Negative electrode for primary lithium electrochemical element

Abstract

An electrode (2) comprising a sheet made of lithium or a lithium alloy coated on at least one of its faces with a coating (5) comprising at least one compound capable of lithiasis at a potential between 0 and 1 V with respect to Li+ / Li, characterized by an electrochemically active surface area S ranging from 100 to 1700 cm² per cm² of lithium or lithium alloy, the electrochemically active surface area being defined by the relation S = 1 + SBET × electrode weight where: - SBET (cm² / g) is the surface area BET of the compound capable of lithiasis at a potential between 0 and 1 V with respect to Li+ / Li; - the electrode weight (g / cm²) is the mass of compound capable of lithiasis at a potential between 0 and 1 V with respect to Li+ / Li deposited per cm² of lithium or lithium alloy. Abbreviated figure: Figure 1

Description

Description Title of the invention: Negative electrode for electro- primary lithium chemical Technical field of the invention

[0001] The technical field of the invention is that of electrochemical elements lithium primary batteries, particularly that of the negative electrodes (anodes) used in such elements. The technical field is also that of pre- preparation of negative electrodes for primary electrochemical elements lithium. Background to the invention

[0002] The terms “element” or “electrochemical element” will be used interchangeably interchangeable in the following. The term "primary" designates an electro- non-rechargeable chemical, also called by the term battery, as opposed to the term “secondary” which designates a rechargeable electrochemical element, also called ac- accumulator.

[0003] — The family of primary lithium electrochemical elements includes the elements whose positive active matter is liquid and those whose active matter positive is solid. Among the elements whose positive active matter is solid, we can cite the elements of type Li / MnO, and Li / CF,. In these elements, the negative electrode is made of metallic lithium or lithium alloy. The active material of the electrode positive is made of MnO, or CF,. When the element is discharged, Mn'YO; to the positive electrode transforms into LiMn'"O,. CF, transforms into carbon. At the negative electrode, the oxidation of metallic lithium into lithium ions occurs. The organic solvents used may be carbonates (such as carbonate of propylene for example) and / or ethers (such as dimethoxyethane or dioxolane). The salt used can be chosen from lithium perchlorate LiCIO4, lithium hexafluoroarsenate LiAsFg, or lithium hexafluorophosphate LiPFç.

