EP4179590A1

EP4179590A1 - Membrane made of a polycrystalline llzo product

Info

Publication number: EP4179590A1
Application number: EP21739688.6A
Authority: EP
Inventors: Costana Mihaela IONICA BOUSQUET; Sylvain Petigny; Vincent Benoît RANIERI
Original assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Current assignee: Saint Gobain Centre de Recherche et dEtudes Europeen SAS
Priority date: 2020-07-09
Filing date: 2021-07-06
Publication date: 2023-05-17
Also published as: FR3112431A1; US20230253675A1; FR3112431B1; WO2022008522A1; KR20230037597A; CN115803928A; JP2023533008A

Abstract

The invention relates to a molten solid electrolyte membrane having a thickness less than 5 mm and intended for a lithium-ion battery, the membrane consisting of a polycrystalline product comprising at least 3.0% amorphous phase and consisting, for more than 95% of its mass, of the elements Li, La, Zr, M and O, M being a dopant chosen from the group formed by Al, P, Sb, Sc, Ti, V, Y, Nb, Hf, Ta, the lanthanides with the exception of La, Se, W, Bi, Si, Ge, Ga, Sn, Cr, Fe, Zn, Na, K, Rb, Cs, Fr, Mg, Ca, Sr, Ba and the mixtures thereof, the contents of these elements, measured after a decarbonatation operation without loss of lithium, being defined by the formula LiaLabZrcMdOi2, wherein the atomic indices are such that: 2.500 < a < 8.500, and 1.000 < b < 3.500, and 0.600 < c < 2.000, and 0 < d < 2.000.

Description

Title: MEMBRANE IN A POUYCRISTAUUIN DE UUZO PRODUCT

Technical area

The invention relates to a solid electrolyte membrane made of an LLZO material, intended for a battery, in particular a lithium ion battery. The invention also relates to such a battery.

The invention also relates to a method of manufacturing such a membrane.

State of the art

_{Garnets of generic formula Li7La 3} ZnOi2 are conventionally called "lithium, lanthanum and zirconium oxide", or "LLZO", electroneutrality being ensured by the oxygen content, the phase of LLLasZnOii possibly being doped with a dopant M for the purpose of improving ionic conductivity and/or sinterability. The dopant M can be in particular Al, P, Sb, Sc, Ti, V, Y, Nb, Hf, Ta, the lanthanides with the exception of La, Se, W, Bi, Si, Ge, Ga, Sn, Cr , Fe, Zn, Na, K, Rb, Cs, Fr, Mg, Ca, Sr, Ba or a mixture of these elements.

The LLZO comes in two crystallographic lattices:

- cubic phase, generally stable above 200°C and exhibiting ionic conductivity;

- quadratic phase, stable at room temperature and having an ionic conductivity lower than that of the cubic phase.

A battery comprising a solid electrolyte membrane made of LLZO is known. Such a membrane is manufactured by sintering and has a substantially planar shape, with a substantially constant thickness, typically around 400 microns. In this application, one seeks the highest possible ionic conductivity, and therefore as much cubic phase as possible.

However, the membrane degrades rapidly when brought into contact with air.

To be stored, the membrane can be isolated in an airtight container, under argon, which increases production costs. Finally, conventionally the battery is at least partially assembled under air, and the degradation of the membrane in contact with the air can limit its performance.

There is therefore a need for a solid electrolyte membrane in LLZO which keeps well when left in contact with air.

An object of the invention is to satisfy, at least partially, this need.

Summary of the invention

According to the invention, this object is achieved by means of a molten solid electrolyte membrane having a thickness of less than 5 mm and intended for a lithium ion battery, the membrane being made of a polycrystalline product comprising less than 3.0% of amorphous phase and consisting, for more than 95% of its mass, of the elements Li, La, Zr, M and O, M being a dopant chosen from the group formed by Al, P, Sb, Sc, Ti, V, Y, Nb, Hf, Ta, lanthanides except La, Se, W, Bi, Si, Ge, Ga, Sn, Cr, Le, Zn, Na, K, Rb, Cs, Lr, Mg, Ca, Sr , Ba and mixtures thereof, the contents of said elements, measured after a decarbonation operation without loss of lithium, being defined by the formula Li _a La _b Zr _c M _d Oi2, in which the atomic indices are such that:

2.500 < a < 8.500, and 1.000 < b < 3.500, and 0.600 < c < 2.000, and 0 < d < 2.000.

As will be seen in more detail in the remainder of the description, the resistance to aging in air of a fused membrane according to the invention is markedly greater than that of sintered membranes.

Finally, the manufacture of a molten polycrystalline product is a well-known technique. In a known manner, the cooling conditions are only adapted so that the amount of amorphous phase is low. The presence of a small quantity of amorphous phase makes it possible to control the ionic conductivity well. In particular, this conductivity does not vary significantly from one sample to another.

Preferably, a membrane according to the invention further comprises one, and preferably several of the following optional characteristics: - at least one of the large faces of the membrane has a roughness Ra of less than 500 nm;

- the total mass quantity of the cubic LLZO and quadratic LLZO phases is greater than 80.0%, in mass percentages based on the mass of the crystallized phases, "LLZO" designating a lithium, lanthanum and zirconium oxide of generic formula LLLasZnOii;

- the total quantity by mass of the cubic LLZO and quadratic LLZO phases is greater than 90.0%, preferably greater than 99.0%, in mass percentages based on the mass of the crystallized phases;

- the cubic LLZO phase represents more than 35% of all the cubic LLZO and quadratic LLZO phases, in mass percentages;

- in the formula LiaLa _b Zr _c M _d Oi2, a is greater than 2.800 and less than 8.300; and/or b is greater than 1.100 and less than 3.300; and/or c is greater than 0.600 and less than 1.900; and/or d is greater than 0.010 and less than 1.900;

- preferably a is greater than 4.500 and less than 8.000; and/or b is greater than 2.000 and less than 3.100; and/or c is greater than 1.000 and less than 1.900; and/or d is greater than 0.100 and less than 1.000;

- preferably a is greater than 6.000 and less than 7.000; and/or b is greater than 2.500 and less than 2.900; and/or c is greater than 1.400; and/or d is greater than 0.200 and less than 0.400;

- the crystallized phases not containing lithium represent, in total, less than 3% of the mass of the crystallized phases;

- the polycrystalline product comprises less than 1.0% of amorphous phase and/or has a relative skeletal density greater than 90%; - the polycrystalline product has a microstructure composed for more than 90% by number of grains having an elongation factor greater than 2.5, called "elongated grains";

- Said elongated grains are substantially parallel to each other;

- preferably

M includes element Y, the atomic index in element Y is greater than 0.005 and less than 0.300, and the sum of the atomic indices in elements M other than element Y is less than 0.300; Where

M includes the element Ce, and the atomic index of said element Ce is less than 0.300; Where

M includes the elements Ti and/or Fe, and the sum of the Ti and Fe atomic indices is less than 0.800; Where

M includes the element Al, the atomic number in element Al is greater than 0.005 and less than 1.300, and the sum of the atomic numbers in elements M other than aluminum is less than 0.300; Where

M includes the elements Ta and/or Nb and/or V, the sum of the atomic indices of Ta, Nb and V elements is greater than 0.010 and less than 1.000, and the sum of the atomic indices of M elements other than Ta elements, Nb and V is less than 0.300; Where

