Technical field This invention relates to the field of batteries and in particular lithium-ion batteries. It relates more specifically to all-solid lithium ion batteries (“Li-ion batteries”) and a novel process for producing such batteries. Prior art Modes of producing lithium-ion batteries (“Li-ion batteries”) presented in numerous articles and patents are known; the work “Advances in Lithium-Ion Batteries” (ed. W. van Schalkwijk and B. Scrosati), published in 2002 (Kluever Academic / Plenum Publishers) provides a good review of the situation. The electrodes of Li-ion batteries may be produced by means of printing or deposition techniques known to a person skilled in the art, and in particular by roll-coating, doctor blade or tape casting. There are various architectures and chemical compositions of electrodes enabling Li-ion batteries to be produced. Recently, Li-ion batteries formed by allsolid thin layers have appeared. These batteries generally have a planar architecture, that is, they are essentially formed by a set of three layers forming a basic battery cell: an anode layer and a cathode layer separated by an electrolyte layer. More recently, Li-ion batteries with three-dimensional structures have been produced using new processes. Such processes are in 2 particular disclosed in documents WO 2013/064 779 A1 or WO 2012/064 777 A1. In these documents, the production of anode, solid electrolyte and cathode layers is performed by electrophoresis. The batteries obtained by this process have a high power density; they also have a high energy density (around twice that of known lithium-ion batteries) due to the very low porosity level and the low thickness of the electrolyte films. In addition, the batteries obtained by these processes do not contain metallic lithium or organic electrolytes. Thus, they may be resistant when subjected to high temperatures. Finally, when they are produced in the form of a “microbattery”-type electronic component, they may then be tested before being welded to circuits, without the risk of damage, in particular when the batteries are in a partially charged or discharged state. However, the performance of these all-solid batteries may be variable. Obtaining sustainable performance over time is dependent not only on the choice of the electrolytes and production parameters but also the overall architecture of the battery. For example, depending on the chemical composition and nature of the electrolyte film, internal resistance may appear at the interfaces with the electrodes. Moreover, certain electrolytes disclosed in these documents are based on sulfides, which are stable within a broad potential range, but which have a tendency to create strong resistance to the transfer of charges at their interfaces with the electrodes. Furthermore, solid sulfide-based electrolytes are extremely hygroscopic, which may make it difficult to implement them on an industrial scale and may cause particular sensitivity to 3 aging. In addition, these documents disclose ionic conductive glass-based electrolytes, such as LiPON or lithiated borate. However, these have a relatively low glass transition temperature and are therefore capable of partially crystallizing during assembly of the battery by heat treatment; this causes their ionic conduction properties to deteriorate. Finally, these components remain relatively sensitive in contact with the atmosphere, making them difficult to implement on an industrial level. Electrolytes containing lithiated phosphate-based materials are also known, the latter being stable in contact with the atmosphere and stable at high potential. However, these electrolytes are usually unstable in contact with anodes in lithium. The instability of these electrolytes in contact with anodes is essentially due to the presence of metallic elements capable of having multiple oxidation states that, when in contact with the low-potential anodes, will be reduced and change oxidation states. This chemical modification gradually renders the electrolyte electrically conductive, which degrades the performance of the battery. This family of electrolytes includes Li1+xAlxTi2- x(PO4)3 (called LATP) in which a titanium reduction may appear at 2.4 V, and Li1+xAlxGe2-x(PO4)3 (called LAGP) in which a germanium