in which 0<x≤3;1≤y≤2.5;0≤a≤1;0≤b≤1; 0≤c≤2 and -2.5≤d≤2.5; M represents at least one element selected from the group consisting of Na, K, Mg, Ca, B, Mn, Fe, Co, Cr, Ni, Al, Cu, Ag, Pr, Y and La;

M' represents at least one element selected from the group consisting of B, Mo, Mn, Ce, Sn, Zr, Si, W, V, Ta, Sb, Nb, Ru, Ag, Fe, Co, Ni, Zn, Al , Cr, La, Pr, Bi, Sc, Eu, Sm, Gd, Ti, Ce, Y and Eu;

X represents at least one element selected from the group consisting of S, F, Cl and Br;

The subscript d represents an oxygen deficiency. The index d can be less than or equal to 0.5.

ii) H _x Ti _y O ₄ in which 0≤x≤1; 0≤y≤2, and

iii) a mixture of compounds i) to ii).

Examples of lithium oxides of titanium belonging to the groupi)are spinel Li₄You₅O₁₂, Li₂TiO_3,there Ramsdellite Li₂You₃O₇, LiTi₂O₄, Li_xYou₂O₄, with 0<x≤2 and Li₂N / A₂You₆O₁₄.

A preferred LTO compound has the formula Li _4-a M _a Ti _5-b M' _b O ₄ , for example Li ₄ Ti ₅ O ₁₂ which is also written Li _4/3 Ti _5/3 O ₄ .

The binder present at the cathode and the anode has the function of reinforcing the cohesion between the particles of active materials as well as improving the adhesion of the mixture according to the invention to the current collector. The binder may contain one or more of the following elements: 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.

The carbonaceous electronic material or conductive material is generally chosen from graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes or a mixture thereof.

The carbonaceous electronic material is distributed throughout the active material particles and the current collector.

By current collector is meant an element such as a pad, plate, sheet or other, made of conductive material, connected to the positive or negative electrode, and ensuring the conduction of the flow of electrons between the electrode and the terminals of the battery. .

The electrode according to the invention is covered over all or part of its surface with a coating layer of an electronic insulating and ion-conductive material.

The coating layer preferably covers at least 50% of the surface of the electrode, preferably at least 75%, more preferably at least 90%, even more preferably at least 95%.

The thickness of the coating layer is preferably from 2 to 50 nm, more preferably from 5 to 10 nm.

By “electronic insulating material”, is meant in the sense of the invention a material incapable of transporting electrons. The electronic conductive behavior of a material is evaluated by measuring its electronic conductivity σe.

The electronic conductivity of a material can be determined using any method known to those skilled in the art. It can for example be measured as follows:

A pellet of the material whose electronic conductivity value is to be determined is prepared by pressing the powder of said material under 5t/cm² then performing sintering at a temperature 30% lower than its melting temperature (expressed in K) for 2 hours . A gold film is then deposited on the surface of the pellet, in order to improve the contact between the current collectors and the sample. The pellet is finally placed between 2 nickel collectors on the surface.

A voltage is applied to the terminals of the electrodes in order to measure the evolution of the current flowing in the pellet as a function of time. The graph obtained plotting the evolution of this current as a function of the applied voltage is a straight line whose slope corresponds to the electronic resistance Re of the pellet. The electronic conductivity of the material is finally calculated by applying the following formula:

where σe represents the electronic conductivity of the material (in Sm ^-1 ), e represents the thickness of the pellet (in m), S the surface of the pellet (in m²) and Re the electronic resistance of the material (in Ohm).

Preferably, the electronic insulating material and ionic conductor has an electronic conductivity less than or equal to 10 ^{- 10} Sm ^-1 , preferably less than or equal to 10 ^{- 12} Sm ^-1 .

By “ionic conductive material”, is meant in the sense of the invention a material capable of transporting ions. The ionic conductive behavior of a material is evaluated by measuring its ionic conductivity σi.

The ionic conductivity of a material can be determined using any method known to those skilled in the art. It can for example be measured as follows:

A pellet of the material whose ionic conductivity value is to be determined is prepared according to the protocol described above before being placed between 2 surface nickel collectors.