[0004] Such primary elements have a problem of transient voltage drop during from the first moments of their discharge. This problem results from the formation on the surface of the negative lithium electrode of a passivation layer which becomes resistant to passage of lithium ions during discharge. This passivation results in a polarization transient increase which manifests itself by a sudden drop in voltage at the beginning of the discharge. This voltage drop occurs in the first moments of the discharge. It is all the more marked when the element is discharged at low temperature or at high current. It is transient but it is nevertheless penalizing for the user because it prevents him from using the full power of the element in the first moments of the dump. Primary elements that do not have this problem of sudden voltage drop have been sought. For example, EP-A-3 038 195 describes a primary electrochemical element comprising a positive electrode based on MnO, or CF, and a negative electrode covered with a carbon material in the form of powder or fibers. Example 1 of this document describes an element based on an electrolyte whose salt is LiBF, and in which the negative electrode is a lithium sheet covered with acetylene black. It was found that the carbon deposit certainly made it possible to reduce the sudden voltage drop but that corrosion phenomena of the negative electrode due to its contact with the electrolyte appeared after one month of storage of the element at a temperature above room temperature.It is therefore sought to provide a primary electrochemical element comprising a negative lithium electrode which satisfies the dual requirement of a low transient voltage drop and good corrosion resistance with respect to the electrolyte. Summary of the invention. To this end, the invention provides an electrode comprising a sheet made of lithium or a lithium alloy coated on at least one of its faces with a coating comprising at least one compound capable of forming lithium at a potential of between 0 and 1 V relative to Li- / Li, characterized by an electrochemically active surface S ranging from 100 to 1700 cm? per cm? of lithium or lithium alloy, the electrochemically active surface being defined by the relationship S = 1+ Sper X electrode weight where: - Seer (CM” / g) is the BET surface area of ​​the compound capable of lithium formation at a potential between 0 and 1 V relative to Li- / Li; - the electrode weight (g / cm?) is the mass of compound capable of forming lithium at a potential between 0 and 1 V relative to Li* / Li deposited per cm? of lithium or lithium alloy. The invention is based on the discovery that an electrode having an electrochemically active surface S ranging from 100 to 1700 cm? per cm° of lithium or lithium alloy makes it possible both to reduce the transient voltage drop and to limit corrosion with respect to the electrolyte. According to one embodiment, the coating further comprises at least one binder. According to one embodiment, the electrode is characterized in that the absolute value of the imaginary component of its complex impedance measured at 4 kHz at 20°C is in the range from 1 to 12 ohm.cm?, the measurement of the impedance being carried out by electrochemical impedance spectroscopy in potentiostatic mode with a potential amplitude of between 5 and 20 mV. According to one embodiment, the electrode is characterized by an electrochemically active surface S ranging from 250 to 1000 cm? per cm? of lithium or lithium alloy. According to one embodiment, the compound capable of forming lithium at a potential of between 0 and 1 V relative to Li- / Li is chosen from carbon or a compound containing an element chosen from the group consisting of silicon, aluminum, magnesium, silver, tin and zinc. According to one embodiment, the thickness of the coating ranges from 1 to 30 μm. According to one embodiment, the coating comprises: - from 80 to 98% by mass of compound capable of forming lithiates at a potential between 0 and 1 V relative to Li* / Li and - from 2 to 20% by mass of said at least one binder. According to one embodiment, the coating comprises: - from 90 to 95% by mass of compound capable of forming lithiates at a potential between 0 and 1 V relative to Li* / Li and - from 5 to 10% by mass of said at least one binder. The invention also relates to a primary electrochemical element comprising: - at least one positive electrode, and - at least one negative electrode which is the electrode as described above, - at least one electrolyte. According to one embodiment, said at least one positive electrode comprises an active material chosen from MnO,, CF, V2Os, FeS», I,, or a mixture thereof, preferably MnO. The invention also relates to a process for preparing a coating on a lithium or lithium alloy sheet, said coating comprising a compound capable of forming lithiates at a potential of between 0 and 1 V relative to Li* / Li, the process comprising the steps of: a) preparation of an ink comprising a mixture of one or more binders with one or more compounds capable of forming lithiates at