WO2001052338A1

WO2001052338A1 - Electrolytic compositions, method for production and electrochemical applications

Info

Publication number: WO2001052338A1
Application number: PCT/FR2001/000120
Authority: WO
Inventors: Guy Campet; Christophe Mingotaud; Armel Poquet; Joseph-Noël PORTIER; Serge Ravaine
Original assignee: Centre National De La Recherche Scientifique (C.N.R.S.)
Priority date: 2000-01-14
Filing date: 2001-01-15
Publication date: 2001-07-19
Also published as: FR2803951B1; AU2001231899A1; FR2803951A1

Abstract

Electrolytic compositions characterized in that they contain at least three constituents in a homogeneous mixture, i.e. one or several polymers acting as a matrix or support membrane with regard to the entire electrolytic composition and ensuring mechanical strength by conferring a state on the composition ranging from a solid state to a gel state; one or several ion conductive salts, said salt or salts being hydrophobic; and one or several salts which can ensure the conductive properties of the composition, said salt or salt being soluble in the fused salt or salts.

Description

'Electrolyte compositions, manufacturing process and electrochemical applications "

The invention relates to new compositions of electrolytes based on polymers and salts. It is also an _e proceeds of making such compositions and their applications for the development of electrochemical systems.

Many electrochemical systems have already been proposed, the most conventional corresponding to cells and batteries for energy storage.

We know, in particular from US Patents 5,728,487 or

US 5,598,293, liquid electrolyte compositions, based on a binary mixture of elements, having hydrophilic properties.

In addition, US Patents 5,683,832 or

US 5,827,602, processes for the preparation of liquid electrolyte having hydrophobic properties and intended for the manufacture of photovoltaic cells.

The major drawback of these electrolyte production methods lies mainly in the fact that, because of their liquid state, their use and their use in electrochemical devices are not easy. Indeed, with electrolytes in a liquid state, it is very difficult to develop flexible devices or adaptable shapes as imposed by the current technological trend, without risk of leakage of one electrolyte or rupture of the layer by shear, thus rendering the system inoperative. In addition, when these electrolytes are hydrophilic, their handling must be carried out in the absence of ambient air under a controlled atmosphere and their stability over time can pose problems (in particular, the appearance of bubbles in the mixture;

More recent electro-chemical systems correspond to electrochromic devices used as displays or as windows with modular transmission, using liquid crystal technology. To make the contrast persistent according to a given angle of observation, which will hamper it, is quite limited, these systems require a continuous supply of liquid crystals. It follows from the operating limitations, both in terms of the persistence of the contrast after switching off the power supply, and in terms of the quality of display, whatever the angle of observation.

The inventors provide a solution to these problems with the aid of electrolyte compositions prepared from certain types of polymers and determined salts.

The invention therefore relates to new electrolyte compositions having sufficient mechanical strength for applications on a flexible support and having hydrophobic or non-hydroscopic properties, that is to say of non-wettability by water.

It also aims to provide a process for the preparation of such easy-to-use electrolyte compositions.

It further relates to the electrochemical applications of these compositions, in particular for manufacturing devices of the cell or battery type, or electrochromic systems.

The electrolyte compositions according to the invention are characterized in that they contain, according to a homogeneous mixture, at least the following three components, namely: - one or more polymers, playing the role of matrix or support membrane vis-à-vis the entire composition of electrolytes and ensuring mechanical strength properties giving the composition a state ranging from solid to the state of frost,

one or more molten ionic conductive salts, this or these salts being hydrophobic (s),

one or more salts capable of ensuring the conductive properties of the composition, this or these salts being soluble in the molten salt or salts, ionic conductors.

According to a preferred arrangement of the invention, the polymer or polymers are chosen from polymers which are transparent in the visible field such as polyacrylates, in particular poly (methyl methacrylate) or PMMA, polycarbonates, polyurethanes or polyterephthalates.

