Field of the invention This invention relates to the field of batteries and in particular lithium ion batteries. It relates more specifically to all-solid-state lithium ion batteries, and a novel process for manufacturing such batteries. 5 Prior art The modes for manufacturing lithium ion batteries ("Li-ion batteries") are presented in many articles and patents, and the work "Advances in Lithium-Ion Batteries" 10 (ed. W. van Schalkwijk and B. Scrosati), published in 2002 (Kluever Academic / Plenum Publishers) provides a good assessment of them. The electrodes of Li-ion batteries can be produced by means of printing or deposition techniques known to a person skilled in the 15 art (in particular: roll coating, doctor blade, tape casting). These techniques make it possible to produce depositions having a thickness of between 50 and 400 μm. Depending on the thickness of the depositions, their porosities and the size of the active particles, the 20 power and energy of the battery may be modulated. More recently, other Li-ion battery architectures have appeared. These are primarily all-solid-state thinfilm microbatteries. These microbatteries have a planar architecture, that is, they consist essentially of an 25 assembly of three layers forming an elementary battery cell: an anode layer and a cathode layer separated by an electrolyte layer. These batteries are said to be “allsolid- state” because the two electrodes (anode and 2 WO 2014/131997 2 PCT/FR2014/050424 cathode) and the electrolyte are made of non-porous solid materials. These batteries have an important advantage owing to their superior performance to those of conventional electrolyte-based batteries including 5 lithium salts dissolved in an aprotic solvent (liquid or gel electrolyte). The absence of liquid electrolyte considerably reduces the risks of internal short-circuit and thermal runaway in the battery. Different vacuum deposition techniques have been 10 used to produce thin-film microbatteries. In particular, physical vapor deposition (PVD) is the technique most commonly used at present to produce these thin-film microbatteries. This technique makes it possible to produce high-quality electrode and electrolyte layers 15 without porosity. These layers are generally thin (generally less than 5 μm) so as not to cause excessive power loss associated with an increase in the electrode thicknesses. Numerous approaches have been proposed in order to 20 produce all-solid-state batteries. In general, these approaches are based only on high-pressure mechanical compaction of electrode and electrolyte material powders (Journal of Power Sources, 2009, 189, 145-148 H. Kitaura). Nevertheless, the electrode and electrolyte layers 25 obtained are porous and the adhesion between them is not optimal, so that the internal resistance of said batteries is too high and does not enable a high power to be generated. To improve the performance of all-solid-state 30 batteries, a number of sintering techniques have been used, either using thermal treatments (Journal of Power Sources, 2007, 174, K. Nagata) or pulsed current 3 WO 2014/131997 3 PCT/FR2014/050424 (Material Research Bulletin, 2008, X. Xu). However, sintering leads to significant shrinkage and/or the use of high temperature. Consequently, it is not possible to perform the all-solid-state electrode deposition on 5 conductive metal substrates, and more specifically aluminum substrates. Indeed, an excessively high temperature would oxidize or significantly deteriorate the metal substrate. Moreover, the layer deposited on the substrate would lead to the appearance of cracks during 10 sintering. These disadvantages require current collectors to be deposited on the ends of the battery cell formed by a cathode/electrolyte/anode stack. Consequently, the restriction associated with the deposition of current collectors does not make it possible to produce a three15 dimensional battery assembly, all-solid-state, monolithic, consisting of a plurality of elementary cells. This invention is therefore intended for producing an all-solid-state monolithic Li-ion battery, the monolithic body consisting of a plurality of elementary 20 cells, by producing dense electrode deposits directly on the two faces of a substrate acting as a battery current collector, and by depositing an all-solid-state dense electrolyte layer on at least one of the dense electrode deposits obtained. 