a potential of between 0 and 1 V relative to Li* / Li and with at least one solvent; b) depositing the ink on a support; c) drying of the ink; (d) transferring the dried ink onto a sheet made of lithium or a lithium alloy; €) compression of the sheet coated with dried ink. According to one embodiment, the support is chosen from aluminum, a polyolefin and a silicone. According to one embodiment, the compound capable of forming lithiates at a potential between 0 and 1 V relative to Li- / Li is carbon having a volume average diameter D,- less than or equal to 10 um. According to one embodiment, the compound capable of forming lithiates at a potential between 0 and 1 V relative to Li- / Li is in the form of carbon platelets whose largest dimension is less than 100 nm. According to one embodiment, in step a), said at least one solvent is N-methylpyrrolidone and the binder used is polyvinylidene fluoride (PVDF). According to one embodiment, said at least one solvent is water and the binders used are a cellulose compound mixed with a copolymer of butadiene and styrene (SBR). According to one embodiment, wherein the sheet coated with the dried ink is included in the electrode. Brief description of the figures Embodiments of the invention are described below in more detail with reference to the figures below. [Fig.1] is a simplified Nyquist diagram. [Fig.2] illustrates the coating of the compound capable of lithium formation at a potential between 0 and 1 V vs. Li* / Li on the surface of the negative lithium electrode of a primary cell. Description of embodiments of the invention The electrode according to the invention is characterized by an electrochemically active surface area ranging from 100 to 1700 cm? per cm? of lithium or lithium alloy. The electrochemically active surface area S of the negative electrode is defined by the relationship: S = 1+ Sper X electrode weight where: - Seer (CM? / g) is the BET surface area of ​​the compound capable of lithium formation at a potential between 0 and 1 V relative to Li- / Li. Sper can be determined by the method described in ISO 9277:2010: - the electrode weight (g / cm?) is the mass of compound capable of forming lithiates at a potential between 0 and 1 V relative to Li* / Li deposited per cm? of lithium or lithium alloy. The surface area of ​​lithium or lithium alloy taken into account in the calculation of the weight is that covered by the compound capable of forming lithiates. It can therefore be either the surface area of ​​a single face of the lithium or lithium alloy sheet in the case of a deposit on a single face, or twice the surface area of ​​a single face in the case of a deposit on both faces. The electrode weight is chosen by the operator during the manufacture of the electrode. A negative electrode is made so that the product of the surface area Sger by the electrode weight plus 1 is in the range of 100 to 1700 cm? per cm? of lithium or lithium alloy. Preferably, the electrochemically active surface S is in the range of 250 to 1000 or 250 to 500 em? per cm? of lithium or lithium alloy. Different combinations of Sper surface area ranges and grammage ranges are suitable as long as the product of these two parameters plus 1 is in the range from 100 to 1700 em? per cm? of lithium or lithium alloy. For example, a Sper surface area of ​​105 to 106 cm? / g or 2x105 to 8x10° cm? / g or 3x10 to Sx105 cm? / g can be chosen. A grammage of 107 to 107 g / em? can be chosen. It has been found that certain electrodes according to the invention are characterized by an absolute value of the imaginary component of their complex impedance measured at 4 kHz at 20°C in the range from 1 to 12 ohm.cm°. Electrochemical impedance spectroscopy is a technique known to those skilled in the art. It consists of measuring the electrical response of an electrochemical element when it is subjected to a sinusoidal current or to a sinusoidal voltage variation. The impedance spectrum of the electrochemical element is recorded as a function of the frequency of the applied sinusoidal signal. The measured complex impedance Z comprises a real component Re(Z) and an imaginary component Im(Z) and is expressed as Z=Re(Z) + jIm(Z). The Nyquist representation consists of plotting in the complex plane the vector whose Cartesian coordinates are respectively the real component Re(Z) and the opposite of the imaginary component -Im(Z) of the impedance Z. This representation is a parametric representation in frequency, that is to say in which the frequency is varied and for each frequency corresponds a point identified by its Cartesian coordinates. These are Re(Z) for the abscissa axis and -Im(Z) for the ordinate axis. We have the following relations: Re(Z) = module(Z) x cos argument(Z) and Im(Z) = module(Z) x sin argument(Z). To determine the absolute value of the imaginary component Im(Z) measured at 4 KHz at 20°C, the impedance diagram of the element is plotted in a frequency range encompassing the value of 4 kHz. The impedance measurement is carried out by electrochemical impedance spectroscopy in potentiostatic mode