A process for preparing a material similar to Prussian Blue and a cathode ink containing it

Abstract

The present invention relates to a process for synthesizing an active material of the Prussian Blue type analogous to the general formula (I) AwM1xM2y(CN)6(I), comprising at least the step of bringing together, in an aqueous medium, under stirring and in an inert atmosphere, at least one cyanide ion source selected from compounds of formula (II) ACN or (III) AaM1(CN)b with an effective amount of at least one salt of formula (IV) M2v(X)k. It further relates to an electrode ink obtained directly in the reaction medium of this process. Figure: none

Description

Title of the invention: Process for preparing a material similar to Prussian Blue and a cathode ink containing it. Technical field

[0001] The present invention relates to the field of electrochemical devices such as metal-ion batteries. More specifically, it aims to provide a method for synthesizing an active material similar to Prussian Blue, useful as an ink in electrochemical systems, particularly in sodium-ion or potassium-ion batteries. Prior art

[0002] Metal-ion battery-type electrochemical devices currently dominate the market for rechargeable electrochemical devices. They have multiple applications, including powering thin embedded systems such as credit cards and smart tags, powering mobile phones, storing energy in photovoltaic cells, and powering electric vehicles.

[0003] Various electrochemical storage systems or electrochemical generators have been developed, including sodium-ion, lithium-ion, potassium-ion, and magnesium-ion batteries. In particular, active materials, especially cathode active materials, for such electrochemical devices are the subject of ongoing research, both to improve the electrochemical performance of these devices and to refine their production processes.

[0004] Among the promising materials for cathode synthesis in metal-ion batteries, Prussian Blue (PBC) analogs, particularly Prussian White materials, allow for the production of cathode materials with particularly interesting electrochemical performance. This is a class of materials with the general formula AxMi[M2(CN)6] where A is an alkali metal, M1 and M2 are transition metals, and x ranges from 0 to 2. When x is close to 2, they are referred to as Prussian White materials.

[0005] For sodium and potassium-based BPAs, the materials are mainly synthesized by precipitation in water of a hexacyanometallate complex A4Mi(CN)6 with a salt of the other transition metal M2.

[0006] Thus, for a potassium-ion battery application, one of the most promising materials is Prussian White K2Mn[Fe(CN)6], exhibiting a theoretical capacity of 155 mAh.g-1 at a potential close to 4 V vs. K+ / K. Its synthesis is generally carried out by precipitation in water of the hexacyanoferrate complex K4 Fe(CN)6 with a manganese salt such as, for example, Mn(NO3)2, Mn(SO4)2, MnCl2 or Mn(CH3CO2)2. A chelating agent is sometimes added to the reaction mixture to control the morphology of the resulting K2Mn[Fe(CN)6] particles. After precipitation of the K2Mn[Fe(CN)6] material, the reaction mixture is washed with water to remove impurities such as potassium, the manganese salt counterion, and any chelating agent. The powder is then dried to remove residual water. Once washed and dried, the K2Mn[Fe(CN)6] powder is mixed with a conductive additive and a binder to form an ink suitable for coating a current collector, thus forming a cathode in an electrochemical storage system or electrochemical generator.

[0007] Thus, the publication by Hosaka et al. ChemSusChem, 2021, 14, 1166-1175 [1] describes an example of the synthesis of the material K2Mn[Fe(CN)6] from K4Fe(CN)6 and MnCl2. Similarly, the publication by Wu et al. Advanced Materials, 2022, 34, 2106876 [2] describes a process comprising the synthesis of a Prussian White material K2Mn[Fe(CN)6], from K4Fe(CN)6 and MnSO4 and several washing steps of the material thus obtained to remove impurities, followed by vacuum drying at 60 °C overnight. The preparation of the ink constitutes a second step in the electrode fabrication process, quite distinct from this synthesis step. Applications WO201856890 Al and EP4170741 Al describe further examples of synthesis of Prussian White material, Na2Fe[Fe(CN)6], and then preparation of a cathode from this material still requiring a two-step process separated by several washing and drying steps.

[0008] As can be seen from the above, these methods of synthesis require, firstly, to produce the active material analogous to BPA, to isolate it from its reaction medium to rid it of contaminating by-products and only secondly, to consider it, in a purified form, for the preparation of an electrode ink.

