CA2304394C - Lipo3 commutation electrode - Google Patents

Abstract

The present invention relates to a lithium electrochemical generator comprising at least one composite electrode comprising an active material, and a first and a second solid electrolyte distributed non-homogeneously in the composite. The first solid electrolyte is of a mineral, glassy or partially vitreous nature, and is a specific conductor for lithium ions, and is preferentially located on the surface of the particles of the active material of the electrode. The second solid electrolyte is of organic nature, comprises a dry polymer electrolyte or gelled mixed conductive ions distributed around dispersed solid phases and acting as deformable lia nt, preferably elastomeric manner, the composite also in contact with the collector and the separator electrolyte of the generator. A thin layer of the first electrolyte wets and covers at least a portion of the surface of the particles of the active material so as to protect the surface covered by the passivation or degradation reactions induced by the second electrolyte, and to maintain the quality of the ion exchange and electronics between the active material of the electrode and the other constituents of the composite, the first electrolyte being impervious to the components of the second electrolyte.

Description

TITLE

Composite treatment with LiPO3 FIELD OF THE INVENTION

The present invention relates to a lithium electrochemical generator having at least one composite electrode comprising an active material and a first and a second solid electrolyte non-homogeneously distributed in the composite. The first solid electrolyte is of a mineral nature, glassy or partially vitreous, and is a specific conductor of lithium ions, and is localized preferentially on the surface of 1 o particles of the active material of the electrode. The second solid electrolyte is of nature organic, comprises a dry polymer electrolyte or gelled mixed conductor ions distributed around the dispersed solid phases and acting as a binder deformable composite also in contact with the collector and the separating electrolyte of generator. A thin layer of the first electrolyte wets and covers at least one part of the particle surface of the active material so as to protect the area covered by the passivation or degradation reactions induced by the second electrolyte and to maintain the quality of ionic and electronic exchanges between matter of the electrode and the other constituents of the composite, the first electrolyte being impervious to the components of the second electrolyte.

PRIOR ART

Polymeric electrolytes are particularly desirable for the manufacturing lithium batteries using composite electrodes in which the Electrode materials are dispersed in the polymer matrix, which then acts as

-2-ion conductor and as a deformable binder active substance powders.
With such electrolytes, it is possible to control the elastomerity and adhesion of the electrolyte binder contact with solids. These systems allow to absorb without damage the volume variations of the electrode materials.

Polymer electrolyte composite electrodes can be 2 types, that is to say dry solvating type operating hot, generally with anodes of lithium; or of gelled type, solvating or not, functioning at the ambient temperature thanks to the addition of polar aprotic liquid solvents in combination with some 1 o lithium-ion type electrodes whose cathodes operate at high voltages (-4V). However, whatever their type, such composite electrodes have tendency to age at cycling and / or time. This aging produces reactions chemical or electrochemical undesirable localized on the surface of the grains of matter active, on the surface of the collectors, and in some cases on the surface of the additive electronic conduction. This phenomenon, which is also generic to generators at organic electrolytes litlum, thus resulting in the formation of passivation or degradation on the surfaces where the ion exchange takes place and e.
The efficiency of the generators is greatly diminished.

In polymeric media, these phenomena are amplified because in the solid state, the products formed by the reaction of the solvent, the salt and the material electrode tend to accumulate due to lack of convection, and are not compensated by the power penetrating liquid electrolytes that can maintain exchanges at the interfaces by their ability to penetrate through passivation or degradation films.
The

-3-phenomena observed are electrochemical decompositions initiated by radicals, acid-base reactions, or oxidation-reduction reactions more or less catalysed by the materials in the presence. Figures la) and lb) illustrate the location possible passivation films on different interfaces where take place exchanges ionic and electronic.

It is therefore common in organic solid medium to see an increase in transfer resistors at the interfaces, in addition to limiting phenomena broadcast ions to the electrodes. Interfaced films are sometimes detectable in electron microscopy and can reach a few hundred nanometers. In in other cases, degradation reactions cause breakage of the structure crystalline surface of the active phases, or cause the formation of soluble species harmful to the good generator operation.

