Electrochemical element for all-solid-state batteries comprising a negative electrode made of silicon

Abstract

Electrochemical element for all-solid-state batteries comprising a negative electrode comprising silicon. The present invention relates to an all-solid-state electrochemical element comprising a positive electrode, a negative electrode, and a layer of solid sulfide electrolyte. The negative electrode comprises a layer of negative electrode material comprising particles of a solid sulfide electrolyte ES1 having a median diameter Dv50 ES1 and particles comprising silicon having a median diameter Dv50 Si in a ratio Dv50 ES1 / Dv50 Si which is in the range of 1.6 to 2.5. Figure for abstract: none

Description

Title of the invention: Electrochemical element for all-solid-state batteries comprising a negative electrode comprising silicon. Technical field

[0001] The present invention relates to the field of energy storage, more specifically to all-solid-state lithium batteries. More particularly, the present invention relates to an all-solid-state electrochemical element comprising a silicon negative electrode whose configuration enhances the electrochemical performance of the batteries. STATE OF THE ART

[0002] The operation of lithium batteries is based on the reversible exchange of lithium ions between a positive electrode and a negative electrode, separated by a separator containing an electrolyte, with lithium being stored at the negative electrode during charging operation.

[0003] In order to increase the energy densities of lithium batteries, it has been proposed to use negative electrodes comprising silicon, silicon having a capacity 10 times greater than that of graphite commonly used in lithium-ion (Li-ion) batteries.

[0004] All-solid-state batteries are a promising next step in Li-ion technology in terms of safety and energy density. All-solid-state technology is based on replacing the liquid electrolyte with a non-flammable and more thermally stable solid electrolyte. All-solid-state technology therefore offers increased safety. The solid electrolyte can, in particular, be a sulfide electrolyte.

[0005] However, technological challenges still need to be overcome due to the solid nature of the battery components. One of these is ensuring a continuous interface between the negative / positive electrodes and the solid electrolyte layer (SEL) to allow for good diffusion of lithium ions and maintain good electrochemical performance (e.g., cycle life). Ensuring a continuous interface is even more difficult when using silicon-based negative electrodes. Indeed, the intercalation / deintercalation of lithium within silicon is accompanied by a significant volumetric expansion of the latter, on the order of 300%. This significant volumetric expansion will lead to the degradation of the electrochemical elements. On the one hand, a degradation of the integrity of the negative electrode can be observed, leading to a decrease in its lifespan.On the other hand, a fracture at the interface between the electrolyte and the electrodes. can be observed with a loss of contact and possible degradation at the contact points between the silicon particles and the sulfide electrolyte.

[0006] Thus, a need remains for the provision of a solution enabling the increase of the electrochemical performance (e.g. cycle life) of Li-ion negative electrode batteries comprising silicon, in particular by enabling the increase of the stability of the electrode-electrolyte interface, but also the stability between the silicon particles and the sulfide electrolyte within the negative electrode, in order to ensure continuous diffusion of lithium between the negative electrode and the SEL and a reduction of contact problems during charging / discharging at the electrode-electrolyte interface. Summary of the invention

[0007] The present invention relates to an all-solid type electrochemical element comprising a positive electrode, a negative electrode and a layer of solid sulfide electrolyte comprising particles of a sulfide electrolyte ES 0 separating the positive electrode and the negative electrode,

[0008] wherein the negative electrode comprises a current collector and a layer of negative electrode material applied to at least one face of the collector, said at least one face facing the solid sulfide electrolyte layer,

[0009] wherein the negative electrode material layer comprises at least: - particles of a solid sulfide electrolyte ES i and having a median diameter Dv50 ES i, - particles comprising silicon and having a median diameter Dv50 Si, - a binder, and - possibly an electronically conductive carbon additive;

[0010] characterized in that the ratio Dv50 ES i / Dv50 Si is within a range of 1.6 to 2.5, preferably from 1.8 to 2.2, the median diameters being determined by laser diffraction particle size analysis.

[0011] The present invention also relates to a method for preparing an all-solid type electrochemical element according to the invention comprising the following steps:

[0012] a. preparation of a negative electrode by applying to at least one face of a current collector a layer of negative electrode material comprising at least: • particles of a solid sulfide electrolyte ES i and having a median diameter Dv50 ES i, • particles comprising silicon and having a median diameter Dv50 Si, • a binder, and • possibly an electronically conductive carbon additive,

[0013] the ratio Dv50 ES i / Dv50 S i being within a range of 1.6 to 2.5, preferably from 1.8 to 2.2, the median diameters being determined by laser diffraction particle size analysis; and

[0014] b. Either superposition of the negative electrode, the solid electrolyte layer and the positive electrode to give an electrochemical element of the all-solid type;

[0015] c. Either coating of a layer of solid electrolyte on the negative electrode and / or the positive electrode and superposition of the negative electrode and the positive electrode to give an electrochemical element of the all-solid type.