An impedance measurement is then performed on the pad to which a sinusoidal voltage with an amplitude of 10mV at different frequencies (between 1MHz and 0.01Hz) is applied. On the Nyquist diagram, the signal from the blocking electrodes is visible at the lowest frequencies. The intersection between the extrapolation of the signal from the blocking electrodes and the axis of the real values of the impedance R _T corresponds to the sum of the ionic resistance Ri and the electronic resistance Re of the pellet.

The ionic resistance R _i is calculated from the relationship Ri = R _T – Re and the ionic conductivity i is calculated by applying the following formula:

where σi represents the ionic conductivity of the material (in Sm ^-1 ), e represents the thickness of the pellet (in m), S the surface of the pellet (in m²) and Ri the ionic resistance of the material (in Ohm).

Preferably, the electronic insulating material and ionic conductor has an ionic conductivity greater than or equal to 10 ^-8 Sm ^-1 , preferably greater than or equal to 10 ^-6 Sm ^-1 .

The electronic insulating and ion-conductive material can be chosen from azides, halides, oxides, phosphates, sulphides, polymers and any of their mixtures.

When the electronic insulating and ion-conductive material is chosen from azides, it is preferably lithium azide Li ₃ N.

When the electronic insulating and ion-conductive material is chosen from halides, it is preferably chosen from materials of formula:

- LiX, with X = F, Cl, Br or I,

- Li ₃ MX ₆ , with M = Y, In, Sc or a lanthanide, and X is a halogen, in particular chosen from Cl, Br and I,

- Li ₆ MX ₈ , with M = V, Fe, C or Ni, and X is a halogen, in particular chosen from Cl, Br and I, and

- Li _2-2z M _1+z X ₄ , with M = Zn, V, Ti, Mn, Mg, Cd, Fe or Cr, 0≤ z≤1 and X is a halogen, in particular chosen from Cl, Br and I .

When the electronic insulating and ion-conductive material is chosen from oxides, it is preferably chosen from metal oxides.

Among the metal oxides suitable for the implementation of the invention, mention may be made in particular of:

- lithium zirconate Li ₂ ZrO ₃ ,

- lithium niobate LiNbO ₃ ,

- lithium titanate Li ₄ Ti ₅ O ₁₂ ,

- sodium-based superionic conductors (NASICON for “ Na Super Ionic Conductor ” in English) of formula Na _1+x Zr ₂ Si _x P _3-x O ₁₂ with 0<x<3,

- lithium-based superionic conductors (LISICON for “ Li Super Ionic Conductor ” in English) of formula Li _2+2x Zn _1-x Si _x GeO ₄ with 0<x<1,

- perovskites, in particular of formula Li_0.33There_0.557TiO₃ (LLTO),

- LIPON-type compounds (Li _3.2 PO _3.8 N _0.2 ), and

- Li ₃ OCl type anti-perovskites _.

When the electronic insulating and ion-conductive material is chosen from phosphates, it is preferably chosen from metal phosphates, more preferably from lithiated metal phosphates, even more preferably from lithiated thio-phosphates such as, for example, Li ₁₀ GeP ₂ S ₁₂ and its derivatives obtained by doping and/or substitution of one or more atoms of lithium Li, or of germanium Ge by one or more metallic elements, in particular tin Sn.

The sulfide compounds present in the coating layer differ from the sulfide compounds present in the electrolytic composition. In particular, the sulphide compounds forming the coating layer exhibit a higher electronic conductivity than the sulphide compounds present in the electrolyte.

When the electronic insulating material and ionic conductor is chosen from sulphides, it is preferably chosen from sulphides having an electronic conductivity less than or equal to 10 ^{-1 0} Sm ^-1 .