Reactions between crystalline or vitreous solids, for example between cathode oxide or chalcogenide and a vitreous electrolyte, are in general slower, and these systems are recognized for their stability as a function of time, temperature and the operating voltage. The disadvantage of solid electrolytes minerals crystalline or vitreous, however, is their rigidity and their fragility, which they do not are not resistant to changes in electrode volume caused by cycling.

SUMMARY OF THE INVENTION

The present invention relates to an electrochemical generator, preferably a lithium electrochemical generator, comprising a cathode and an anode of which

-4-least one of them is a composite electrode comprising an active material, preferably in the form of dispersed particles, a current collector, and at least a first and a second solid electrolyte preferably distributed so no-homogeneous in the composite, the first and the second electrolyte comprising optionally one or more electronic conduction additives in form dispersed.
The first electrolyte comprises a solid conductor of mineral nature, glassy or partially vitreous, localized preferentially on the surface of the grains of the active material.
The second electrolyte comprises a solid of organic nature, comprising preferentially a dry or gelled polymer electrolyte and mixed conductor ions 1 o distributed around the dispersed solid phases and acting as a binder deformable composite also in contact with the collector and the separating electrolyte of generator. A thin layer of the first electrolyte wets and covers at least one part of the particle surface of the active material so as to protect the area covered with particles of passivation or degradation reactions and maintain the quality of ionic and electronic exchanges between the active ingredient the electrode and other constituents of the composite. In addition, the first electrolyte is impervious to components of the second electrolyte, the latter being distributed in at least one part of composite so as to ensure the conductivity of the ions as well as a role of deformable binder, preferably elastomeric, between the components of the composite electrode so with the current collector and the electrolyte separator of the generator.

In a second aspect of the invention, there is disclosed a composite electrode comprising an active material, a current collector, a first electrolyte solid mineral and a second organic electrolyte, the first and the second electrolyte comprising

-5-optionally one or more electronic conduction additives in form dispersed; the second electrolyte being in contact with the collector and acting as a binder deformable composite; in which the first electrolyte wets and covers at least part of the surface of the particles of the active material so as to protect the surface passivation or degradation reactions and to maintain the quality of the trades ions and electronics between the active material and the other constituents composite, the first electrolyte being impervious to the components of the second electrolyte.

Finally, in a third aspect of the invention, a method is described of Manufacturing an electrode according to the present invention, comprising:

a) mixing particles of electrode active material in a solution aqueous first mineral electrolyte optionally comprising an additive of conduction;

b) drying the solution of step a) to obtain a powder of particle of material active partially or completely covered with the first mineral electrolyte;

c) mixing the powder obtained in b) with a second organic electrolyte optionally comprising a conduction additive; and d) coating a current collector with the mixture obtained in c).

In a preferred embodiment, the first electrolyte is a lithium ion conductor. In another preferred embodiment, the first electrolyte is vitreous or partially vitreous, and is conductive of ions alkaline lithium and potassium. In another preferred embodiment, the first electrolyte mainly comprises lithium polyphosphate of approximate formula

-6-(LiPO3) n in which n> 3, and has a minimum ionic conductivity of 10 "10 S / cm at the operating temperature.

In another preferred embodiment, the conduction additive comprises carbon black, graphites, metals such as silver and copper, and the compounds semimetals such as carbides, borides, and silicones in forms dispersed, and their mixtures.

In another preferred embodiment, the second electrolyte comprises:

1 o - a solvating polymer which is dry or gelled by a polar aprotic solvent made conductive by the addition of a soluble lithium salt or a polyelectrolyte; or a gel comprising a low solvating polymer, an aprotic liquid solvent polar and a dissolved lithium salt.

The solvating polymer may comprise, for example, a polymer electrolyte comprising a lithium salt and a homopolymer, a copolymer, a structure comb, or a crosslinked or interpenetrating network of a polyether. Preferably, electrolyte polymer adheres to the particles of the active material.

