Garnet-type oxides have an ideal structure of chemical formula A382(X04)3 and generally crystallize into a body-centered cubic lattice belonging to the Ia3d space group. The cation sites A, B and X respectively have a coordination number with oxygen of VIII, VI and IV. Synthetic garnets are mainly known for their magnetic and dielectric properties. However, it has been observed that certain garnets may have a high enough Li+ ionic conductivity to use them as solid electrolyte of lithium batteries. Thus, in 2007, teams succeeded in preparing a novel garnet of formula Li7la3Zr2012 20 (LLZO) and obtained a total conductivity of the order of 3x1 o-4 S/cm. Other studies also showed that the ionic conductivity is highest when the garnet has a cubic structure rather than a tetragonal structure. Other teams have shown that the ionic conductivity was improved when the LLZO garnet comprises another chemical element such as aluminum or niobium. 25 Due to their high conductivity, LLZO garnets may be used as solid electrolyte in lithium batteries. Technical background 30 EP 2353203 81 describes a process for preparing a garnet by a coprecipitation technique. 5 wo 2021/219806 PCT/EP2021/061307 2 WO 2019/090360 describes a process for bringing an LLZO garnet into contact with a solution of a lithium salt such as LiPFe or LiBF4. It is observed that the NMR spectrum given in figure 5 is different from that obtained with the product of the invention. Technical problem The surface of LLZO garnets is capable of being modified in contact with the moisture and C02 present in the atmosphere, which leads to a modification of the conductivity at the interface of the solid. This has been demonstrated for 10 example in Phys. Chem. Chem. Phys. 2014, 16 (34), 18294-18300 https://doi.org/1 0.1 039/c4cp02921f or in J. Mater. Chem. A 2014, 2(1 ), 172- 181. https://doi.org/1 0.1 039/C3TA 13999A. Specifically, it is observed that LiOH and/or lithium carbonate are formed at the surface of the garnet particles when these particles are in contact with an ambient atmosphere (see also in 15 this regard Sharafi & Sakamoto, J. Mater. Chem. A, 2017, 5, 13475). 20 It would therefore be useful to have garnets that have adequate ionic conductivity for use as solid electrolyte of a lithium battery and that can be stored and handled under normal conditions. The process of the invention aims to stabilise said garnets without degrading their physicochemical properties and in particular their ionic conductivity. Figures 25 Fig. 1 represents the IR-ATR spectrum of the inorganic compound M of LLZO type used as starting material in the examples i.e. comparative example 1. Fig. 2 represents the IR-ATR spectrum of the fluorinated inorganic compound of example 2. These two spectra represent the intensity of the signal in arbitrary units (au) as a function of the wave number in cm-1. 30 Fig. 3 represents SEM-EDS analysis i.e. absolute intensity of the elements F (K lines) and La (M lines) measured as a function of the position on the line profile for fluorinated LLZO solid particles prepared according to example 1. wo 2021/219806 PCT/EP2021/061307 3 Fig. 4 represents SEM-EDS analysis i.e. absolute intensity of the elements F (K lines) and La (M lines) measured as a function of the position on the line profile for fluorinated LLZO solid particles prepared according to comparative example 2 (fluorinated LLZO by solid state synthesis). 5 Brief description of the invention The process of the invention is described in claims 1 to 11. More precisely, the process is a fluorination process which consists in bringing an atmosphere comprising difluorine gas into contact with an inorganic compound M having a garnet-type structure, which is based on the elements Li, La, Zr, A and 0 and 1 0 for which the relative composition of the Li, La, Zr and A cations corresponds to the formula (I): wherein: • A denotes at least one element chosen from the group formed of AI, Ga, 15 Nb, Fe, Wand Ta; • x, z and w denote real numbers; • 1.20 < z :::; 2.1 0; more particularly 1.20 < z :::; 2.05; more particularly still 1.50:::; z:::; 2.00; • 0 < w:::; 0.80; more particularly 0 < w:::; 0.60; more particularly still 0 < w:::; 20 0.30; more particularly still 0 < w:::; 0.25; • 4.00 :::; x :::; 1 0.50; more particularly 5.10 :::; x :::; 9.1 0; more particularly still 6.20:::; X:::; 7.70. The atmosphere comprising the difluorine gas is denoted by the expression 25 "fluorinated atmosphere". 