Such sulfide compounds are chosen in particular from materials of formula [(Li ₂ S) _y (P ₂ S ₅ ) _1-y ] _(1-z) (LiX) _z

Or :

X is a halogen, chosen in particular from Cl, Br and I, or an oxygen atom,

0<y<1

0≤z≤1

When the electronic insulating and ion-conductive material is chosen from polymers, it is preferably chosen from homopolymers and copolymers of poly(oxyethylene) (POE) or polyethylene glycol; poly(propylene) (PP); poly(propylene) carbonate (PPC); polymers of the alkyl (meth)acrylate type, in particular methyl poly(meth)acrylates (PMA and PMMA); poly(meth)acrylonitrile (PAN); poly(dimethylsiloxane) (PDMS); cellulose and their derivatives, in particular cellulose acetates; poly(vinylidene fluoride) (PVdF); polyvinylpyrrolidone (PVP); polystyrene sulfonate (PSS); poly(vinyl chloride) (PVC); polyethylenes, in particular poly(ethylene terephthalate) (PET); polyimides and mixtures thereof.

Among the copolymers which can be used, mention may in particular be made of copolymers of the poly(oxyethylene)-polystyrene sulfonate type.

These various polymers can comprise lithium salts such as LiTFSI, LiFSI, LiPF ₆ , LiClO ₄ . In addition, these polymers may contain traces or significant amounts of organic solvents, and in particular ethylene carbonate (EC), diethyl carbonate (DEC), dimethoxyethane (DME), dioxolane (DOL)…

It can also be ionic liquid polymer.

Preferably, the electronic insulating and ion-conductive material is chosen from metal oxides; metal phosphates, preferably from lithiated metal phosphates; and any mixture thereof.

Advantageously, the electronic insulating material and ionic conductor is chosen from lithium niobate LiNbO ₃ , substituted lithium phosphates, compounds of the LIPON type (Li _3.2 PO _3.8 N _0.2 ) and any one of their mixtures.

More advantageously, the electronic insulating material and ionic conductor is chosen from lithium niobate LiNbO ₃ , compounds of the LIPON type (Li _3.2 PO _3.8 N _0.2 ) and any one of their mixtures.

Advantageously, the electrode according to the invention is such that A1 <6, the parameter A1 being calculated as follows:

Or :
e represents the thickness of the coating layer (in m),
i represents the ionic conductivity of the electronic insulating material and ionic conductor (in Sm ^-1 ),
S(mat. act) represents the ratio of the surface developed by the active material to the total surface of the electrode (in m² of active material per cm² of electrode).

More advantageously, the electrode is such that A1≤4, preferably A1≤1.5, more preferably A1≤0.

Advantageously, the electrode according to the invention is such that A2 > 10, the parameter A2 being calculated as follows:

Or :
e represents the thickness of the coating layer (in m),
e represents the electronic conductivity of the electronic insulating material and ionic conductor (in Sm ^-1 ), and
S(cond.) represents the ratio of the surface of active material and of carbonaceous electronic material to the total surface of the electrode (in m ² per cm ² of electrode).

More preferably, the electrode is such that A2 ≥ 12, preferably A2 ≥ 13.0.

The surface of the electrode is porous.

Preferably, the electrode has a porosity greater than or equal to 30%, more preferably greater than or equal to 40%, advantageously ranging from 40 to 60%

According to one embodiment, at least some of the pores of the electrode are at least partially filled with a solid electrolytic material, preferably chosen from solid electrolytic materials that conduct lithium.

The solid electrolyte can be of any known type. It is chosen in particular from sulfur electrolytes, electrolytes of the oxide type, polymer electrolytes, hybrid polymer/ceramic electrolytes and any one of their mixtures.

Preferably, the solid electrolyte is chosen from sulfur electrolytes and polymers.

More preferentially, the solid electrolyte is chosen from sulfur electrolytes, that is to say comprising sulfur, more preferentially from sulphide electrolytes, alone or mixed with other constituents, such as polymers or gels. Mention may thus be made of partially or completely crystallized sulphides as well as amorphous ones. Examples of these materials can be selected from sulphides of composition A Li₂S–B P₂S₅(with 0<A<1.0<B<1 and A+B=1) and their derivatives (for example with LiI, LiBr, LiCl doping, etc.); sulphides of argyrodite structure; or type LGPS (Li₁₀GEP₂S₁₂), and its derivatives. The sulphides forming the electrolytic layer differ from the sulphide compounds forming the coating layer in that they have an ionic conductivity greater than 10^-2S. .m^-1and electronics between 10^-8and 10^{- 10} S.m^-1. The electrolytic materials may also include oxysulphides, oxides (garnet, phosphate, anti-perovskite, etc.), hydrides, polymers, gels or ionic liquids that conduct lithium ions.