In another preferred embodiment, the active material is used as anode and includes oxides, nitrides, carbon, graphites or their mixtures operating at a potential lower than 1.6 volts compared to a electrode metallic lithium.

-7-In another preferred embodiment, the anode comprises lithium, a lithium alloy, a carbon insertion compound or graphite.

IN THE DRAWINGS

Figure la illustrates a composite electrode before cycling;

Figure lb illustrates the formation of passivation layers on an electrode composite after cycling;

Figure 2a illustrates an example of composite electrode according to the present invention before cycling;

Figure 2b illustrates the formation of passivation layers on an electrode composite according to the present invention after cycling;

Figure 3a illustrates a composite electrode according to the present invention containing agglomerates of active particles prior to cycling;

Figure 3b illustrates the formation of passivation layers on the electrode of the Figure 3a after cycling;

Figure 4 illustrates a micrograph of a LiCoO2 powder, (LiPO3) õ and black of carbon obtained by spray-drying; and Figure 5 illustrates a micrograph of a LiV3O8 powder, (LiPO3) õ and black of carbon.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the optimization of performance and chemical and electrochemical stability of a composite electrode of a generator at lithium, the electrode having a solid dual electrolytes system. The first

-8-electrolyte is a mineral solid, preferentially vitreous and conductive Li + ions, used in a thin layer to wet and cover at least a portion of the active material of the electrode so as to chemically stabilize the surface of the particles said material and to maintain the quality of ionic and electronic exchanges with the other components of the composite electrode. The second electrolyte is a organic electrolyte, preferentially a dry or gelled and deformable polymer electrolyte, in which whichone Composite is distributed, this second electrolyte being used as a binder for particles of active material of the electrode in contact with the first mineral electrolyte.
An additive electronic conduction may be present in the first electrolyte, in the second electrolyte, or both, to facilitate the transport of ions and electrons. The first solid mineral electrolyte used according to the present invention is chosen to be chemically compatible with the active material of the electrode, for avoid that other components of the generator and / or the second organic electrolyte be soluble.
If this were the case, this would cause the formation of passivation films or products degradation at the surface of the active material of the electrode.

The present invention furthermore comprises means for implementing the vitreous solid electrolytes, double electrolyte composite electrode solid as well than generator.

By the combination within the same electrode of the two types solid electrolytes, which are distributed in the composite and located in roles In addition, the present invention makes it possible to circumvent the limitations of art prior. The first solid electrolyte is preferentially glassy and driver of

-9 Li + ions, and is used on the surface of the active material of the electrode, which it wet at least in part and protects the components of the second electrolyte, in this case the polymer, the lithium salt or any other product in solution. The fact that the first solid electrolyte vitreous does not dissolve the components of the second organic electrolyte allows of to protect the covered surfaces, thus preventing the formation of passivation which are harmful to good electrical contacts, and degradations undesirable also reduce the effectiveness of electrical contacts. The layer of the first electrolyte vitreous applied to the active material is preferentially present under slim shape and contains, in a preferred embodiment, a conduction additive scattered electronics 1 o in order to confer a mixed conductor character to the first electrolyte glassy, facilitating thus the ionic and electronic exchanges in the protected area. The Figures 2a) and 2b) illustrate such an implementation, in which there is an additive of conduction in the first vitreous electrolyte and in the second polymer electrolyte organic. The how the particle processing of the active material of the electrode protects some areas of contact despite the aging of the composite is illustrated in b) where the films of Passivations are shown.

In addition, the present invention includes compatible vitreous electrolytes with a wide range of electrode materials, especially with oxides such acids 2o the vanadium oxides V205, V6013 and LiV3Og, which are otherwise incompatible with basic compounds such as silicates and polysilicates of metals alkaline, because they react irreversibly with vanadium oxide. In the present invention, phosphates, polyphosphates, borates and polyborates of lithium or of potassium, and mixtures thereof, represent electrode materials preferred.

-10-Various additives known to stabilize the formation of glass can also to be added to the first vitreous electrolyte of the invention insofar as they do not are not incompatible with the materials of the electrode. Such training agents glass include partially or fully hydrolysed silica, titanates, aluminates, partially or fully hydrolysed siloxanes, and mixtures thereof.