M includes the element Ta and the atomic number in element Ta is greater than 0.050 and less than 0.900, and the sum of the atomic numbers in elements M other than the element Ta is less than 0.300; Where

M includes the elements Sr and/or Ba and/or Ca and/or Mg, the sum of the atomic indices in elements Sr, B a, Ca and Mg is greater than 0.005, and the sum of the atomic indices in elements M other than the elements Sr, B a, Ca and Mg is less than 0.300; Where

M includes the elements Na and/or K, the sum of the atomic indices in elements Na and K is greater than 0.005, and the sum of the atomic indices in elements M other than the elements Na and K is less than 0.300;

- preferably still

M includes element Y, the atomic index in element Y is greater than 0.005 and less than 0.200, and the sum of the atomic indices in elements M other than element Y is less than 0.100; Where M comprises the element Ce, and the atomic index of said element Ce is less than 0.200; Where

M includes the elements Ti and/or Fe, and the sum of the Ti and Fe atomic indices is less than 0.600; Where

M includes the element Al, the atomic number in element Al is greater than 0.150 and less than 0.700, and the sum of the atomic numbers in elements M other than aluminum is less than 0.100; Where

M includes the elements Ta and/or Nb and/or V, the sum of the atomic indices in elements Ta, Nb and V is greater than 0.300 and less than 0.700, and the sum of the atomic indices in elements M other than the elements Ta, Nb and V is less than 0.100; Where

M includes the elements Sr and/or Ba and/or Ca and/or Mg, the sum of the atomic indices in elements Sr, B a, Ca and Mg is greater than 0.100, and the sum of the atomic indices in elements M other than the elements Sr, B a, Ca and Mg is less than 0.100; Where

M includes the elements Na and/or K, the sum of the atomic indices in Na and K elements is greater than 0.100, and the sum of the atomic indices in M elements other than the Na and K elements is less than 0.100.

The invention also relates to a method for manufacturing a membrane according to the invention, said method comprising the following steps: a) mixing of raw materials so as to form a starting charge suitable for obtaining, at the end of the step c), a said polycrystalline product, b) melting of the starting charge until a liquid mass is obtained, c) cooling until complete solidification of said liquid mass, the cooling preferably being carried out at a higher speed at 200° C./s, d) polishing the polycrystalline product obtained at the end of step c) so as to obtain a molten membrane according to the invention.

Preferably, step c) comprises the following steps: c1”) pouring the liquid mass, in the form of a jet, between two rollers; c2”) solidification by cooling the liquid mass cast in contact with the rollers until a block of polycrystalline product is obtained, at least partially solidified. The invention finally relates to a lithium ion battery comprising a fused membrane according to the invention, preferably manufactured according to a method according to the invention, placed between an anode and a cathode of said battery.

Definitions

The term “molten membrane” is used to refer to a membrane made of a material obtained directly by melting a starting charge, in the form of a liquid mass, then solidifying said liquid mass. By “directly obtained”, it is meant that the material is obtained immediately after said solidification. Such a process is notably different from a synthesis in molten salts. Preferably, the melting is above 1200°C.

A membrane made of a sintered material is not a "molten membrane", even if the grains agglomerated by sintering are fused grains.

A “polycrystalline” material is called a solid material made up of a multitude of crystallites of varying size and orientation, as opposed to a single-crystal linen material made up of a single crystal. The polycrystalline character of a material can for example be highlighted using observations made with a scanning electron microscope to highlight the grain boundaries and/or by Raman spectrometry. In the absence of special precautions, a molten product is polycrystalline.

The “relative skeletal density” of a product corresponds to the ratio equal to the skeletal density of said product divided by the absolute density of said product, expressed as a percentage.

“Skeletal density” of a product means the ratio equal to the mass of said product divided by the skeletal volume it occupies. The skeletal volume of the product corresponds to the sum of the volumes of the material and of the closed pores, said skeletal volume being determined on a membrane or a plate by helium pycnometry.

By "absolute density" of a product is meant the ratio equal to the mass of dry matter of said product after grinding to a fineness such that there remains substantially no closed porosity, divided by the volume of said mass of matter dry after grinding, said volume being able to be determined by helium pycnometry.

A "decarbonation without loss of lithium" operation is a classic operation during which a material is heated in such a way as to eliminate the carbonates without extract lithium. For example, the material can be heated under the conditions described in the examples.

The elements of the periodic table from atomic number 58 (cerium) to atomic number 71 (lutetium) are called "lanthanides".

By “precursor” of a compound or of an element, is meant a constituent capable of supplying said compound or element, respectively, during the implementation of a manufacturing process according to the invention.

Unless otherwise indicated, and in particular in the formula Li _a La _b Zr _c M _d Oi2 in which the indices a, b, c, d and 12 are atomic indices, all the contents of the constituents according to the invention are mass percentages expressed based on the product.

"Containing", "including" or "comprising", shall be construed broadly unless otherwise specified.

detailed description

Membrane

A solid electrolyte membrane according to the invention is intended for a lithium ion battery. Its dimensions are adapted for this purpose.

Conventionally, such a membrane has the general shape of a thin plate, of substantially constant thickness, and of which at least one of the two faces (or “large faces”), preferably both faces, are polished.

The thickness of the membrane is less than 5 mm, preferably less than 4 mm, preferably less than 3 mm, preferably less than 2 mm, preferably less than 1 mm, preferably less than 800 μm, preferably less than to 600 μm, preferably less than 400 μm, and/or preferably greater than 40 μm, preferably greater than 50 μm, preferably greater than 100 μm, preferably greater than 150 μm.

In one embodiment, the thickness of the membrane is greater than 600 μm, preferably greater than 800 μm, or even greater than 1 mm.

The length and width are matched to the battery. Typically, the length and/or the width is greater than 1 mm, preferably greater than 2 mm, preferably greater than 5 mm, or even greater than 10 mm, and/or preferably less than 300 mm, or even less than 200 mm, or even less than 100 mm.

The membrane may in particular have the shape of a rectangular plate or of a disc.

The roughness Ra of at least one of the large faces of the membrane, preferably of the two large faces of the membrane, measured according to standard ISO 4287:1997, is typically less than 500 nm, preferably less than 400 nm, preferably less than 300 nm, preferably less than 200 nm, preferably less than 100 nm, preferably less than 50 nm, preferably less than 40 nm, or even less than 30 nm.

Until the present invention, LLZO membranes were made of a sintered material. A membrane according to the invention is “melted”. The membrane is therefore not an agglomerate of particles, but the result of shaping a block obtained by cooling a liquid mass. The microstructure of the polycrystalline product which constitutes a membrane according to the invention is therefore specific.

micro structure

The percentage of amorphous phase of the polycrystalline product is particularly low and cannot be precisely determined with conventional methods such as X-ray diffraction. Preferably, to evaluate a low amorphous phase content, a surface percentage is evaluated, which can be measured as described in the examples.

Preferably, the content of amorphous phase, expressed in surface percentages, is less than 3.0%, less than 2.5%, preferably less than 2.0%, preferably less than 1.5%, preferably less 1.0%, or even less than 0.5%, or even substantially zero.