Examples of sulfide electrolytic compositions are described in particular in Park, KH, Bai, Q., Kim, DH, Oh, DY, Zhu, Y., Mo, Y., & Jung, YS (2018). Design Strategies, Practical Considerations, and New Solution Processes of Sulfide Solid Electrolytes for AllSolidState Batteries. Advanced Energy Materials , 1800035.

Typically, at least 50% by volume of the pores of the electrode are filled with a solid electrolyte material, preferably at least 70% by volume, more preferably at least 80% by volume.

Advantageously, the coating layer and the electrolytic composition are made of separate materials.

The invention also relates to a method for manufacturing an electrode as defined above, this method comprising:

a) the provision of an electrode, positive or negative,

b) the deposition on all or part of the surface of said electrode of a coating layer of an electronic insulating and ion-conductive material as defined above,

c) optionally, the deposition by infiltration in at least part of the pores of the electrode of a solid electrolytic material as defined above, and

d) optionally, a treatment allowing the solidification of the electrolyte, preferably by heat treatment or by ultraviolet radiation.

The deposition of the coating layer on the surface of the electrode can be carried out according to any method known to those skilled in the art.

Preferably, the coating layer is deposited by atomic layer deposition (ALD in English for “ Atomic Layer Deposition ”), by molecular layer deposition (MLD in English for “ Molecular Layer Deposition ”), by chemical deposition in chemical vapor deposition (CVD), physical vapor deposition (PVD), dip coating or impregnation.

Advantageously, the coating layer is formed from a precursor composition comprising at least one precursor compound of the electronic insulating and ion-conductive material and at least one solvent.

Preferably, the precursor compound of the electronic insulating and ion-conductive material is chosen from a source or target compound of the electronic insulating and ion-conductive material targeted or of a similar composition making it possible, under a reactive atmosphere, to obtain the composition profile desired by PVD or PLD (deposition of LiPON from a Li ₃ PO ₄ target under a partial nitrogen atmosphere) or, precursors making it possible to obtain the compositions targeted by ALD or MLD.

As precursor compounds that can be used in an ALD-type process, mention may be made in particular by way of example of: lithium tert-butoxide LiO ^t Bu, lithium hexamethyldisilazide LiN(SiMe ₃ ) ₂ , niobium ethanolate Nb( OEt) ₅ , diethyl phosphoramidate H ₂ NP(O)(OC ₂ H ₅ ) ₂ , trimethylphosphate.

Depending on the deposition protocol, these precursor compounds can be used with deionized water, as well as with different carrier gases (argon, for example) or reactive atmospheres (partial pressure of nitrogen, oxygen or ozone, For example).

Preferably, the solvent is inert with respect to the compounds present in the precursor composition, in particular with respect to the precursor compound of the electronic insulating and ion-conductive material.

By "inert solvent" is meant within the meaning of the invention a chemical compound capable of dissolving or diluting a chemical species without reacting with it.

According to one embodiment, the method according to the invention further comprises, after step 2), an additional step of depositing in at least part of the pores of the electrode a solid electrolytic material as defined below. above.

Advantageously, the solid electrolytic material is introduced into the pores of the electrode by the infiltration of the electrolytic material in liquid form.

When the electrolytic material comprises a polymer, the infiltration step can be carried out before the polymerization of the material, by infiltration of a composition comprising the precursor monomers of the polymer followed by a polymerization step inside the pores, or well after the polymerization but before the crosslinking of the polymer. The infiltration step can also be carried out from the polymer electrolyte in the molten state.

The sulfide-type electrolytic materials can be introduced into the pores of the electrode directly in molten form or else in the form of a precursor composition prepared by dissolving the sulfide-type compound in a solvent.