with a potential amplitude between 5 and 20 mV. Then, the absolute value of the imaginary component of the impedance Z is plotted on the Nyquist diagram for a frequency of 4 kHz. [Fig.1] is a simplified Nyquist diagram showing how the absolute value of the imaginary component of the impedance is plotted. The frequency of 4 kHz corresponds to the apex of the semicircle formed in the high frequencies on the Nyquist diagram. The impedance measurement can also be carried out at the precise frequency of 4 kHz without sweeping the frequency range. At this frequency of 4 kHz, the negative electrode contributes mainly to the impedance of the element. The contribution of the positive electrode is negligible. The absolute value of the imaginary component of the impedance Z is multiplied by the surface area of ​​lithium or lithium alloy covered with the compound capable of becoming lithiated. This quantity in Ohm.cm* makes it possible to normalize the electrochemical impedance per unit area of ​​coated negative electrode and therefore to compare different impedance values ​​that may have been obtained with different formats. of elements. When this absolute value is in the range from 1 to 12 ohm.cm?, we see that we have both a reduction in polarization and good resistance of the negative electrode to corrosion of the electrolyte. Below the value of 1 ohm.cm?, the impedance is certainly low but we observe the appearance of corrosion at the negative electrode probably due to an electrochemically active surface area that is too high on the negative electrode. Above the value of 12 ohm.cm), the reduction in the transient voltage drop is not very significant. The compound capable of forming lithium at a potential of between 0 and 1 V relative to Li* / Li may be chosen from carbon and a compound containing a chemical element chosen from the group consisting of silicon, aluminum, magnesium, silver, tin and zinc. Preferably, it is carbon. Graphite, carbon black, carbon nanotubes, graphene, graphitized graphene may be used. Carbon in graphitic form is preferred. The graphite may be in the form of particles having a volume average diameter Dvs of less than or equal to 10 μm. This diameter may be measured by laser diffraction. The carbon may be in the form of platelets whose largest dimension is less than 100 nm. Scanning electron microscopy can measure the size of the platelets. When carbon black is used, it forms agglomerates. Scanning electron microscopy is suitable for measuring the size of these agglomerates. A first method particularly suitable for the manufacture of the negative electrode according to the invention comprises the following steps: An ink is prepared by mixing one or more binders, one or more compounds capable of forming lithiates at a potential of between 0 and 1 V relative to Li* / Li and at least one solvent. The binder has the effect of strengthening the cohesion between the particles of compound capable of forming lithiates and of improving their adhesion to the lithium or lithium alloy sheet. The binder(s) may be chosen from: polyvinylidene fluoride (PVDF) and its copolymers such as polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE) and its copolymers, polyacrylonitrile (PAN), poly(methyl)- or (butyl)methacrylate, polyvinyl chloride (PVC), poly(vinyl formal), a polyester, block polyetheramides, acrylic acid polymers, methacrylic acid, an acrylamide, itaconic acid, sulfonic acid, an elastomer and cellulose compounds. The elastomer may be chosen from a styrene-butadiene copolymer (SBR), butadiene-acrylonitrile rubber (NBR), hydrogenated butadiene-acrylonitrile rubber (HNBR). A mixture of several of these elastomers is possible. Preferably, in the case of an aqueous solvent, the binder is a mixture of carboxymethylcellulose (CMC) and a styrene-butadiene copolymer (SBR). In the case of an organic solvent such as N-methylpyrrolidone (NMP), the binder can be polyvinylidene fluoride (PVDF). The ink is deposited on a support preferably having non-stick properties, that is to say the adhesion is sufficiently low to allow subsequent transfer of the coating onto the lithium or lithium alloy sheet. The support can be aluminum, a polyolefin or a silicone. The ink solvent is evaporated, for example, by passing the ink-coated support through an oven. The coating obtained may be thin, i.e., have a thickness ranging from 1 to 30 μm. This thin and homogeneous coating may be obtained by using a large quantity of solvent relative to the quantity of lithium compound and binder, i.e., by using a low ink dry matter content. Preferably, the ink is formulated so that when dried, the coating comprises: - from 30 to 98% by mass of compound capable of forming lithiates at a potential between 0 and 1 V relative to Li* / Li and - from 2 to 20% by mass of said at least one binder. Preferably, the coating comprises: - from 90 to 95% by mass of compound capable of forming lithiates at a potential between 0 and 1 V relative to Li+Li and - from 5 to 10% by mass of said at least one binder. The coating is peeled off the support and transferred to a