According to another preferred arrangement of the invention, advantageously used in combination with the previous one, the hydrophobic salt or molten salts correspond to the formula:

^R 4 in which at least two of the substituents R_ to R5 are different and represent an alkyl or alkylene radical C _] _ to C_2 / straight or branched chain, optionally substituted by one or more groups -F, -OH, - COR, -COOR, where R represents a hydrogen atom or an alkyl radical in C ^ to C5, -NH2, -NHR or -JMP, R ', or R is as defined above and R', _dentιque or different αe R, represents an alkyl radical in C__ to C5, the other identical or different substituents, being chosen rarτ. -h, -OH, -M1 or ur Cj_ a C] _2 alkyl radical, ^and X ^~ represents a counter anion.

Very special salts preferred with regard to the hydrophobic properties sought correspond to the above formula in which R] _ and R4 represent different alkyl groups in C ^ to C5, R2 R3 and R5 represent a hydrogen atom and X ^~ is a counter anion.

The invention relates in particular to the use as a nyαrophobic molten salt of bistrifluoromethanesulfonimide (TFSI) -l-ethyl-3 methyl-imidazolium.

Other suitable salts are described by Bonhote et al in Inorg. Che. 35, 1168-1178 (1996).

According to another preferred arrangement of the invention, advantageously used with at least one of the preceding arrangements, the salt or the salts capable of ensuring the conductive properties are of the M ⁺ Y ^{~ type} , or M ⁺ is chosen from among cation soluble in the molten salt or salts, such as Lι ⁺ , H ⁺ , Na ⁺ , K ⁺ , that is to say small cations, and Y- is an anion soluble in the molten salt or salts.

Prefer anions include: Clθ ^~ PF ^~, AsF ~, CF3SO3-, CF ₃ ^COO-, (CF ₃ Sθ2) 2 ^N_ 'C ₃ F ₇ COO ^_.

A salt of this type which is particularly advantageous with regard to its conductive properties and solubility in bistrifluoromethanesulfonimide (TFSI) -l-ethyl-3 methyl-imidazolium is constituted by Lι (TFSI).

The electrolyte compositions of the invention contain the various constituents mentioned above in proportions respectively established according to the envisaged application, which may require a state ranging from the solid state to the gel state.

The invention also relates to a process for obtaining such compositions.

This process is characterized in that a homogeneous mixture is formed, using an organic solvent, of the said polymer (s), of the said ionic conductive, nyαrophobic salt (s) in which (or which) is (are) incorporated (s) one or more salts capable of ensuring the conductive properties.

The organic solvent is chosen from those compatible with the components used. It is preferably a solvent with a low boiling point to allow its rapid evaporation. Mention will in particular be made of dichloromethane.

The respective proportions of the various constituents are adapted as indicated above so as to obtain a mixture which can be easily spread and which presents itself according to the requirements required for a given application in a solid form, or almost solid or close to a gel state.

The electrolyte compositions of the invention are used in electrochemical systems belonging to various families.

Thus, according to a first embodiment of an electrochromic system 1 (cf. FIG. 1) using the electrolyte 2 obtained by the implementation of the process which is the subject of the invention, this system is intended in particular for applications relating to the display, optical devices with variable transmission, or glasses.

The electrochromic device 1 is formed by the superposition of elements comprising: a first substrate 3 (or support), flexible or rigid, produced in particular from glass or from plastic material, which gives the electrochromic device its mechanical strength,

- a first electrode formed on the one hand by a current collector 6 made from a conductive material which can in particular be tin oxide doped with antimony or fluorine, or mdium oxide doped with tin, and on the other hand an agent 7 ensuring or not the color transition under the effect of the passage of a current or the application of a voltage, formed from a mixed conductive polymer such as polyaniline (PANI) or polypyrrole or an inorganic material such as Prussian blue, vanadium oxide (V2O5) or tungsten oxide (O3),

of a thickness of electrolyte 2 formed from the ternary mixture,

- a second electrode formed on the one hand by a current collector 5 made from a conductive material which may in particular be tin oxide doped with antimony or fluorine, or medium oxide doped with tin, and on the other hand an agent 8 ensuring the color transition under the effect of the passage of a current or the application of a voltage, consisting for example of a mixed conductive polymer such as polyaniline (PANI) or polypyrrole or an inorganic material such as Prussian blue, vanadium oxide (2O5) or tungsten oxide (WO3),

and a second substrate 4 possibly identical to said first substrate 3, said electrochromic device being intended for variable transmission or display applications (cf. FIG. 1 j.