Preferably, when the electrolytic material is chosen from sulphides, its infiltration into the pores of the electrode is carried out by the succession of the following steps:

A) the preparation of a precursor composition by dissolving the solid electrolytic material in a solvent,

B) the impregnation of the pores of the electrode with the precursor composition prepared in A),

C) evaporation of the solvent, and

D) the densification of the material.

Preferably, the solvent used for the preparation of the precursor composition is chosen from organic solvents, more preferably from ethanol, methanol, tetrahydrofuran (THF), hydrazine, water, acetonitrile, ethyl acetate, 1,2-dimethoxyethane and mixtures thereof.

The impregnation of the pores of the electrode can be carried out according to any known method. It can in particular be produced by dipping the electrode in the precursor composition (“ dip-coating ” in English).

The evaporation of the solvent is typically carried out under reduced pressure and under heating. Solvent evaporation techniques under reduced pressure are well known to those skilled in the art who will be able, depending on the solvent present in the precursor composition, to select a suitable pressure range and temperature range.

The densification of the material is carried out by pressing, hot or cold, preferably cold. Preferably, the pressure applied is between 20 and 1000 MPa, more preferably between 300 and 800 MPa.

Examples of electrode impregnation techniques are in particular described in Dong Hyeon Kim et al., Nano Lett ., 2017, 17, 5, 3013-3020; S. Yubuchi et al., J. Matter . Chem . A , 2019, 7, 558-566 and S. Yubuchi et al., Journal of Power Sources , 2019, 417, 125-131.

The invention also relates to an electrochemical element comprising a stack between two electronically conductive current collectors, said stack comprising:

- a positive electrode,

- a negative electrode, and

- a layer comprising a solid electrolytic composition, preferably chosen from solid sulphide-based electrolytes, separating said positive electrode and said negative electrode,

at least one of said positive electrode and said negative electrode being as defined above.

“Electrochemical element” means an elementary electrochemical cell made up of the positive electrode/electrolyte/negative electrode assembly, allowing the electrical energy supplied by a chemical reaction to be stored and returned in the form of current.

According to a first embodiment, the electrochemical element according to the invention comprises an electrode as defined above and an electrode not having a coating layer as defined above.

Preferably, according to this first embodiment, the electrode according to the invention is the negative electrode.

According to a second embodiment, the two electrodes (the negative electrode and the positive electrode) are as defined above.

The electrochemical elements according to the invention called here "macrobatteries" typically have an electrical charge greater than 100 mAh. They differ from micro-batteries and typically have a capacity greater than 0.1 Ah.

The electrochemical element according to the invention is particularly suitable for lithium accumulators, such as Li-ion, primary Li (non-rechargeable) and Li-S accumulators.

The invention also relates to a method for manufacturing an electrochemical element as defined above.

Preferably, the process for manufacturing the electrochemical element comprises the following steps:

i) the provision of a positive electrode and a negative electrode, at least one of said positive electrode and said negative electrode being as defined above, and

ii) the formation, between said positive electrode and said negative electrode, of a layer comprising a solid electrolytic composition.

According to another object, the invention also relates to an electrochemical module comprising the stack of at least two elements according to the invention, each element being electrically connected with one or more other element(s), in particular via their collectors current.

According to another object, the present invention also relates to a battery comprising one or more modules according to the invention, and/or one or more boxes according to the invention.

“Battery” means the assembly of several modules.

Said assemblies can be in series and/or parallel.

figure

Figure 1 is a schematic representation of the different steps of the method for preparing an electrode according to the invention.

Referring to Figure 1, the method according to the invention begins with the supply of an electrode (not shown) comprising a current collector (not shown) on which is deposited an electrode material 10. The material of The electrode 10 comprises particles of active material 12 and particles of carbonaceous electronic conductor material 14.

During step A, a coating layer 16 made of an electronic insulating and ion-conductive material is deposited on the surface of the electrode material 10.