foil made of lithium or a lithium alloy. This may be lithium alloyed with one or more of the elements selected from Mg, Al, Zn, Si, B, Ge, Ga, In and Sn. Preferably, these are the elements Al, Zn and Mg. The cohesion of the lithium compound particles with each other and their adhesion to the lithium or lithium alloy sheet is promoted by compression. The sheet onto which the coating has been transferred is placed under a press which can, for example, exert a pressure force ranging from 0.1 to 1 ton / cm². The negative electrode according to the invention is thus obtained. A second method suitable for manufacturing the negative electrode according to the invention includes the following steps: A dispersion of particles of the compound capable of forming lithiates at a potential of between 0 and 1 V relative to Li+ / Li is prepared in a solvent and the solvent is then allowed to evaporate to obtain a homogeneous deposit of the compound. The deposition of the compound can either be carried out first on a substrate such as that described in the first method and then the deposit is transferred to the surface of the lithium. Alternatively, it can be carried out directly on a lithium or lithium alloy sheet using a solvent that is compatible, i.e. non-reactive, with the lithium or lithium alloy. Unlike the first method, the coating obtained by the second method does not contain a binder. The compound capable of forming lithiates at a potential of between 0 and 1 V relative to Li- / Li is preferably graphite or carbon nanoplatelets. When the compound is pre-deposited on a substrate, this substrate is preferably aluminum. The solvent used can be propanol or dioxolane or cyclohexane or an alkene. When the compound is deposited directly onto a lithium or lithium alloy foil, dioxolane and an ether, for example dimethoxyethane (DME), can be used as a solvent that is not reactive with lithium. The deposit is then compressed onto the surface of the lithium or lithium alloy under the same conditions as those set out for the first process. An electrochemical beam is formed by superimposing at least one positive electrode, at least one separator, at least one negative electrode, each positive electrode being separated from the neighboring negative electrode by a separator. The positive electrode comprises an active material which may be selected from MnO>, CF, V:O,, FeS,, I,, or a mixture thereof, preferably MnO,. The electrochemical bundle is impregnated with an organic solvent. The organic solvent may be selected from the group consisting of carbonates, ethers, esters, lactones, and a mixture thereof. The carbonate may be propylene carbonate (PC), ethylene carbonate (EC), fluorinated ethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or a mixture thereof. The ether may be dimethyl ether (DME), tetrahydrofuran (THF), dioxolane, or a mixture thereof. The lactone may be gamma-butyrolactone. The solvent may also be selected from dimethyl sulfide (DMS) or dimethyl sulfoxide (DMSO), or a mixture thereof. The organic solvent contains one or more salts that may be selected from the group consisting of lithium tetrafluoroborate (LiBF;), lithium hexafluorophosphate (LiPFs), lithium perchlorate (LiCIO4), lithium bis(fluorosulfonyl)imide lithium Li(FSO»),N (LiFSI), lithium bis(trifluoromethylsulfonyl)imide Li(CF; SO,),N (LITFSI), lithium 4,5-dicyano-2-(trifluoromethyl) imidazolide (LITDI), lithium bis(oxalato)borate (LiBOB), lithium tris(pentafluoroethyl)trifluorophosphate LiPF,(CF,CF;); (LiFAP), lithium triflate LiCF;SO; or a mixture of several of these. It is also possible to use an ionic liquid with the solvents and salts mentioned above. The ionic liquid can be chosen from the 1-butyl 1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSD), 1-butyl 1-methyl pyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMP-FAP), ethyl-(2-methoxyethyl) dimethyl ammonium bis(trifluoromethylsulfonyl)imide, 1-methyl-1-propyl-piperidinium bis(trifluoromethylsulfonyl)imide, 1-methyl-1-propyl-piperidinium bis(fluorosulfonyl)imide, 1-methyl-1-propyl-pyrrolidinium bis(fluorosulfonyl)imide and mixtures thereof. The element format can be of any type, for example cylindrical, button or pouch type. In the case of a cylindrical format, the electrochemical bundle is wound into a spiral and then introduced into the container. It is impregnated with electrolyte and the opening of the container is sealed with a lid. In the case of a button format, a positive electrode, a separator and a negative electrode are placed on the bottom of the container. The electrodes and the separator are impregnated with electrolyte. A lid is placed on the upper electrode. The edges of the container are crimped against the lid to seal the electrochemical element. In the case of a pouch-type element, a stack of a positive electrode, a separator and a negative electrode is made. This assembly is inserted into a flexible pouch. The pouch is formed by welding the edges of two multi-layer films, each multi-layer film comprising a metal layer, generally aluminum, sandwiched between two layers of