[0009] The present invention aims precisely to propose a process enabling the synthesis of the active material and the preparation of the ink for analogous Prussian Blue (BPA) type cathode materials to be carried out in a single step, in particular for Na-ion and K-ion batteries.

[0010] More specifically, the present invention aims to provide a simple, inexpensive (minimizing steps and syntheses of complex precursors) and environmentally friendly (synthesis in water, at a temperature close to ambient) implementation method.

[0011] It also aims to propose a method for synthesizing a cathode material of the Prussian Blue (BPA) type, making it possible to eliminate the steps washing and drying are commonly required to remove the synthesis by-product or even unreacted manganese or iron salt.

[0012] It also aims to propose a synthesis process allowing access to an ink with improved electrochemical properties. Summary of the invention

[0013] Thus, according to a first of its aspects, the present invention proposes a method for synthesizing an active material of the analogous Prussian Blue type with general formula (I): AwMlxM2y(CN)6(I)

[0014] in which: - A represents a sodium atom, Na, or a potassium atom, K, - M1 and M2, identical or different, are chosen from the transition metals Ti, Nb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and preferably from Fe and Mn, - w varies from 0.5 to 2.2 and is preferably on the order of 2,

[0015] - x varies from 0 to 2

[0016] - y varies from 0 to 2 and

[0017] - x+y = 2

[0018] and its hydrates, said process comprising at least the step of bringing together, in an aqueous medium, under stirring and under an inert atmosphere, at least one source of cyanide ion selected from compounds of formula (II) and compounds of formula (III):

[0019] (II) ACN

[0020] (III) AaMl(CN) and its hydrates

[0021] in which

[0022] A and Ml are such as defined in formula (I) a varies from 2 to 4 and b varies from 4 to 6 in formula (III) with an effective amount of at least one salt of formula (IV) (IV) M2v(X)k in which - M2 is such as defined in general formula (I) - X is chosen from the patterns TFSI, FSI, PF6, C1O4 and BF4 - v varies from 1 to 2 and - k varies from 1 to 4 said compound of formula (I) being formed in the state of precipitate.

[0023] In one embodiment, the cyanide ion source is chosen from compounds of formula (II) or compounds of formula (III).

[0024] In the embodiment, where M1 and M2 are identical in formula (I), said process involves at least one compound of formula (II) and one compound of formula (IV) or at least one compound of formula (III) and one compound of formula (IV) whose metallic salts, M1 and M2, are of the same chemical nature.

[0025] In the embodiment variant, where Ml and M2 are different in formula (I), said process brings together a compound of formula (III) and a compound of formula (IV) whose metal salts, Ml and M2, are of different chemical natures.

[0026] In particular, said compound of general formula (I) is obtained by mixing with at least one compound of formula (V) (V) A(X) in which - A represents a Na or K atom and - X is chosen from the patterns TFSI, FSI, PF6, C1O4 and BF4

[0027] As can be seen from the examples below, the inventors have, against all expectations, found that the implementation of a compound of general formula (IV) as a precursor of transition metal salt makes it possible to satisfy the objectives specified above.

[0028] The counterion of the salt of the transition metal M2, considered in formula (IV), forms an impurity of formula (V) which it is not useful to remove by washing. A mixture of the compounds of general formula (I) and (V) can therefore be used as such to form an electrode ink.

[0029] Present in the ink, the compound of formula (V) will remain on the cathode, coated with the ink, and advantageously contribute to the proper functioning of the battery during cycling. These compounds of formula (V), which are in a solid state due to their chemical nature, can thus participate in the formation of the passive layer that develops between the negative electrode and the electrolyte during charging at low potential values, called the solid electrolyte interphase (SEI). The formation of such a passive layer sometimes also develops between the positive electrode and the electrolyte, called in English the "Cathode Electrolyte Interphase" (CEI). Furthermore, these compounds of formula (V) can also act as electrolyte salts.

[0030] According to another aspect of it, the present invention relates to an electrode ink, containing, in an aqueous or organic medium, and preferably aqueous, at least one active material of the analogous Prussian Blue type of general formula (I): AwMlxM2y(CN)6(I) in which: - A represents a sodium atom, Na, or a potassium atom, K, - M1 and M2, identical or different, are chosen from the transition metals Ti, Nb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and preferably from Fe and Mn, - w varies from 0.5 to 2.2 and is preferably on the order of 2 - x varies from 0 to 2 - y varies from 0 to 2 and - x+y = 2 and its hydrates, in mixture with at least one compound of general formula (V)(V)A(X) in which - A represents a Na or K atom, and - X is chosen from TFSI, FSI, PF6, C1O4 and BF4 and

[0031] at least one conductive additive and, where appropriate, at least one binding agent.