Advantageously, a low content of amorphous phase limits the variations in ionic conductivity from one sample to another of the polycrystalline product.

Preferably, the total mass quantity of the oxides containing lithium, of the hydroxide phases containing lithium, and of the carbonate phases containing lithium is greater than 95.0%, preferably greater than 96.0%, preferably greater than 97, 0%, preferably greater than 98.0%, preferably greater than 99.0%.

In other words, the total mass quantity of the phases which are not oxides, hydroxides or carbonates containing lithium is preferably less than 5%, of preferably less than 4%, preferably less than 3%, preferably less than 2%, preferably less than 1%, in mass percentages based on the crystallized phases.

Preferably, the total mass quantity of the cubic LLZO and quadratic LLZO phases is greater than 80.0%, preferably greater than 90.0%, preferably greater than 92.0%, preferably greater than 94.0%, of preferably greater than 95.0%, preferably greater than 96.0%, preferably greater than 97.0%, preferably greater than 98.0%, preferably greater than 99.0%, or even greater than 99.5 %, in mass percentages based on the mass of the crystallized phases.

Preferably, the cubic LLZO phase represents more than 35%, preferably more than 40%, preferably more than 45%, preferably more than 50%, preferably more than 60%, preferably more than 70%, preferably more than 80%, preferably more than 90%, preferably more than 95% of all of the cubic LLZO and quadratic LLZO phases, in mass percentages.

More preferably, the oxide phases containing lithium other than the LLZO phases, the hydroxide phases containing lithium, and the carbonate phases containing lithium together represent more than 95% of the crystallized phases containing lithium other than the LLZO phases.

The oxide phases containing lithium other than the LLZO phases, the hydroxide phases containing lithium, and the carbonate phases containing lithium are preferably chosen from LLO, LiOH, L12CO3 and their mixtures, preferably L12CO3.

The crystallized phases not containing lithium preferably represent, in total, less than 5%, preferably less than 3%, preferably less than 2%, preferably less than 1%, in mass percentages based on the crystallized phases .

The content and nature of the LLZO obtained depend in particular on the composition of the starting charge. The closer the chemical composition of the starting charge is to that of the desired LLZO, the greater the amount of said LLZO in the polycrystalline product.

In one embodiment, the polycrystalline product has a microstructure composed for more than 90% by number of grains having an elongation factor of less than 1.6, preferably less than 1.4, preferably less than 1.25, even less than 1.20, the elongation factor being equal to the ratio of the largest dimension of the grain on the smallest dimension of said grain, measured perpendicular to the largest dimension of the grain, on a cross-sectional view of the polycrystalline product. When the grains of the product have a preferred orientation, the cut is made parallel to said preferred direction. In particular, when the liquid mass of molten material has been cooled by contact with a cold plate, the cut must be made perpendicular to said plate. The preferred orientation of the grains is the direction of the length of the majority of the grains.

Preferably, the polycrystalline product has an average grain size greater than 10 μm, preferably greater than 20 μm, preferably greater than 30 μm, preferably greater than 40 μm, preferably greater than 50 μm, or even greater than 60 μm , or even greater than 70 μm, and/or preferably less than 500 μm, preferably less than 450 μm, preferably less than 400 μm, preferably less than 350 μm, preferably less than 300 μm, or even less than 250 μm , said mean size being measured by a “Mean Linear Intercept” method. A measurement method of this type is described in standard ASTM E1382.

In one embodiment, the polycrystalline product has a microstructure composed for more than 10%, even for more than 20%, even for more than 30%, even for more than 40%, even for more than 50%, even for more of 60%, even for more than 70%, even for more than 80%, even for more than 90%, even for more than 95%, even for more than 99% in number, of elongated grains, preferably having a factor elongation greater than 3, or even greater than 4, or even greater than 5.

Composition

Preferably, in the formula LiaLa _b Zr _c M _d Oi2,

- a is greater than 2.800, preferably greater than 3.000, preferably greater than

3,500, preferably greater than 4,000, preferably greater than 4,500, preferably greater than 4,800, preferably greater than 5,000, or even greater than

5,500, or even greater than 6,000, and/or less than 8,300, preferably less than 8,000, preferably less than 7,500, preferably less than 7,000; and or

- b is greater than 1.100, preferably greater than 1.200, preferably greater than 1.300, or even greater than 1,500, or greater than 1,800, or greater than 2,000, or greater than 2,200, or greater than 2,400, or greater than 2,500, and /Where less than 3.300, preferably less than 3.100, preferably less than 3.000, preferably less than 2.900; and or

- c is greater than 0.600, preferably greater than 0.700, preferably greater than 0.800, or even greater than 0.900, or greater than 1.000, or greater than 1.200, or greater than 1.400 and/or less than 1.900; and or

- d is greater than 0.010, preferably greater than 0.050, or even greater than 0.100, or even greater than 0.200, and/or less than 1.900, preferably less than 1.800, preferably less than 1.700, preferably less than 1.500, preferably less than 1.300, preferably less than 1.200, preferably less than 1.100, preferably less than 1.000, preferably less than 0.900, preferably less than 0.800, preferably less than 0.700, preferably less than 0.600, or even less than 0.500 , or even less than 0.400.

Preferably, the composition of the polycrystalline product respects several of the preferred conditions above relating to the atomic indices a, b, c and d.

M can be introduced into the starting charge to be melted as traces in a raw material. The atomic index d takes these additions into account.

M is preferably selected from the group formed by Al, Sb, V, Y, Nb, Hf, Ta, Ce, Si, Na, K, Mg, Ca, Sr, Ba and mixtures thereof, preferably from the group formed by Al, V, Y, Nb, Hf, Ta, Si, Na, Mg, Ca, Sr and mixtures thereof.

In a particular embodiment, M comprises the element Y, the atomic index of said element Y being less than 0.300, preferably less than 0.200 and greater than 0.005, preferably greater than 0.010.

In a particular embodiment, M comprises the element Ce, the atomic index of said element Ce being less than 0.800, preferably less than 0.600, preferably less than 0.400, preferably less than 0.300, or even less than 0.200 and /or greater than 0.005, preferably greater than 0.010, or even greater than 0.050, or even greater than 0.100.

In a particular embodiment, M comprises Ti and/or Fe, the sum of the atomic indices in Ti and/or Fe being less than 0.800, preferably less than 0.700, preferably less than 0.600 and/or greater than 0.005, preferably greater than 0.010, or even greater than 0.050, or even greater than 0.100, or even greater than 0.200, or even greater than 0.300.

In a particular embodiment, the polycrystalline product is such that: - the atomic index in element Al is greater than 0.005, preferably greater than 0.010, preferably greater than 0.050, preferably greater than 0.100, preferably greater than 0.150, and/or, preferably less than 1.300, preferably less than 1.200, preferably less than 1.100, preferably less than 1.000, preferably less than 0.900, preferably less than 0.800, preferably less than 0.700, preferably less than 0.600, and

- the sum of the atomic indices in elements M other than aluminum is less than 0.300, preferably less than 0.200, preferably less than 0.100.

