FR2803951A1 - ELECTROLYTE COMPOSITIONS, METHOD OF MANUFACTURE AND ELECTROCHEMICAL APPLICATIONS - Google Patents

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

The subject of the invention is novel electrolyte compositions based on polymers and salts. It also relates to a method of manufacturing such compositions and their applications for the development of electrochemical systems.

Numerous electrochemical systems have already been proposed, the most conventional corresponding to batteries and batteries for storing energy.

US Pat. No. 5,728,487 or US Pat. No. 5,598,293 discloses liquid electrolyte compositions based on a binary mixture of elements having hydrophilic properties.

In addition, US Pat. No. 5,683,832 or US Pat. No. 5,827,602 discloses processes for producing liquid electrolyte having hydrophobic properties and intended for the manufacture of photovoltaic cells.

The major disadvantage of these electrolyte production processes lies mainly in the fact that due to their liquid state, their use and their implementation 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 the 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 away from the ambient air under a controlled atmosphere and their stability over time can cause problems (in particular, appearance of bubbles in the mixture).

More recent electrochemical systems correspond to electrochromic devices used as displays or as transmissive transmission windows, using liquid crystal technology. To make the contrast persistent at a given viewing angle, which in general is quite limited, these systems require continuous supply of the liquid crystal. This results in operating limitations, both in terms of the persistence of the contrast after cut-off of the power supply, as well as the viewing quality, 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 specific 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 non-wettability by water.

It is also intended to provide a method for producing such easy-to-use electrolyte compositions.

It also relates to the electrochemical applications of these compositions, in particular to manufacture battery-type or battery devices, 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, acting as matrix or support membrane vis-à-vis -vis the whole of the electrolyte composition and ensuring mechanical strength properties conferring on the composition a state ranging from the solid state to the gel state, - one or more molten ionic conductive salts, this or these salts being hydrophobic, - 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 embodiment of the invention, the polymer or polymers are chosen from transparent polymers in the visible range such as polyacrylates, especially poly (methyl methacrylate) or PMMA, polycarbonates, polyurethanes or polyterephthalates. in which at least two of the substituents R1 to R5 are different and represent a straight or branched chain C1 to C12 alkyl or alkylene radical, optionally substituted by one or more -F, -OH, -COR, -COOR groups where R represents a hydrogen atom or a C1-C5 alkyl, -NH2, -NHR or -NR, R 'radical, where R is as defined above and R', which is identical to 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-C12 alkyl radical, and X- represents a counter-anion.

Salts which are especially preferred with regard to the desired hydrophobic properties correspond to the above formula in which R 1 and R 4 represent different C 1 to C 5 alkyl groups, R 2, R 3 and R 5 represent a hydrogen atom and X - is a counter anion.

The invention is directed in particular to the use as a hydrophobic molten salt of bistrifluoromethanesulfonimide (TFSI) -1-ethyl-3-methylimidazolium.

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

According to another preferred arrangement of the invention, advantageously used with at least one of the

       the foregoing, the salt or salts capable of providing the conductive properties are of the M + Y- type, where M + is chosen from a cation which is soluble in the molten salt or salts, such as Li +, H +, Na +, K +, c i.e., small cations, and Y- is a soluble anion in the molten salt (s).

Preferred anions include: C104-, PF6, ASF6, CF3SO3-, CF3C00, (CF3SO2) 2N, C3F7C00-.

A salt of this type which is particularly advantageous with regard to its conductive properties and solubility in bistrifluoromethanesulfonimide (TFSI) -1-ethyl-3-methylimidazolium is constituted by Li (TFSI).

The electrolyte compositions of the invention contain the various constituents mentioned above in respective proportions established according to the intended 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, with the aid of an organic solvent, of said one or more polymers, of said hydrophobic ionic conductive salt or salts, in which (or which) is (are) incorporated (s) one or more salts capable of providing conductive properties.

The organic solvent is chosen from those compatible with the components used. It is preferably a low-boiling solvent to allow its rapid evaporation. In particular, dichloromethane is mentioned.

The respective proportions of the various constituents are adapted as indicated above so as to obtain an easily spreadable mixture which is present according to the requirements required for a given application in a solid or quasi-solid form 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 (see FIG. 1) using the electrolyte 2 obtained by the implementation of the method which is the subject of the invention, this system is intended in particular for applications falling within the scope of the invention. display, optical devices with variable transmission, or glasses.

The electrochromic device 1 is formed of the superposition of elements comprising - a first substrate 3 (or support), flexible or rigid, made in particular of glass or plastic material, which gives the electrochromic device its mechanical strength, - a first an electrode formed on the one hand by a current collector 6 made from a conductive material which may in particular be tin oxide doped with antimony or with fluorine, or with doped indium oxide with tin, and on the other hand with 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 conductive polymer such as polyaniline (PANI) or polypyrrole or an inorganic material such as Prussian blue, vanadium oxide (V205) or tungsten oxide (WO3), - an electrolyte thickness 2 formed of the ternary mixture, - a second electrode formed on the one hand by a collar current reader 5 made from a conductive material which may be in particular tin oxide doped with antimony or fluorine, or indium oxide doped with tin, and other of 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 (PAN!) or the polypyrrole or an inorganic material such as Prussian blue, vanadium oxide (V205) 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. figure 1).