30 The invention also relates to a process for fluorination of an oxide that consists in bringing an atmosphere containing difluorine gas into contact with the oxide of formula (II): wherein: • A denotes at least one element chosen from the group formed of AI, Ga, Nb, Fe, Wand Ta; wo 2021/219806 PCT/EP2021/061307 4 • x1, z and w denote real numbers; • 1.20 < z :::; 2.1 0; more particularly 1.20 < z :::; 2.05; more particularly still 1.50:::; z:::; 2.00; • 0 < w:::; 0.80; more particularly 0 < w:::; 0.60; more particularly still 0 < w 5 :::; 0.30; more particularly still 0 < w:::; 0.25; • x1 is a positive real number which is such that the electroneutrality of the oxide is ensured. The invention also relates to the fluorinated inorganic compound obtained by 10 the process of the invention. This inorganic compound is as defined in one of claims 12 to 26. 15 The invention also relates to an electrode as defined in claim 27 and to the use of the fluorinated inorganic compound as defined in claims 28 and 29. The invention will now be described in greater detail. Detailed description of the invention The starting inorganic compound M has a garnet-type structure and is based 20 on the elements Li, La, Zr, A and 0 for which the relative composition of the Li, La, Zr and A cations corresponds to the formula (I): LixLa3ZrzAw (I) wherein: • A denotes at least one element chosen from the group formed of AI, Ga, 25 Nb, Fe, Wand Ta; • x, z and w denote real numbers; • 1.20 < z :::; 2.1 0; more particularly 1.20 < z :::; 2.05; more particularly still 1.50:::; z:::; 2.00; • 0 < w:::; 0.80; more particularly 0 < w:::; 0.60; more particularly still 0 < w:::; 30 0.30; more particularly still 0 < w:::; 0.25; • 4.00 :::; x :::; 1 0.50; more particularly 5.10 :::; x :::; 9.1 0; more particularly still 6.20:::; X:::; 7.70. wo 2021/219806 PCT/EP2021/061307 5 The inorganic compound M is a garnet based on the elements Li, La, Zr, A and 0. As the element hafnium is often naturally present in the ores from which the zirconium is extracted and therefore in the starting compounds used for the preparation of the inorganic compound M, everything which is described in the 5 present application also applies considering that the element zirconium is partially replaced by the element hafnium. Thus, the invention applies more particularly also to an inorganic compound M comprising the element hafnium. The invention may therefore apply more particularly to a starting inorganic compound M in the form of garnet based on the elements Li, La, Zr, Hf, A and 10 0 for which the relative composition of the Li, La, Zr, Hf and A cations corresponds to the formula (Ia): 15 LixLa3(Zr(1-a)+Hfa)zAw (Ia) wherein x, z and ware as described above and a is a real number between 0 and 0.05, more particularly between 0 and 0.03, or even between 0 and 0.02. The atomic ratio Hf/Zr = a/(1-a) is between 0 and 0.05, more particularly between 0 and 0.03, or even between 0 and 0.02. This ratio may be between 0.0006 and 0.03, or even between 0.0006 and 0.025. 20 A denotes at least one element chosen from the group formed of AI, Ga, Nb, Fe, W and Ta or a combination of said elements. According to a particular embodiment, A may thus denote the combination of the element AI and of an element A chosen from the group formed of Ga, Nb, Fe, Wand Ta. 25 The inorganic compound M is electrically neutral. The anions that ensure the electroneutrality of the inorganic compound M are essentially 0 2- anions. It is however possible that other anions such as for example OH- and/or C032- anions contribute to the electroneutrality of the inorganic compound M. 30 z may be within one of the following ranges: 1.20 < z:::; 2.1 0; more particularly 1.20 < z:::; 2.05; more particularly still1.50:::; z:::; 2.00. More particularly, 1.90:::; z:::; 2.1 0. More particularly still z:::; 2.00. wo 2021/219806 PCT/EP2021/061307 6 w may be within one of the following ranges: 0 < w:::; 0.80; more particularly 0 < w :::; 0.60; more particularly still 0 < w :::; 0.30; more particularly still 0 < w :::; 0.25. More particularly still w:::: 0.05. 