[0016] Finally, the invention relates to the use of an electrochemical element according to the invention to maintain a capacity retention of at least 80% after at least 150 charge / discharge cycles.

[0017] Other aspects of the invention are as described below. FIGURES

[0018] [Fig.1] Fig.1 schematically represents an all-solid electrochemical element according to the present invention.

[0019] [Fig.2] Fig.2 represents an evaluation of the cycling performance of a negative electrode according to the invention and of a negative electrode outside the invention.

[0020] [Fig.3] Fig.3 schematically represents the interface between the SEL and the negative electrode of an electrochemical element according to a particular embodiment of the invention (the solid sulfide electrolyte particles ES o have a median diameter Dv50 ES 0 such that the ratio Dv50E S o / Dv5OSi is within a range of 0.5 to 1.5).

[0021] [Fig. 4] Figure 4 shows an evaluation of the cycling performance of a negative electrode according to the invention and of a negative electrode not included in the invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The inventors discovered that by appropriately choosing the particle sizes of the solid sulfide electrolyte and the silicon-compounding particles of the negative electrode of an electrochemical element, it could be taken advantage of the swelling of the silicon to form a continuous interface between the SEL and the negative electrode and thus meet the above-expressed need.

[0023] Thus, the present invention relates to an all-solid type electrochemical element comprising a positive electrode, a negative electrode, and a layer of solid sulfide electrolyte comprising particles of an ES0 sulfide electrolyte separating the positive and negative electrodes. The negative electrode comprises a current collector and a layer of negative electrode material applied to at least the face of the collector facing the solid sulfide electrolyte layer. The negative electrode material layer comprises at least: - particles of a solid sulfide electrolyte ES i having a median diameter Dv50 ES i, - particles comprising silicon and having a median diameter Dv50 Si, - a binder, and - possibly an electronically conductive carbon additive.

[0024] The ratio Dv50 ES i / Dv50 S i is in the range of 1.6 to 2.5, preferably in the range of 1.8 to 2.2.

[0025] The median diameter “Dv50” designates the diameter for which 50% by volume of the particles have an equivalent diameter less than or equal to the value considered, and 50% by volume of the particles have an equivalent diameter greater than the value considered. The expression “equivalent diameter” designates the diameter of a sphere having the same volume as this particle. The measurement / determination of the median diameters is carried out by laser diffraction particle size analysis. More specifically, the diameters can be measured using a Malvern Mastersizer 2000 particle size analyzer employing a laser diffraction technique; the samples are dispersed in a solvent.

[0026] The expression "electrochemical element" refers to an elementary electrochemical cell consisting of the assembly positive electrode / solid electrolyte layer (SEL) / negative electrode, allowing the electrical energy supplied by a chemical reaction to be stored and released in the form of current.

[0027] The various components of the electrochemical element of the present invention are as described below. Negative electrode

[0028] The term "negative electrode" refers, when the battery is discharging, to the electrode functioning as the anode, the anode being defined as the electrode where an electrochemical oxidation reaction (electron emission) takes place. The term "negative electrode" also refers to the electrode from which the electrons are released and from which the cations (Li+) are released during discharge.

[0029] The negative electrode comprises a current collector and a layer of negative electrode material.

[0030] The term "current collector" commonly refers to an element such as a pad, plate, sheet or other, of 2D or 3D structure, made of conductive material (also referred to as "conductive support"), connected to an electrode (positive or negative), ensuring the conduction of the flow of electrons between the electrode and the terminals of the battery.

[0031] The nature of the current collectors suitable for the invention is not limited. Current collectors conventionally used for the negative electrodes of lithium electrochemical elements can thus be considered.

[0032] The current collector is preferably a two-dimensional conductive support such as a solid or perforated metal strip, for example copper, nickel, steel, stainless steel or aluminum. The conductive support may be made of a copper-based alloy, aluminum or an aluminum-based alloy, stainless steel.

[0033] The current collector at the negative electrode is generally in the form of a copper strip.

[0034] The current collector is coated with a layer of negative electrode material. The layer of negative electrode material is applied at least to the face of the current collector facing the SEL. In some embodiments, the layer of negative electrode material may be applied to both faces of the current collector.

[0035] The negative electrode material layer comprises at least: - particles of a solid sulfide electrolyte ES i having a median diameter Dv50 ES i, - particles comprising silicon and having a median diameter Dv50 Si as active material, - a binder, and - possibly an electronically conductive carbon additive.

[0036] In some embodiments, the negative electrode material layer consists of the components mentioned above.

