FR3058573A1 - ELECTROCHEMICAL CELL FOR LITHIUM ION BATTERY COMPRISING A SPECIFIC POSITIVE ELECTRODE ON ALUMINUM COLLECTOR AND A SPECIFIC ELECTROLYTE - Google Patents

Abstract

The invention relates to an electrochemical cell for a lithium-ion battery comprising: a negative electrode; a positive electrode comprising, as active material, an oxide compound having the general formula LIMO 2, in which M is a member selected from Ni, Co, Mn, Al, Mg and mixtures thereof, said positive electrode being associated an aluminum current collector; and an electrolyte disposed between said negative electrode and said positive electrode, said electrolyte comprising, as lithium salt, lithium bis (trifluoromethylsulfonyl) imide, and comprising, as organic solvent, trifluoropropylene carbonate.

Description

Holder (s): ATOMIC ENERGY AND ALTERNATIVE ENERGY COMMISSIONER Public establishment, RHODIA OPERATIONS Simplified joint-stock company.

Extension request (s)

Agent (s): BREVALEX Limited liability company.

FR 3 058 573 - A1

Q4) ELECTROCHEMICAL CELL FOR LITHIUM-ION BATTERY COMPRISING A SPECIFIC POSITIVE ELECTRODE ON AN ALUMINUM MANIFOLD AND A SPECIFIC ELECTROLYTE.

The invention relates to an electrochemical cell for a lithium-ion battery comprising:

-a negative electrode;

a positive electrode comprising, as active material, an oxide compound corresponding to the general formula LIMO ₂ , in which M is an element chosen from Ni, Co,

Mn, Al, Mg and mixtures thereof, said positive electrode being associated with an aluminum current collector; and

an electrolyte disposed between said negative electrode and said positive electrode, said electrolyte comprising, as lithium salt, lithium bis (trifluoromethylsulfonyl) imide, and comprising, as organic solvent, trifluoropropylene carbonate.

ELECTROCHEMICAL CELL FOR LITHIUM-ION BATTERY COMPRISING A SPECIFIC POSITIVE ELECTRODE ON AN ALUMINUM MANIFOLD AND A

SPECIFIC ELECTROLYTE

DESCRIPTION

TECHNICAL AREA

The present invention relates to an original lithium-ion battery cell comprising an original association between a specific positive electrode on an aluminum current collector and a specific electrolyte, making it possible in particular to obtain excellent performance without the phenomenon of anodic dissolution of the aluminum constituting the current collector.

The general field of the invention can thus be defined as that of batteries of the lithium-ion type.

Batteries of the lithium-ion type are increasingly used as an autonomous energy source, in particular in portable electronic equipment (such as mobile phones, laptops, tools), where they are gradually replacing the batteries nickel-cadmium (NiCd) and nickel-metal hydride (NiMH). They are also widely used to provide the power supply necessary for new micro applications, such as smart cards, sensors or other electromechanical systems.

Batteries of the lithium-ion type operate on the principle of insertion-disinsertion (or lithiation-delithiation) of lithium according to the following principle.

During the discharge of the battery, the lithium disinserted from the negative electrode in ionic form Li ⁺ migrates through the ion-conducting electrolyte and comes to be inserted in the crystal lattice of the active material of the positive electrode. The passage of each Li ⁺ ion in the internal circuit of the battery is exactly compensated by the passage of an electron in the external circuit, thus generating an electric current. The density of mass energy released by these reactions is both proportional to the potential difference between the two electrodes and to the quantity of lithium which will be inserted in the active material of the positive electrode.

When charging the battery, the reactions occurring within the battery are the reverse reactions of the discharge, namely that:

the negative electrode will insert lithium into the network of the material constituting it; and

-the positive electrode will release lithium.

By virtue of this operating principle, batteries of the lithium-ion type require two different insertion compounds at the negative electrode and at the positive electrode.

Whether for the negative electrode or the positive electrode, each of them is, advantageously, associated with a metal current collector, which, as its name suggests, makes it possible to convey the current, therefore the electrons , towards the outside of the electrochemical cell.