5 The relative compositions of the cations may be more particularly the following: • A is chosen from the group formed of Nb, Ta or a combination of these two elements; • 1.20 < z :::; 2.1 0; more particularly 1.20 < z :::; 2.05; more particularly 1.50:::; z:::; 2.00; 10 • 0.10 < w :::; 0.80; more particularly 0.20 < w :::; 0.80; more particularly 0.20 < w:::; 0.50; • 6.20 :::; x :::; 1 0.35; more particularly 6.20 :::; x :::; 8.84; more particularly 6.50:::; X:::; 7.48. 15 The relative compositions of the cations may be more particularly the following: • A denotes W; • 1.20 < z :::; 2.1 0; more particularly 1.20 < z :::; 2.05; more particularly 1.50:::; z:::; 2.00; • 0.10 < w :::; 0.80; more particularly 0.20 < w :::; 0.80; more particularly 20 0.20 < w:::; 0.50; • 5.40 :::; x :::; 1 0.20; more particularly 5.40 :::; x :::; 8.58; more particularly 6.00:::; X:::; 7.26. The relative compositions of the cations may be more particularly the following: 25 • A is chosen from the group formed of AI, Ga, Fe, or a combination of these elements; • 1.90 < z :::; 2.1 0; more particularly 1.95 :::; z :::; 2.05; more particularly 1.95:::; z:::; 2.00; • 0.10 < w :::; 0.80; more particularly 0.20 < w :::; 0.60; more particularly 30 0.10 < w:::; 0.25; • 4.60 :::; x :::; 1 0.05; more particularly 5.20 :::; x :::; 8.32; more particularly 6.25:::; X:::; 7.37. wo 2021/219806 PCT/EP2021/061307 7 The empirical formula of the inorganic compound and therefore the values of the real numbers z, wand x are deduced from a chemical analysis of the inorganic compound. To do this, use may be made of the chemical analysis techniques known to those skilled in the art. Such a method may consist in preparing a 5 solution resulting from the chemical attack of the inorganic compound M and in then determining the composition of this solution. Use may for example be made of ICP (Inductively Coupled Plasma), more particularly ICP-MS (ICP coupled with mass spectrometry) or ICP-AES (ICP coupled with atomic emission spectrometry). 10 The inorganic compound M has a garnet-type structure. It is considered that its crystalline structure generally consists of a skeleton of LaOs dodecahedra (La of coordination number 8) and of ZrOe octahedra (Zr of coordination number 6). More particularly, it may be composed of a skeleton of LaOs dodecahedra of 15 coordination number 8 (24c site) and of ZrOe octahedra of coordination number 6 (16a site). In the garnet-type structure, the Li atoms may be present at the 24d tetrahedral sites or 48g and 96h octahedral sites. It is possible that most of these atoms are present at these sites. 20 The dopant A may itself occupy an Li or Zr site. It is considered that the dopant AI, Ga or Fe is generally at an Li site. It is considered that the dopant Nb, Wand Ta is generally at a Zr site. The inorganic compound M preferably has a cubic structure. The structure is 25 determined using x-ray diffraction. This structure is generally described as belonging to the Ia3d space group. It is also possible for this structure to belong to the l-43d space group, in particular when A=Ga, Fe or AI+Ga. The inorganic compound M is prepared using LLZO garnet preparation 30 techniques which are known to those skilled in the art. Reference may be made to the methods given by reference in Journal of the Korean Ceramic Society 2019; 56(2): 111-129 (DOl: https://doi.org/10.4191/kcers.2019.56.2.01). It is possible for example to prepare it using a solid-state method by which the oxides wo 2021/219806 PCT/EP2021/061307 8 or salts of the constituent elements of the oxide are intimately mixed, then the mixture obtained is calcined at a high temperature, typically above 900°C. More particularly, use may for example be made of the method described in EP 2353203 81 which comprises the following steps: (1) Li2C03, La(OH)3, Zr02 and 5 an oxide, a carbonate, a hydroxide or a salt of at least one element A are intimately mixed, for example by milling in a liquid medium such as ethanol; (2) the mixture obtained is calcined in air at a temperature of at least 900°C for a period of at least 1 hour; (3) Li2C03 is intimately mixed with the calcined product, for example by milling in a liquid medium such as ethanol; (4) the mixture 1 0 obtained is calcined in air at a temperature of at least 900°C, then at a temperature of at least 11 00°C. Generally, an oxide of the element A is used for this synthesis. Use may be made of the precise conditions