FR2995455A1 - METHOD FOR OPERATING A LITHIUM-ION TYPE BATTERY - Google Patents

Abstract

The invention relates to a method of operating a lithium-ion battery comprising at least one cell comprising a negative electrode (called a first electrode) and a positive electrode (called a second electrode), between which an ion-conducting electrolyte is arranged. and comprising a third lithium ion source electrode, said method comprising: a) a step of preparing said first electrode, comprising a lithiation operation by the third electrode of an electrode comprising a material based on at least one metal or semi-metallic element M capable of forming an alloy with lithium, so as to obtain said first electrode comprising an active material comprising an alloy of at least one metallic or semi-metallic element M and lithium in a molar ratio Li / M up to 5; b) a step of operation by cycling said lithium accumulator between said negative electrode and said positive electrode without total delithiation of said negative electrode.

Description

TECHNICAL FIELD The present invention relates to a method of operating a lithium-ion type accumulator and to an accumulator of this specific type that is compatible with the implementation of a lithium-ion type accumulator. of this process.

The general field of the invention can thus be defined as that of lithium-ion type accumulators. Lithium-ion batteries are increasingly being used as a source of autonomous energy, particularly in portable electronic equipment (such as mobile phones, laptops, tools), where they are gradually replacing accumulators nickel-cadmium (NiCd) and nickel-metal hydride (NiMH). They are also widely used to provide the power supply needed for new micro applications, such as smart cards, sensors or other electromechanical systems. Lithium-ion type accumulators operate on the principle of insertion-deinsertion (or lithiation-delithiation) of lithium according to the following principle. Upon discharge of the battery, the deinserted lithium of the ionic negative electrode Li + migrates through the ionic conductive electrolyte and interposes into the crystal lattice of the active material of the positive electrode. The passage of each Li + ion in the internal circuit of the accumulator is exactly compensated by the passage of an electron in the external circuit, thereby generating an electric current. The specific energy density released by these reactions is both proportional to the potential difference between the two electrodes and the amount of lithium that will be interposed in the active material of the positive electrode.

During the charging of the accumulator, the reactions occurring within the accumulator are the reverse reactions of the discharge, namely that: the negative electrode will insert lithium into the network of the material constituting it; the positive electrode will release lithium. By this principle of operation, the lithium-ion type accumulators require two different insertion compounds to the negative electrode and the positive electrode. The positive electrode is generally based on a lithic oxide of transition metal of the lamellar oxide type of formula LiM02, where M denotes Co, Ni, Mn, Al and mixtures thereof, such as LiCoO 2, LiNiO 2, Li (Ni, Co, Mn, Al) O; or of the spinel structure oxide type, such as LiMn 2 O 4. The negative electrode may be based on a carbon material, and in particular based on graphite.

Graphite has a theoretical specific capacity of the order of 370 mAh / g (corresponding to the formation of the LiC6 alloy) and a practical specific capacity of the order of 320 mAh / g. However, graphite exhibits high irreversibility during the first charge, a continuous loss of capacity in cycling and a prohibitive kinetic limitation in the case of a high charge / discharge regime (for example, for a C / 2 charge regime). In order to improve the insertion properties of lithium into the negative electrode, researchers have focused their efforts on finding new electrode materials. Thus, they have discovered that materials or elements capable of forming an alloy with lithium are capable of constituting excellent alternatives to the use of graphite. Thus, it has been demonstrated that the insertion of silicon into a negative electrode makes it possible to significantly increase the practical specific capacity of the negative electrode related to the insertion of lithium into it, which is 320 mAh / g for a graphite electrode and of the order of 3580 mAh / g for a silicon-based electrode (corresponding to the formation of the Li15Si4 alloy during the insertion at room temperature of the lithium in silicon). Thus, by means of simple forecasts, it is possible to envisage a gain of about 40 and 35%, respectively in energy density and in mass energy, if the graphite is replaced by silicon in a conventional accumulator. the "lithium-ion" industry. Moreover, the operating potential window of the lithium-silicon alloy of formula Li15Si4 (0.4-0.05 V / Li-Li) higher than that of graphite makes it possible to avoid the formation of a deposit of lithium metal and the associated risks, while leaving the possibility of carrying out faster charges. In addition, it is established that the formation reaction of the lithium-silicon alloy, leading to a very high specific practical capacity (of the order of 3578 mAh / g), is reversible.