In the context of an electrochromic display device exclusively, the system is analogous to the previous case, with the exception of a current collector 5 or 6, which is now metallic and possibly deposited on a substrate 4 The choice of the nature of the current collectors 5 and 6 and of the coloring transmitting agents 7 and 8 is made according to the desired application. In particular, the state of coloring and discoloration, the range of voltage necessary for the reversible switching between these two states as well as the time this switching are parameters to be taken into account to make this choice.

In the case of an electrochemical device that designed for specific display applications (ectrochromic devices;, requiring the display of a message with alpha-numeric characters, provision is made for placing the layer of material having a specific color on the electrode according to a matrix structure, in order to be able to apply at one or more points of said matrix structure a voltage or a current so as to allow, at this or these particular points, the transition of colors and therefore the formation of the message considered.

According to a second embodiment of an electrochemical system 1 using the electrolyte 2 obtained by the implementation of the process which is the subject of the invention, it is intended for applications relating to energy storage and more precisely designed for making batteries (see Figure 2).

The structure of this type of electrochemical device is almost similar to that previously described which specifically targeted electrochromic devices with variable transmission or display.

The battery-forming element comprises two conductive supports 3, 4, flexible or rigid, (fabric of metallic or carbon fibers, metallic sheets enclosing, on the one hand an electrolyte layer 2 based on the ternary mixture, and on the other hand , electrodes 5, 6 formed for example of inorganic oxide nanocπstallm (Snθ2> / 'Mn.02 ¹ . In addition, electrochemical devices functioning as the battery does not require as eiectrochromes display devices using the principle of optical reflection or electrochromic devices using the principle _of an optical transmission, to be developed with materials _t ransparents in the field of visible wavelengths.

This is why the elements forming a support or substrate will be made of an adequate material in terms of resistance or mechanical strength and compatibility with the other components, and the same will apply to the other parts forming the electrodes.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an embodiment thereof devoid of any limiting character. In the figures:

- Figure 1 illustrates a block diagram of an electrochemical device with variable transmission or by display (electrochromic devices);

- Figure 2 illustrates a block diagram of an electrochemical device operating as a battery.

Example I: Preparation of an electrochromic system

First of all, a layer of WO3 is deposited on a glass plate covered with a layer of FTO (Fluorite doped Tin Oxide, conductivity 6 / square of thickness 300 nm). This deposit is made according to the method patented in 1994 by Donnelly corporation (US patent n ° 5,277,986). A very homogeneous deposit of O3 is thus obtained by "dip-coatmg".

On another substrate identical to the first, a poly (aniline) film is electrodeposited. For this, a potential of 750 mV is applied for 5 minutes in a PANI solution. (1M), HC1 (3M). The counter electrode used is a platinum electrode. The film is cycle ten times at -300 / + 500mV in HCl (1M), compared to a reference electrode g / AgCl.

Example II: Prepara ti on of an electrolyte composi ti on

An electrolytic membrane is produced by mixing 1 ml of bistrifluoromethanesulfonimide (TFSI) -l-ethyl-3 methyl mida olium containing 10% by mass of LiTFSI with between 0.2 and 0.8 g of oz lj metnyl methacrylate and 3 ml of dιchlororιe ^~ ιanε. Once the PPM ™ - is completely dissolved and after partial evaporation of the solvent CH2Cl2, so as to obtain a viscous solution, this mixture is spread on a support.

Examples III to VIII: Prepara ti on of different electrochromic systems

- Example III:

The mixture of at least three components is spread over the film of WO3 in the discolored state. The residual solvent is removed by heating slightly under a primary vacuum. The second plate is pressed on it so that the bubbles are evacuated (the two plates being assembled in a transparent state). The sealing of the system thus obtained is not compulsory, the adhesion properties and the mechanical strength of the electrolyte can make this step optional.

The system is polarized using a galvanostat potentiostat. Potential cycles varying from -1.5 V (discolored state) to 1.5 V (colored state) are applied. It is observed that the system has an intense, reversible and homogeneous coloration which does not undergo degradation after 10,000 cycles. - Example IV:

The production of the film of WO3 as well as that of the electrolyte ~, t. C'pitiques to those described in Example 1 The same current collectors are used.