It may in particular be advantageous to associate an aluminum current collector with at least one of the electrodes, since aluminum has, among other things, for advantage, a low density, which allows a gain in mass energy density for the cell.

On the other hand, using aluminum as a current collector at least for the positive electrode arises the difficulty of the phenomenon of anodic dissolution, which occurs in particular with active materials of positive electrode, which allow access to a voltage. cell of at least 4 V and with lithium salts, such as bis (trifluoromethylsulfonyl) lithium imide (known by the abbreviation LiTFSI), which turns out to be a particularly interesting salt, because it forms little or no hydrofluoric acid in case of degradation, unlike other lithium salts like LÎPF6 and can be used at higher temperatures and in a less protective atmosphere.

To solve this problem of anodic dissolution in the aforementioned context, several solutions have been proposed, including:

the introduction of an addition salt, in addition to LiTFSI, such as BF4, which induces, however, an increase in the sensitivity to humidity of the electrolyte;

the passivation of the aluminum collector consisting in creating a passivation film on the surface of the aluminum, with a view to reducing the corrosion rate of the latter, this solution however having a temporary appearance due to the progressive degradation of the film passivation;

-the search for alternatives to aluminum as a current collector, for example, carbon collectors; and

the use of alternative salts to LiTFSI such as bis (perfluoroethylsulfonyl) lithium imide (known by the abbreviation LiBETi), making it possible to induce a slight shift in the dissolution potential of aluminum without however eliminating the problem.

Also, in view of what already exists, the authors of the present invention have set themselves the aim of proposing an electrochemical cell for a lithium-ion battery capable of delivering a high voltage (of at least 4 V) using aluminum for the current collector for at least the positive electrode and a specific imide salt, without this inducing, during operation of the cell, a phenomenon of anodic dissolution of aluminum.

Starting from this, they discovered, surprisingly, that by using, as the organic solvent of the electrolyte, a specific solvent, it is possible to work in the abovementioned environment without being limited by the phenomenon of anodic dissolution of the 'aluminum.

STATEMENT OF THE INVENTION

Thus, the invention relates to an electrochemical cell for a lithium-ion battery comprising:

-a negative electrode;

a positive electrode comprising, as active material, an oxide compound corresponding to the general formula LÎMO2, in which M is an element chosen from Ni, Co, Mn, Al, Mg and the mixtures thereof, said positive electrode being associated an aluminum current collector; and

an electrolyte placed between said negative electrode and said positive electrode, said electrolyte comprising, as lithium salt, lithium bis (trifluoromethylsulfonyl) imide (also known by the abbreviation LiTFSI), and comprising, as organic solvent, carbonate trifluoropropylene.

The reasoned choice of the organic solvent constituting the electrolyte makes it possible to avoid the phenomenon of anodic dissolution of the aluminum constituting the current collector of the positive electrode. In addition, the other characteristics of the cells of the invention make it possible to obtain:

-a voltage of at least 4 V, thanks to the specific choice of active material of the positive electrode; and

-a good conduction of lithium ions thanks to the choice of a specific lithium imide salt, without risk of the phenomenon of degradation of these into hydrofluoric acid.

Before going into more detail in the description of this invention, we specify the following definitions.

By negative electrode is meant, conventionally, in what precedes and what follows, the electrode which acts as anode, when the battery delivers current (that is to say when it is in the process of discharging ) and which acts as a cathode, when the battery is in the process of charging.

By positive electrode is meant, conventionally, in the foregoing and what follows, the electrode which acts as a cathode, when the battery delivers current (that is to say when it is in the process of discharging) and which acts as an anode when the battery is in the process of charging.

According to the invention, the positive electrode is an electrode comprising, as active material, an oxide compound of formula (I) below:

LiMOz (D in which M is an element chosen from Ni, Co, Mn, Al, Mg and mixtures thereof, and preferably still, with M being an element chosen from Ni, Co, Mn and mixtures of these.