Nevertheless, the use of silicon in a negative electrode of a lithium battery poses a number of problems. In particular, during the formation reaction of the silicon-lithium alloy (corresponding to the insertion of lithium into the negative electrode in charge process), the volume expansion between the delithiated phase and the lithiated phase can reach values ranging from 240 to 400%. This strong expansion, followed by a contraction of the same amplitude (corresponding to the disinsertion of lithium in the negative electrode during the discharge process) can quickly lead to irreversible mechanical damage to the electrode and in particular a sputtering of said electrode and, as a result, degradation of the electrode / electrolyte interface. These phenomena can cause a rapid degradation of the electrochemical performance of the electrodes made from this type of materials.

To maintain the initial electrochemical performance, it is possible to limit the cycling capacity of the electrodes, in order to limit the depth of lithiation and thus reduce the volume expansion of the latter. Thus, for example, by limiting the cycling capacity of a negative electrode active material based on silicon particles at 1200 mAh / g, this amounts to subjecting said particles to a lithiation rate ranging from 0 to 1.25. which makes it possible to obtain good electrode performance in terms of cyclability.

However, for negative electrodes comprising this type of particles in combination with a split-carbon electrically conductive additive and with a polymeric binder, it is not possible to obtain sufficient electrochemical performance in terms of practical specific capacity. and coulombic efficiency (for example, greater than 99.7%) over more than one hundred cycles, all the more so since the surface capacitance of the electrodes is high (typically greater than 1 mAh / cm 2), this which notably prevents the integration of this type of electrode in lithium-ion type accumulators. To find a solution to these drawbacks, the authors of the present invention have developed a method of operating a lithium-ion battery and a specific accumulator. SUMMARY OF THE INVENTION Thus, the authors of the present invention have surprisingly discovered a method of operating a lithium-ion battery comprising at least one cell comprising a negative electrode (referred to as a first electrode) and a positive electrode. (A second electrode) between which is disposed a lithium ion conductive electrolyte and comprising a third lithium ion source electrode, said method comprising: a) a step of preparing said first electrode, comprising a lithiation operation by the third electrode of an electrode comprising a material based on at least one metallic or semi-metallic element M capable of forming an alloy with lithium, so as to obtain said first electrode comprising an active material comprising an alloy of at least one element M metal or semimetallic and lithium in a molar ratio Li / M up to 5; b) a step of operation by cycling said lithium accumulator between said negative electrode and said positive electrode without total delithiation of said negative electrode. By proceeding in this way, the negative electrode comprises during a cycling (that is to say during a charge-discharge process) always lithium inserted, which is to say that the electrode Negative remains lithiated continuously during the cycling of the negative electrode.

Step a) can be described as in situ lithiation step, knowing that the first electrode is obtained by lithiation through a third electrode belonging to said accumulator. This step a) can be performed only before the implementation of step b) or can be performed between two cycles of step b) or simultaneously with step b). The aforementioned element M is, as mentioned above, an element M capable of forming an alloy with lithium, this element being either a metal element or a semi-metallic element. As examples of metal element, mention may be made of aluminum, tin, germanium and mixtures thereof.