A second film of Prussian blue (BP) is electrodeposited on the second substrate. We make a solution FeCi3 (10 ^~ 2JM), K ^ FeCNg (10 ^_2 M). A cathode current of 40 μA / cm ² is applied for 5 minutes. The film is cycled ten times at - 400 / + 500mV in KC1 (0.5M), compared to an Ag / AgCl reference electrode.

The assembly of the system and the electrochemical tests carried out are identical to those described in Example No. I. It is observed that the system exhibits an intense, reversible and homogeneous coloration which does not undergo degradation after 10,000 cycles.

- Example V:

A system is produced according to the procedure described in Example I, the collectors used being ITO films (Tin doped Indium Oxide) deposited on glass plates (conductivity: 24 / square).

The assembly of the system and the electrochemical tests carried out are identical to those described in Example I. It is observed that the system has an intense, reversible and homogeneous coloration which does not undergo degradation after 10,000 cycles.

- Example VI:

A system is produced according to the procedure described in Example III, the collectors used being ITO films deposited on glass plates (conductivity: 24 / square).

The assembly of the system and the electrochemical tests carried out are identical to those described in Example II. We observe that the system has an intense, reversible and homogeneous coloration which does not undergo degradation after 10,000 cycles.

- Example VII:

A system is produced according to the procedure described in Example III, the collectors used being ITO films (conductivity: 60 / square) deposited on poly (ethylene terephthalate) (PET). i n

The assembly of the flexible system and the electrochemical tests carried out are identical to those described in Example I). It is observed that the system has an intense, reversible and homogeneous coloration which does not undergo degradation after 15 10000 cycles.

- Example VIII:

A system is mounted according to the procedure described in 0 Example I. The film of W0 ₃ is produced on an ITO film deposited on PET.

The PANI film is produced on a layer of gold deposited by evaporation on PET. 5

The assembly of the flexible system and the electrochemical tests carried out are identical to those described in Example I. It is observed that the system has an intense, reversible and homogeneous coloring which does not undergo degradation after 0 10000 cycles.

Examples IX and X: Preparation of an electrochemical system for

5 - Example IX:

The examples described above use electrode materials deposited in thin layers (approximately 300nm; . The aim being to have a very marked color difference between the two states (system charged or not) These systems can also be used as rechargeable lithium batteries of the "rock g-chair" type To increase the energy capacity of these batteries, ± i is necessary to deposit on each electrode approximately ten times more active material using the deposition procedures described above.

The realization of one electrolyte as well as the shaping of the system are similar to those presented previously.

These batteries cycle very reversibly (over 10,000 cycles) with a capacity of the order of 10 mAh / g.

Example X:

The electrodes of the "rock g-chair" battery can also be produced from powders using a mass percentage of 60. (W0 ₃ , PANI or BP), 10c of graphite and 10% of PMMA. It is completed by adding 20 ° of hydrophobic liquid lithium salt. These materials can be spread on flexible stainless steel current collectors for example.

These batteries cycle very reversibly (more than 10,000 cycles) with a capacity of the order of lOmAh / g.

The invention as previously written offers multiple advantages because the manufacturing process completely overcomes the constraint related to the presence of moisture, this allows to consider manufacturing of multiple devices (electrochromic systems, electrochemical systems batteries) in enclosures without the presence of a controlled atmosphere. In addition, electrochromic devices have a memory effect over time and their reading is easy, whatever the angle of orientation.

It remains to be understood that the present invention is not limited to the exemplary embodiments described and shown above, but that it encompasses all variants thereof.

Claims

RE VE ND I CAT I ON S

1 / Electrolyte compositions characterized in that they contain, according to a homogeneous mixture, at least the following three components, namely:

- one or more polymers, playing the role of matrix or support membrane vis-à-vis the entire composition of electrolytes and ensuring mechanical properties giving the composition a state ranging from solid to the state of frost,

one or more salts capable of ensuring the conductive properties of the composition, this or these salts being soluble in the inactive conductive molten salt or salts.

2 / Compositions according to claim 1, characterized in that the polymer or polymers are chosen from transparent polymers in the visible field such as polyacrylates, in particular poly (methyl methacrylate) or PMMA, polycarbonates, polyurethanes or polyterephthalates .