plastic material. The pouch thus formed is filled with an electrolyte and then sealed. [Fig.2] schematically represents an electrochemical beam (1) comprising a negative electrode according to the invention (2), a separator (3) impregnated with electrolyte, a positive electrode (4). The face of the negative electrode opposite the separator is covered with a coating (5) of the compound capable of lithiating at a potential between 0 and 1 V relative to Li / Li. EXAMPLES Various primary electrochemical elements in button format have been manufactured. The positive electrode comprises an active material made of MnO2. The lithium foil used at the negative electrode is a disc with a diameter of 14 mm having an area of ​​1.54 cm” per side. The table below summarizes the characteristics of the different elements. [Tables 1] Surface |Surface Value Polarization |Corrosion | BET of electrochemistry [absolute from |n to n after carbon |cally Im(Z) at -40°C one month | e active from 4kHz to after 1 of (m? / g) |the electrode |20°C months storage | negative (cm [(chm.cm?”) |storage at Jat 65°C ? of carbon 65°C (V) / cm? of lithium) | | [150 |u1 |B [Graphite |226 [12 jen [12 Jos B° [Graphite |2.21 I weigh 62 0.65 C* [Graphite [16.23 BrE “|1948 08 |Ls |50 [p* Black of |12.99 carbon * example outside of invention ** does not include lithium weight The coating of the negative electrodes of elements B, C and D was obtained by the dispersion process with a first step of producing the coating on an aluminum substrate and then transferring the coating onto a lithium foil. That of the negative electrode of element B' was obtained by the ink formation process. The coating of the electrode of example B' contains 10% by mass of poly(vinylidene fluoride) PVDF. The electrolyte is the same for all elements. It is a mixture of propylene carbonate (PC), tetrahydrofuran (THF), dioxolanc in which the LiCIO4 salt is dissolved. The electrochemical impedance measurement was carried out in potentiostatic mode with a Biologic VMP-3 type potentiostat-galvanostat equipped with a spec- impedance troscopy using a potential amplitude of 10 mV in a frequency range between 1 MHz and 10 mHz. The Nyquist diagram was plotted for each of these elements. The absolute value of the imaginary component was recorded at a frequency of 4 kHz. The effectiveness of the coating in reducing polarization was measured by applying a current density of 2 mA / cm? at -40°C for one second across the elements and measuring the voltage across the element resulting from the passage of the current. This voltage is proportional to the polarization of the element. After storage for one month at 65°C, the elements were disassembled and their negative electrode inspected. The following results were noted: Element A, whose negative electrode is devoid of carbon, has a polarization of 1.1 V, higher than that of element B according to the invention. The absolute value of the imaginary component of its impedance is 15 ohm.cm?, therefore higher than 12 ohm.cm. This high value can explain the strong polarization of this element. Cell B, whose negative electrode is coated with carbon, has a polarization of 0.5 V, which is the lowest value among all the cells tested. After the storage test at 65°C, observation of the negative electrode shows the presence of lithium over the entire surface of the electrode. The lithium corrosion rate of this negative electrode is sufficiently slow compared to the storage conditions. The absolute value of the imaginary component of its impedance is 1.2 chm.cm?, therefore in the range from 1 to 12 ohm.cm?. Cell B', whose negative electrode is coated with carbon, has a polarization of 0.65 V, which is very satisfactory. After the storage test at 65°C, observation of the negative electrode shows the presence of lithium over the entire surface of the electrode. The lithium corrosion rate of this negative electrode is sufficiently slow compared to the storage conditions. The absolute value of the imaginary component of its impedance is 6.2 ohm.cm?, therefore in the range from 1 to 12 ohm.cm?. In comparison with cell B, the presence of binder in the coating of the negative electrode of cell B° makes it possible to reinforce the cohesion between the carbon particles. The negative electrode of elements C and D has an impedance whose absolute value of the imaginary component is 0.8 and 0.5 ohm.cm?, therefore outside the range from 1 to 12 ohm.cm?. After storage for one month at 65°C, the electrode contains almost no metallic lithium. Without wishing to be bound by theory, the applicant is of the opinion that the significant corrosion is due to an electrochemically active surface that is too high; in fact, the lithium metal is inserted into the carbon particles; the surface area of ​​exposure of the carbon with the electrolyte being very high (in fact, the theoretical electrochemically active surface is 1948 and 6494 cm? of carbon per cm? of lithium for elements C and D respectively), the reaction processes between lithium in the reduced state and the electrolyte are then accelerated.