[0032] In particular, the ink according to the invention is directly formed in the synthesis medium of an analogous Prussian Blue type active material of general formula (I) prepared according to a process according to the invention.

[0033] According to another aspect of it, the present invention relates to the use of an ink as defined above to prepare a cathode.

[0034] The present invention further relates to a cathode characterized in that it comprises a current collector on which an ink according to the invention is applied.

[0035] In particular, it relates to a cathode comprising a current collector on which is applied an active material of analogous type Prussian Blue of general formula (I) in mixture with at least one compound of general formula (V), said mixture having been obtained according to the process of the invention.

[0036] According to another aspect, the present invention relates to a method for preparing an electrode, in particular a cathode, comprising at least the steps of: a) To have an ink according to the invention b) Apply said ink to the surface of a current collector, for example, of the aluminium foil type; and c)- Dry the said collector coated with the said ink.

[0037] More particularly, an electrode, especially a cathode, can be obtained by a process comprising at least the steps of: a') Have the synthesis medium in which a compound of analogous type Prussian Blue of general formula (I) has been prepared according to the process of the invention and containing said compound of general formula (I) thus formed;

[0038] b') Apply at least in part said synthesis medium containing said analogue Prussian blue of general formula (I) formed, and further containing at least one conductive additive and where appropriate a binding agent, on the surface of a collector and;

[0039] c') Dry the collector coated with said synthesis medium.

[0040] The invention further relates, according to another of its aspects, to an electrochemical system comprising at least one cathode according to the invention.

[0041] Other characteristics, variants and advantages of the composite materials according to the invention, their preparation and implementation, will become clearer from the description, examples and figures that follow.

[0042] In the following text, the expressions "between ... and ...", "ranging from ... to ..." and "varying from ... to ..." are equivalent and are meant to mean that the limits are included, unless otherwise stated. Brief description of the drawings

[0043] [Fig. 1] presents the diffractogram obtained by X-ray diffraction of the electrode produced in comparative example 1.

[0044] [Fig.2] presents the galvanostatic curves of the first five cycles obtained at C / 10 of the button cell developed in comparative example 1.

[0045] [Fig.3] presents the diffractogram obtained by X-ray diffraction of the electrode produced in Example 2.

[0046] [Fig.4] shows the galvanostatic curves of the first five cycles obtained at C / 10 of the button cell developed in example 2.

[0047] [Fig.5] presents the diffractogram obtained by X-ray diffraction of the electrode produced in Example 3.

[0048] [Fig.6] shows the galvanostatic curves of the first five cycles obtained at C / 10 of the button cell developed in example 3. Detailed description

[0049] Process for synthesizing an active material of the analogous type Prussian Blue, known as BPA, according to the invention

[0050] As mentioned previously, the process of the invention aims to form an active BPA material of general formula (I)

[0051] AwMlxM2y(CN)6(I)

[0052] in which: - A represents a sodium atom, Na, or a potassium atom, K, - M1 and M2, identical or different, are chosen from the transition metals Ti, Nb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and preferably from Fe and Mn, - w varies from 0.5 to 2.2 and is preferably on the order of 2 - x varies from 0 to 2 and is preferably not equal to 0 - y varies from 0 to 2 and is preferably not equal to 0 - x+y = 2

[0053] and its hydrates.

[0054] For the purposes of the invention, the expressions "Prussian Blue analogue active material of general formula (I)", "BPA type active material of general formula (I)", "Prussian Blue analogues of formula (I)" and "compound of general formula (I)" are used interchangeably.

[0055] For the purposes of this invention, the terms "Na atom", "K atom", and the symbols M1 and M2 are intended to cover the charged and uncharged forms of the elements considered. For example, Na covers Na+ and M1 covers Mn++.

[0056] For the purposes of the invention, the term "of the order of 2" means that the index in question, such as w, can be equal to 2 but also to decimal values ​​close to 2.

[0057] Advantageously M1 and M2 are different.

[0058] According to a particular embodiment, M1 is Mn and M2 is Fe.

[0059] According to another particular embodiment, M1 and M2 are Fe.