As examples of semi-metallic element, mention may be made of silicon. These elements are particularly interesting because they have a very high theoretical specific capacity (for example, of the order of 3600 mAh / g for silicon) compared to materials such as graphite commonly used to enter the negative electrode constitution. . The material based on at least one metallic or semi-metallic element M may be in the form of only one element M (for example, pure silicon), an alloy of element (s) M or a composite material based on at least one element M. The composite material based on at least one element M may be made of a material comprising silicon and another element chosen from carbon, tin and aluminum , germanium and mixtures thereof. Advantageously, the material based on at least one metallic or semi-metallic element M advantageously has a total reversible capacity greater than 2500 mAh / g, specific examples corresponding to this characteristic being the following: pure silicon ( whose theoretical specific capacity is 3600 mAh / g); a silicon-carbon composite, the carbon content of which will not exceed 30% by mass; a silicon-tin composite, the tin content of which will not exceed 40% by mass; a silicon-aluminum composite, the aluminum content of which will not exceed 40% by mass; and a silicon-germanium composite, the germanium content of which will not exceed 55% by mass. For example, when the material comprises elements M1, M2, -, Mn in proportions Y1, Y2, -, Yilf each element respectively having an effective reversible capacitance of X 1 f X2, xn, then the reversible capacitance total of the material corresponds to the sum (xiyi + x2y2 + ... + xnyn). It is understood that this total reversible capacity does not take into account the irreversible capacity linked to the parasitic reactions, such as, in particular, surface reactions. The material based on at least one metallic or semi-metallic element M may be in the form of nanometric particles, for example, particles having an average particle diameter of less than 200 nm. The material based on at least one metallic or semi-metallic element M may coexist with other materials such as organic binders, electrically conductive materials, and mixtures thereof. The organic binders may be polymeric binders, advantageously chosen from electrochemically stable polymers, for example, in a window of potentials ranging from 0 to 5 V relative to Li / Li, such polymers possibly being cellulosic polymers. The electrically conductive materials may be carbonaceous materials, in particular carbon materials in divided form, such as spherical particles, fibers. More specifically, it may be carbon black, carbon fibers, acetylene black, carbon nanotubes and mixtures thereof. From a practical point of view, step a) may be performed by galvanostatic means, that is to say by applying a current of constant intensity for a time necessary for the incorporation of lithium in the desired molar ratio , that is to say a molar ratio of up to 5 between an electrode based on a material comprising a metallic or semimetal element M (this electrode being a precursor of said first electrode) and said third electrode, this electrode being separated from said third electrode by a lithium ion conductive electrolyte, which will be described in more detail in connection with the description of step b). Said third electrode, which is a lithium source electrode, is advantageously an electrode comprising, as active material, metallic lithium, a lithium metal alloy or a lithium insertion material such as a lithiated metal oxide. Lamellar oxide type transition of formula LiM02, wherein M denotes Co, Ni, Mn, Al and mixtures thereof, such as LiCoO2, LiNiO2, Li (Ni, Co, Mn, Al) O2 or a lithium oxide of spinel structure, such as LiMn204. Said third electrode preferably has a practical specific capacity of at least 1/3 of the practical specific capacity of the negative electrode. Said third electrode is preferably located outside the electrochemical core of the accumulator (that is to say outside the electrochemical cell comprising the first and second electrodes, between which an ion conducting electrolyte is arranged. lithium). This third electrode may possibly be removed once step a) has been performed, for example, during a degassing step (vacuum drawing and heat-sealing when the packaging of the accumulator is of the flexible bag type, for example). It can be connected to the circuit via a metal grid or strip type collector or any conductive material or simply be self-supporting and in contact with a collector. From the point of view of its location, this third electrode may for example be located in the middle of the turns when the electrodes are wound 30 or outside the turns. It can also be placed next to the electrochemical core in the degassing pocket for cells with a flexible sachet package. It should be noted that this electrode is different from a reference electrode, since at a time of the implementation of the method of the invention (in this case, step a)), a current flows through this electrode to lithiate the negative electrode. On the other hand, this does not exclude the fact that this electrode can be used as a reference electrode in step b) to follow the state of charge (known by the abbreviation SOC for "State of Charge"). or the state of health (known by the abbreviation SOH for "State of Health") of the accumulator after step a) performed. The intensity delivered across the negative electrode and the third electrode is set so as to generate a lithiation phenomenon of the abovementioned negative electrode active material until the desired molar ratio is obtained. being determined by measuring the practical specific capacity of said material. Indeed, according to Faraday's law, the quantity of electricity Q (in Ah) which passes through the electrolyte is fixed, in galvanostatic mode, by the relation: Q = I (t) .dt in which: -I denotes the imposed current (in A); and -t denotes the duration of application of this current. The metallic lithium of the positive electrode is converted to Li + and releases an electron, while Li + will be incorporated into the active material of the negative electrode. For one mole of Li, the charge corresponds to a faraday (1 F = 96487 C.mol 1 = 26.8 Ah.mo1-1). The amount of charge per mole of reacted lithium (Q / n) can be expressed by the following relationship: xF = (Q / n) = (I * t) / (m / M) = (I * t * M where x = (I * t * M) / (26.8 * m) in which: -x is the number of moles of lithium reacted per mole of active material; -t is the duration of application of the current (in h); -M is the molar mass of the active material (in g.mo1-1) and m is the mass of the active material (in g). The specific capacity of the active material (expressed in mAh.g-1) being expressed by the following value: C = (Q / m) = (26.8 * x * 1000) / M, it is thus possible, by measuring this When the current I is applied, it is easy to go back up to the desired molar ratio and once reached, to stop the imposition of the current. Preferably, during step a), the material based on at least one metallic or semi-metallic element M is lithiated in a molar ratio corresponding to the obtaining of a specific practical capacity corresponding to at least one one third of the total reversible capacitance of said material, preferably at least 2/3 of said total reversible capacitance (this total reversible capacitance corresponding, for a negative electrode, to the quantity of electricity generated during the reversible disinsertion of the lithium atoms and does not include lithium atoms, which are trapped during the first charge, especially at the surface of the active material).