Step B then consists of a step of infiltrating a solid electrolyte composition 18 inside the pores 20 of the electrode material 10 and on the surface of the coating layer 16. The particles of active material 12 and the particles of carbonaceous electronic material 14 thus find themselves covered with two successive layers 16 and 18. The coating layer 16 is in direct contact with the particles 12 and 14 while the solid electrolyte layer 18 is deposited on the surface. of the coating layer 16.

Step C finally consists of a step of drying the electrolyte composition and compressing the material in order to obtain an electrode according to the invention.

Examples

The examples according to the invention C1 to C15 are collated in Tables 1 and 3. The comparative examples C1* to C4* are collated in Tables 2 and 3.

1- Preparation of the positive electrodes

The positive electrodes according to the invention C1 to C14 are prepared according to the following protocol:

^1st step: production of a porous electrode without solid electrolyte

The positive electrodes are prepared using a method similar to that used for conventional Li-ion batteries with a liquid electrolyte. The conductive carbon (a carbon black or VGCF fibers with different specific surfaces varying from 15 to 200m²/g) is dispersed in a solvent (N-methyl-2-pyrrolidone), to which is added a binder (PVDF – polyvinylidene fluoride ) then the active material of the NMC type of composition: Li(Ni _0.33 Mn _0.33 Co _0.33 ) _{O 2} . The quantity of binder is 5% and those of the other constituents are indicated in table 1. The quantity of solvent is adapted so that the mixture has a viscosity allowing a homogeneous deposit of the ink on the current collector in aluminum. After the deposit has been made, the electrode is dried at 120° C. for 1 hour.

Calendering of the electrode is then carried out so as to achieve a porosity of approximately 70%.

^2nd step: realization of the coating layer

A coating layer of LiNbO₃ is then deposited on the surface of the electrode obtained at the end of step 1 by atomic layer deposition (ALD in English for “Atomic Layer Deposition”) according to a procedure adapted from those described in the publication: B. Wang, Y. Zhao, M.N. Banis, Q. Sun, K.R. Adair, R. Li, T.K. Sham, X. Sun, Atomic layer deposition of lithium niobium oxides as potential solid-state electrolytes for lithium-ion batteries, ACS Appl. Mater. Interfaces, 10 (2018), p. 1654-1661

Successive deposition cycles are carried out on the positive electrode obtained in step 1, with lithium tert-butoxide LiO ^t Bu and niobium ethanolate Nb(OEt) ₅ as precursors. The ratio between the amount of Lithium ions and the amount of Niobium ions deposited ranges from 2:1 to 1:4.

Several successive deposition cycles are carried out in order to obtain the desired thickness and concentration. The thicknesses of the deposits are reported in tables 1 and 2.

^3rd step: introduction of the solid electrolyte into the positive electrode

The pores of the electrode are then impregnated with a sulphide electrolyte of the Li ₃ PS ₄ type. To do this, Li ₂ S and P ₂ S ₅ powders are dissolved in anhydrous acetonitrile in a stoichiometric quantity to reach the Li ₃ PS ₄ composition with a mass concentration close to 5% by mass in the solution.

After having mixed the solution for 6 hours, the porous electrode obtained at the end of the ^2nd stage is coated by soaking ( dip-coating ) in the solution. The electrode is then dried in a glove box and then heated under vacuum at 150° C. for 2 hours.

The electrode is then compressed under a pressure of 2t/cm².

The comparative positive electrodes C1* to C3* are prepared analogously, except that:

- for the comparative electrode C1*: no coating layer is deposited on the surface of the electrode,

- for the comparative electrodes C2* and C3*: the LiNbO ₃ coating layer is replaced by a LiLAO ₂ or LLZO coating layer.

2- Preparation of the negative electrodes

The same method of preparation as that described above for the preparation of the positive electrodes is used for the manufacture of the negative electrode according to the invention C15, with the exception that:

- the active material is graphite powder,

- the current collector is made of copper, and

- the coating layer is LIPON.