In a particular embodiment, the polycrystalline product is such that:

- the sum of the atomic indices in elements tantalum, niobium and vanadium is greater than 0.010, preferably greater than 0.050, or even greater than 0.100, or even greater than 0.200, or even greater than 0.300 and/or, preferably, less than 1.000, of preferably less than 0.900, preferably less than 0.800, preferably less than 0.700, and

- the sum of the atomic indices in elements M other than the elements tantalum, niobium and vanadium is less than 0.300, preferably less than 0.200, preferably less than 0.100.

In a particular preferred embodiment, the polycrystalline product is such that:

- the tantalum atomic index is greater than 0.010, preferably greater than 0.050, or even greater than 0.100, or greater than 0.200, or greater than 0.300 and/or, preferably, less than 1.000, preferably less than 0.900, preferably less than 0.800, preferably less than 0.700, and

- the sum of the atomic indices in elements M other than the tantalum element is less than 0.300, preferably less than 0.200, preferably less than 0.100.

In a particular embodiment, the polycrystalline product is such that:

- the atomic index of yttrium element is greater than 0.005, preferably greater than 0.010 and/or, preferably less than 0.300, preferably less than 0.200, and

- the sum of the atomic indices in elements M other than the yttrium element is less than 0.300, preferably less than 0.200, preferably less than 0.100. In a particular embodiment, the polycrystalline product is such that:

- the sum of the atomic indices in the elements strontium, barium, calcium and magnesium is greater than 0.005, preferably greater than 0.010, preferably greater than 0.050, or even greater than 0.100 and/or preferably less than 1.500, preferably less than 1.300 , preferably less than 1.000, and

- the sum of the atomic indices in elements M other than the elements strontium, barium, calcium and magnesium is less than 0.300, preferably less than 0.200, preferably less than 0.100.

In a particular embodiment, the polycrystalline product is such that:

- the sum of the atomic indices in the elements sodium and potassium is greater than 0.005, preferably greater than 0.010, preferably greater than 0.050, preferably greater than 0.100 and/or, preferably less than 1.500, preferably less than 1.300, preferably less than 1,000, and

- the sum of the atomic indices in elements M other than the elements sodium and potassium is less than 0.300, preferably less than 0.200, preferably less than 0.100.

Preferably, the quantity by mass of elements other than Li, La, Zr, M and O is less than 4.0%, preferably less than 3.0%, preferably less than 2.0%, preferably less than 1 .5%, preferably less than 1.0%, preferably less than 0.5%. Preferably the elements other than Li, La, Zr, M and O are unavoidable constituents, introduced involuntarily and necessarily with the raw materials.

Properties

The relative skeletal density of the polycrystalline product is preferably greater than 85%, preferably greater than 88%, preferably greater than 90%, preferably greater than 92%, preferably greater than 94%, preferably greater than 95% , preferably greater than 96%, preferably greater than 97%, preferably greater than 98%, preferably greater than 98.5%, preferably greater than 99%, preferably greater than 99.5%, preferably greater at 99.8%.

Advantageously, the ionic conductivity is improved thereby.

Process

The invention also relates to a manufacturing method comprising steps a) to d). Advantageously, a method according to the invention makes it possible to obtain high relative densities. In addition, it avoids a step of forming a powder, then sintering.

In step a), a starting charge for manufacturing a membrane according to the invention is formed from compounds of lithium, lanthanum, zirconium and optionally element M, in particular in the form of oxides and/or carbonates and/or hydroxides and/or oxalates and/or nitrates, and/or precursors of the elements lithium, lanthanum, zirconium and M. The composition of the starting charge can be adjusted by addition of pure oxides or mixtures of oxides and/or precursors, in particular LEO, L12CO3, LiOH, La203, ZrCE, a lanthanum carbonate, a zirconium hydrate, oxide(s) of the element M , carbonate(s) of the element M, hydroxide(s) of the element M. The use of oxides and/or carbonates and/or hydroxides and/or nitrates and/or of oxalates improves the availability of oxygen necessary for the formation of phase Li _a LabZr _c MdOi2 and its electroneutrality, and is therefore preferred.

Preferably, at least one, or even all of the lanthanum, zirconium and M elements are introduced into the starting charge in the form of oxides. In a particular embodiment, oxide powders are used to provide the lanthanum, zirconium and M elements, and a carbonate powder to provide the lithium element.

Preferably, the compounds providing the elements lithium, lanthanum, zirconium and M are chosen from L12CO3, L12O, LiOH, La2Ü ₃ , ZrÜ2, the carbonates of the element M, the hydroxides of the element M, and the oxides of the m element.

Preferably, the compounds providing the elements lithium, lanthanum, zirconium and M together represent more than 90%, preferably more than 99%, in mass percentages, of the constituents of the starting charge. Preferably, these compounds represent, together with the impurities, 100% of the constituents of the starting charge.

Preferably, no compound other than those providing the elements lithium, lanthanum, zirconium and M, or even any compound other than L12CO3, L12O, LiOH, La20 ₃ , ZrO2, the carbonates of the element M, the hydroxides of the element M , and the oxides of the element M are not deliberately introduced into the starting charge. In one embodiment, the sum of L12CO3, L12O, LiOH, La2O ₃ , ZrO2, the carbonates of element M, the hydroxides of element M, and the oxides of element M represents more than 99% by mass of the starting charge. The quantities of lithium, lanthanum, zirconium and element M of the starting charge are essentially found in the polycrystalline product produced. A part of the elements, such as for example lithium, which varies according to the melting conditions, can volatilize during the melting step. By his general knowledge, or by simple routine tests, the person skilled in the art knows how to adapt the quantity of these elements in the starting charge according to the content he wishes to find in the molten products and the melting conditions. implemented.

The particle sizes of the powders used can be those commonly encountered in melting processes.

Intimate mixing of the raw materials can be carried out in a mixer. This mixture is then poured into a melting furnace.

In step b), the starting charge is melted.

All known furnaces are possible, such as an induction furnace, a plasma furnace or other types of Héroult furnace, provided that they allow the starting charge to be completely melted. Melting in a crucible in a heat treatment furnace, preferably in an electric furnace, preferably in an oxygenated environment, for example under air, is also possible. Electrofusion advantageously allows the manufacture of large quantities of polycrystalline product with interesting yields.

One can for example use a Héroult-type arc furnace comprising two electrodes and whose tank has a diameter of approximately 0.8 m and can contain approximately 180 kg of molten liquid.

In step b), the energy supplied is preferably greater than 1100 kWh/T of starting load, preferably greater than 1200 kWh/T. Preferably, the energy supplied is between 1200 kWh/T and 1800 kWh/T, preferably between 1300 kWh/T and 1600 kWh/T. The voltage is for example 130 volts and the power 200 kW.

An induction furnace can also advantageously be implemented.

After melting, the starting charge is in the form of a liquid mass, which may optionally contain a few solid particles, but in an insufficient quantity for them to be able to structure said mass. By definition, to maintain its shape, a liquid mass must be contained in a container. The general environment of the liquid mass can be neutral, reducing or oxidizing, preferably oxidizing, preferably being air.

The temperature of the molten liquid, for example measured from the stream of said molten liquid before step c), is preferably higher than the melting temperature of the polycrystalline product, preferably higher than 1200° C., or even higher than 1250 °C, or even above 1300°C and preferably below 1650°C, preferably below 1600°C, preferably below 1550°C, preferably below 1500°C.