The material obtained at the end of step a) and constituting the first electrode is structurally different from those obtained metallurgically (in particular, by metallurgy of the powders), in particular as regards their degree of crystallinity, in this sense that they are partly amorphous. The negative electrode will moreover advantageously have a high density of energy density, such as a density of energy density higher than 1800 mAh / cm3 and a high surface density, for example, a surface density at least equal to 2 , 5 mAh / cm 2, these densities being determined on the basis of the theoretical specific capacities of the active materials used.

Preferably, it has, in addition, a total reversible capacitance greater than that of the positive electrode. The use of a prelithiated electrode in a lithium battery has several advantages.

During the implementation of step b), a fraction of the inserted lithium ions contributes to the growth of the electrode / electrolyte interface, forming products of the carbonates or lithium oxide type on the surface of the particles constituting the negative electrode. These reactions are irreversible, so that the lithium ions consumed for the formation of these products no longer participate in the cycling of the electrode and contribute to the irreversible capacity between the charge and the discharge. Prélithier the active material of negative electrode thus makes it possible to have a large source of lithium ions in the active material of the negative electrode and thus improves the coulombic efficiency at each cycle (which corresponds to the percentage of electric charge stored in the accumulator during charging, which is recoverable during discharge). During the implementation of step b), it is possible to cycle the material in a lithiation domain, where the surface variations are reduced and the stability of the electrode / electrolyte interface is improved. Indeed, if the variation of volume is linear with the rate of lithiation, the variation of surface is not it.

Thus, for the same capacity (or the same quantity of lithium ions inserted) cycled, the surface variation is lower for an active material prelithiated with respect to a material, which is not. Thus, for example, for a silicon electrode (more precisely, composed of spherical silicon particles) cycled over a capacitance range of 1200 mAh / g, the surface area of the particles will vary less between 2400 and 3600 mAh / g ( which means, on the one hand, that the electrode has been prelithiated up to 3600 mAh / g, which corresponds to a Li / Si molar ratio of 3.75 and that the cycling of the material has been carried out on a field of molar ratio ranging from 2.5 to 3.75) that between 0 and 1200 mAg / g (which corresponds to cycling said material over a range of 0 to 1.25 molar ratio).

Preferably, step b) is carried out over a range of capacities of up to 2/3 of the total reversible capacity of the active material (which corresponds to a restricted cycling domain), so that the electrode always remains lithiated.

More specifically, step b) can be performed over a capacity range corresponding to 1/3 of the total reversible capacitance of the material. More preferably, the operating method of the invention is carried out according to the following methods: step a) is carried out under conditions sufficient to obtain a negative electrode material having a molar ratio Li / M (M being metallic or semi-metallic element M as defined above) of at least 1/3 of the molar ratio when said material is completely alloyed with lithium; and, preferably, a Li / M molar ratio at least equal to 2/3; step b) is carried out over a range of capacities corresponding to at most 2/3 of the total reversible capacity of the material, and preferably to at most 1/3 of the total reversible capacity of the material. Thus, for example, for a negative electrode based on an active material consisting of nano particles of pure silicon, with a total reversible capacity of 3600 mAh / g corresponding to a molar ratio of 3.75 when the silicon is completely lithiated, the step of preparing said electrode can result in an electrode having a Li / Si molar ratio of 2.5. The cycling operation step (s) carried out on a range of capacities corresponding to 1/3 of the total reversible capacity of the material, thus amounts to cycling over a range of capacitances of 1200 mAh / g, which amounts to To say in other words that, during cycling: the molar ratio Li / Si evolves from 3.75 to 2.5 during the discharge; and the Li / Si molar ratio increases from 2.5 to 3.75 during charging. The electrode is thus subjected to a restricted cycling domain (1/3 of its total reversible capacity) while being in a high lithiation domain (greater than 2/3 of its total reversible capacity). For this type of material, in such a field, there is a small surface variation and thus a good stability of the material even if the number of cycles becomes very important. Moreover, working in a 1200 mAh / g capacitance range achieves a very significant mass energy density gain over commonly used negative electrode active materials, such as graphite. , whose accessible capacity range can not go beyond 372 mAh / g.