of example 1 of EP 2353203 81 suitable for any composition of formula (1). Use may also be made of the solid-state method described in J. Mater. Chem. A, 2014, 2, 172 (DOl: 15 10.1 039/c3ta13999a) which comprises the following steps: (1) Li2C03, La(OH)3, Zr02 and an oxide, a carbonate, a hydroxide or a salt of at least one element A are intimately mixed; (2) the mixture obtained is calcined in air at a temperature of at least 1 ooooc for at least 10 hours; (3) the calcined product is then milled with a mortar and screened to recover only particles <75 mm which are then 20 milled in isopropyl alcohol. It is also possible to prepare the inorganic compound M using a co-precipitation method via which a solution comprising the salts of the elements La, Zr and A (for example a solution of conitrates) is brought into contact with a basic solution, 25 so as to obtain a precipitate, then to bring the precipitate into contact with a lithium salt and to calcine the precipitate/lithium salt mixture at a temperature of at least 900°C. Use may be made of the precise conditions of example 1 of US 2019/0051934 suitable for any composition of formula (I). 30 Other methods are described in the following documents: JP 2012-224520, US 2018/0248223, US 2019/0051934 or EP 3135634 81 (see in particular example 1 ). wo 2021/219806 PCT/EP2021/061307 9 The inorganic compound M of formula (I) comprises or essentially consists of the oxide of formula (II): Lix1La3ZrzAw012 (II) wherein A, z and w are as described above and x1 is a positive real number 5 which is such that the electroneutrality of the oxide is ensured. x, z and ware as described above. As regards the real number x1, it is such that the electroneutrality of the oxide is ensured. In order to do this, the proportion of the constituent elements of the oxide other than lithium, i.e. of the elements Zr, 1 0 La and A and optionally Hf, is also taken into account. For the calculation of x1, the following oxidation states are also taken into account: Li +I; Zr +IV; Hf +IV; La +Ill; AI +Ill; Ga +Ill; Nb +V; Fe +Ill, W +VI; Ta +V. For example, for an oxide consisting of the elements Li, AI, La and Zr with z=1.99 and w=0.22 (as given by the chemical analysis), x1 is equal to 6.38 (x1 = 24- 3x3- 4x1.99- 3x0.22). 15 It will be noted that in the preparation of the inorganic compound M, the calcination step or steps which are carried out at high temperatures have the effect of volatilizing lithium. To compensate for this, the lithium is generally provided in excess relative to the stoichiometry of the oxide of formula (I), so that 20 x > x1. That which has been described above with regard to the possible presence of the element hafnium also applies to the oxide of formula (II). Thus, it will be remembered that the invention therefore applies also to an oxide of formula 25 (lla): Lix1La3(Zr(1-a)+Hfa)z012 (lla) x1, z and a being as described above. The oxide of formula (II) or else of formula (I Ia) is of garnet type. It is considered 30 that its crystalline structure generally consists of a skeleton of LaOs dodecahedra (La of coordination number 8) and of ZrOe octahedra (Zr of coordination number 6). More particularly, it may be composed of a skeleton of LaOs dodecahedra of coordination number 8 (24c site) and of ZrOe octahedra of coordination number 6 wo 2021/219806 PCT/EP2021/061307 10 (16a site). In the garnet-type structure, the Li atoms may be present at the 24d tetrahedral sites or 48g and 96h octahedral sites. It is possible that most of these atoms are present at these sites. 5 This oxide preferably has a cubic structure. The structure is determined using xray diffraction. This structure is generally described as belonging to the Ia3d space group. It is also possible for this structure to belong to the l-43d space group, in particular when A=Ga, Fe or AI+Ga. 10 The fluorination is carried out by bringing the inorganic compound M (and therefore the oxide of formula (II)) into contact with an atmosphere comprising difluorine (F2) gas. The fluorinated atmosphere may be essentially constituted of difluorine gas. 15 The proportion of difluorine in the atmosphere is greater than 99.0%, or even 99.5%, or even 99.9%. All these proportions are expressed as volume %. An example of an atmosphere comprising difluorine is given in the examples. The fluorination