LiPON is deposited by Atomic Layer Deposition (ALD) under conditions adapted from those described in the publications:
- AC Kozen, AJ Pearse, C.-F. Lin, M. Noked, GW Rubloff, Atomic layer deposition of the solid electrolyte LiPON, Chem. Mater., 27 (2015), p. 5324-5331
- M. Nisula, Y. Shindo, H. Koga, M. Karppinen Atomic layer deposition of lithium phosphorus oxynitride, Chem. Mater., 27 (2015), p. 6987-6993

The comparative negative electrode C4* is prepared analogously. However, no coating layer is deposited on the surface of the comparative electrode C4*.

The data relating to each of the electrodes C1 to C15 and C1* to C4* are given in tables 1 and 2 below. The values of the electronic and ionic conductivities of the coating materials, measured according to the protocols defined above, are also reported there as well as the values of the parameters A1 and A2, calculated for each electrode by applying the formulas given above.

The percentages are given by mass relative to the total mass of the electrode materials.

* percentage of carbon in the mixture without taking into account the solid electrolyte introduced into the pores

* percentage of carbon in the mixture without taking into account the solid electrolyte introduced into the pores

3- Realization of the accumulator

In a pellet mold with a diameter of 7 mm containing an electrode washer prepared under the conditions described above, 50 mg of sulphide electrolyte of composition (Li ₃ PS ₄ ) _0.8 (LiI) _0.2 are added to produce the electrolytic layer making it possible to ensure the electronic insulation between the 2 electrodes. The assembly is then compressed to 5t/cm².

After demoulding, a lithium pellet with a diameter of 6mm and a thickness of 100µm is placed on the electrolytic layer and compressed to around 50 bar.

The assembly is then placed in a sealed electrochemical cell allowing the electrical connection with the 2 electrodes, while maintaining a mechanical pressure of approximately 50 bar.

4- Evaluation of electrode performance

The mass of mixture in mg for making the electrode is equal to the desired surface capacity in mAh/cm² multiplied by the surface of the electrode and divided by 150 mAh/g.

Each of the cells is then charged at C/10 up to a voltage of 4.3V if the electrode tested is a positive electrode or 0V if it is a negative electrode. The discharge is carried out at a rate of 1C down to a voltage of 2.5V or 1V depending on whether it is a positive or negative electrode respectively.

The voltage difference at 1C related to the surface coating is measured. It corresponds to the voltage difference during discharge at 1C at low depth of discharge (for example after 10min) between the treated and untreated electrode and makes it possible to measure the impact of the coating layer on the performance of the electrode. This value is expressed in V.

After the discharge at 1C, the cell is then recharged at C/10 at a temperature of 60°C then maintained at 4.3V or 0.05V depending on whether it is respectively a positive or negative electrode. The "electrolyte decomposition current", corresponding to the absolute value of the oxidation or reduction current of the electrolyte depending on whether it is respectively a positive or negative electrode, is measured after a period of 50h charge. It is expressed in µA per cm² of electrode.

5- Results

The results obtained are given in Table 3 below.

Voltage difference at 1C (V) Electrolyte decomposition current (μA/cm²) Electrodes according to the invention C1 < 0.01 2.3 C2 < 0.01 1.9 C3 < 0.01 0.6 C4 < 0.01 0.2 C5 < 0.01 4.3 C6 < 0.01 1.9 C7 < 0.01 1.1 C8 < 0.01 1.0 C9 < 0.01 0.9 C10 < 0.01 1.5 C11 < 0.01 1.5 C12 < 0.01 0.9 C13 < 0.01 2.0 C14 < 0.01 0.5 C15 0.144 5.2 Comparative electrodes C1* < 0.01 > 50 C2* > 2 < 0.1 C3* < 0.01 > 50 C4* < 0.01 > 50

It is thus observed that the electrodes according to the invention C1 to C15 for which A1<4 and A2>10 have:
- a voltage difference at 1C of less than 0.15V, and
- an electrolyte decomposition current is less than 10 µA/cm².

The low voltage difference at 1C reflects the fact that the electrochemical performance of the electrode is almost unaffected by the presence of the coating layer.

The low decomposition current demonstrates that the electrolyte is stable: it does not react with the materials of the electrodes.

For the comparative electrodes C1* and C4*, free of coating layer, the decomposition current of the electrolyte is greater than 50µA/cm²: the electrolyte and the materials react with each other.