The third lithium source electrode makes it possible, in a first step (in particular during step a)), to obtain a negative electrode comprising an active material comprising lithium and silicon in a Li / Si molar ratio of 2.5 . The amount of lithium contained in the positive electrode makes it possible to obtain a silicon cycling capacity of 1200 mAh / g (corresponding to a Li / Si molar ratio which varies from 2.5 to 3.75 during charging and 3.75 to 2.5 when discharging the negative electrode).

The positive electrode conventionally comprises a lithium lithium insertion compound mentioned above. As examples of lithiated compounds that may be included in the constitution of the positive electrodes of the accumulators of the invention, mention may be made of polyanionic lithiated compounds of transition metals, lithiated oxides and mixtures thereof. Examples of polyanionic lithium compounds of transition metals include lithiated compounds having the following general formula: LixMly (X0) n 30 wherein: * Mi represents an element selected from Mn, Fe, Co, Ni, Cu , Mg, Zn, V, Ti, Al, Si, B, Cr, Mo and mixtures thereof; X represents an element selected from P, Si, Ge, S, V and As; * x, y, z and n are integers or positive decimal numbers chosen so that the total charge of the cations compensates for the total charge of the anions, so that the compound is electrically neutral. Preferably, M1 represents a member selected from Mn, Fe, Co, Ni, Cu, V, Ti, B, Cr, Mo and mixtures thereof. More precisely, such compounds may correspond to the case where X corresponds to the phosphorus element P, in which case these compounds constitute lithium phosphate compounds. Such compounds may be, for example, compounds of formula LiM1PO4, with M1 being as defined above, such as LiFePO4. A specific compound of the same family may also be Li3V2 (PO4) 3. As examples of lithiated oxide compounds, mention may be made of the lamellar type compounds of the following formula: LiM 2 O 2 wherein M2 is a member selected from Ni, Co, Mn, Al, Mg and mixtures thereof. As examples of such oxides, lithium oxides LiCoO 2, LiNiO 2 and mixed oxides Li (Ni, Co, Mn) O 2 (such as Li (NiI / NMC designation), Li (Ni, Co, Al) O2 (such as Li (Ni0.8Co0.15A10.05) 02 also known as NCA) or Li (Ni, Co, Mn, Al) O2. In particular, the oxides Li (Ni0.8Coo1.5A10.05) 02 and Li (Ni1 / 3Mni / 3C01 / 3) 02 make it possible to achieve similar or substantially higher electrochemical performances than the LiMO 2 type oxides ( with M representing a single metal and not a mixture) for a lower or equal cost and improved chemical stability especially in the charged state. Mention may also be made of the super-stoichiometric lamellar oxide compounds of the following formula: Li (i + x) M30y in which: -M3 is a member selected from Ni, Co, Mn and mixtures thereof; X and y are as follows: 0.5 <x <2 and 2 <y <3 Other examples of lithiated oxides include lithiated oxides comprising manganese and / or aluminum . More specifically, they may be high-voltage spinel oxides having the following formula: ## STR1 ## where a, b, c and d are between -0.1 and -0.1. and +0.1, i.e. each of the parameters a, b, c and d is greater than or equal to -0.1 and less than or equal to +0.1. In particular, a lithiated oxide according to this definition and particularly advantageous is the oxide of formula LiNi0.5Mn1, 504, which has the particularity of having a lithium insertion / de-insertion potential of the order of 4.7 V (this potential being expressed relative to the reference torque Li + / Li). Mention may also be made, as lithiated oxides comprising manganese, of the lithium oxides of formula LiMn 2 O 4 or LiNiMnO 4. Regarding the electrolyte, it may be a liquid electrolyte comprising a lithium salt. Thus, for example, the liquid electrolyte may comprise a solvent or mixture of carbonate-type solvents, such as ethylene carbonate, propylene carbonate, dimethyl carbonate or diethyl carbonate, and / or a solvent. or a mixture of ether-type solvents, such as dimethoxyethane, dioxolane, dioxane, tetraethyleneglycoldimethylether (known by the abbreviation TEGDME) and mixtures thereof in which a lithium salt is dissolved. By way of example, the lithium salt may be selected from the group consisting of LiPF6, LiC104, LiBF4, LiA5F6, LiCF3SO3, LiN (CF3SO2) 3 / LiN (C2F5SO2), lithium bistrifluoromethylsulfonylimide (known abbreviated as LiTFSI) LiN [SO2CF3] 2 and mixtures thereof. There may be ionic continuity between the three aforementioned electrodes, which may be provided by a separator soaked with a liquid electrolyte as defined above and in contact with said electrodes. The invention also relates to a lithium-ion type battery adapted for implementing the method of the invention, said battery comprising at least one cell comprising a negative electrode (said first electrode) and a positive electrode (said second electrode) between which is disposed a lithium ion conductive electrolyte and comprising a third electrode adapted to be connected to said first electrode and lithium ion source. The characteristics relating to the electrodes and to the electrolyte are identical to those described previously in the context of the description of the process. This third electrode may be removable, that is to say it may be optionally removed before the operating step or may be retained during the operating step and be used as reference electrode. Each of these electrodes may be associated with an electrically conductive current collector, this collector possibly being in the form of a metal strip. The third electrode may be located on the same plane as the aforementioned negative electrode without being vis-à-vis the positive electrode.