25 Subject matter of the invention This invention relates to a process for producing all-solid-state batteries, said batteries including at least one dense layer containing anode materials ("anode 30 layer"), at least one dense layer containing solid electrolyte materials ("electrolyte layer"), and at least one dense layer containing cathode materials ("cathode 4 WO 2014/131997 4 PCT/FR2014/050424 layer"), in order to obtain an all-solid-state battery consisting of an assembly of a plurality of elementary cells, the process including the following steps: a) a dense anode layer and a dense cathode layer are 5 each deposited on their respective conductive substrates, said conductive substrates being capable of serving as an anode and cathode current collector, respectively; b) a dense solid electrolyte layer is deposited on at least one of the two layers obtained in step a); 10 c) a layer containing at least one Ms bonding material is deposited on at least one of the layers obtained in step a) and /or b); with the understanding that the depositions of the layers of step a), b) and c) are not all performed by electrophoresis; 15 d) the layer obtained in step c) is stacked face-toface with a layer obtained in step a), b) or c); e) a thermal treatment and/or mechanical compression promoting contact between said two layers stacked faceto- face is performed in order to obtain an all-solid20 state assembly of elementary cells, capable of functioning as a battery. Preferably, the deposition of the anode and cathode layer is performed on the two faces of their respective conductive substrates. 25 In a preferred embodiment, the thermal treatment performed in step e) is performed at a temperature TR which, preferably, does not exceed 0.7 times the melting or decomposition temperature (expressed in C), and more preferably does not exceed 0.5 times (and even more 30 preferably does not exceed 0.3 times) the melting or decomposition temperature (expressed in C) of the at least one most fusible Ms bonding material subjected to 5 WO 2014/131997 5 PCT/FR2014/050424 said thermal treatment step. Similarly, the mechanical compression of the assembly obtained in step e) is performed at a pressure of between 10 and 100 MPa, preferably between 10 and 50 MPa. 5 The deposition of the layers of step a), b) and c) are performed by vapor phase and/or by wet deposition, and mores specifically at least one of the following techniques: i) physical vapor deposition (PVD), and more 10 specifically vacuum evaporation, laser ablation, ion beam, cathode sputtering; ii) chemical vapor deposition (CVD) and more specifically plasma-enhanced chemical vapor deposition (PECVD), laser-assisted chemical vapor deposition (LACVD), 15 or aerosol-assisted chemical vapor deposition (AA-CVD); iii) electrospraying; iv) aerosol deposition; v) electrophoresis; vi) sol-gel; 20 vii) dipping, more specifically dip-coating, spincoating or the Langmuir-Blodgett process. The Ms bonding material is preferably selected from one or more of the following materials: a) oxide-based materials chosen from Li3.6Ge0.6V0.4O4; 25 Li2O-Nb2O5; LiSiO4; Li2O; Li14Zn(GeO4)4; Li6Zr2O7; Li8ZrO6; Li0.35La0.55TiO3; Li0.5La0.5TiO3; Li7La3Zr2O12; Li5+xLa3(Zrx,A2- x)O12 with A=Sc, Ti, V, Y, Nb, Hf, Ta, Al, Si, Ga, Ge, Sn and 1.4 ≤ x ≤ 2; b) nitride- or oxynitride-based materials chosen 30 from Li3N; Li3PO4-xN2x/3, Li4SiO4-xN2x/3, Li4GeO4-xN2x/3 with 0 < x 4 or Li3BO3-xN2x/3 with 0 < x < 3; lithium and phosphorus oxynitride-based materials (called LiPON) that may