corresponds to a reaction between a solid and a gas. It may 20 be carried out in static mode according to which the inorganic compound M and the fluorinated atmosphere are introduced into a sealed chamber, preferably placed under vacuum beforehand, and left to react. In the case of being placed under vacuum beforehand, a low vacuum of at least 1 o-2 mbar may be applied. An initial F2 pressure of between 100 and 500 mbar may be 25 applied. Reference may also be made to the fluorination procedure described in the article "Fluorinated nanodiamonds as unique neutron reflector'', Carbon, Volume 130, April 2018, pages 799-805 and also to the examples. According to a variant of the static mode described above ("pulsed" mode), the fluorinated atmosphere in the chamber is introduced in several goes into the 30 sealed chamber containing the inorganic compound M and, between two additions, the fluorinated atmosphere is left to react with the solid. The static mode and the variant thereof may be carried out according to the protocol wo 2021/219806 PCT/EP2021/061307 11 described in detail in the examples (see examples 3-4 and example 5 respectively). The fluorination process may also advantageously be carried out in dynamic 5 mode according to which the fluorinated atmosphere is introduced continuously into an open chamber containing the inorganic compound M. The volume flow rate (measured at 20°C and at atmospheric pressure) of the fluorinated atmosphere which flows into the open chamber may be between 1 0 and 100 ml/min, more particularly between 10 and 30 ml/min. Reference may 1 0 also be made to the procedure described in the article "The synthesis of microporous carbon by the fluorination of titanium carbide", Carbon, Volume 49, Issue 9, August 2011, pages 2998-3009. The dynamic mode may be carried out according to the protocol described in detail in examples 1 and 2. 15 Regardless of the mode used, at the end of the fluorination, the excess difluorine, like the products of the reaction, are purged by an inert gas (such as for example N2 or He) and neutralized in a soda lime trap positioned downstream of the reactor. 20 Regardless of the mode used, the total duration of the contact between the solid and the fluorinated atmosphere is between 2 minutes and 4 hours, or even between 2 minutes and 2 hours, or even between 30 minutes and 2 hours. 25 The fluorination is carried out at a temperature which is variable. This may be between 20°C and 300°C, preferably between 20°C and 250°C. It is preferably carried out at a "low" temperature, preferably between 20°C and 50°C, so as not to degrade the physicochemical properties, in particular the conductivity, of the oxide. 30 Of course, from a practical point of view, regardless of the mode, it is preferable to use a chamber that is resistant to corrosion by difluorine. The material of the chamber must therefore be corrosion resistant which makes it 5 wo 2021/219806 PCT/EP2021/061307 12 possible to also prevent any contamination by elements present at its surface. Use may advantageously be made of a chamber made of nickel passivated by NiF2. The solid may be placed on a plate also made of passivated nickel inserted in the chamber. To promote contact between the solid and the gas, the solid could be arranged in the form of a bed, the thickness of which may advantageously be less than or equal to 5 mm. The inorganic compound M is preferably in the form of a powder to promote contact with the fluorinated atmosphere. This powder may 10 have a d50 of less than 50 1-Jm, more particularly of less than 30 1-Jm. d50 corresponds to the median diameter of a size distribution (by volume) obtained by the laser diffraction technique on a dispersion of the solid in a liquid medium, in particular in water. 