The lithium ion electrolyte is an electrolyte of the same nature as that described above.

This electrolyte may advantageously be in contact, preferably via a separator soaked with said electrolyte, with the three aforementioned electrodes, so as to ensure ionic continuity. The accumulator can be in different formats, such as a cylindrical coil, a prismatic coil or a stack, the format is not a primary criterion.

Other features and advantages of the invention will emerge from the additional description which follows and which relates to particular embodiments. Of course, this additional description is only given as an illustration of the invention and does not in any way constitute a limitation. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of an accumulator used in the context of Example 1 for carrying out a process not in accordance with the invention. Figure 2 is a sectional view of an accumulator used in the context of Example 1 for carrying out a method according to the invention. FIGS. 3 and 4 are graphs which respectively illustrate the evolution of the normalized capacitance C (the value 1 corresponding to a practical specific capacitance of 1200 mAh / g) obtained in charge and in discharge C (curves a) and b ) with the first accumulator and curves c) and d) for the second accumulator) as a function of the number of cycles N and the evolution of the coulombic efficiency E (in%) obtained with the first accumulator (curve a) and the second accumulator (curve b) according to the number of cycles N.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS EXAMPLE 1 In this example, two accumulators have been tested: a first accumulator, in which there is no step of prelithiation of the negative electrode, which amounts to saying that the accumulator is not in accordance with the invention; a second accumulator, in which there is a step of prelithiation of the negative electrode, which amounts to saying that the accumulator is in accordance with the invention. Said first accumulator is shown in FIG. 1 (by reference numeral 1) comprising: a positive electrode 3 comprising LiNixMnyCozO2 (with x, y and z being equal to 1/3) as the active material, as a conductive additive; electricity, split carbon and polymeric binder of carboxymethylcellulose and provided on its upper side with an aluminum current collector 4 extended by an aluminum tab 5 to allow external connection of the accumulator; a negative electrode 6 comprising, as active material, nanoscale particles of silicon, as an electrically conductive additive, of the split carbon and as polymeric binder of carboxymethylcellulose and provided on its lower face with a current collector 7, extended copper nickel tab 8 to allow external connection of the accumulator; a separator 9 made of polypropylene (thickness 25 μm) impregnated with an electrolyte comprising a lithium salt, LiPF 6 1M dissolved in a mixture of carbonate solvents (more specifically, a mixture of ethylene carbonate and carbonate of diethylene in a 1: 1 volume ratio), disposed between said positive electrode and said negative electrode; a package 10 of the flexible bag type intended to contain all the aforementioned elements. Said second accumulator conforming to the implementation of the method of the invention comprises: a positive electrode 11 of the same nature as that of the first accumulator provided on its upper face with a current collector 12 made of aluminum extended by a leg aluminum 13 for enabling external connection of the accumulator; a negative electrode 14 of the same nature as that of the first accumulator provided on its underside with a copper current collector 15 extended by a nickel tab 16 intended to allow an external connection of the accumulator; a separator 17 of the same nature as that of the first accumulator disposed between said positive electrode and said negative electrode and also in contact with the third electrode described below, so as to have an ionic continuity between the first, the second and the third electrodes; a third metal lithium electrode 18 being located on the same plane as the aforementioned negative electrode without being opposite the positive electrode, this third electrode being provided on its lower face with a current collector; extended copper nickel tab 20 to allow external connection of the accumulator-a packaging 21 of the flexible bag type to contain all of the aforementioned elements. The second accumulator is subjected, in the first place, to a step of prelithiation of its negative electrode (that is to say step a) of the method of the invention). To do this, it is sufficient to connect the negative electrode and said third electrode and to circulate a current of the negative electrode to the third electrode in galvanostatic mode at a rate of C / 100 at room temperature. More specifically, the galvanosplastic mode consists of imposing a constant current of intensity I and following the evolution of the potential V across the electrodes over time t, the measurement being done in dynamic mode. The current imposed between the two electrodes is such that the imposed regime is equal to C / 100, here about 125 pA, applied for 67 hours, until the Li / Si ratio in the negative electrode is equal to 2 5.