reduction may appear at 1.8 V. Aside from the electrochemical degradation of the electrolytes and other aging phenomena associated with the sensitivity to air of certain constituents of the Liion battery cell, the degradation of performance of Liion batteries may also come from the cathode. In fact, 4 lithium insertion materials used to produce cathodes have reversible behavior only in a certain potential range. When the level of lithium inserted decreases below a certain threshold, crystallographic modifications may appear, causing irreversible losses in performance of the cathode materials. However, conventional Li-ion batteries as well as thin-layer Li-ion batteries using metallic lithium anodes have lithium ion storage capacities (at the anode level) greater than that at the cathode. In fact, in the case of batteries with metallic lithium anodes, the capacity of the anode is practically unlimited, and the lithium may be deposited onto the anode as it arrives. For standard Li-ion batteries using liquid electrolytes with lithium salts, an anode capacity lower than that of the cathode may lead to the formation of metallic lithium precipitates in the battery during charging. These precipitates form when the cathode produces lithium ions in excess of what the anode is capable of accepting. As the formation of metallic lithium precipitates in a battery cell is capable of causing a risk of thermal runaway, it is essential to ensure that the anodes have sufficient capacities to prevent the appearance of such a risk. Although it is more of a safety measure, this architecture may in some cases lead to an extraction of too many lithium ions from the cathode, in particular during high-power cycling phases on charged batteries. This may irreversibly deteriorate the insertion capacity of the battery and lead to its aging. In addition, the aging of the battery and the loss of its capacity may also result from the precipitation of lithium ions in the porosities of the electrodes, thereby 5 reducing the quantity of lithium ions available for operation of the battery, as well as the loss of contacts between the electrode particles. A first objective of the present invention is to produce all-solid thin-layer batteries, in which the materials used for the electrolyte layers are stable in contact with anodes and cathodes in order to improve the operation and lifetime of said batteries. Yet another objective is to produce all-solid thinlayer batteries in which the materials used for the electrolyte layers do not enable the formation of metallic lithium precipitates, or internal resistance at the interfaces with the electrodes. Another objective of the invention is to produce thin-layer batteries by a process capable of being implemented on an industrial level in a relatively simple manner. Objects of the invention A first object of the invention concerns a process for producing an all-solid thin-layer battery including the following series of steps: a) a layer including at least one anode material (referred to here as “anode material layer”) is deposited on its conductive substrate, preferably selected from the group formed by a metal sheet, a metal strip, a metallized insulating sheet, a metallized insulating strip, a metallized insulating film, said conductive substrates, or conductive elements thereof, capable of serving as an anode current collector; b) a layer including at least one cathode material (referred to here as “cathode material layer”) is 6 deposited on its conductive substrate, preferably selected from the group formed by a metal sheet, a metal strip, a metallized insulating sheet, a metallized insulating strip, a metallized insulating film, said conductive substrates, or conductive elements thereof, capable of serving as a cathode current collector, with the understanding that steps a) and b) can be reversed; c) on the layer obtained in step a) and/or b), a layer including at least one solid electrolyte material (referred to here as “electrolyte material layer”) is deposited, chosen from: - Li3(Sc2-xMx)(PO4)3 with M = Al or Y and 0 ≤ x ≤ 1; or - Li1+xMx(Sc)2-x(PO4)3 with M = Al, Y, Ga or a mixture of the three compounds and 0 ≤ x ≤ 0.8; or - Li1+xMx(Ga1-yScy)2-x(PO4)3 with 0 ≤ x ≤ 0.8; 0 ≤ y ≤ 1 and M = Al or Y; or a mixture