[0060] Representative of compounds of general formula (I) may in particular be cited the following compounds: K2Mn[Fe(CN6)], K2Fe[Fe(CN6)], Na2Mn[Fe(CN6)] and Na2 Fe[Fe(CN6)].

[0061] According to the invention, the compounds of general formula (I) are formed by bringing together, in aqueous medium, under agitation and under an inert atmosphere, at least one hexacyanoferrate complex chosen from the compounds of formula (II) and the compounds of formula (III)

[0062] (II) ACN (III) AaMl(CN)b and its hydrates In which - A and Ml are such as defined in general formula (I) - a varies from 2 to 4 and b varies from 4 to 6 in formula (III) with an effective amount of at least one salt of formula (IV) (IV) M2v(X)k in which - M2 is such as defined in general formula (I) - X is chosen from the patterns TFSI, FSI, PF6, C1O4 and BF4 _v varies from 1 to 2 and - k varies from 1 to 4. Representative examples of compounds with general formula (II) include KCN and NaCN.

[0063] Representative of compounds of general formula (III) may be cited in particular K4Fe(CN)6, K4Mn(CN)6Na4Fe(CN)6Na4Mn(CN)6, K2Ni(CN)4 and their hydrates.

[0064] As specified above, depending on whether M1 and M2 are identical in general formula (I) or not, the choice of the compound with general formula (II) or (III) is adjusted.

[0065] It is also possible to consider the joint implementation of at least one compound of general formula (II) and at least one compound of general formula (III).

[0066] In particular, when Ml and M2 are identical in formula (I), the process according to the invention can bring together in a first variant a compound of formula (II) and a compound of formula (IV) or in a second variant, a compound of formula (III) and a compound of formula (IV) whose metal salts, Ml and M2 are of the same chemical nature.

[0067] If Ml and M2 are different in formula (I), the process according to the invention brings together a compound of formula (III) and a compound of formula (IV) whose metallic salts, Ml and M2, are of different chemical natures.

[0068] In one embodiment, the process according to the invention brings together a compound of formula (III) and in particular K4Fe(CN)6.3H2O to form the compound of formula (I) which is K2Mn[Fe(CN)6].

[0069] With regard to compounds of general formula (III), they are not water-soluble.

[0070] According to a particular embodiment, X is TFSI, FSI or PF6.

[0071] According to a preferred embodiment of the invention, the molar ratio between the complex hexacyanoferrate of formula (II) or (III) and said salt of formula (IV) is such that the reaction between these two compounds is complete.

[0072] According to an advantageous embodiment, a compound of general formula (III) and a compound of general formula (IV) are brought together in a stoichiometric ratio salt of formula (IV) / compound of formula (III) adjusted to condition the desired ratio M1 / M2 in formula (I).

[0073] Generally, the mixing of at least one compound of formula (II) or of formula (III) with at least one salt of formula (IV) is carried out in aqueous medium, under agitation and under an inert atmosphere.

[0074] In particular, the bringing together of the compound of formula (II) or (III) with a compound of formula (IV) is carried out in a reactor containing water, preferably deionized water.

[0075] Such a reaction in an aqueous medium aims to form an active BPA material of general formula (I) according to an environmentally friendly process.

[0076] The mixing of all the reactants is also carried out under an inert atmosphere to avoid any oxidation of the salts it contains.

[0077] An "inert atmosphere" is understood to mean an atmosphere devoid of reactive gases, composed of non-reactive (inert) gases such as nitrogen, carbon dioxide, argon or helium.

[0078] Generally, the two compounds of formulas (II) and (III) are brought together at a temperature close to room temperature. However, higher temperatures may be considered provided they do not adversely affect the expected reaction or the stability of the reactants or the expected compounds. As illustrated in the examples below, this mixing can take place between 15°C and 35°C, preferably between 19°C and 25°C.

[0079] The two compounds of formulas (II) and (III) are brought together under stirring.

[0080] Advantageously, agitation is maintained until complete precipitation of the compound of general formula (I) thus formed.

[0081] At the end of the reaction, a precipitate is obtained comprising said compound of general formula (I) and at least compound of general formula (V).

[0082] As previously stated, together with the compound of general formula (I) is indeed formed at least one compound of general formula (V) (V) A(X)

[0083] in which

[0084] -A represents a Na or K atom and

[0085] -X is chosen from the patterns TFSI, FSI, PF6, C1O4 and BF4

[0086] According to one embodiment, the process leads to the formation of compound K2 Mn[Fe(CN)6] obtained in mixture with at least one compound of general formula (V) chosen from KTFSI, KFSI, KPF6, KCLO4 and KBF4 and preferably from KTFSI.