3 / Compositions according to claim 1 or 2, characterized in that the molten hydrophobic salt or salts correspond to the formula:

in which at least two of the substituents R 1 to R 5 are different and represent a C 1 to C 2 alkyl or alkylene radical with a straight or branched chain, optionally substituted by one or more groups -F, -OH, -COR, -COOR , where R represents a hydrogen atom or an alkyl radical in C to C5, -NH2, -NHR or -NR, R ', or R is as defined above and R', identical or different from R, represents a C1-C5 alkyl radical, the other identical or different substituents being chosen from -H, -OH, -NH2 or a C1-C2 alkyl radical, and X ^~ represents a counter anion.

4 / Compositions according to claim 3, characterized in that R and R4 represent different alkyl groups in C to ^c 12 ' ^R 2' ^R 3 ^e t ^R 5 represent a hydrogen atom and X ^~ is a counter anion.

5 / Compositions according to claim 4, characterized in that they contain as hydrophobic molten salt of bistrifluoromethanesulfonimide (TFSI) -l-ethyl-3-methylimidazolium

6 / Compositions according to any one of claims 1 to 5, characterized in that the salt or salts capable of ensuring the conductive properties are of the M ⁺ Y ^{~ type} , where M ⁺ is chosen from a cation soluble in the or the molten salts and Y ^~ is an anion soluble in the molten salt or salts.

7 / Compositions according to claim 6, characterized in that M ⁺ is chosen from Lι ⁺ , H ⁺ , Na ⁺ , K ⁺ .

8 / Compositions according to Claim 6, characterized in that ï ^~ is selected from CIO4-, ^~ PF, AsF ^"CF3SÛ3 ^~, CF3C00", (CF ₃ S0 ₂₎ 2 ^N_ 'C3F7COO ^".

9 / Compositions according to claim 6, characterized in that the salt is Lι (TFSI).

10 / A method of developing an electrolyte according to any one of claims 1 to 9, characterized in that forms a homogeneous mixture, using an organic solvent, of said polymer (s) of said hydrophobic ionic conductive salt (s), in which (or which) is (are) incorporated one or more salts capable of ensuring the conductive properties.

] i / Proc according to claim 10, characterized in ~ e that the organic solvent used to mix the various components of one electrolyte is a low boiling solvent to allow rapid evaporation, such as in particular dichloromethane.

12 / Electrochemical device (1) using the electrolyte according to any one of claims 1 to 9, characterized in that it comprises an assembly formed by the superposition:

a first substrate (3) (or support), flexible or rigid, produced in particular from glass or plastic material, which gives the electrochromic device its mechanical strength,

- a first electrode formed on the one hand by a current collector (6) produced from a conductive material which can in particular be tin oxide doped with antimony or fluorine, or the oxide of mdium doped with tin, and on the other hand of an agent (7) ensuring or not the transition of coloring under the effect of the passage of a current or the application of a voltage , formed from a mixed conductive polymer such as polyaniline (PANI) or polypyrrole or from an inorganic material such as Prussian blue, vanadium oxide (2O5) or tungsten oxide (WO3),

- an electrolyte thickness (2),

- a second electrode formed on the one hand by a current collector (5) produced from a conductive material which may in particular be etam dope oxide with antimony or flucr, or indium oxide doped with stam, and ^{on the} other hand an agent (8) ensuring the color transition under the effect the passage of a current or the application of a voltage, consisting for example of a mixed conductive polymer such as polyaniline (PANI) or polypyrrole or of an inorganic material such as Prussian blue, oxide vanadium (V2O5) o- tungsten oxide WO3),

- And of a second substrate (4) possibly identical to said first substrate (3), said electrochemical device being intended for applications of electrocnromic devices with variable transmission or with display.

13 / electrochemical device (1) using 1 electrolyte according to any one of claims 1 to 9, characterized in that it comprises two support plates (3, 4, flexible or rigid, enclosing, on the one hand a layer of electrolyte (2) based on the ternary mixture, and on the other hand, electrodes (5, 6) formed for example of inorganic oxide nanocπstallm (Sn.02) / (Mnθ2).

14 / Application of the device according to claim 13 to energy or battery storage.