15 Regarding the fluorinated inorganic compound The invention also relates to the fluorinated inorganic compound which is obtained at the end of the process described above. The chemical composition of this compound corresponds essentially to that given by one of the chemical formulae given above, it being understood that the compound also comprises 20 the element fluorine. The invention thus also relates to an inorganic compound which has a garnettype structure and which is based on the elements 0, Li, Zr, A and optionally Hf, the relative proportions of which are those of the formula (I), this compound 25 also comprising the element F and having at least one of the following characteristics: • a signal located between -125.0 and -129.0 ppm, more particularly between -126.0 and -128.0 ppm, more particularly still between -126.5 and -127.5 ppm, on a (19F) solid-state NMR spectrum, the reference at 30 8=0 ppm being that of the compound CF3COOH; • a ratio R less than or equal to 50%, more particularly less than or equal to 40%, more particularly still less than or equal to 30% or 20% or 10%, R being the ratio between the intensity of the vibrational band of the C5 wo 2021/219806 PCT/EP2021/061307 13 0 bond of the carbonate groups (symmetric stretching v) located around 1 090 cm-1 to the intensity of the stretching band of the bonds in the ZrOe octahedra located around 648 cm-1, these two intensities being determined by Raman spectroscopy. Further details are given below on the characterization of this inorganic compound. -Characterization by (19F) solid-state NMR 10 The (19F) solid-state NMR spectrum of the inorganic compound may have a signal located between -125.0 and -129.0 ppm, more particularly between - 126.0 and -128.0 ppm, more particularly still between -126.5 and -127.5 ppm. The chemical shifts are given by taking CF3COOH as reference at 8=0 ppm. This signal is generally symmetrical. This signal is generally attributed to a 15 fluorine involved in an Li-F bond. The NMR spectrum may advantageously be obtained with magic-angle spinning of 30 kHz. 20 Use may more particularly be made of the measurement conditions given in the exam pies. By the same spectroscopic technique and under the same conditions, it is also possible to observe a signal between -98.0 and -102.0 ppm, more particularly 25 between -99.0 and -101.0 ppm, more particularly still between -99.5 and - 100.5 ppm and/or a signal between -58.0 and -62.0 ppm, more particularly between -59.0 and -61.0 ppm, more particularly still between -59.5 and -60.5 ppm. The signals are generally attributed to the formation of La-F and Zr-F bonds respectively. 30 - Characterization by Raman spectroscopy The effect of the fluorination may also be demonstrated using Raman spectroscopy. Thus, the fluorinated inorganic compound has a ratio R less wo 2021/219806 PCT/EP2021/061307 14 than or equal to 50%, more particularly less than or equal to 40%, more particularly still less than or equal to 30% or 20% or 10%, R being the ratio between the intensity of the vibrational band of the C-0 bond of the carbonate groups (symmetric stretching v) located around 1 090cm-1 to the intensity of the 5 stretching band of the bonds in the ZrOe octahedra located around 648 cm-1. 10 It is generally considered that the C-0 vibrational band of the carbonate groups is located at 1 090±20 cm-1. This band is generally located between 1080 and 1100 cm-1. It is generally considered that the stretching band of the ZrOe octahedra is located at 648±20 cm-1. This band is generally located between 638 and 658 cm-1. 15 It is furthermore observed that the inorganic compound may have the same R ratio after storage in an air-filled sealed flask for a period of at least two months, in particular of two months. - Characterization by infrared spectroscopy in attenuated total reflection (ATR) 20 mode The effect of the fluorination may also be demonstrated using infrared spectroscopy in attenuated total reflection (ATR) mode. Specifically, the carbonate groups have vibrational modes V3 and v2 respectively located between 1350 and 1600 cm-1 and between 890 and 1350 cm-1. Thus, the 25 intensity of the vibrational mode V3 and/or of the vibrational mode v2 of the carbonate groups, these modes being respectively located between 1350 and 1600 cm-1 and between 890 and 1350 cm-1, is less than or equal to 50%, more particularly less than or equal to 40%, more particularly still less than or equal to 30% or 20% or 10%. 