[0087] As illustrated in the examples below, the process according to the invention is particularly advantageous for forming an electrode ink, in particular a cathode.

[0088] This ink is advantageously formed directly, according to the process of the invention, in the synthesis medium of an active material of the analogous type Prussian Blue of general formula (I).

[0089] More specifically, it then derives from the implementation, in said aqueous medium, of at least one conductive additive and at least one binding agent.

[0090] Thus, the process according to the invention may include the addition in its aqueous reaction medium of at least one conductive additive and, optionally, of at least one binding agent to form an electrode ink.

[0091] According to this embodiment, the conductive additive can be added to said aqueous medium prior to or after the addition of at least one compound of formula (IV) and at least one compound chosen from the compounds of general formula (II) and the compounds of general formula (III).

[0092] According to one embodiment, the binding agent is added to said aqueous medium prior to or subsequent to the addition of said compounds of general formula (II) or (III) and (IV).

[0093] According to another embodiment, the binding agent and the additive are added after the formation of the expected compound of formula (I). Driver additive

[0094] The term “conductive additive” means an electronic conductive additive.

[0095] Thus, the said conductive additive(s) can be chosen from carbon fibers, carbon black, carbon nanotubes, graphene, graphite, and metallic particles, such as metallic nanowires or nanoparticles.

[0096] The metallic particles may be, for example, aluminium, copper, nickel, silver, gold, platinum, titanium, palladium, zinc or alloys thereof.

[0097] Preferably, the electronically conductive additives are chosen from carbon-based additives, such as carbon nanofibers and carbon black. Binder

[0098] The binder is generally of a polymeric nature.

[0099] Such binders can be chosen from among fluorinated binders, in particular from among polytetrafluoroethylene, polyvinylidene fluoride, carboxymethylcellulose and its derivatives, polysaccharides, polyacrylates, latex in particular of the styrene-butadiene type. Ink

[0100] Thus, the invention further relates to an electrode ink, in particular a cathode, containing, in aqueous or organic medium, at least one active material of the analogous type Prussian Blue of general formula (I) in mixture with at least one compound of general formula (V) as defined above, at least one conductive additive and where appropriate at least one binding agent.

[0101] According to a particular variant, such an ink comprises, as an active material of the analogous Prussian Blue type, at least K2Mn[Fe(CN)6] and comprises at least one compound of general formula V selected from KTFSI, KPF6, KFSI, KCLO4 and KBF4.

[0102] In particular, an ink according to the invention may comprise, as a percentage by weight of dry matter:

[0103] a. 40 to 60% of at least one analogous active material of Prussian Blue type of general formula I and preferably at least K2MnFe(CN)6,

[0104] b. 25 to 35% of at least one compound of general formula V, preferably chosen from KTFSI and KFSI,

[0105] c. 10 to 20% of at least one conductive additive; and

[0106] d. 7 to 10% of at least one binding agent.

[0107] The Prussian Blue analogues of formula (I) and the ink obtained according to the invention are particularly interesting as an active material for an electrode and in particular a positive electrode or cathode. Electrode

[0108] Conventionally, the electrode is in contact with a current collector. This collector can be chosen from materials such as copper, aluminum, nickel, carbon felt, or stainless steel for a positive electrode.

[0109] This electrode can in particular be obtained by a process comprising at least the steps of: a) To have an ink according to the invention b) Apply said ink to the surface of a collector and c) Dry said collector coated with said ink in particular at a temperature between 50°C and 100°C, preferably 60°C and 90°C, and in particular for 8 to 60 hours, preferably for 10 to 50 hours.

[0110] More particularly, this electrode can be obtained by a process comprising at least the steps of: a') Have available the synthesis medium of a compound of analogous type Prussian Blue of general formula (I) prepared according to the process of the invention with said medium containing said compound of general formula (I) thus formed;

[0111] b') Apply at least in part said synthesis medium containing said analogue Prussian blue of general formula (I) formed, and further containing at least one conductive additive, in particular as defined above, and preferably a binding agent, in particular as defined above, on the surface of a collector and;

[0112] c') Dry said collector coated with said synthesis medium, in particular at a temperature between 50°C and 100°C, preferably 60°C and 90°C, in particular for 8 to 60 hours, preferably for 10 to 50 hours.