also 6 WO 2014/131997 6 PCT/FR2014/050424 contain silicon (called LiSiPON), boron (called LiPONB), sulfur (called LiPONS), zirconium or aluminum (called LiPAON) or a combination of aluminum, boron, sulfur and/or silicon; the lithium and boron oxynitride-based 5 materials (called LiBON) that may also contain silicon (called LiSiBON), sulfur (called (LIBONS) or aluminum (called LiBAON) or a combination of aluminum, sulfur and silicon; and more specifically materials of the LixPOyNz type with x ~ 2.8 and 2y = 3z with 0.16 ≤ z ≤ 0.46; or 10 LiwPOxNySz with (2x+3y+2z) = (5+w) and 3.2 ≤ x ≤ 3.8; 0.13 ≤ y ≤ 0.4; 0 ≤ z ≤ 0.2; 2.9 ≤ w ≤ 3.3; or LitPxAlyOuNvSw with (5x+3y)=5; (2u+3v+2w) = (5+t); 2.9 ≤ t 3.3; 0.84 ≤ x ≤ 0.94; 0.094 ≤ y ≤ 0.26; 3.2 ≤ u ≤ 3.8; 0.13 ≤ v ≤ 0.46; 0 ≤ w ≤ 0.2; or Li1.9Si0.2P1.0O1.1N1.0; or Li2.9PO3.3N0.46; or 15 Li6-0.75xP1.75xZr2-2xO7-yNz with z ≤ 14/3; 2y = 3z and x ≤ 0.8; or Li8-3.5xP1.5xZr1-xOz6-yNz with x ≤ 0.8; z ≤ 4 and 2y = 3z; or Li8-3xLaxZrO6-yNz with O < x ≤ 2; z ≤ 4 and 2y = 3z; or Li3(Sc2-xMx)(PO4-yNz) with x ≤ 2; z ≤ 8/3; 2y = 3z and M=Al, Y or Al1-aYa with a<1; 20 c) sulfide-based materials chosen from: LixM1-yM'yS4 with M=Si, Ge, Sn and M'=P, Al, Zn, Ga, Sb; Li2S; B2S3; P2S5; 70Li2S-30P2S5; Li7P3S11; Li10GeP2S12; Li7PS6; Li3.25Ge0.25P0.75S4; Li10MP2S12 with M = Si, Ge, Sn and mixtures between Li2S and one of the compounds among P2S5, 25 GeS2, Ga2S3 or SiS2; d) phosphate or borate-based materials chosen from Li3PO4; LiTi(PO4)3; Li1+xAlxM2-x(PO4)3 (where M = Ge, Ti, and/or Hf and 0 < x 1); Li1.3Al0.3Ti1.7(PO4)3; Li1+x+yAlxTi2- xSiyP3-yO12 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1); Li1+x+zMx (Ge1- 30 yTiy)2-xSizP3-zO12 (where 0 ≤ x ≤ 0.8, 0 ≤ y ≤ 1.0, 0 ≤ z ≤ 0.6); 2(Li1.4Ti2Si0.4P2.6O12)-AlPO4; LixAlz-yGaySw(PO4)c or LixAlz-yGaySw(BO3)c or LixGez-ySiySw(PO4)c or LixGez- 7 WO 2014/131997 7 PCT/FR2014/050424 ySiySw(BO3)c or more generally LixMz-yM'ySw(PO4)c or LixMzyM'ySw( BO3)c with 4 < w < 20, 3 < x < 10, 0 ≤ y ≤ 1 , 1 ≤ z ≤ 4 and 0 < c < 20 and M or M' an element among Al, Si, Ge, Ga, P, Zn, Sb; or Li3Sc2-xMxPO4 with M = Al, Y or Al1- 5 aYa with a<1; e) mixed materials chosen from the mixtures between Li2S and one of the compounds among Li3PO4, Li3PO4-xN2x/3, Li4SiO4-xN2x/3, Li4GeO4-xN2x/3 with 0 < x < 4 or Li3ΒO3-xN2x/3 with 0 < x < 3; the mixtures between Li2S and/or B2S3 10 SiS2, P2S5, GeS2, Ga2S3 and a compound of the LiaMOb type, which may be a lithium silicate Li4SiO4, a lithium borate Li3BO3 or a lithium phosphate Li3PO4. According to a specific embodiment, the at least one Ms bonding material comprises/consists of at least one 15 polymer capable of being impregnated with a lithium salt, the polymer preferably being chosen from the group formed by polyethylene oxide, polyimides, vinylidene polyfluoride, polyacrylonitrile, polymethyl methacrylate, polysiloxanes, and lithium salt preferably being chosen 20 from the group formed by LiCl, LiBr, LiI, Li(ClO4), Li(BF4), Li(PF6), Li(AsF6), Li(CH3CO2), Li(CF3SO3), Li(CF3SO2)2N, Li(CF3SO2)3, Li(CF3CO2), Li(B(C6H5)4), Li(SCN), Li(NO3). Advantageously, the thickness of the layer of the at 25 least one Ms bonding material is less than 100 nm, preferably less than 50 nm, and even more preferably less than 30 nm. In a preferred embodiment, the layer containing at least one Ms bonding material is a nanoparticle layer 30 deposited on at least one of the dense layers obtained in step a), b) or c). Advantageously, it is deposited by electrophoresis. 