[0037] The expression "solid sulfide electrolyte" refers to solid sulfur-based electrolytes typically used for the manufacture of all-solid-state batteries.

[0038] The chemical nature of the suitable solid sulfide electrolytes for the invention is not limited. Compounds commonly used as solid electrolytes may be used. Thus, suitable solid electrolytes include sulfur compounds alone or in mixtures with other constituents. More specifically, oxide-type electrolytes, partially or completely crystalline sulfides, and amorphous sulfides may be used.

[0039] Illustrative examples of sulfide electrolytes are described by Park, K. h. et al (2018), Design Strategies, Practical Considerations, and New Solution Processes of Sulfie Solid Electrolytes for All-Solid-State Batteries. Advanced Energy Materials, 1800035.

[0040] For example, the solid sulfide electrolyte ES i can be selected from sulfides of composition A Li2S - B P2S5 (with 0 <A<l ,0<B<l et A+B = 1) et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI, Li2O, SiS2, GeS2, SnS2, ZnS, Li3PO4...) ; les sulfures de structure argyrodite ; ou les sulfures ayant une structure cristallographique similaire au composé LGPS (Lii0GeP2Si2), et leurs dérivés.

[0041] The solid sulfide electrolyte ES i can in particular be chosen from:

[0042] - Li3PS4

[0043] - the set of phases [(Li2S)y (Li2O)t(P2S5)i_y_t](i_z)(LiX)z, with X representing one or several halogen elements and 0 <y<l; 0<z<l; 0<t< 1 ;

[0044] - compounds having an argyrodite structure such as Li6PS5X, with X representing Cl, Br or I, or Li7P3Sn;

[0045] - sulfide electrolytes having the equivalent crystallographic structure of LiioGeP2Si2 compound including for example substitutions, dopings and / or vacancies;

[0046] - the phases [(Li2S)y(P2S5)iy](iz)(LiX)z(with X chosen from among the halogens; 0 <y<l; 0 <z<l),

[0047] - (Li3PS4)o.8(LiI)o.2.

[0048] Preferably, the solid sulfide electrolyte ES i is a Li6PS5X type electrolyte with X representing Cl, Br or I, or a mixture thereof.

[0049] Particles comprising silicon may be particles made of silicon, that is to say particles comprising exclusively silicon (Si), or be silicon-carbon composite particles (Si-C) or even silicon oxide particles SiOx where 0 <x<2.

[0050] The silicon-containing particles useful in the context of the present invention have a median diameter Dv50 Si such that the ratio between the median diameter of the particles of the solid sulfide electrolyte ES i and the median diameter of the silicon-containing particles (Dv50 ES i / Dv50 Si) is in the range of 1.6 to 2.5. The ratio Dv50 ES i / Dv50 Si is preferably in the range of 1.8 to 2.2. It has been found that when the ratio Dv50 ES i / Dv50 Si is in such ranges, the negative electrodes exhibit better cycleability (see [Fig. 2]). It is understood that the median diameter of the silicon-containing particles is measured in the initial state, i.e., uncharged.

[0051] In some embodiments, the median diameter Dv50 Si of the particles comprising silicon is in the range of 1 to 10 pm, preferably 2 to 5 pm.

[0052] The negative electrode material layer includes a binder. It is understood that this layer may include a mixture of binders.

[0053] The term “binder” refers to the agents that give the composition and / or the electrode the cohesion of the different components and its mechanical strength and its adhesion to the current collector. Examples of binders include polymers such as polyvinylidene fluoride (PVDF) and its copolymers (e.g., polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP)), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl) or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formyl), polyester, polyether block amides, acrylic acid polymers, methacrylic acid polymers, acrylamide polymers, itaconic acid polymers, sulfonic acid polymers, elastomers (e.g., poly(styrene / butadiene) (SBR) and hydrogenated butadiene-acetonitrile copolymers (HNBR)), and cellulosic compounds (e.g., carboxymethyl cellulose (CMC)).

[0054] The negative electrode material layer may include an electronically conductive carbon additive. This carbon additive is typically distributed within the electrode so as to form an electronically percolating network between the silicon and the current collector. The carbon additive is generally selected from graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes, carbon fibers, such as vapor-deposited carbon fibers (VGCF), or a mixture thereof.

[0055] The negative electrode material layer generally comprises: - from 5 to 60%, preferably from 25 to 50%, preferably from 40 to 50% by weight of particles of a solid sulfide electrolyte ES i, - from 40 to 94.5%, preferably from 40 to 70%, by weight of particles comprising silicon, - 0.5 to 10%, preferably 1 to 8%, by weight of a binder, and - possibly from 0.1 to 5%, preferably from 0.1 to 4%, by weight of one or several carbon-based additive(s) with electronic conductivity,

[0056] the % by weight being expressed in relation to the total weight of the negative electrode material layer.