[0113] Step (b) or (b') of the preceding processes can be carried out by coating, by a printing technique, by extrusion or by co-lamination. A person skilled in the art is able to adjust the conditions for implementing these different techniques.

[0114] As illustrated in the following examples, a cathode comprising an ink according to the process of the invention, makes it possible to access an electrochemical system, such as an ion battery, exhibiting good electrochemical performance, in particular in terms of cycling stability and resistance to high charge / discharge rates. Electrochemical system

[0115] The invention therefore also relates to an electrochemical system comprising at least one cathode (I) according to the invention.

[0116] The electrochemical system in which the cathode according to the invention is implemented can in particular be a rechargeable electrochemical accumulator.

[0117] Advantageously, such an electrode can be implemented in a battery in cation-ion configuration, in particular a sodium-ion or potassium-ion battery.

[0118] Other characteristics, variants and advantages of the composite materials according to the invention, their preparation and implementation, will become clearer from reading the examples and figures that follow, given by way of illustration and not limitation of the invention. Examples

[0119] In the following examples, the following products are used: - C65 carbon black (Super P), as a conductive carbon additive, marketed by MTI Corporation, - Carboxymethylcellulose (CMC), as a binder, marketed by Ashland (ref 7HXF), and used in the form of CMC 7HXF at 2 m% in water.

[0120] Comparative Example 1: Synthesis of a cathode whose ink is formed from Mn(CH3COO)2

[0121] The various constituents listed below were added in the order they are listed to a 25 ml beaker containing 7 ml of degassed water under argon and magnetic stirring: - 285 mg of Carbon super P C65; - 1.24 g of K4Fe(CN)6.3H2O; - 0.71 g of Mn(CH3COO)2.

[0122] A white precipitate was obtained corresponding to a Prussian White K2 Mn[Fe(CN)6]-Carbon super P C65 composite. 143 mg of carboxymethyl cellulose (CMC) were then added to the mixture along with 3 ml of water to obtain a satisfactory viscosity for the ink. Dispersion was carried out using Dispermat® for 15 minutes at 2000 rpm.

[0123] The ink thus formed was then coated onto an aluminum current collector. After drying overnight in air at 70 °C, electrodes with a diameter of 14 mm were pelletized. As the adhesion of the ink to the aluminum was rather weak, the electrodes were not calendered.

[0124] The total mass of dry matter is 1.997 g. The mass proportion of Prussian White in the electrode is therefore 1 / 1.997 or 50.1 m%.

[0125] The electrodes obtained were characterized by X-ray Diffraction (XRD). The diffractogram obtained, illustrated in [Fig. 1], is characteristic of a material The "Prussian White" type, with a monoclinic structure and space group P2i / n, is present. The two most intense peaks at 65° and 79° correspond to aluminum in the current collector. No peaks attributable to potassium acetate are observed, indicating that the compound is in amorphous form in the electrode.

[0126] The electrodes were then tested in button cells against potassium metal. The electrodes were dried under vacuum at 80 °C for 48 hours. The button cells were manufactured in a glove box, using the electrode obtained according to the invention as the cathode, potassium metal as the anode, glass fiber (Whatman GF / D) as the separator, and 100 pL of an organic electrolyte (0.7 M KPF6 in EC:DEC (1:1 vol) + 2 m% FEC). The galvanostatic curves of the first five cycles obtained at C / 10 are shown in [Fig. 2].

[0127] The irreversible capacitance during the first charge is significant. Clearly, the potassium acetate formed as a by-product during the synthesis of K2Mn[Fe(CN)6] affects the system's performance. From the second cycle onward, the galvanostatic curve is more conventional: the two plateaus corresponding to the oxidation (charging) or reduction (discharging) of iron and manganese are clearly visible. The initial reversible capacitance is approximately 70 mAh.g, which is considerably lower than that obtained according to the invention (see examples 2 and 3).

[0128] Example 2: Synthesis of a cathode whose ink is formed according to the invention from the precursor Mn(TFSI)2,

[0129] In a 25 mL beaker containing 10 mL of argon-degassed water and magnetic stirring, 1.24 g of K4Fe(CN)6·3H2O and 1.79 g of Mn(TFSI)2 were added. A white precipitate was obtained, and the solution thickened significantly, corresponding to the production of Prussian White K2Mn[Fe(CN)6] and KTFSI impurity. 285 mg of supercarbon P C65 and 143 mg of CMC were then added to the mixture, along with 4 mL of water, to obtain a viscosity suitable for ink. Dispersion was carried out using a Dispermat® for 15 minutes at 2000 rpm.