Claims

Demands

1. Electrode (2) comprising a foil made of lithium or a lithium alloy coated on at least one of its faces with a re- garment (5) comprising at least one compound liable to lithium at a potential between 0 and 1 V relative to Li* / Li, characterized by an electrochemically active surface S ranging from 100 to 1700 cm²? per cm? of lithium or lithium alloy, the electrochemical surface- being mimentally active, defined by the relation S = 1 + Sger X electrode weight where: - Sser (cm² / g) is the BET surface area of ​​the compound likely to lithiace a potential between 0 and 1 V relative to Li* / Li; - the electrode weight (g / cm³?) is the mass of compound above susceptible to lithiasis at a potential between 0 and 1 V relative to Li* / Li deposited per cm? of lithium or lithium alloy.

2. Electrode according to claim 1, wherein the coating It also includes at least one binder.

3. Electrode according to claim 1 or 2, the electrode being characterized in what the absolute value of the imaginary component of its impedance The complex measured at 4 kHz at 20°C is within the range of 1 at 12 ohm.cm, the impedance measurement being carried out by spectroscopy electrochemical impedance in potentiostatic mode with a potential amplitude between 5 and 20 mV.

4. Electrode according to any one of claims 1 to 3, characterized by a electrochemically active surface area S ranging from 250 to 1000 cm² per cm²? of lithium or lithium alloy.

5. Electrode according to any one of claims 1 to 4, wherein the compound capable of lithiasis at a potential between 0 and 1 V relative to Li* / Li is chosen from carbon or a compound containing a element chosen from the group consisting of silicon, aluminum, the magnesium, silver, tin and zinc.

6. Electrode according to any one of claims 1 to 5, wherein the thickness The coating thickness ranges from 1 to 30 µm.

7. Electrode according to any one of claims 2 to 6, wherein the re- Clothing includes: - 80 to 98% by mass of compound susceptible to lithiasis at a potential between 0 and 1 V relative to Li* / Li and - from 2 to 20% by mass of said at least one binder.

8. Electrode according to claim 7, wherein the coating understand : - 90 to 95% by mass of compound susceptible to lithiasis at a potential between 0 and 1 V relative to Li+ / Li and - 5 to 10% by mass of said at least one binder.

9. Primary electrochemical element (1) comprising: - at least one positive electrode (4), and - at least one negative electrode (2) which is the electrode according to one of the claims 1 to 8, - at least one electrolyte.

10. | Primary electrochemical element according to claim 9, wherein said at least one positive electrode comprises an active material chosen from MnO, CF, V2O5, FeS, I, or a mixture thereof, of MnO preference..

11. Method for preparing a coating (5) on a lithium sheet or of a lithium alloy, said coating comprising a super- compound susceptible to lithiasis at a potential between A and 1 V relative to Li* / Li, the process comprising the steps of: a) preparation of an ink comprising a mixture of one or more binders with one or more compounds likely to lithify to a potential between 0 and 1 V relative to Li* / Li and with at least one solvent; b) depositing ink onto a support; c) drying of the ink; d) transfer of dried ink onto a sheet made of lithium or of a lithium alloy; e) compression of the sheet coated with dried ink.

12. A method according to claim 11, wherein the support is chosen among the aluminum, a polypropylene and a silicone.

13. A method according to any one of claims 11 to 12, wherein the compound capable of lithiasis at a potential between 0 and 1 V relative to Li* / Li is carbon with a volume average diameter D,s0 less than or equal to 10 µm.

14. A method according to any one of claims 11 to 13, wherein the compound capable of lithiasis at a potential between 0 and 1 V relative to Li* / Li is in the form of carbon wafers whose dimensions the largest is less than 100 nm.

15. A method according to any one of claims 11 to 14, wherein, in step a), said at least one solvent is N-methylpyrrolidone and the binder used is polyvinylidene fluoride (PVDPF).

16. A method according to any one of claims 11 to 14, wherein said at less a solvent is water and the binders used are a cel- compound lulosic acid mixed with a butadiene-styrene copolymer (SBR).

17. A method according to any one of claims 11 to 16, wherein the sheet coated with dried ink is included in the electrode according to one of the claims 2 to 8.