In step c), the cooling rate is preferably greater than 50°C/s, preferably greater than 100°C/s, preferably greater than 200°C/s.

In one embodiment, the cooling rate is greater than 200°C/s and preferably less than 10,000°C/s, preferably less than 1000°C/s, preferably less than 800°C/s. s, preferably less than 600° C./s.

Advantageously, a high cooling rate makes it possible to increase the mass quantity of cubic LLZO phase, on the basis of the mass of the crystallized phases. A high cooling rate also makes it possible, advantageously, to reduce the amount of amorphous phase.

A high cooling rate finally makes it possible to create a temperature gradient making it possible to create a microstructure having a large quantity of elongated grains, oriented in the direction of the greatest temperature gradient. In particular, cooling by contact with a cooled plate makes it possible to orient the elongated grains substantially perpendicular to the plate.

The anisotropy may decrease as the region under consideration is further away from the cooled plate.

In a preferred embodiment, the anisotropy results from the passage of the liquid mass between two rollers which are themselves cooled.

In one embodiment, step c) comprises the following steps: c') pouring the liquid mass into a mould; c2′) solidification by cooling of the liquid mass cast in the mold until an at least partially solidified block is obtained; c3') demoulding of the block. In step c1′), the liquid mass is poured into a mold capable of withstanding the bath of molten liquid. Preferably, graphite or cast iron molds are used. Molds are also described in US 3,993,119. In the case of an induction furnace, the coil is considered to constitute a mould. Casting is preferably carried out under air.

In step c2′), the liquid mass poured into the mold is cooled until an at least partially solidified block is obtained. The use of a mold of the type of those described in US Pat. No. 3,993,119 advantageously makes it possible to obtain a high mass quantity of cubic LLZO phase, on the basis of the mass of the crystallized phases.

At step c3’), the block is unmolded. Preferably, the block is removed from the mold as soon as it has sufficient rigidity to substantially retain its shape.

Preferably, in step c1′) and/or in step c2′) and/or after step c3′), said liquid mass in the process of solidification is brought into contact, directly or indirectly, with a fluid oxygenated, preferably comprising more than 20% by volume of oxygen, preferably a gas, preferably air. This bringing into contact can be carried out as soon as casting takes place.

To facilitate bringing the liquid mass into contact with the oxygenated fluid, it is preferable to unmold the block as quickly as possible, if possible before complete solidification, and then to immediately begin bringing it into contact with the oxygenated fluid. Solidification then continues in step c3′).

Preferably, contact with the oxygenated fluid is maintained until the complete solidification of the block.

After complete solidification, a block is obtained capable of giving, after step d), a membrane whose thickness is less than 5 mm, preferably less than 4 mm, preferably less than 3 mm, preferably less than 2 mm, preferably less than 1 mm, preferably less than 800 μm, preferably less than 600 μm, preferably less than 400 μm, and preferably greater than 40 μm, preferably greater than 50 μm, preferably greater than 100 pm, preferably greater than 150 pm. In a preferred embodiment, step c) comprises the following steps: c1”) pouring the liquid mass, in the form of a jet, between two rolls, preferably both rotating and/or cooled; c2”) solidification by cooling the liquid mass cast in contact with the rollers until an at least partially solidified block is obtained. In step c1”), the liquid mass is poured in the form of a jet between two rollers capable of resisting the molten liquid, so as to laminate the jet of molten liquid. Preferably the rollers are made of steel. Preferably they are driven by opposite rotational movements, so as to laminate the jet of liquid. Preferably said rollers are cooled, preferably using a circulation of fluid, preferably a liquid, preferably water, preferably without said liquid being in contact with the jet of molten liquid.

At step c2”), the jet of liquid flowing between the rollers is cooled until an at least partially solidified block is obtained. The use of such a process advantageously makes it possible to obtain, after complete solidification, a plate having a high relative skeletal density and of low thickness, which, after step d), makes it possible to obtain a membrane suitable for a battery to lithium ions.

Preferably, in step c1”) and/or in step c2”), said liquid mass in the process of solidification is brought into contact, directly or indirectly, with an oxygenated fluid, preferably comprising more than 20% in volume of oxygen, preferably a gas, preferably air.

Under the effect of melting, then cooling, the elements Li, La, Zr, M and O combine in the form of cubic LLZO phase, quadratic LLZO phase, or even other phases containing lithium, (and in particular other oxide phases containing lithium, hydroxide phases containing lithium, and carbonate phases containing lithium) and/or phases not containing lithium.

In step d), the polycrystalline product obtained at the end of step c) is polished so as to reduce its roughness.

A fused membrane according to the invention is thus obtained.

Preferably, the polishing is carried out on at least one, preferably each of the two large faces of the membrane.

Preferably, after polishing, the roughness Ra of at least one of the large faces of the membrane, preferably of each of the two large faces of the membrane is less than 500 nm, preferably less than 400 nm, preferably less than 300 nm, preferably less than 200 nm, preferably less than 100 nm, preferably less than 50 nm, preferably less than 40 nm, or even less than 30 nm.

In one embodiment, in step d), the thickness of the polycrystalline product obtained at the end of step c) is reduced, preferably until a thickness of less than 5 mm is obtained, preferably less than 4 mm, preferably less than 3 mm, preferably less than 2 mm, preferably less than 1 mm, preferably less than 800 μm, preferably less than 600 μm, preferably less than 400 μm, and preferably greater than 40 μm, preferably greater than 50 μm, preferably greater than 100 μm, preferably greater than 150 μm.

The reduction may result totally or partially from the polishing operation.

In a preferred embodiment, the thickness of the polycrystalline product is limited from the melting, in particular during a step cl”).

In one embodiment, machining makes it possible to reduce the length and/or the width of the polycrystalline product obtained at the end of step c).

The final length of the membrane obtained is preferably greater than 1 mm and less than 300 mm, typically between 10 mm and 100 mm. The final width of the membrane is preferably greater than 1 mm and less than 300 mm, typically between 10 mm and 100 mm.

In one embodiment, the polycrystalline product and/or the membrane are cut in such a way as to retain only regions having a high quantity of elongated grains.

Preferably, immediately before or after step d), preferably after step d), the membrane is dried, preferably at a temperature above 90° C., preferably above 100° C., and/or preferably less than 200° C., preferably less than 150° C., the holding time at this temperature being preferably greater than 5 hours, preferably greater than 10 hours, preferably greater than 20 hours, or even greater than 50 hours and / or preferably less than 200 hours, preferably less than 100 hours.

Examples

Characterization methods The characterization methods below, described in the context of the examples, can also be used to characterize the invention more generally.

The chemical analysis is determined using the following method:

Before analysis, the samples are preferably stored under vacuum or in a neutral atmosphere, for example under argon, in order to avoid carbonation.

The samples to be characterized are then dry ground in an RS 100 grinder marketed by the Retsch company, equipped with a bowl and a tungsten carbide roller, so as to have a maximum size of less than 160 μm (this is that is to say that more than 99.5% by mass of the particles of the ground powder have a size of less than 160 microns).

In the two hours following the end of the grinding, the carbon content of the powder obtained is determined by instrumental gas analysis (or "Instrumental gas analysis"), for example on a carbon / sulfur analyzer EMIA-820V from HORIBA Scientific.