[0130] The ink was then coated onto an aluminum current collector using a 150 µm thick squeegee. After drying overnight in air at 70 °C, electrodes with a diameter of 14 mm were pelletized. The electrodes were calendered at 10 tons.

[0131] The total mass of dry matter on the coated strip is 3.278 g. The mass proportion of Prussian White in the electrode is therefore 1 / 3.278, or 30.5 m%. Furthermore, the proportion of KTFSI in the electrode is 1.850 / 3.278, or 56.4 m%.

[0132] The mass of dry matter on the electrodes obtained after cutting is approximately 3.40 mg. This consists of 1.04 mg of Prussian White and 1.92 mg of KTFSI.

[0133] The electrodes obtained were first characterized by X-ray Diffraction (XRD). The resulting diffractogram is shown in [Fig. 3]. The two most The intense peaks at 65° and 79° correspond to the aluminum in the current collector. The other peaks are attributable either to Prussian White or to KTFSI salt.

[0134] The electrodes were then tested as button cells against potassium metal. The electrodes were dried under vacuum at 80 °C for 48 hours. The button cells were fabricated in a glove box, using the previously obtained electrode as the cathode, potassium metal as the anode, glass fiber (Whatman GF / D) as the separator, and 100 pL of an organic electrolyte (0.7 M KPF6 in EC:DEC (1:1 vol) + 2 m% FEC). The galvanostatic curves of the first five cycles obtained at C / 10 are shown in [Fig. 4]. The significant irreversible capacitance observed in Example 1 is not observed in the present case: the KTFSI impurity is not degraded during the first charge (unlike potassium acetate). The two plateaus relating to the oxidation (charging) or reduction (discharging) of iron and manganese are clearly visible. Considering that Prussian White represents 30.5 m% of the total dry matter, an initial reversible capacity of approximately 125 mAh.g 1 was obtained, which is much higher than that obtained in example 1.

[0135] Example 3: Synthesis of a cathode whose ink is formed according to the invention from the precursor Mn(TFSI)2

[0136] In a 25 ml beaker containing 4 ml of argon-degassed water, 143 mg of CMC (equivalent to 7.145 g of CMC 7HXF at 2 m% in water) and 285 mg of super carbon P C65 were added. The constituents were incorporated with a spatula and then dispersed using a Dispermat® at 2000 rpm for 5 minutes. The ink base was thus formed.

[0137] A 5 ml aqueous solution, degassed under argon and containing 1.24 g of K4pe(CN) 6.3H2O, was then added dropwise to the ink base, which was continuously dispersed in the Dispermat® at 2000 rpm for 5 minutes. Finally, a 5 ml aqueous solution, degassed under argon and containing 1.79 g of Mn(TFSI)2, was added dropwise and then dispersed in the Dispermat® at 2000 rpm for 5 minutes. A fairly thick and heterogeneous ink was obtained. The ink was dispersed again in the Dispermat®, this time at 5000 rpm for 5 minutes to obtain a homogeneous ink.

[0138] The ink was then coated onto an aluminum current collector using a 150 µm thick squeegee. After drying overnight in air at 70 °C, electrodes with a diameter of 14 mm were pelletized. The electrodes were calendered at 10 tons.

[0139] The electrodes obtained were characterized by X-ray Diffraction (XRD). The resulting diffractogram is shown in [Fig. 5]. The two most intense peaks at 65° and 79° correspond to the aluminum of the current collector. The other peaks are attributable either to Prussian White or to KTFSI.

[0140] The electrodes were then tested as button cells against potassium metal. The electrodes were dried under vacuum at 80 °C for 48 hours. The button cells were fabricated in a glove box, using the electrode obtained above as the cathode, potassium metal as the anode, glass fiber (Whatman GF / D) as the separator, and 100 pL of an organic electrolyte (0.7 M KPF6 in EC:DEC (1:1 vol) + 2 m% FEC). The galvanostatic curves of the first four cycles obtained at C / 10 are shown in [Fig. 6]. Considering that Prussian White represents 30.5 m% of the total dry matter, an initial reversible capacity of approximately 120 mAh.g⁻¹ was obtained, equivalent to that obtained in Example 2.