The invention also uses the more conductive properties of electrolytes polymers, gelled or not, in order to optimize the power performance of electrode composite in that the polymer electrolyte is distributed around the particles of 1 o active material of the electrode and the electronic conduction additive, where appropriate, way to bind the particles together and with the current collector of the electrode. The second polymer electrolyte of the composite, which acts as a binder, allows also to ensure adhesion and ion exchange with the electrolyte separator generator, preferentially a film based on a polymer electrolyte.

The present invention utilizes an aqueous process for treating the active material of the electrode in dispersed form with the first electrolyte glassy in solution, optionally in the presence of a conduction additive, also scattered. The solution is then either filtered and the residue dried, or treated by spray-drying ("spray dried ") to form individual particles partially or totally wet by the first vitreous electrolyte, or agglomerated particles comprising the material electrode, the adhering glass and the electronic conduction additive, the case applicable. The particles have a porosity rate more or less accessible to the second electrolyte polymer when introducing the latter. Figures 3a) and 3b) illustrate the

-11-formation of more or less porous mineral agglomerates and more or less penetrated by the second polymer electrolyte. Agglomerated particles can be partially or completely penetrated by the second electrolyte, so as to reduce the surface material active which is brought into contact with the second electrolyte.

Methods for forming composite electrodes from electrolytes polymers are known and can be adapted for the purposes of this invention.
For example, the application of polymer solutions, the application of of molten polymers or the application of pre-polymers or low-level monomers masses 1 o less viscous which will be crosslinked / polymerized after they are shaped in composite.
The use of glass compositions using potassium is also included in the present invention insofar as the potassium is exchanged with the lithium and does not interfere with the operation of the lithium generator.

The following examples are provided to illustrate certain modes of production of the invention, and should not be interpreted as limiting the scope.
Example 1 An aqueous solution of the vitreous mineral solid electrolyte formulation general (LiPO3) õ is prepared as follows. An aqueous solution of (LiPO3) õ is prepared by dissolving 75 g of polymetaphosphoric acid ((HPO3) õ) in 325 g water (this solution may also include a lower alcohol) and is by the partly following or in total neutralized by the addition of lithium hydroxide monohydrate (LiOH H20 =),

-12-in a molar ratio (HPO3) õ / LiOH of 1, corresponding to the addition of 39.6 g of LiOH = H20.

Example 2 A dispersion consisting of 0.25 g of LiV3O8 is stirred rigorously with 100 mL of the aqueous solution of (LiPO3) õ prepared according to Example 1. The dispersion thus prepared shows a brown color typical of LiV3O8 oxide.
This observation demonstrates the chemical stability of the neutral aqueous solution of electrolyte solid type (MPO3) õ where M is Li or K, with acidic electrode materials represented by LiV3O8. An identical solution containing an excess of base (LiOH) a as a result of making the solution greenish. A green color is probably associated with a reduced state of vanadium resulting from a possible decomposition water in basic medium. Such an observation is also noted with V205 when treated sodium silicate. The green color results from the basic effect of silicates of metals alkalis and their incompatibility with acidic oxides such as V205.
A
identical solution containing an excess of acid (LiPO3) õ makes the solution orange, which is possibly associated with V205 formation following the probable formation of a acid vanadyl anion in an acid medium.

2 o Example 3 93 g of polymetaphosphoric acid (HPO3) n are dissolved in 6 liters of water, then neutralized by the addition of 49 g of LiOH = H20 corresponding to a ratio molar (HPO3) õ / LiOH of 1. To this solution, 491 g of an aqueous dispersion of black of carbon (KetjenblackTM EC-600) containing 5% by weight of carbon black is mixed of

- 13-energetically with the aqueous solution of lithium polymetaphosphate, then 1 kg of LiCoO2 is added to supplement the aqueous dispersion to be atomized ("spray drying ").
This dispersion is spray-dried in dry air using a "spray-dryer" from Buchi brand model B-190TM (Brinkmann Instruments Division). The type atomization used is the nozzle atomization in parallel current, that is to say that the atomized product and the drying air flows in the same direction. The micrograph (Figure 4) of the powder obtained shows individual particles coated for the most part with glass.
The analysis of phosphorus by Auger spectroscopy shows particles individual LiCoO2 mostly covered with glass and droplets spherical 1 o (LiPO3) n and carbon resulting from non-optimized conditions of the "spray drying ".