[0057] Before the current collector is coated with the negative electrode material layer, it can be coated, on one or both of its faces, with a coating designed to improve the electronic conductivity between the negative electrode material layer and the conductive support. The coating material can be selected from the group consisting of amorphous carbon, graphite, carbon fibers, carbon nanotubes, and mixtures thereof.

[0058] The negative electrode generally has a thickness in the range of 10 to 60 µm, preferably 10 to 40 µm. The thickness of the negative electrode can be measured, before assembly of the electrochemical element, by means of a Palmer-type thickness gauge (or precision measuring instrument). After assembly of the electrochemical element, the thickness of the negative electrode can be measured by scanning electron microscopy (SEM). Solid sulfide electrolyte layer (SEL)

[0059] The chemical nature of the suitable solid sulfide electrolytes ES O for the SEL is not limited. Thus, the solid sulfide electrolytes previously described in connection with the negative electrode can be used. For example, the solid sulfide electrolyte ES o can be selected from sulfides of composition A Li2S - B P2S5 (with 0 <A<l ,0<B<l et A+B = 1) et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI,...) ; les sulfures de structure argyrodite ; ou les sulfures ayant une structure cristallographique similaire au composé LGPS (Lii0GeP2Si2), et leurs dérivés.

[0060] The solid sulfide electrolyte ES of the SEL may be of the same chemical nature as the solid sulfide electrolyte ES i of the negative electrode or may be of a different chemical nature. In other words, the chemical formulas of the solid sulfide electrolyte ES o and ES i may be identical or different.

[0061] The median diameter Dv50 ES 0 of the particles of the solid sulfide electrolyte ES ode la SEL may be equal to that of the particles of the solid sulfide electrolyte ES i of the negative electrode, or may be different, either smaller or larger. In all these embodiments, the solid sulfide electrolyte ES ode la SEL may be of the same chemical nature as the solid sulfide electrolyte ES i of the negative electrode or be of a different chemical nature. Thus, the sulfide electrolytes ES i and ES can be selected, independently of each other, from the group consisting of sulfides of composition A Li2S - B P2S5 with 0 <A<l ,0<B<l et A +B = 1 et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI,...) ; les sulfures de structure argyrodite ; les sulfures ayant une structure cristallographique similaire.

[0062] In certain embodiments, the SEL comprises, or is made up of, solid sulfide electrolyte particles ES₀ having a median diameter Dv₅₀ ES₀ such that the ratio Dv₅₀ ES₀ / Dv₅₀Si is within a range of 0.5 to 1.5, preferably from 0.8 to 1. The ratio Dv₅₀ ES₀ / Dv₅₀Si may, in particular, be equal to 1. It has been shown that such embodiments exhibit improved cycle life (see [Fig. 4]). In these embodiments, the solid sulfide electrolyte ES₀ of the SEL and the solid sulfide electrolyte ES₀ of the negative electrode may be of the same chemical nature or of different chemical natures.

[0063] In addition to the solid sulfide electrolyte particles ES 0, the SEL may include particles of a solid sulfide electrolyte ES 2. The solid sulfide electrolyte particles ES 0 differ from the particles of a solid sulfide electrolyte ES 2 by the chemical nature of the sulfide electrolyte or by their size. In certain modes In this embodiment, the solid sulfide electrolyte particles ES0 differ from the solid sulfide electrolyte particles ES2 by the chemical nature of the sulfide electrolyte. In some embodiments, the median diameters Dv50 ES0 and Dv50 ES2 of the solid sulfide electrolyte particles ES0 and ES2 are different. In such embodiments, the sulfide electrolyte particles ES0 constitute a first particle population and the sulfide electrolyte particles ES2 constitute a second particle population. A solid electrolyte solution (SEL) whose solid sulfide electrolyte particles exhibit such a bimodal particle size distribution can be as described in French patent application No. FR2401440. The solid sulfide electrolyte ES0 may be of the same chemical nature as the solid sulfide electrolyte ES2 or of a different chemical nature.

[0064] The solid sulfide electrolytes ES 0 and ES 2 may be of a different chemical nature than the solid sulfide electrolyte ES i, may both be of the same chemical nature as the solid sulfide electrolyte ES i, or only one of them may be of the same chemical nature as the solid sulfide electrolyte ES L. Thus, the sulfide electrolytes ES 0, ES 1, and ES 2 may be independently selected from the group consisting of sulfides of composition A Li2S - B P2S5 with 0 <A<l ,0<B<l et A+B = 1 et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI,...) ; les sulfures de structure argyrodite ; les sulfures ayant une structure cristallographique similaire au composé LGPS (Lii0GeP2Si2), et leurs dérivés.In some embodiments, one of the populations of solid sulfide electrolyte particles (ES O or ES 2) has a median diameter Dv50 (Dv50 ES 0 or Dv50 ES 2 ) such that the ratio median diameter Dv50 (Dv50 ES 0 or Dv50 ES 2 ) / Dv50 Si is within a range of 0.5 to 1.5, preferably from 0.8 to 1. The ratio may in particular be equal to 1. .