From a structural point of view, the oxide compound of the above formula has a lamellar structure.

As examples of such oxide compounds, mention may be made of lithium oxides LiCoCh, LINI02 and mixed oxides Li (Ni, Co, Mn) O2 (such as Li (Nii / 3Mni / 3Coi / 3) O2) also known as NMC).

In addition to the presence of an active material, such as those defined above, the positive electrode may comprise a polymeric binder, such as polyvinylidene fluoride (PVDF), a carboxymethylcellulose mixture with a latex of the styrene and / or butadiene type. as well as optionally one or more electrically conductive adjuvants, which may be carbonaceous materials such as carbon black, carbon fibers obtained in the vapor phase (known by the abbreviation VGCF).

Thus, from a structural point of view, the positive electrode can be in the form of a composite material comprising a matrix of polymeric binder (s), within which charges constituted by the active material are dispersed. and possibly the adjuvant or conductors of electricity.

The positive electrode is associated, according to the invention, with an aluminum current collector, which means, in other words, that it is directly in contact with this collector, to allow the routing of electric current to the outside of the electrochemical cell. The current collector can be in the form of an aluminum strip. The positive electrode, for its part, can be in the form of a coated layer on the current collector.

The above-mentioned electrolyte comprises at least one lithium salt, which is lithium bis (trifluoromethylsulfonyl) imide, and comprising, as organic solvent, trifluoropropylene carbonate.

The lithium bis (trifluoromethylsulfonyl) imide has the following formula (II):

^ llX

The lithium salt may be present in the electrolyte at a concentration ranging from 0.5 to 3 mol / L.

Trifluoropropylene carbonate, meanwhile, has the following formula:

Trifluoropropylene carbonate advantageously constitutes the only organic solvent included in the electrolyte, which means, in other words, that trifluoropropylene carbonate constitutes 100% (by volume or by mass) of the organic solvent or alternatively , in other words, that the organic solvent consists solely of trifluoropropylene carbonate.

It is understood that the carbon of trifluoropropylene can exist in one or other of its enantiomers or mixtures thereof.

In addition, the electrolyte can comprise at least one additive corresponding to one of the following formulas (IV) and (V):

in which R ¹ and R ² represent, independently of one another, H, Cl or F, provided that R ¹ and R ² do not both represent H.

Compound (V) can be used interchangeably in its various isomeric forms.

The compound of formula (IV) can be designated by the name of vinylidene carbonate.

Concerning the compound of formula (V), a specific compound falling within this definition and particularly suitable is the compound of formula (Va) below:

O (Va) this compound also being called fluoroethylene carbonate.

The compound of formula (IV) or (V) may be present in the electrolyte in a content ranging from 0.5 to 10% by mass relative to the mass of the organic solvent and of the lithium salt.

More specifically, it can be present in a content ranging from 1 to 5% by mass, more preferably from 2% or 10% by mass relative to the mass of the organic solvent and of the lithium salt.

A specific electrolyte entering, advantageously, in the cells of the invention is an electrolyte comprising, in addition, vinylidene carbonate up to 2% relative to the mass of the lithium salt and of the organic solvent and more specifically, an electrolyte comprising only LiTFSI, trifluoroethylene carbonate and vinylidene carbonate up to 2% relative to the mass of LiTFSI and trifluoroethylene carbonate.

The electrolyte can be caused to impregnate a porous separator, which is disposed between the positive electrode and the negative electrode of the electrochemical cell.

This separator can be made of a porous material, such as a polymeric material, capable of receiving in its porosity the liquid electrolyte. For example, it may be a porous polyacrylonitrile separator.

The negative electrode is an electrode comprising, as active material, a lithium insertion material, which can be, for example, a carbonaceous material, such as graphite.

In addition, the negative electrode may comprise a polymeric binder, such as polyvinylidene fluoride (PVDF), a carboxymethylcellulose mixture with a latex of the styrene and / or butadiene type.