8 WO 2014/131997 8 PCT/FR2014/050424 Advantageously, the conductive anode or cathode current substrates are metal sheets, optionally coated with a noble metal, or polymer sheets, optionally coated with a noble metal, or graphite sheets, optionally coated 5 with a noble metal. More specifically, the conductive anode or cathode current substrates in the form of metal sheets are aluminum, copper or nickel. More specifically, the conductive anode or cathode current substrates in the form of polymer sheets are selected from the following 10 polymers: polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polypropylene (PP), Teflon® (PTFE), polyimide (PI) and more specifically Kapton®. Advantageously, the noble metal is selected from the following metals: gold, platinum, palladium, vanadium, 15 cobalt, nickel, manganese, niobium, tantalum, chromium, molybdenum, titanium, palladium, zirconium, tungsten or any alloy including at least one of these metals. The invention also relates to an all-solid-state battery capable of being produced by the process 20 according to the invention, said battery including a monolithic body formed by at least one dense layer containing anode materials, at least one dense layer containing solid electrolyte materials and at least one dense layer containing cathode materials; preferably, the 25 monolithic body of the battery consists of a plurality of elementary cells connected in parallel. Advantageously, the electrical continuity between two adjacent cells is ensured by the electrolyte. The battery capable of being obtained by the process 30 according to the invention can be an all-solid-state multilayer battery. 9 WO 2014/131997 9 PCT/FR2014/050424 In one embodiment of the battery according to the invention, said battery includes at least one encapsulation layer, preferably a ceramic or glassceramic layer. Advantageously, said battery includes a 5 second encapsulation layer deposited on said first encapsulation layer, said second layer preferably being made of silicone polymer. Advantageously, the battery includes terminals where the cathode and anode current collectors are visible. 10 Preferably, the anode connections and cathode connections are located on opposite sides of the stack. Advantageously, the terminals are also covered with a nickel layer in contact with electrochemical cells, said nickel layer being covered with a tin layer. 15 Preferably, said at least one encapsulation layer covers four of the six faces of said battery, the two other battery faces being covered with terminals. In certain embodiments, the battery capable of being obtained by the process according to the invention is 20 entirely inorganic. Advantageously, the battery obtained according to the invention is entirely inorganic. Description of the figures 25 Figures 1(a), 1(b), 1(c), 1(d), 1(e) and 1(f) show products capable of being obtained according to a plurality of embodiments according to the invention. Figure 2 shows a stack of an anode and a cathode covered with an electrolyte layer and an Ms bonding 30 material layer. 10 WO 2014/131997 10 PCT/FR2014/050424 Figure 3 show a battery capable of being obtained according to an embodiment of the deposition process of the invention. Figures 4 and 5 schematically show the steps for 5 producing a battery according to two embodiments according to the invention. Figure 6 schematically shows a cathode film (lefthand side of the figure) and an anode film covered with an electrolyte layer (right-hand side of the figure), the 10 two films including patterns cut out by punching. The black arrow shows the operation of alternate stacking of cathode and anode sheets covered with electrolyte, with their cutout patterns stacked in a head-to-tail configuration. The punching may be performed on the metal 15 substrate before the electrode layers are deposited. Figure 7 schematically shows a detail of the stacking of the cathode and anode sheets covered with an electrolyte layer resulting from the stacking shown in figure 6. 20 Figure 8 shows a multilayer battery capable of being obtained by the process according to the invention, according to a particular embodiment. More specifically, the multilayer battery includes: - a plurality of substrate layers 20 made of a metal 25 sheet, or a metal sheet covered with a noble metal, or a polymer sheet metalized with a noble metal, or a graphite sheet covered with a noble metal; - a plurality of solid electrolyte layers 22; - a plurality of thin anode layers 21; 30 - a plurality of thin cathode layers 24; - a plurality of Ms bonding material layers (not shown in the figure); 11 WO 2014/131997 11 PCT/FR2014/050424 - at least one thin encapsulation layer 37 capable of consisting of a polymer, a ceramic or glass-ceramic, capable of being, for example, in the form of an oxide, nitride, phosphates, oxynitride or siloxane. 