In the context of an exclusively display electrochromic device, the system is analogous to the preceding case, with the exception of a current collector 5 or 6, which is now metallic and optionally deposited on a substrate 4 or 3.

The choice of the nature of the current collectors 5 and 6 and the staining agents 7 and 8, is according to the desired application. In particular, the state of coloration and discoloration, the voltage range required for the reversible switching between these two states and the switching time, are parameters to take into account to make this choice.

In the case of an electrochemical device designed for specifically display applications (electrochromic devices), requiring the display of a message with alphanumeric characters, provision is made to place 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 current so as to allow, at these or these particular points, the color transition and thus 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 method which is the subject of the invention, the latter is intended for applications relating to energy storage and more specifically designed. for the production of 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 element comprises two conductive supports 3, 4, flexible or rigid, (fabric of metal or carbon fibers, metal foils) enclosing, on the one hand, an electrolyte layer 2 based on the ternary mixture, and on the other hand on the other hand, electrodes 5, 6 formed for example of nanocrystalline inorganic oxide (SnO 2), (MnO 2).

In addition, electrochemical devices operating as a battery do not require, as electrochromic display devices using the principle of optical reflection or electrochromic devices using the principle of optical transmission, to be elaborated with transparent materials in the wavelength domain of the visible.

This is why the support or substrate elements will be made of a suitable material in terms of strength or mechanical strength and compatibility with the other components and it will be the same for the other parts forming the electrodes.

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures - Figure 1 illustrates a block diagram of an electrochemical device with variable transmission or display (electrochromic devices); - Figure 2 illustrates a block diagram of an electrochemical device operating as a battery.

<I> <U> Example I </ U> </ I> # <I> <U> Preparation of an electrochromic system </ U> </ I> is first deposited on a glass plate coated with a layer of FTO (Fluorite doped Tin Oxide, conductivity 6n / square of thickness 300 nm), a layer of WO3. This deposit is made according to the method patented in 1994 by Donnelly Corporation (US Patent No. 5,277,986). This gives a very homogeneous deposit of W03 by "dip-coating".

On another substrate identical to the first, a poly (aniline) film is electrodeposited. A potential of 750 mV for 5 minutes is applied in a solution of PANI (1M), HCl (3M). The counter electrode used is a platinum electrode. The film is cycled a dozen times at -300 / + 500mV in HC1 (iM), relative to a reference electrode Ag / AgCl.

<I> <U> Example II: Preparation of an electrolyte composition </ U> </ I> an electrolyte membrane is made by mixing 1 ml of bistrifluoromethanesulfonimide (TFSI) -1-ethyl-3-methyl-imidazolium containing 10 % by weight of LiTFSI with 0.2 to 0.8 g of poly (methyl methacrylate) and 3 ml of dichloromethane. Once the PPMA is completely dissolved and after partial evaporation of the CH 2 Cl 2 solvent, so as to obtain a viscous solution, this mixture is spread on a support.

<I> <U> Examples </ U> </ I> III - to <I> <U> VIII: </ U> </ I> Preparation <I> <U> of different systems </ U> </ I> <U> electrochromic </ U> <I> - Example III </ I> The mixture of at least three components is spread on the film of WO3 in the decolorized 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 the transparent state). The sealing of the system thus obtained is not mandatory, 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 ranging from -1.5V (discolored state) to 1.5V (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. The production of the W03 film as well as that of the electrolyte are identical to those described in Example 1. The same current collectors are used.

A second Prussian blue (BP) film is electrodeposited on the second substrate. A solution FeCl 3 (10-2M), K 3 FeCN 6 (10M) is produced. A cathode current of 40 pA / cm 2 is applied for 5 minutes. The film is cycled a dozen times at -400 / + 500mV in KCl (0.5M), relative 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.

<I> - Example V </ I> 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). n / 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.

<I> - Example VI </ I> A system is made according to the procedure described in Example III, the collectors used being ITO films deposited on glass plates (conductivity: 24 n / square).

The assembly of the system and the electrochemical tests carried out are identical to those described in Example II. It is observed that the system has an intense, reversible and homogeneous coloration which does not undergo degradation after 10,000 cycles. Example <I> VII </ I> A system is carried out according to the procedure described in Example III, the collectors used being ITO films (conductivity: 60 n / square) deposited on poly (terephthalate). ethylene) (PET).

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 10,000 cycles.

<I> - Example VIII </ I> A system is mounted according to the procedure described in Example I. The W03 film is produced on an ITO film deposited on PET.