In the context of the comparative electrode C2* for which A1=18.7, a voltage difference at 1C greater than 2V is observed. This high voltage difference reflects a significant alteration of the electrochemical properties of the electrode by the LiLaO ₂ coating layer.

In the context of the comparative electrode C3* for which A2 = - 3.5, it can be seen that the decomposition current of the electrolyte is greater than 50 µA/cm². The presence of the LLZO coating layer does not prevent reactions between the electrolyte and the materials of the electrode.

Claims (13)

Electrode usable in an energy storage device comprising at least one active material and at least one carbon electronic material, said electrode being covered, over all or part of its surface, with a coating layer of an electronic insulating and conductive material ion, said electrode being such that A1 < 6 and A2 > 10,
with :


Or :
e represents the thickness of the coating layer (in m),
i represents the ionic conductivity of the electronic insulating material and ionic conductor (in Sm ^-1 ),
S(mat. act) represents the ratio of the surface developed by the active material to the total surface of the electrode (in m² of active material per cm² of electrode),
e represents the electronic conductivity of the electronic insulating material and ionic conductor (in Sm ^-1 ), and
S(cond.) represents the ratio of the surface of active material and of carbonaceous electronic material to the total surface of the electrode (in m ² per cm ² of electrode). Electrode according to Claim 1, in which the electronic insulating and ionically conducting material has an electronic conductivity of less than or equal to 10 ^{- 10} Sm ^-1 , preferably less than or equal to 10 ^{- 12} Sm ^-1 . Electrode according to either of Claims 1 and 2, in which the electronic insulating and ionic conductive material has an ionic conductivity greater than or equal to 10 ^-8 Sm ^-1 , preferably greater than or equal to 10 ^-6 Sm ^-1 . Electrode according to any one of the preceding claims, in which the electronic insulating and ionically conducting material is chosen from halides, oxides, phosphates, sulphides, polymers and any one of their mixtures. Electrode according to any one of the preceding claims, in which the thickness of the coating layer ranges from 2 to 50 nm, preferably from 5 to 10 nm Electrode according to any one of the preceding claims, in which the coating layer covers at least 50% of the surface of the electrode, preferably at least 75%, more preferably at least 90%, even more preferably at least 95% . An electrode according to any preceding claim, wherein the electrode is porous and at least a portion of the pores of the electrode is at least partially filled with a solid electrolyte material, preferably a solid sulfur electrolyte material. Method of manufacturing an electrode according to any one of claims 1 to 7 comprising:
a) the provision of an electrode,
b) the deposition on all or part of the surface of the electrode of a coating layer as defined in any one of claims 1 to 6,
c) optionally, the deposition by infiltration in at least part of the pores of the coating layer of a solid electrolytic material, preferably of a solid sulfur-containing electrolytic material, and
d) optionally, a treatment allowing the solidification of the electrolyte, in particular by heat treatment or by ultraviolet radiation. Electrochemical element comprising a stack between two electronically conductive current collectors, said stack comprising:
- a positive electrode;
- a negative electrode;
- a layer comprising a solid electrolytic composition separating said positive electrode and said negative electrode, the electrolytic composition comprising at least one solid electrolytic compound, preferably chosen from solid sulfur-containing electrolytic compounds and polymers;
said element being characterized in that at least one of said positive electrode and of said negative electrode is as defined in any one of claims 1 to 7. Element according to Claim 9, in which both the said positive electrode and the said negative electrode are covered, over all or part of their surface, with a coating layer, identical or different, as defined in any one of the claims 1 to 6. Method of manufacturing an element according to one of claims 9 and 10 comprising:
i) the provision of a positive electrode and a negative electrode, at least one of said positive electrode and said negative electrode being as defined in any one of claims 1 to 7 or having been obtained by carrying out a method according to claim 8, and
ii) the formation, between said positive electrode and said negative electrode, of a layer comprising a solid electrolytic composition. Electrochemical module comprising the stack of at least two elements according to any one of claims 9 and 10, each element being electrically connected with one or more other element(s). Battery comprising one or more modules according to claim 12.