What is more, in the same way as for the positive electrode, the negative electrode can be presented, from a structural point of view, as a composite material comprising a matrix of polymeric binder (s), within which are dispersed charges constituted by the active material, such as graphite.

The negative electrode can also be associated with a metal current collector, such as a copper current collector. This means, in other words, that it is directly in contact with this collector, to allow the routing of electric current to the outside of the electrochemical cell. The current collector can be in the form of a copper strip. The negative electrode, on the other hand, can be in the form of a coated layer on the current collector.

Finally, the invention relates to a lithium battery comprising one or more electrochemical cells as defined above.

Other characteristics and advantages of the invention will appear from the additional description which follows and which relates to particular embodiments.

Of course, this additional description is given only by way of illustration of the invention and in no way constitutes a limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1 to 4 are graphs illustrating the evolution of the intensity I (in mA) as a function of the potential E (in V) with, respectively:

FIGS. 1 and 2 for the first cycle and the tenth cycle with the second electrochemical cell of Example 1 below; and

FIGS. 3 and 4 for the first cycle and the tenth cycle with the first electrochemical cell of example 1 below.

FIGS. 5 and 6 are graphs illustrating cycling curves for two comparative cells defined in example 2.

FIG. 7 is a graph illustrating the evolution of the capacitance C as a function of the number of cycles N for electrochemical cells defined in example 2 below.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

EXAMPLE 1

This example does not illustrate, as such, an electrochemical cell according to the invention, but aims to demonstrate that trifluoropropylene carbonate limits the anodic dissolution of aluminum in the presence of a TFSI salt.

To do this, a first electrochemical cell is prepared in the form of a button cell comprising:

as a negative electrode, a negative electrode made of metallic lithium; and

-as a positive electrode, an aluminum electrode; and

an electrolyte disposed between said positive electrode and the negative electrode, comprising LiTFSI 1 M in trifluoropropylene carbonate.

By way of comparison, a second electrochemical cell similar to the first electrochemical cell described above is prepared, except that the electrolyte comprises LITFSI 1 M in a mixture (ethylene carbonate / propylene carbonate) 1 : 1 by volume.

These two cells are subjected to cyclic voltammetry tests between 2.5 V and 4.2 V at 1 mV / S at room temperature.

The profiles obtained are reproduced in FIGS. 1 to 4 in the appendix, illustrating the evolution of the intensity I (in mA) as a function of the potential E (in V) with, respectively:

FIGS. 1 and 2 for the first cycle and the tenth cycle respectively with the second electrochemical cell; and

FIGS. 3 and 4 for the first cycle and the tenth cycle respectively with the first electrochemical cell.

We can observe in Figures 1 and 2 (1 ^st and 10 ^th cycles), that the dissolution causes a significant rise in current above 3.7 V for the cell comprising a mixture of carbonates with a characteristic curve crossing of anodic dissolution. For Figures 3 and 4, this curve intersection does not appear and the profile flattens even over the cycles, meaning that the active surfaces passivate as they go.

EXAMPLE 2

This example illustrates electrochemical cells in accordance with the invention and, for comparison, electrochemical cells not in accordance with the invention, in order to demonstrate the contribution of the invention concerning the phenomenon of anodic dissolution of aluminum.

In this example, each electrochemical cell is in the form of a button cell comprising:

as a negative electrode, a negative electrode comprising, as active material, graphite and as a polymeric binder, a mixture of carboxymethylcellulose with a latex of the styrene butadiene type in respective proportions 97.4 / 1.3 / 1.3, said electrode negative being deposited on a copper current collector;

as a positive electrode, a positive electrode comprising, as active material, LiNii / 3Mni / 3Coi / 3O2, as electrically conductive material, carbon black SP and carbon fibers VGCF and as polymeric binder, PVDF in respective proportions 92/2/2/4, said positive electrode being deposited on an aluminum current collector; and

an electrolyte disposed between said positive electrode and the negative electrode.