5 Advantageously, this encapsulation layer includes a ceramic or glass-ceramic layer covered with an epoxy or silicone resin; - terminals 35, 36, which make it possible to use alternately positive and negative electrical connections 10 on each of the ends. These terminals make it possible to produce electrical connections in parallel between the different battery elements. For this, only the connections (+) emerge at one end, and the (-) are available at the other ends. Preferably, the connections 15 (+) and (-) are laterally offset and the encapsulation serves as a dielectric substance for preventing the presence of a short-circuit on said ends. The terminals 35, 36 are shown here as a double layer but may be produced as a single layer. 20 Detailed description of the invention Definitions An "all-solid-state" battery is a battery in which 25 the electrodes and the electrolyte are solid and do not include a liquid phase, even impregnated in the solid phase. An "all-solid-state multilayer battery" according to the invention is a one-piece battery formed by a stack of 30 a plurality of "elementary cells". An "elementary cell" in the present invention is an electrochemical cell consisting of an anode and a cathode with insertion of 12 WO 2014/131997 12 PCT/FR2014/050424 lithium ions, separated by a solid electrolyte conducting lithium ions. An "Ms bonding material" refers to any lithium ionconducting material enabling the anode layer and the 5 cathode layer to be assembled, in which at least one of said anode and cathode layers is covered with an electrolyte layer, thermally treated and/or mechanically compressed, in order to form, by stacking, an all-solidstate multilayer battery after a low-temperature thermal 10 treatment and/or by mechanical compression of said stack. In certain embodiments according to the invention “the batteries are all-inorganic, i.e. they do not include polymer in the electrodes or in the electrolyte, but may include elemental carbon (for example graphite). 15 In the context of this invention, a “dense” layer is a layer having a density greater than 85% of the theoretical density of the massive body, and preferably more than 90% or even 95%. In the context of this invention, the size of a 20 particle is its greatest dimension. Thus, a “nanoparticle” is a particle in which at least one of the dimensions is less than 100 nm. The “particle size” or “average particle size” of a powder or a group of particles is given as D50. 25 Detailed description 1. Materials for cathode electrolyte and anode According to the invention, the materials used to 30 produce a cathode layer are preferably, but not entirely, chosen from one or more of the following materials: 13 WO 2014/131997 13 PCT/FR2014/050424 (i) the oxides: LiMn2O4, LiCoO2, LiNiO2, LiMn1.5Ni0.5O4, LiMn1.5Ni0.5-xXxO4 (where X is selected from Al, Fe, Cr, Co, Rh, Nd, other rare earth elements, and where 0 < x < 0.1 ), LiFeO2, LiMn1/3N1/3Co1/3O4; 5 (ii) the phosphates: LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4, Li3V2(PO4)3; the phosphates of formula LiMNPO4, with M and N (M  N) selected from Fe, Mn, Ni, Co, V; (iii) all of the lithiated forms of the following chalcogenides: V2O5, V3O8, TiS2, TiOySz, WOySz, CuS, CuS2. 10 According to the invention, the materials used to produce an anode layer are preferably, but not entirely, chosen from one or more of the following materials: (i) tin oxynitrides (with a typical formula SnOxNy); (ii) mixed silicon and tin oxynitrides (typical 15 formula SiaSnbOyNz with a>0, b>0, a+b≤2, 00, b>0, a+b≤2, 0