[0065] The SEL generally has a thickness ranging from 5 to 250 µm. The thickness of the SEL can be measured by the same methods as those described for measuring the thickness of the negative electrode.

[0066] In certain embodiments, the SEL comprises, or is made up of, sulfide electrolyte particles ES0 and the sulfide electrolytes ES0 and ES1 are of the same chemical nature, preferably they are selected from the group consisting of sulfides of composition A Li2S - B P2S5 with 0 <A<l ,0<B<l et A+B = 1 et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI,...) ; les sulfures de structure argyrodite ; les sulfures ayant une structure cristallographique similaire au composé LGPS (LiioGeP 2Si2), et leurs dérivés. Dans ces modes de réalisation, les particules comprenant du silicium peuvent être des particules constituées de silicium.

[0067] In certain embodiments, the SEL comprises, or is made up of, sulfide electrolyte particles ES0, and the sulfide electrolytes ES0 and ES1 are of the same chemical nature and are of the type Li6PS5X, with X representing Cl, Br, or I, or a mixture thereof. In these embodiments, the particles comprising silicon may be particles made of silicon. Positive electrode

[0068] The term "positive electrode" refers to the electrode where electrons enter, and where discharged cations (Li+) arrive.

[0069] Within the framework of the present invention, the positive electrode can be of any known type used in Li-ion batteries.

[0070] The positive electrode generally consists of a conductive support used as a current collector which is coated on at least one of its faces with a positive electrode formulation, which typically contains at least one positive electrode active material, solid electrolyte particles as previously described, and an electronically conductive carbon additive.

[0071] Typically the positive electrode also includes a binder, such as those previously mentioned for the negative electrode.

[0072] The active material of the positive electrode is not particularly limited by the present invention. Thus, it can be: - a lithium oxide of at least one transition metal chosen from: i. a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMnyCozMt)O2(NMC) where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; ii. a lithium oxide of nickel, cobalt and aluminium of formula Liw(NixCoyAlzMt)O2(NCA) where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ; iii. a compound of formula Lii+xMi xO2 yFy with cubic crystal structure where 0 <x<0,5 et 0<y<l et M représente un élément choisi dans le groupe constitué de 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 et Sm et des mélanges de ceux-ci ; iv. a lithium nickel manganese oxide (NMX) of formula Lia(Nii.xyzMnxCoyMz)O2 with 0.9 <a<l,l ; 0,60<l-x-y-z<0,80 ; 0<x ; 0<y<0,02 ; 0<z ; et M étant choisi dans le groupe consistant en Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ga, Ta, Nd, Pr, La and mixtures thereof; and v. a lithium oxide of nickel and manganese with the formula Liw(NixMnyCozMt)O2 where 1.1 <w<1,6 ; 0<x ; 0,50<y<0,80 ; 0<z<0,02 ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci ;

[0073] or - a lithium phosphate of at least one transition metal chosen from:

[0074] a) a lithium iron phosphate of formula LixFei yMyPO4 (LFP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Mn, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ;

[0075] b) a lithium manganese phosphate of formula LixMni yMyPO4 (LMP), where 0.8 <x<l,2 ; 0<y<0,6 et M est choisi dans le groupe consistant en Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Fe, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ;

[0076] c) a lithium manganese and iron phosphate of formula: LixMni y zFeyMzPO4 (LMFP) where 0.8 <x<l,2 ; 0,5<l-y-z<l; 0<y+z<0,5 ; 0<y<0,50 et 0<z<0,2 et M est choisi dans le groupe constitué de Al, B, Mg, K, Si, Ca, Ti, V, Cr, Co, Cu, Ni, Zn, Y, Zr, Nb, W, Pb, Mo, S et des mélanges de ceux-ci ; et

[0077] d) a lithium vanadium fluorophosphate of formula iv) Lii+XVPO4F (LVPF) where 0 <x<0,15, ou à un de ses dérivés de formule Lii+xVi yMyPO4Fz (LVMPF) où0<x<0,15, 0<y<0,5, 0,8<z<l,2 et M est choisi dans le groupe consistant en Ti, Al, Y, Cr, Cu, Mg, Mn, Fe, Co, Ni, et Zr ;

[0078] or - a mixture of compounds a) to d) and i) to v).