Claims

Demands

1. A process for synthesizing an active material of the analogous type Prussian Blue of general formula (I): (I) AwMlxM2y(CN)6 in which: - A represents a sodium atom, Na, or a potassium atom, K, - Ml and M2, identical or different, are chosen from the transition metals Ti, Nb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and preferably from Fe and Mn, - w varies from 0.5 to 2.2 and preferably is on the order of 2 - x varies from 0 to 2 - y varies from 0 to 2 and - x+y = 2 and its hydrates, said process comprising at least the step of bringing together, in aqueous medium, under stirring and under an inert atmosphere,at least one cyanide ion source chosen from the compounds of formula (II) and the compounds of formula (III): (II) ACN (III) AaMl(CN)b and its hydrates in which A and Ml are as defined in formula (I) a varies from 2 to 4 and b varies from 4 to 6 in formula (III) with an effective amount of at least one salt of formula (IV) (IV) M2v(X)k in which - M2 is as defined in general formula (I) - X is chosen from the motifs TFSI, FSI, PF6 and BF4 - v varies from 1 to 2 and - k varies from 1 to 4, said compound of formula (I) being formed in the precipitate state.

2. A process according to the preceding claim, wherein said compound of general formula (I) is obtained by mixing with at least one compound of formula (V) (V) A(X), in which -A represents a Na or K atom and -X is chosen from the TFSI, FSI, PF6 and BF4 patterns

3. A process according to any one of the preceding claims wherein said compound of formula (III) is K4Fe(CN)6.3H2O and the compound of formula (I) obtained is K2Mn[Fe(CN)6].

4. A process according to the preceding claim in which said compound K2Mn[Fe(CN)6] is obtained in mixture with at least one compound of general formula (V) selected from KTFSI, KFSI, KPF6 and KBF4 and preferably from KTFSI.

5. A method according to any one of the preceding claims further comprising the addition in said aqueous medium of at least one conductive additive and at least one binding agent to form an electrode ink.

6. Electrode ink, containing, in aqueous or organic medium, at least one active material of the analogous type Prussian Blue of general formula (I): (I) AwMlxM2y(CN)6 in which: A represents a sodium, Na, or potassium atom, K, Ml and M2, identical or different, are selected from the transition metals Ti, Nb, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and preferably from Fe and Mn, w varies from 0.5 to 2.2 and preferably is on the order of 2, x varies from 0 to 2, y varies from 0 to 2 and x+y = 2 and its hydrates, in mixture with at least one compound of general formula (V): (V) A(X) in which -A represents a Na or K atom and -X is selected from the motifs TFSI, FSI, PF6 and BF4 and at least one conductive additive and optionally at least one agent binder.

7. Ink according to claim 6 wherein the active material of the analogous type Prussian Blue is at least K2Mn[Fe(CN)6] and comprising at least one compound of general formula V selected from KTFSI, KPF6, KFSI and KBF4.

8. Ink according to claim 6 or 7 formed directly in the synthesis medium of an analogous Prussian Blue type active material of general formula (I) prepared according to the process as defined in claims 1 to 5.

9. Use of an ink according to any one of claims 6 to 8 to prepare an electrode in particular a cathode.

10. A method for preparing an electrode, in particular a cathode, comprising at least the steps of: a) Disposing of an ink according to any one of claims 6 to 8, b) Applying said ink to the surface of a current collector and c) Drying said collector coated with said ink.

11. A method for preparing an electrode, in particular a cathode, comprising at least the steps of: a') Disposing of the synthesis medium in which a Prussian Blue analogous compound of general formula (I) as defined in claim 1 has been prepared according to the method according to any one of claims 1 to 5 with said medium containing said compound of general formula (I) thus formed, b') Applying at least part of said synthesis medium containing said Prussian Blue analog of general formula (I) formed, and further containing at least one conductive additive and optionally a binding agent, to the surface of a collector and; c') Drying the collector coated with said synthesis medium.

12. Cathode characterized in that it comprises a current collector on which is applied an active material of analogous type Prussian Blue of general formula (I) as defined in claim 1 in mixture with at least one compound of general formula (V) as defined in claim 2, said mixture having been obtained according to the process defined in claims 1 to 5.

13. Electrochemical system comprising at least one cathode according to the preceding claim.

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