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

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 10,000 cycles.

<I> <U> Examples IX and X: Preparation of an Electrochromine System </ I> of Battery Type <I> - Example IX </ I> The examples described above use electrode deposited in thin layers (about 300 nm). The goal is to have a very marked color difference between the two states (system loaded or not). These systems can also be used as rechargeable lithium batteries of the "rocking chair" type. To increase the energy capacity of these batteries, it is necessary to deposit on each electrode about ten times more active material using the deposition procedures described above.

The realization of the electrolyte and the shaping of the system are similar to those presented above. These batteries cycle very reversibly (more than 10000 cycles) with a capacity of about 10 mAh / g.

<I> - Example X </ I> The electrodes of the "rocking chair" battery can also be made from powders using a weight percentage of 60% (W03, PANI or BP), 10% graphite and 10% by weight. % PMMA. It is completed by adding 20% of liquid hydrophobic lithium salt. These materials can be spread on flexible stainless steel current collectors for example.

The realization of the electrolyte and the shaping of the system are similar to those presented above.

These batteries cycle very reversibly (more than 10000 cycles) with a capacity of the order of lomAh / g. The invention as previously written offers many advantages because the manufacturing method completely eliminates the constraint related to the presence of moisture, which allows to consider manufacturing multiple devices (electrochromic systems, electrochemical systems). battery type) in enclosures without presence of controlled atmosphere. In addition, the electrochromic devices have a memory effect over time and their reading is easy, whatever the angle of orientation.

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

Claims (1)

CLAIMS 1 - Electrolyte compositions characterized in that they contain, in a homogeneous mixture, at least the following three components, namely - one or more polymers, acting as matrix or membrane support vis-à-vis the whole of the electrolyte composition and providing mechanical strength properties conferring on the composition a state ranging from the solid state to the gel state, - one or more ionic conducting molten 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 inonic conductive salt or salts. 2 - Compositions according to claim 1, characterized in that the polymer or polymers are chosen from transparent polymers in the visible range such as polyacrylates, especially poly (methyl methacrylate) or PMMA, polycarbonates, polyurethanes or polyterephthalates . 3 - Compositions according to claim 1 or 2, characterized in that the salt or the molten hydrophobic salts correspond to the formula

    in which at least two of the substituents R1 to R5 are different and represent a straight or branched chain C1 to C12 alkyl or alkylene radical, optionally substituted by one or more -F, -OH, -COR, -COOR groups where R represents a hydrogen atom or a C1-C5 alkyl, -NH2, -NHR or -NR, R 'radical, where R is as defined above and R', which is identical to 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-C12 alkyl radical, and X- represents a counter-anion. 4 - Compositions according to claim 3, characterized in that R1 and R4 represent different alkyl groups C1 to C12, R2, R3 and R5 represent a hydrogen atom and X- is a counter anion. 5 - Compositions according to claim 4, characterized in that they contain as hydrophobic melted salt of bistrifluoromethanesulfonimide (TFSI) -1-ethyl-3-methylimidazolium. 6 - Compositions according to any one of claims 1 to 5, characterized in that the salt or salts capable of providing the conductive properties are of the type M + Y-, where M + and Y- is a soluble anion in the molten salts. 7 - Compositions according to claim 6, characterized in that M + is selected from Li +, H +, Na +, K +. 8 - Compositions according to claim 6, characterized in that Y- is selected from C104-, PF6-, ASF6-, CF3SO3-, CF3C00-, (CF3SO2) 2N-, C3F7C00-. 9 - Compositions according to claim 6, characterized in that the salt is Li (TFSI). 10 - Process for preparing an electrolyte according to any one of claims 1 to 9, characterized in that a homogeneous mixture, using an organic solvent, of said polymers or said salt ionic, hydrophobic conductive fusions, in which (or which) is (are) incorporated (s) one or more salts capable of ensuring the conductive properties. 11 - Process according to claim 10, characterized in that the organic solvent used to mix the various components of the 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 of the superposition - a first substrate (3) (or support), flexible or rigid , in particular made of 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) made from a conductive material which can be in particular tin oxide doped with antimony or fluorine, or indium oxide doped with tin, and on the other hand with an agent (7) which may or may not provide 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 (V205) or tungsten oxide (WO3), an electrolyte generator (2), - a second electrode formed on the one hand by a current collector (5) made from a conductive material which may be in particular tin oxide doped with antimony or fluorine, or indium oxide doped with tin, and on the other hand an agent (8) providing 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 (V205) or oxide tungsten (W03), and a second substrate (4) possibly identical to said first substrate (3), said electrochemical device being intended for applications of electrochromic devices with variable transmission or display. 13 - Electrochemical device (1) using the 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 electrolyte layer (2) based on the ternary mixture, and secondly, electrodes (5, 6) formed for example of nanocrystalline inorganic oxide (SnO 2), (MnO 2). 14 - Application of the device according to claim 13 for storing energy or battery.