Once the prelithiation of the negative electrode of the second accumulator has been carried out, the first and second accumulators have been galvanostatically cycled under the same conditions, namely the same charging and discharging regime (here, C / 10, ie a current of 400 pA), the same potential terminals (from 2.5 to 4.2 V), the same pressure applied to the accumulators during cycling. The two accumulators were cycled according to the protocols described above for several tens of cycles and their electrochemical performances were compared as illustrated in FIGS. 3 and 4 in the appendix, which respectively illustrate the evolution of the normalized capacity (FIG. the value 1 corresponding to a practical specific capacity of 1200 mAh / g) obtained in charge and in discharge C (expressed in mAh / g) (curves a) and b) with the first accumulator and curves c) and d) for the second accumulator) as a function of the number of cycles N and the evolution of coulombic efficiency E obtained with the first accumulator (curve a) and the second accumulator (curve b) as a function of the number of cycles N. Through this first For example, both stability in terms of practical specific capabilities and high coulombic efficiency for the second accumulator are apparent. These same conclusions can be repeated when the number of cycles increases (for example, when it goes to 150).

Claims (25)

REVENDICATIONS1. A method of operating a lithium-ion battery comprising at least one cell comprising a negative electrode (said first electrode) and a positive electrode (said second electrode), between which is disposed a lithium ion conducting electrolyte and comprising a third electrode lithium ion source, said method comprising: a) a step of preparing said first electrode, comprising a lithiation operation by the third electrode of an electrode comprising a material based on at least one metal element M or semi-metallic alloy capable of forming an alloy with lithium, so as to obtain said first electrode comprising an active material comprising an alloy of at least one metal or semimetallic element M and lithium in a molar ratio Li / M up to at 5 ; b) a step of operation by cycling said lithium accumulator between said negative electrode and said positive electrode without total delithiation of said negative electrode. 25 2. The method of claim 1, wherein the metal element M is selected from aluminum, tin, germanium and mixtures thereof. 30 3. The method of claim 1, wherein the semi-metallic element M is silicon. 4. Process according to any one of the preceding claims, in which the material based on at least one metallic or semi-metallic element M is in the form of only a single element M, an alloy of element (s) M or a composite material based on at least one element M. 5. Method according to claim 4, wherein the composite material based on at least one element M is a material comprising silicon and another element selected from carbon, tin, aluminum, germanium and mixtures of these. 6. Method according to any one of the preceding claims, wherein the material based on at least one metallic or semi-metallic element M has a total reversible capacitance greater than 2500 mAh / g. 7. A process according to any one of the preceding claims, wherein the material based on at least one metallic or semi-metallic element M is selected from: pure silicon; a silicon-carbon composite, the carbon content of which will not exceed 30% by mass; A silicon-tin composite, the tin content of which will not exceed 40% by weight, a silicon-aluminum composite, the aluminum content of which will not exceed 40% by mass; and a silicon-germanium composite, the germanium content of which will not exceed 55% by mass. 5 A process according to any one of the preceding claims, wherein the material based on at least one metallic or semimetal element M coexists with another material selected from organic binders, electrically conductive materials and mixtures of these. 