A first series of tests is carried out with two comparative cells, called the first cell and the second cell, the first cell comprising an electrolyte comprising LITFSI IM, a mixture (ethylene carbonate / propylene carbonate) 1: 1 and the second cell comprising an electrolyte comprising LiTFSI IM, a mixture (ethylene carbonate / propylene carbonate) 1: 1 and 2% of vinylidene carbonate relative to the mass of LiTFSI and of the mixture (ethylene carbonate / propylene carbonate) , the tests consisting of galvanostatic cycles carried out at different charge / discharge speeds between 2.8V and 4.15V (i.e. 4.25V vs. Li on the NMC side).

The results are reported in Figures 5 and 6 attached in the appendix, which illustrate the evolution of the voltage U (in V) as a function of the duration T (in s) for the first cell and the second cell respectively. The cells cycle only once or twice with the appearance of strong polarization, this problem essentially arising from the phenomenon of anodic dissolution.

A second series of tests is then carried out with a cell in accordance with the invention, to determine the evolution of the discharge capacity as a function of the number of cycles N.

The results are shown in FIG. 7, which illustrates the evolution of the capacity C (in%) during cyclings at C / 20 as a function of the number of cycles N (between 45 and 75 cycles) for the second cell (non-compliant) to the invention) explained above and a cell according to the invention, namely comprising an electrolyte comprising LiTFSI, trifluoropropylene carbonate and vinylidene carbonate (up to 2% by mass relative to the mass of LiTFSI and trifluoroethylene carbonate).

It can be observed that the electrochemical cell according to the invention has better cyclability (top curve a) compared to the cell comprising carbonate solvents (bottom curve b).

Claims (10)

1. Electrochemical cell for lithium-ion battery comprising: -a negative electrode; a positive electrode comprising, as active material, an oxide compound corresponding to the general formula UIVIO2, in which IVI is an element chosen from Ni, Co, Mn, Al, Mg and the mixtures thereof, said positive electrode being associated an aluminum current collector; and an electrolyte disposed between said negative electrode and said positive electrode, said electrolyte comprising, as lithium salt, lithium bis (trifluoromethylsulfonyl) imide, and comprising, as organic solvent, trifluoropropylene carbonate. 2. The electrochemical cell according to claim 1, in which the oxide compound is a lithiated oxide of formula LiCoCL, LiN1O2 or Li (Ni, Co, Mn) Ü2. 3. An electrochemical cell according to claim 1 or 2, in which the oxide compound is a lithiated oxide of formula LiN11 / 3IVIni / 3Coi / 3C> 24. An electrochemical cell according to any one of the preceding claims, wherein the positive electrode comprises a polymeric binder and, optionally, one or more electrically conductive adjuvants. 5. An electrochemical cell according to any one of the preceding claims, in which the organic solvent consists solely of trifluoropropylene carbonate. 6. An electrochemical cell according to any one of the preceding claims, in which the electrolyte further comprises at least one additive corresponding to one of the following formulas (IV) and (V): Ri R ² (IV) (V) in which R ¹ and R ² represent, independently of one another, H, Cl or F, provided that R ¹ and R ² do not both represent H. 7. An electrochemical cell according to claim 6, in which the compound of formula (V) corresponds to the following specific formula (Va): R O (Va) this compound also being called fluoroethylene carbonate. 8. An electrochemical cell according to any one of the preceding claims, in which the electrolyte is an electrolyte further comprising, as additive, vinylidene carbonate of formula (IV) up to 2% relative to the mass of the lithium salt and organic solvent. 9. An electrochemical cell according to any one of the preceding claims, in which the negative electrode comprises, as active material, a carbonaceous material. 10. An electrochemical cell according to any one of the preceding claims, in which the carbonaceous material is graphite. 11. Electrochemical cell according to any one of the preceding claims, in which the negative electrode is associated with a current collector 5 metallic. 12. The electrochemical cell according to claim 11, in which the metal current collector is a copper collector. 13. Lithium battery comprising one or more electrochemical cells as defined according to any one of claims 1 to 12. S.60351 l (mA) l (mA) 2/3 T (s)