If the carbon content is less than 0.3%, dissolution by hydrochloric acid attack is carried out and the content of the various elements is determined by inductively coupled plasma spectrometry or ICP-AES.

If the carbon content is greater than 0.3%, the powder is placed in a magnesia crucible. The crucible is placed in an electric furnace then raised to 950° C. and maintained at this temperature for 15 minutes. After cooling, the heat-treated powder is brought into solution by attacking with hydrochloric acid and the content of the various elements is determined by inductively coupled plasma spectrometry or ICP-AES.

The nature and quantity of crystallized phases are determined by the following conventional method:

The samples to be characterized are ground dry in an RS 100 grinder marketed by the company Retsch, equipped with a bowl and a tungsten carbide roller, so that they are in the form of a powder. exhibiting a refusal at 40 μm of less than 5% by mass.

The acquisitions are carried out using a device of the D8 Endeavor type from the company Bruker, over an angular range 2Q between 5° and 80°, with a step of 0.01°, and a counting time of 0.68 s/step. The front optic has a 0.3° primary slit and a 2.5° Soller slit. The sample is rotating on itself at a speed equal to 15 rpm, with use of the automatic knife. The rear optics have a 2.5° Soller slit, a 0.0125 mm nickel filter and a 1D detector with an aperture equal to 4°.

The diffraction patterns are then qualitatively analyzed using EVA software and the ICDD2016 database.

File 182312 of the ICSD database makes it possible to identify the cubic LLLasZnOii phase and file 246816 of the ICSD database makes it possible to identify the quadratic _{LÎ7La 3 Zr20i2 phase.}

The highlighted phases, especially the cubic and quadratic LLZO phases, may show a slight shift in peaks compared to the data sheets used. In particular, the quadratic LLZO phase, optionally doped, is generally less distorted than the _{quadratic LÎ7La 3} Zr20i2 phase of the ICSD database file, and the characteristic peaks of said phase can be positioned at greater 2Q diffraction angles. lower than those indicated in the ICSD database sheet.

When secondary phases are identified, they are preferably crystallized phases of the group formed by orthorhombic La2Zr207 (ICDD sheet -01-070-5602), orthorhombic LiLa02 (ICDD sheet 00-019-0722), monoclinic LLZKL (ICDD sheet 01-01- 070-8744), monoclinic L12CO3 (ICDD sheet 01-087-0728), _{hexagonal La20 3} (ICDD sheet 01-071-5408), monoclinic Z1Ό2 (ICDD sheet 00-37-1484), and mixtures thereof.

Once the phases present have been identified, the measurement of the mass quantity of the cubic and quadratic LLZO phases as well as the other crystallized phases is carried out by Rietveld refinement using the HighScore Plus software.

Before starting the refinement, it is necessary to check that the width of the base of the peaks (“profile base width”) is at least equal to 20.

The Rietveld refinement must be carried out in manual mode according to the following strategy, the transition from one step to the next only taking place after ensuring that the refinement has converged:

- refinement of the background signal with the Chebychev I function. Refinement of the zero, of the "fiat background" and "1/x" parameters and of the first 6 coefficients. All these parameters can be released at the same time, then - refinement of the scale factor of the different phases simultaneously, then

- refinement of the mesh parameters and of the profile parameter W of the cubic LLZO phase and of the quadratic LLZO phase, simultaneously, the mesh parameters a, b and c of the quadratic LLZO phase being necessarily constrained so that the mesh remains quadratic during the refinement, then

- refinement of the profile parameters U then V of the cubic LLZO or quadratic LLZO phase present in the greatest quantity, then

- refinement of the “peak shape 1” shape parameter of the cubic LLZO or quadratic LLZO phase only if only one of these two phases is present, then

- refinement of the profile parameters U then V of the cubic LLZO or quadratic LLZO phase present in the smallest quantity, then

- refinement of the mesh parameters of the other phases identified, simultaneously, then

- refinement of the profile parameter W of the other phases identified, simultaneously, then

- refinement of the profile parameters U, V and "peak shape 1" of each of the other identified phases with the exception of LLC0 ₃ of monoclinic structure, successively only if a sufficient number of distinct and well-defined reflections of said phases is observed .

The surface percentage of amorphous phase is determined by the following method:

Three samples, each of dimensions substantially equal to 50 mm x 15 mm x 2 mm are taken without using water, for example using a hammer, in the sample. Each sample is then glued in a sample holder and then undergoes polishing, in order to obtain a good surface condition, said polishing being carried out at least with a grade 220 paper used with an alcohol-based lubricant, then with using diamond suspensions in a mixture of polyethylene glycol and polypropylene glycol. The surface obtained is then cleaned with pure isopropanol. The polished surface obtained is the surface that will be analyzed by Raman imaging.

Each sample is then introduced into a Raman DXRxi spectrometer marketed by Thermo Scientific. The acquisition of the images and the calculation of the areas of the different phases present are carried out using the software provided by the manufacturer. The images are taken under the following conditions:

- wavelength: 532 nm,

- power equal to 6 mW at the level of the sample,

- diffraction grating: 1800 lines,

- spectral range: 100 to 3000 cm ¹ ,

- detector: EMCCD camera or "Electron Multiplying Charge Coupled Device", with a resolution equal to 1600 x 200 pixels, cooled by the Peltier effect thanks to a thermoelectric module,

- exposure time: less than 10ms,

- number of passages: 10 at least,

- measurement step: 500 nm,

- objective used: at least x50, preferably xlOO,

- spatial resolution: 500 nm with linear displacement magnetic stage and high precision optical encoders.

For each of the samples, two images of dimensions 0.25 mm ² , preferably of dimensions 500 μm×500 μm are produced. In total, for each product, 6 images are therefore produced.

Each image is reconstructed point by point. Each point corresponds to a Raman spectrum. Each phase, whether crystallized or amorphous, has a unique spectral signature. The distribution of the phases present can be viewed by assigning a color code to each phase, i.e. to each type of spectrum obtained. The crystallized phases identified by X-ray diffraction are first identified. Then, in a second step, the unassigned zones are analyzed so as to determine whether they consist of crystallized phases or of amorphous phases. At the end of the treatment, the image obtained represents the distribution of the different crystallized and amorphous phases present. For each of the images, the amorphous phase area is calculated in pixels, as well as the total area of the image.

The surface percentage of amorphous phase of the product is equal to the sum of the surfaces of the zones of amorphous phases of each image divided by the sum of the total surfaces of the images, expressed as a percentage.

The average grain size was measured by the “Mean Linear Intercept” method. A method of this type is described in standard ASTM E1382. According to this standard, lines of analysis are traced on images of the polycrystalline product, then, along each line of analysis, the lengths, called “intercepts”, are measured between two consecutive grain boundaries intersecting said line of analysis.

The average length "G" of the intercepts "I" is then determined.

For the products of the examples, the intercepts were measured on images, obtained by scanning electron microscopy, of samples of molten polycrystalline products, said sections having previously been coated in a resin and polished until obtaining a mirror quality , said polishing being carried out at least with a grade 220 paper used with an alcohol-based lubricant, then using diamond suspensions in a mixture of polyethylene glycol and polypropylene glycol, the surface obtained then being cleaned with using pure isopropanol. The magnification used for taking the images is chosen so as to visualize approximately 40 grains on an image. 5 images per polycrystalline product were produced.