[0079] In certain embodiments, the active material of the positive electrode is a lithium oxide of nickel, manganese and cobalt of formula Liw(NixMnyCozMt)O2(NMC) where 0.9 <w<l,l ; 0<x ; 0<y ; 0<z ; 0<t ; M étant choisi dans le groupe constitué de Al, B, Mg, Si, Ca, Ti, V, Cr, Fe, Cu, Zn, Y, Zr, Nb, W, Mo, S, Sr, Ce, Ta, Ga, Nd, Pr, La et des mélanges de ceux-ci.

[0080] The electronically conductive carbon additive for the positive electrode is generally selected from graphite, carbon black, acetylene black, soot, graphene, carbon nanotubes, carbon fibers, such as vapor-deposited carbon fibers (VGCF), or a mixture thereof.

[0081] The nature of the current collector is not limited. Current collectors conventionally used for the positive electrodes of lithium electrochemical elements can thus be considered. The current collector of the positive electrode layer is typically made of aluminum.

[0082] The current collector of the positive electrode can also be coated, on one or both of its faces, with a coating designed to improve the electronic conductivity between the layer of positive electrode material and the conductive support. The coating material can be selected from the group consisting of amorphous carbon, graphite, carbon fibers, carbon nanotubes, and mixtures thereof.

[0083] The positive electrode generally has a thickness in the range of 10 to 200 µm, preferably 40 to 150 µm. The thickness of the positive electrode can be measured by the same methods as those described for measuring the thickness of the negative electrode.

[0084] In certain embodiments, the electrochemical element of the present invention is such that:

[0085] - the solid electrolyte layer has a thickness ranging from 5 to 250 pm, and / or

[0086] - the negative electrode has a thickness ranging from 20 to 60 pm, and / or

[0087] - the positive electrode has a thickness ranging from 100 to 200 pm.

[0088] A schematic representation of an electrochemical element according to the present invention is shown in [Fig. 1]. The electrochemical element (1) comprises: - a positive electrode (2) comprising a current collector (3) and a positive electrode formulation (4); - a layer of solid electrolyte (SEL) (5); - a negative electrode (6) comprising a current collector (7) and a layer of negative electrode material (8).

[0089] The negative electrode material layer (8) shown in [Fig. 1] comprises: - particles (9) of a solid sulfide electrolyte ES i having a median diameter Dv50 ES i, - particles (10) comprising silicon and having a median diameter Dv50 Si, - a binder (11), and - an electronically conductive carbon additive (12).

[0090] The electrochemical element is suitable for energy storage, particularly in mobile, stationary (for the storage of renewable energies for example), space or aeronautical devices.

[0091] The electrochemical element can be prepared by any suitable process known to a person skilled in the art. In particular, the electrochemical element can be prepared by a process comprising the following steps:

[0092] a. preparation of a negative electrode by applying to at least one face of a current collector a layer of negative electrode material comprising at least: • particles of a solid sulfide electrolyte ES i having a median diameter Dv50 ES i, • particles comprising silicon and having a median diameter Dv50 Si, • a binder, and • possibly an electronically conductive carbon additive,

[0093] the ratio Dv50 ES i / Dv50 S i is within a range of 1.6 to 2.5, preferably from 1.8 to 2.2, the median diameters being measured by laser diffraction particle size analysis;

[0094] b. superposition of the negative electrode, the solid electrolyte layer and the positive electrode to give an all-solid type electrochemical element.

[0095] In this embodiment, the negative electrode, the solid electrolyte layer and the positive electrode are prepared separately and then assembled.

[0096] Alternatively, the process for preparing an electrochemical element according to the invention may comprise the following steps: a. preparation of a negative electrode as previously described; b. coating of a layer of solid electrolyte on the negative electrode and / or the positive electrode; c. superposition of the negative and positive electrodes to give an electrochemical element of the all-solid type.

[0097] The present invention also relates to an electrochemical module comprising the stacking of at least two electrochemical elements according to the invention, each electrochemical element being electrically connected with one or more other element(s).

[0098] The term “module” therefore refers here to the assembly of several electrochemical elements, the assemblies being able to be in series and / or parallel.

[0099] The present invention also relates to an accumulator or battery comprising one or more modules according to the invention.

[0100] The term “battery” refers to the assembly of one or more modules according to the invention. EXAMPLES Example 1

[0101] Negative electrodes were prepared in a glove box under an inert atmosphere. The negative electrodes contain silicon particles as the active material, a solid sulfide electrolyte of the argyrodite (ES) type, an electronically conductive carbon additive, and a binder.

[0102] Two different particle sizes for the ES of the negative electrode (ES i) were tested: - ES whose particles have a median diameter Dv50 of 4 pm; - ES whose particles have a median diameter Dv50 of 7 pm.