30 As for the R ratio, the inorganic compound may have this same intensity after storage in an air-filled sealed flask for a period of at least two months, in particular of two months. wo 2021/219806 PCT/EP2021/061307 15 - Proportion of fluorine The proportion of fluorine in the compound expressed by weight of the element fluorine relative to the total weight, is generally less than or equal to 1 0.0%, 5 more particularly less than or equal to 7.0%, more particularly still less than or equal to 5.0%. This proportion is generally greater than or equal to 0.01 %, more particularly greater than or equal to 0.1 0%, more particularly still greater than or equal to 0.50%. This proportion may be between 0.01% and 1 0.0%, more particularly between 0.10% and 1 0.0%, or even between 0.10% and 10 7.0%. This proportion may be determined using centesimal analysis or else by 19F NMR. For the determination of the proportion of fluorine by NMR, use may be made of an internal standard containing the element fluorine, the signals of which do not coincide with those of the inorganic compound. For example, use may be made of a PVDF homopolymer. With the PVDF standard, use may in 15 particular be made of the following formula: A2 ml [F] % by weight=- X - X [F]PVDF Al m2 with A 1 the sum of the areas of the fluorine signals of the PVDF, m 1 the mass of PVDF, A2 the sum of the areas of the fluorine signals of the inorganic compound, m2 the mass of the inorganic compound and [F]PvoF the 20 concentration by mass of the fluorine in the PVDF, namely 59. It is observed that the fluorination process has the effect of reducing the amount of carbonate groups which are present, in particular at the surface of the solid, or even of making them disappear. This reduction/disappearance is 25 gradual depending in particular on the contact time between the solid and the fluorinated atmosphere. The process of the invention therefore makes it possible to decarbonate the surface of the solid, which ensures an effective protection thereof, in particular even after storage of the solid in the open air. 30 The fluorination is carried out under "mild" conditions so that the crystalline structure of the starting solid is not adversely affected. In other words, the fluorinated inorganic compound has the same crystalline structure as the wo 2021/219806 PCT/EP2021/061307 16 starting solid. It therefore preferably has a cubic structure. The structure is determined using x-ray diffraction. This structure is generally described as belonging to the Ia3d space group. It is also possible for this structure to belong to the l-43d space group, in particular when A=Ga, Fe or AI+Ga. 5 Furthermore, the fluorinated inorganic compound generally consists of a skeleton of LaOs dodecahedra (La of coordination number 8) and of ZrOe octahedra (Zr of coordination number 6). More particularly, it may be composed of a skeleton of LaOs dodecahedra of coordination number 8 (24c site) and of ZrOe octahedra of coordination number 6 (16a site). In the garnet- 1 0 type structure, the Li atoms may be present at the 24d tetrahedral sites or 48g and 96h octahedral sites. 15 Furthermore, the fluorination does not generally result in a broadening of the xray diffraction peaks. Use of the fluorinated inorganic compound The fluorinated inorganic compound may be used as solid electrolyte of a lithium battery. It may also be used in the preparation of a lithium battery. The fluorinated inorganic compound may be used in the preparation of an electrode 20 E. The electrode E may be a positive electrode (Ep) or a negative electrode (En). The electrode E typically comprises: • a metal support; 25 • a layer of a composition (C) in contact with the metal substrate, said 30 composition (C) comprising: (i) the fluorinated inorganic compound as described; (ii) at least one electroactive compound (EAC); (iii) optionally at least one material which conducts the Li ions other than the fluorinated oxide (LiCM); (iv) optionally at least one electrically-conductive material (ECM); (v) optionally a lithium salt (LIS); (vi) optionally at least one polymer binder material (P). wo 2021/219806 PCT/EP2021/061307 17 The term electroactive compound (EAC) denotes a compound which may incorporate lithium ions into its structure and release them during the charging and discharging of the battery. The nature of EAC varies depending on whether 5 it is a positive or negative electrode: 1) positive electrode E0 EAC may be a chalcogenide-type compound of formula LiMe02 wherein: -Me denotes at least one metal chosen from the group formed of Co, Ni, Fe, Mn, Cr, AI and V; 10 - Q denotes 0 or S. EAC may more particularly be of formula LiMe02. Examples of EAC are given below: LiCo02, LiNi02, LiMn02, LiNixC01-x02 (0