The average size "D" of the grains of a polycrystalline product is given by the relationship: D = 1.56.1'. This formula is derived from formula (13) of “Average Grain Size in Polycrystalline Ceramics” M. I. Mendelson, J. Am. Cerm. Soc. Flight. 52, No.8, pp443-446.

Roughness is measured using a Mitutoyo Surftest SJ-210 roughness tester, model 178-560-01D, equipped with a 178-296 probe, used with:

- a Gaussian filter,

- a sampling length equal to 0.8 mm and an evaluation length equal to 4 mm when the roughness Ra is between 100 nm and 2000 nm,

- a sampling length equal to 0.25 mm and an evaluation length equal to 1.25 mm when the roughness Ra is between 20 nm and 100 nm.

Air aging is measured as follows:

A molten LLZO membrane according to the invention and a reference membrane, in LLZO obtained by sintering a powder consisting of melted particles of LLZO.

The membranes are then examined with the naked eye to assess their physical integrity. The following examples are provided for illustrative purposes and do not limit the invention. The fused membranes were fabricated as follows.

The following starting raw materials were first thoroughly mixed in a mixer:

- for all the examples, a powder comprising more than 99.4% by mass of lithium carbonate L12CO3, the median size of which is equal to 26 μm, and comprising traces of the elements Na, Mg and Ca;

- for all the examples, a powder comprising more than 99.4% by mass of lanthanum oxide La20 ₃ , the median size of which is less than 10 μm, and comprising traces of the elements Y, Fe, Ca , Si and Ti;

- for all the examples, a CC10 zirconia powder marketed by the European Society of Refractory Products, comprising more than 98.5% by mass of Z1Ό2 and, in trace amounts, the elements Al, Si, Na, Hf, Fe, Ca, Mg and Ti;

- for example 2, a powder comprising more than 99.8% by mass of Ta2Ü5, the maximum particle size of which is less than 10 μm, and comprising in particular the trace elements of the elements Fe, Al, Si, Ca, Mg and Ti.

For example 1, the elements Al and/or Ca and/or Fe and/or Hf and/or Mg and/or Na and/or Si and/or Ti and/or Ta and/or Y result from the presence of these elements, in trace amounts, in the raw materials used.

For each of the examples, the starting charge is defined in the following table 1, in mass percentages:

[Table 1]

For each example, the starting charge of a mass of 25 kg was poured into a Héroult-type arc melting furnace. It was then melted with a voltage of 130 Volts and an applied energy substantially equal to 1500 kWh/T, in order to melt the entire mixture completely and homogeneously.

When the fusion was complete, the mass of molten liquid was poured in the form of a jet between two rolls of diameter equal to 800 mm, in steel cooled using a circulation of water so that their surface temperature is equal to 16°C, with opposite rotational movements, at a speed equal to 5 rpm, and separated from each other by an equal distance to 2.5 mm, so as to entrain and laminate the jet between said rollers. The temperature of the jet of molten liquid was between 1300°C and 1450°C.

After passing through the rollers, plates with a thickness substantially equal to 2 mm are recovered.

Tables 2 and 3 below provide the chemical composition and the crystallographic composition of these plates. Polishing the plates as described below does not alter these results.

The surface percentage of amorphous phase in each of the examples was measured below 3%.

[Table 2]

5 [Table 3]

On a plate of each example, polishing is carried out on each of the two large faces so as to obtain a fused membrane with a thickness equal to 1.5 mm and having a roughness Ra, measured on each of the two large faces, of less than 100 n.

Reference sintered pellets were made as follows.

200 g of molten plates of each example are ground in an agate bowl, with agate balls and pure acetone so as to obtain a powder having a median size equal to 9 μm. Immediately after drying in an oven at 50° C. for 30 minutes, said powder is broken down by hand.

Immediately after crumbling, each powder is then shaped by uniaxial pressing, so as to obtain a pellet having a diameter equal to 13 mm and a mass substantially equal to 1 g under the following pressing conditions:

- pressing at a pressure equal to 2 tonnes for 30 seconds,

- relaxation of constraints for 60 seconds,

- pressing at a pressure equal to 3.5 tonnes for 30 seconds,

- relaxation of constraints for 60 seconds,

- pressing at a pressure equal to 5 tons for 30 seconds.

Each pellet is then placed on an MgO plate, said MgO plate being placed on a bed of L12CO3 powder disposed in a first alumina gazette. A second alumina gazette is then placed upside down on the first alumina gazette. The assembly is then introduced into an electric furnace, so as to sinter each pellet, under air and at atmospheric pressure in the following thermal cycle:

- rise of the ambient temperature to 1185°C at a rate equal to 100°C/h,

- maintained at 1150°C for 6 hours,

- descent to ambient temperature at a speed equal to 100°C/h, then descent at natural speed.

Each sintered pellet obtained has a thickness equal to 1.5 mm.

The stability to aging in air of the fused membranes of Examples 1 and 2 according to the invention was compared with that of the reference sintered pellets. After 6 months of storage, the fused membranes according to the invention are intact. The sintered pellets of reference disintegrates strongly, that is to say lose their physical integrity, after only 15 days of storage.

This stability of the membranes according to the invention is considered as a signature of the fusion process. In other words, it reflects the fact that these membranes were obtained directly by fusion.

The inventors have also observed that a membrane according to the invention having a relative skeletal density of less than 90% exhibits less aging than a sintered reference membrane of the same relative skeletal density. In other words, and without being able to explain it theoretically, with substantially identical chemistry and relative skeletal density, a fused membrane according to the invention exhibits less aging in air than a sintered reference membrane.

The inventors have also observed that a limited variation in the relative skeletal density of the fused membranes according to the invention does not substantially modify their resistance to ageing.

As is now clear, the method according to the invention allows the membranes to be stored, manufactured and used in air, which considerably reduces the costs and widens the spectrum of possible applications. Lower air aging also makes it possible to limit the resistance at the interfaces and therefore to maintain a high ionic conductivity when the battery is assembled in air.

These examples also make it possible to demonstrate the effectiveness of the process according to the invention for manufacturing in a simple and economical manner, in industrial quantities, membranes comprising large quantities of optionally doped LLLasZnOii phase.

The material which constitutes a membrane according to the invention is preferably the result of the solidification of an entirely liquid liquid mass before being cooled in order to be solidified. Its manufacturing process is then very simple since it suffices to melt the raw materials, preferably in the form of powders, then, after obtaining a bath of molten liquid, to solidify this bath to obtain a block under the shape of the membrane or from which it is possible to extract the membrane. Of course, the present invention is not limited to the embodiments described provided by way of illustrative and non-limiting examples.

In particular, the membranes according to the invention are not limited to particular shapes or dimensions.