[0103] Silicon particles have a median diameter Dv50 of 4 pm.

[0104] The behavior of the prepared negative electrodes was evaluated in a half-cell configuration with a Li-In counter electrode.

[0105] The solid electrolyte layer (SEL), separating the negative electrode and the counter electrode, is made with the same sulfide electrolyte (ES 0) as that of the negative electrode.

[0106] The following two configurations were evaluated:

[0107] [Tables] Configuration 1 Configuration 2 Negative electrode ES i: ES Dv50=7 pm If Dv50= 4 pm ES i: ES Dv50=4 pm If Dv50 = 4 pm SEL ES o: ES Dv50=7 pm ES o: ES Dv50=4 pm

[0108] The cycling performance of the half-cells was evaluated. The results of the performance tests are shown in [Fig. 2] (circle: negative electrode with configuration 1; diamond: negative electrode with configuration 2). For each test, at least 3 experiments were carried out to ensure reproducibility.

[0109] The results show that the half-cell with configuration 1 achieves a capacity close to the theoretical capacity of silicon (3580 mAh / g Si). The half-cell with configuration 2, on the other hand, achieves a capacity of only 2700 mAh / g Si, or 25% less than configuration 1.

[0110] The results also show that a negative electrode with configuration 1 (difference in particle size within the negative electrode) has better cyclability with a capacity retention of 70% after 100 cycles versus 30% when the negative electrode has configuration 2 (no difference in particle size within the negative electrode). Example 2

[0111] Negative electrodes were prepared in a glove box under an inert atmosphere. The negative electrodes contain silicon particles as the active material, a solid sulfide electrolyte of the argyrodite (ES) type, an electronically conductive carbon additive, and a binder.

[0112] The following ES (ES i) is used in the negative electrode: - ES whose particles have a median diameter Dv50 of 7 pm.

[0113] Silicon particles have a median diameter Dv50 of 4 pm.

[0114] The negative electrode therefore has the structure of configuration 1 of example 1.

[0115] The behavior of the prepared negative electrodes was evaluated in a complete cell configuration with a positive electrode comprising, as active material, a lithium oxide of nickel, manganese and cobalt (NMC).

[0116] The solid electrolyte layer (SEL), separating the negative electrode and the positive electrode, is made with a sulfide electrolyte of the same nature as the ES of the negative electrode.

[0117] Two different particle sizes for the ES of the SEL (ES 0) were tested: - ES whose particles have a median diameter Dv50 of 4 pm; - ES whose particles have a median diameter Dv50 of 7 pm.

[0118] Thus, the following two configurations were evaluated:

[0119] [Tables2] Configuration 3 Configuration 4 Negative electrode ES x: ES Dv50=7 pm If Dv50= 4 pm ES x: ES Dv50= 7 pm If Dv50 = 4 pm SEL ES o: ES Dv50= 7 pm ES o: ES Dv50= 4 pm

[0120] A schematic illustration of the interface between the SEL and the negative electrode of an electrochemical element according to configuration 4 is shown in [Fig.3] (sulfide electrolyte particles (13) of the SEL (5); negative electrode (6); solid sulfide electrolyte particles (9) of the negative electrode (6); particles comprising silicon (10); binder (11); electronically conductive carbon additive (12)).

[0121] The cycling performance of the cells was evaluated. The results of the performance tests are shown in [Fig. 4] (circle: configuration 3; diamond: configuration 4). For each test, at least 3 experiments were carried out to ensure reproducibility.

[0122] The results show that the cell with configuration 4 exhibits better cycle life with a capacity retention of 95% after 150 cycles. The cell with configuration 3 exhibits a rapidly declining capacity, reaching approximately 70% capacity retention after 140 cycles.

[0123] As shown in [Fig. 3], during charging (transition from the initial state to the charged state), the silicon particles (10) swell. Contact between the silicon particles (10) of the negative electrode and the sulfide electrolyte particles (13) of the SEL (5) is particularly favored when the silicon particles (10) have a median diameter close to or even equal to the median diameter of the sulfide electrolyte (13) of the SEL (5). The interface between the negative electrode and the SEL is of higher quality (better continuity), offering better reproducibility of the charge / discharge cycles.