of the two compounds; or - Li1+xMx(Ga)2-x(PO4)3 with M = Al, Y; or a mixture of the two compounds and 0 ≤ x ≤ 0.8; or - Li3+y(Sc2-xMx)QyP3-yO12 with M = Al and/or Y and Q = Si and/or Se, 0 ≤ x ≤ 0.8 and 0 ≤ y ≤ 1; or - Li1+x+yMxSc2-xQyP3-yO12 with M = Al, Y, Ga or a mixture of the three compounds and Q = Si and/or Se, 0 ≤ x ≤ 0.8 and 0 ≤ y ≤ 1; or - Li1+x+y+zMx(Ga1-yScy)2-xQzP3-zO12 with 0 ≤ x ≤ 0.8; 0 ≤ y ≤ 1; 0 ≤ z ≤ 0.6 with M = Al or Y or a mixture of the two compounds and Q = Si and/or Se; - Li1+xNxM2-xP3O12 with 0 ≤ x ≤ 1 and N = Cr and/or V, M = Sc, Sn, Zr, Hf, Se or Si, or a mixture of these compounds; d) the following are stacked, layer upon layer, in series: 7 - a layer including at least one anode material coated with a layer including at least one electrolyte material obtained in step c) with a layer including at least one cathode material coated or not with a layer including at least one electrolyte material obtained in step c); - or a layer including at least one cathode material coated with a layer including at least one electrolyte material obtained in step c) with a layer including at least one anode material coated or not with a layer including at least one electrolyte material obtained in step c); e) a heat treatment and/or a mechanical compression of the stack obtained in step d) is carried out in order to obtain an all-solid thin-layer battery. In a particular embodiment of the process according to the invention, when a layer of electrolyte material is deposited on the layer obtained in step a), a layer of at least one material chosen from the following is optionally deposited on the layer obtained in step b): - Li3(Sc2-xMx)(PO4)3 with M = Al or Y and 0 ≤ x ≤ 1; or - Li1+xMx(Sc)2-x(PO4)3 with M = Al, Y, Ga or a mixture of two or three compounds and 0 ≤ x ≤ 0.8; or - Li1+xMx(Ga1-yScy)2-x(PO4)3 with 0 ≤ x ≤ 0.8; 0 ≤ y ≤ 1 and M = Al or Y; or a mixture of the two compounds; or - Li1+xAlxTi2-x(PO4)3 with 0 ≤ x ≤ 1; or - Li1+xAlxGe2-x(PO4)3 with 0 ≤ x ≤ 1; or - Li1+x+zMx(Ge1-yTiy)2-xSizP3-zO12 with 0 ≤ x ≤ 0.8; 0 ≤ y ≤ 1; 0 ≤ z ≤ 0.6 and M = Al, Ga or Y or a mixture of two or three of these compounds; or - Li3+y(Sc2-xMx)QyP3-yO12, with M = Al and/or Y and Q = 8 Si and/or Se, 0 ≤ x ≤ 0.8 and 0 ≤ y ≤ 1; or - Li1+x+yMxSc2-xQyP3-yO12 with M = Al, Y, Ga or a mixture of the three compounds and Q = Si and/or Se, 0 ≤ x ≤ 0.8 and 0 ≤ y ≤ 1; or - Li1+x+y+zMx(Ga1-yScy)2-xQzP3-zO12 with 0 ≤ x ≤ 0.8; 0 ≤ y ≤ 1; or 0 ≤ z ≤ 0.6 with M = Al or Y or a mixture of the two compounds and Q = Si and/or Se; - Li1+xNxM2-xP3O12 with 0 ≤ x ≤ 1 and N = Cr and/or V, M = Sc, Sn, Zr, Hf, Se or Si or a mixture of these compounds. According to the invention, the layers including at least one anode material, at least one cathode material and at least one solid electrolyte material are deposited by one or more techniques selected from the following techniques: (i) physical vapor deposition (PVD), and more specifically by vacuum evaporation, laser ablation, ion beam, or cathode sputtering; (ii) chemical vapor deposition (CVD), and more specifically plasma-enhanced chemical vapor deposition (PECVD), laser-assisted chemical vapor deposition (LACVD), or aerosol-assisted chemical vapor deposition (AA-CVD); (iii) electrospraying; (iv) electrophoresis; (v) aerosol deposition; (vi) sol-gel; (vii) dipping, more specifically dip-coating, spincoating or the Langmuir-Blodgett process. Advantageously, said anode and/or cathode and/or electrolyte layers are produced by deposition of nanoparticles, respectively, of anode, cathode or 9 electrolyte material, by one or more techniques selected from the following techniques: electrospraying, electrophoresis, aerosol deposition, and dipping. Preferably, the anode, cathode and electrolyte layers are all deposited by electrophoresis, preferably from nanoparticles of cathode material(s), electrode material(s) and anode material(s). According to the invention, the anode material layer a) is produced from material chosen from the following: (i) tin oxynitrides (typical formula SnOxNy); (ii) lithiated iron phosphate (typical formula LiFePO4); (iii) mixed silicon and tin oxynitrides (typical formula SiaSnbOyNz with a>0, b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b≤2, 00, b>0, a+b>0, a+b≤2, 00, b>0, a+b≤2, 0