Claims

1. Molten solid electrolyte membrane having a thickness of less than 5 mm and intended for a lithium ion battery, the membrane being made of a polycrystalline product comprising less than 3.0% of amorphous phase and consisting, for more than 95% of its mass, elements Li, La, Zr, M and O, M being a dopant chosen from the group formed by Al, P, Sb, Sc, Ti, V, Y, Nb, Hf, Ta, Se, W, Bi , Si, Ge, Ga, Sn, Cr, Fe, Zn, Na, K, Rb, Cs, Fr, Mg, Ca, Sr, Ba, lanthanides with the exception of La, and mixtures thereof, the contents of said elements , measured after a decarbonation operation without loss of lithium, being defined by the formula LiaLa _b Zr _c M _d Oi2, in which the atomic indices are such that:

2.500 < a < 8.500, and 1.000 < b < 3.500, and 0.600 < c < 2.000, and 0 < d < 2.000, the membrane being made of a material obtained by melting a starting charge, in the form of a mass liquid, then solidification of said liquid mass, the material being obtained immediately after said solidification.

2. Membrane according to the immediately preceding claim, in which the total mass quantity of the cubic LLZO and quadratic LLZO phases is greater than 80.0%, in mass percentages based on the mass of the crystallized phases,

“LLZO” designating a lithium, lanthanum and zirconium oxide of generic formula LLLasZnOii.

3. Membrane according to the immediately preceding claim, in which the total quantity by mass of the cubic LLZO and quadratic LLZO phases is greater than 90.0%, in mass percentages based on the mass of the crystallized phases.

4. Membrane according to the immediately preceding claim, in which the total quantity by mass of the cubic LLZO and quadratic LLZO phases is greater than 99.0%, in mass percentages based on the mass of the crystallized phases.

5. Membrane according to any one of the preceding claims, in which the cubic LLZO phase represents more than 35% of all of the cubic LLZO and quadratic LLZO phases, in mass percentages.

6. Membrane according to any one of the preceding claims, in which, in the formula Li _a La _b Zr _c M _d Oi2, a is greater than 2.800 and less than 8.300; and b is greater than 1.100 and less than 3.300; and c is greater than 0.600 and less than 1.900; and d is greater than 0.010 and less than 1.900.

7. Membrane according to the immediately preceding claim, in which a is greater than 4.500 and less than 8.000; and b is greater than 2.000 and less than 3.100; and c is greater than 1.000 and less than 1.900; and d is greater than 0.100 and less than 1.000.

8. Membrane according to the immediately preceding claim, in which a is greater than 6.000 and less than 7.000; and b is greater than 2.500 and less than 2.900; and c is greater than 1.400; and d is greater than 0.200 and less than 0.400.

9. Membrane according to any one of the preceding claims, in which the crystallized phases not containing lithium represent, in total, less than 3% of the mass of the crystallized phases.

10. Membrane according to any one of the preceding claims, comprising less than 1.0% of amorphous phase and/or has a relative skeletal density greater than 90%, the "relative skeletal density" of a product being equal to the skeletal density of said product divided by the absolute density of said product, expressed as a percentage, the "skeletal density" being equal to the mass of said product divided by the skeletal volume it occupies, the "skeletal volume" of the product being the sum of the volumes of matter and closed pores, said skeletal volume being determined on a membrane or plate by helium pycnometry, the "absolute density" being equal to the mass of dry matter of said product after grinding to a fineness such that substantially no porosity remains closed, divided by the volume of said mass of dry matter after grinding.

11. Membrane according to any one of the preceding claims, having a microstructure composed for more than 90% by number of grains having an elongation factor greater than 2.5, called "elongated grains".

12. Membrane according to the immediately preceding claim, wherein said elongated grains are parallel to each other.

13. Membrane according to any one of the preceding claims, in which M comprises the element Y, the atomic index in element Y is greater than 0.005 and less than 0.300, and the sum of the atomic indices in elements M other than the element Y is less than 0.300.

14. Membrane according to the immediately preceding claim, in which the atomic index in element Y is less than 0.200, and the sum of the atomic indices in elements M other than element Y is less than 0.100.

15. Membrane according to any one of claims 1 to 12, in which

M includes the element Ce, and the atomic index in said element Ce is less than 0.300.

16. Membrane according to the immediately preceding claim, in which the atomic index of said element Ce is less than 0.200.

17. Membrane according to any one of claims 1 to 12, in which M comprises the elements Ti and/or Fe, and the sum of the atomic indices in Ti and Fe is less than 0.800.

18. Membrane according to the immediately preceding claim, in which the sum of the Ti and Fe atomic indices is less than 0.600.

19. Membrane according to any one of claims 1 to 12, in which

M includes the element Al, the atomic number in element Al is greater than 0.005 and less than 1.300, and the sum of the atomic numbers in elements M other than aluminum is less than 0.300.

20. Membrane according to the immediately preceding claim, in which the atomic index in element Al is greater than 0.150 and less than 0.700, and the sum of the atomic indices in elements M other than aluminum is less than 0.100.

21. Membrane according to any one of claims 1 to 12, in which

M includes the elements Ta and/or Nb and/or V, the sum of the atomic indices of Ta, Nb and V elements is greater than 0.010 and less than 1.000, and the sum of the atomic indices of M elements other than Ta elements, Nb and V is less than 0.300.

22. Membrane according to the immediately preceding claim, in which the sum of the atomic indices in elements Ta, Nb and V is greater than 0.300 and less than 0.700, and the sum of the atomic indices in elements M other than the elements Ta, Nb and V is less than 0.100.

23. Membrane according to any one of claims 1 to 12, in which M comprises the element Ta and the atomic index in element Ta is greater than 0.05 and less than 0.900, and the sum of the atomic indices in elements M other than the Ta element is less than 0.300.

24. Membrane according to any one of claims 1 to 12, in which M comprises the elements Sr and/or B a and/or Ca and/or Mg, the sum of the atomic indices in elements Sr, Ba, Ca and Mg is greater than 0.005, and the sum of the atomic indices in M elements other than the Sr, Ba, Ca and Mg elements is less than 0.300.

25. Membrane according to the immediately preceding claim, in which the sum of the atomic indices in elements Sr, B a, Ca and Mg is greater than 0.100, and the sum of the atomic indices in elements M other than the elements Sr, Ba, Ca and Mg is less than 0.100.

26. Membrane according to any one of claims 1 to 12, in which M comprises the elements Na and/or K, the sum of the atomic indices in elements Na and K is greater than 0.005, and the sum of the atomic indices in elements M other than the elements Na and K is less than 0.300.

27. Membrane according to the immediately preceding claim, in which the sum of the atomic indices in elements Na and K is greater than 0.100, and the sum of the atomic indices in elements M other than the elements Na and K is less than 0.100.

28. Membrane according to any one of the preceding claims, of which at least one of the large faces has a roughness Ra of less than 500 nm.

29. Lithium ion battery comprising a membrane according to any one of the preceding claims, said membrane being disposed between an anode and a cathode of said battery.

30. Process for manufacturing a membrane according to any one of claims 1 to 28, said process comprising the following steps: a) mixing raw materials so as to form a starting charge suitable for obtaining, at the end of step c), a said polycrystalline product, b) melting of the starting charge until a liquid mass is obtained, c) cooling until complete solidification of said liquid mass, the cooling preferably being carried out at a speed greater than 200°C/s, d) polishing the polycrystalline product obtained at the end of step c) so as to obtain a molten membrane according to any one of claims 1 to 28, step c) comprising the following steps: (1) pouring the liquid mass, in the form of a jet, between two rollers; c2”) solidification by cooling the liquid mass cast in contact with the rollers until a block of polycrystalline product is obtained, at least partially solidified.