Claims

Demands

1. An all-solid type electrochemical element comprising a positive electrode, a negative electrode and a layer of solid sulfide electrolyte comprising particles of a sulfide electrolyte ES 0 separating the positive electrode and the negative electrode, wherein the negative electrode comprises a current collector and a layer of negative electrode material applied to at least one face of the collector, said at least one face facing the layer of solid sulfide electrolyte, wherein the active material composition layer comprises at least: - particles of a solid sulfide electrolyte ES i and having a median diameter Dv50 ES i, - particles comprising silicon and having a median diameter Dv50 Si, - a binder, and - optionally an electronically conductive carbon additive;characterized in that the ratio Dv50 ES i / Dv50 S i is within a range of 1.6 to 2.5, preferably from 1.8 to 2.2, the median diameters being determined by laser diffraction particle size analysis.;

2. Electrochemical element according to claim 1 wherein the solid sulfide electrolyte particles ES o have a median diameter Dv50 ES 0 such that the ratio Dv50 ES o / Dv5O Si is in a range from 0.5 to 1.5, preferably from 0.8 to 1, in particular the ratio Dv50 ES o / Dv5O Si is equal to 1.

3. Electrochemical element according to claim 1 or 2 in which the solid sulfide electrolyte particles ES have a median diameter Dv50 ES different from Dv50 ES i.

4. Electrochemical element according to any one of claims 1 to 3 wherein the solid sulfide electrolyte layer comprises, in addition to the solid sulfide electrolyte particles ES₂ which constitute a first particle population, a second particle population of a solid sulfide electrolyte ES₂, the diameters medians Dv50 ES oet Dv50 ES respectively of the first and second particle populations being different.

5. Electrochemical element according to any one of claims 1 to 4 wherein the sulfide electrolytes ES 0, ES i and ES 2 are, independently of each other, selected from the group consisting of sulfides of composition A Li2S - B P2S5 with 0 <A<l ,0<B<l et A+B = 1 et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI,...) ; les sulfures de structure argyrodite ; les sulfures ayant une structure cristallographique similaire au composé LGPS (Lii0GeP2Si2), et leurs dérivés.

6. Electrochemical element according to any one of claims 1 to 3 wherein the sulfide electrolytes ES and ES1 are of the same chemical nature, preferably selected from the group consisting of sulfides of composition A Li2S - B P2S5 with 0 <A<l ,0<B<l et A+B = 1 et leurs dérivés (par exemple avec dopage Lil, LiBr, LiCI,...) ; les sulfures de structure argyrodite ; les sulfures ayant une structure cristallographique similaire au composé LGPS (Lii0GeP2Si2 ), et leurs dérivés.

7. Electrochemical element according to any one of claims 1 to 3 wherein the solid sulfide electrolytes ES o and ES i are of the same chemical nature and are of the type Li6PS5X with X representing Cl, Br or I, or a mixture thereof.

8. Electrochemical element according to any one of claims 1 to 7 wherein the particles comprising silicon are particles made of silicon.

9. Electrochemical element according to any one of claims 1 to 8 wherein the median diameter Dv50 Si of particles comprising silicon varies from 1 to 10 pm, preferably from 2 to 5 pm.

10. Electrochemical element according to any one of claims 1 to 9, wherein the binder is selected from the group consisting of polyvinylidene fluoride (PVDF) and its copolymers, polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl) or (butyl) methacrylate, polyvinyl chloride (PVC), poly(vinyl formaldehyde), polyester, polyether block amides, acrylic acid polymers, acid methacrylic, acrylamide, itaconic acid, sulfonic acid, elastomers and cellulosic compounds.

11. Electrochemical element according to any one of the claims 1 to 10 in which the negative electrode material layer comprises at least: - from 5 to 60%, preferably from 25 to 50%, preferably from 40 to 50% by weight of particles of a solid sulfide electrolyte ES i, - from 40 to 94.5%, preferably from 40 to 70%, by weight of particles comprising silicon, - 0.5 to 10%, preferably 1 to 8%, by weight of a binder, and - possibly from 0.1 to 5%, preferably from 0.1 to 4%, by weight of one or more electronically conductive carbon additive(s), the percentages by weight are expressed relative to the total weight of the negative electrode material layer.

12. A method for preparing an all-solid type electrochemical element according to any one of claims 1 to 11 comprising the following steps: (a) preparation of a negative electrode by applying to at least one face of a current collector a layer of negative electrode material comprising at least: • particles of a solid sulfide electrolyte ES i and having a median diameter Dv50 ES i, • particles comprising silicon and having a median diameter Dv50 Si, • a binder, and • possibly an electronically conductive carbon additive, the ratio Dv50 ES i / Dv50 S i being within a range of 1.6 to 2.5, preferably 1.8 to 2.2, the median diameters being determined by laser diffraction particle size analysis; and (b) Either superposition of the negative electrode, the solid electrolyte layer and the positive electrode to give an electrochemical element of the all-solid type;

13. (c) Either coating of a layer of solid electrolyte on the negative electrode and / or the positive electrode and superposition of the negative electrode and the positive electrode to give an electrochemical element of the all-solid type. Use of an electrochemical element according to any one of claims 1 to 11 to maintain a capacity retention of at least 80% after at least 150 charge / discharge cycles.

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