9. The process of claim 8 wherein the organic binders are polymeric binders. The method of claim 8 or 9, wherein the electrically conductive materials are carbonaceous materials in divided form. 20 11. A method according to any one of the preceding claims, wherein step a) is performed by galvanostatic means, ie by applying a current of constant intensity for a time necessary for the incorporation of the lithium at a molar ratio of up to 5 between a material-based electrode comprising a metallic or semi-metallic element M (this electrode being a precursor of said first electrode) and said third electrode, this electrode being separated from said third electrode; electrode by a lithium ion conductive electrolyte. 12. A method according to any one of the preceding claims, wherein, in step a), the material based on at least one metallic or semi-metallic element M is lithiated in a molar ratio corresponding to obtaining a practical specific capacity corresponding to at least one third of the total reversible capacity of said material, preferably corresponding to at least 2/3. 13. A method according to any one of the preceding claims, wherein the third electrode is an electrode comprising, as an active material, lithium metal, a lithium metal alloy or a lithium insertion material. 20 The method of any of the preceding claims, wherein the positive electrode comprises a lithiated lithium insertion compound. 25 The process according to claim 14, wherein the lithiated lithium insertion compound is a lamellar oxide of the following formula: LiM 2 O 2 wherein M2 is a member selected from Ni, Co, Mn, Al, Mg and mixtures thereof. -this. The process according to claim 14, wherein the lithiated lithium insertion compound is an over-stoichiometric lamellar oxide of the following formula: Li (i + x) M30y wherein: -M3 is a member selected from Ni, Co, Mn and mixtures thereof; x and Y correspond to the following relations: 0.5 <x <2 and 2 <y <3 17. The method of claim 14, wherein the lithiated lithium insertion compound is a high-voltage spinel oxide having the following formula: Li i-aNi 0.5-bMnI, 5-c04-d with a, b , c and d being between -0.1 and +0.1, that is, each of the parameters a, b, c and d is greater than or equal to -0.1 and less than or equal to + 0.1. 18. The process of claim 14, wherein the lithiated compound has the following general formula: LixMly (X0) n wherein: M1 represents a member selected from Mn, Fe, Co, Ni, Cu, Mg, Zn , V, Ti, Al, Si, B, Cr, Mo and mixtures thereof; X represents an element selected from P, Si, Ge, S, V and As; * x, y, z and n are integers or positive decimal numbers chosen so that the total charge of the cations compensates for the total charge of the anions, so that the compound is electrically neutral. 19. The method of claim 18, wherein the lithiated oxide has the following formula: LiM1PO4 wherein M1 is as defined in claim 18. 20. Process according to any one of the preceding claims, in which: step a) is carried out under conditions sufficient to obtain a negative electrode material having a molar ratio Li / M (M being the metallic element M). or semi-metal as defined in claim 1) of at least 1/3 of the molar ratio when said material is completely alloyed with lithium; and, preferably, a Li / M molar ratio at least equal to 2/3; step b) is carried out over a range of capacities corresponding to at most 2/3 of the total reversible capacity of the material, and preferably to at most 1/3 of the total reversible capacity of the material. 21. Accumulator of the lithium-ion type suitable for carrying out the method of the invention as defined in any one of claims 1 to 20, said accumulator comprising at least one cell comprising a negative electrode (called the first electrode) and a positive electrode (said second electrode) between which is disposed a lithium ion conductive electrolyte and comprising a third electrode adapted to be connected to said first electrode and lithium ion source. 22. The battery according to claim 21, wherein the lithium ion conductive electrolyte is in contact via a soaked separator of said electrolyte, with both the negative electrode, the positive electrode and said third electrode. An accumulator according to claim 21 or 22, wherein said third electrode is on the same plane as the aforementioned negative electrode without facing the positive electrode. The accumulator of claim 21 or 22, wherein said third electrode is removed prior to the operating step. 25. The accumulator of claim 21 or 22, wherein said third electrode is retained during the operating step and is used as a reference electrode.