Example 4 208 g of polymetaphosphoric acid (HPO31, are dissolved in 8.4 liters of water, then neutralized by the addition of 109 g of LiOH = H20 corresponding to a ratio molar (HPO3) õ / LiOH of 1. To this solution, 1.756 kg of an aqueous dispersion of black of Carbon (KetjenblackTM EC-600) containing 5% by weight of carbon black is mixed energetically with the aqueous solution of lithium polymetaphosphate, then 1.5 kg of LiV3O8 is added to complete the aqueous dispersion to be atomized ("spray drying ").
This dispersion is spray-dried in dry air using a "spray-dryer" whose procedure is described in Example 3 above. The micrograph (Figure 5) of the powder obtained shows agglomerates of LiV3Og and vitreous electrolyte containing the additive electronic conduction. The surface powder chemically stabilized by recovery glassy electrolyte contains 15% by volume (LiPO3) ,,, 8% carbon black and 77%
LiV3O8.

-14-Example 5 208 g of polymetaphosphoric acid (HPO3) õ are dissolved in 8.4 liters of water then neutralized by the addition of 109 g of LiOH = H20 corresponding to a ratio molar (HPO3) õ / LiOH of 1. To this solution, 1.756 kg of an aqueous dispersion of black of Carbon (KetjenblackTM EC-600) containing 5% by weight of carbon black is mixed energetically with the aqueous solution of lithium polymetaphosphate, then 1.5 kg of V205 is added to complete the aqueous dispersion to be atomized ("spray drying ").
This dispersion is spray-dried in dry air using a "spray-dryer" whose procedure is described in Example 3 above. The micrograph of the powder obtained shows agglomerates of V205 and vitreous electrolyte containing the additive of conduction electronic. This last result is similar to that observed in Example 4.

Example 6 In this example, a composite cathode is made using the particles obtained according to Example 4 for solvent preparation and spreading using a template in one step a composite electrode on a covered aluminum collector a protective coating based on carbon and an inert organic binder. We use this last composite cathode for the realization of the electrochemical generator according to following steps.

The spreading solution is formed of an ethylene oxide copolymer of molar mass of about 50 000 g / mol in solution in acetonitrile at a concentration about 15% by weight and a LiTFSI salt in an O / Li molar ratio of 30/1 by

- 15-compared to the polymer. The particles of agglomerates of LiV3O8 and electrolyte glassy containing the electronic conduction additive, obtained according to Example 4, are scattered by mechanical stirring in the presence of carbon black (KetjenblackTM EC600) and the suspension is coated on the coated aluminum collector protective based on carbon and an inert organic binder. The composite cathode as well obtained is dried at 80 ° C. for 24 hours before being assembled with an anode of lithium previously laminated with a 15 micron polymer electrolyte acting as separator, the latter consisting of a copolymer of ethylene oxide containing a salt lithium LiTFSI at a concentration corresponding to a molar ratio O / Li relative to the polymer.

When cycled at 80 C, this battery shows an initial use corresponding to the capacity of the cathode provided, which confirms that all the material active is good accessible by one or the other solid electrolytes of the composite. This result confirms 1s that this embodiment of the solid double electrolyte composite according to the invention allows access of lithium ions to the active material of the cathode even if the two electrolytes whose ionic conductivities are very different coexist in contact with the active material.

Although the present invention has been described using implementations specific, it is understood that several variations and modifications may add to implemented, and the present application is intended to cover such changes, uses or adaptations of the present invention according to, in general, the principles of invention and including any variation of the present description which will become known or

-16-Convention in the field of activity in which this invention, and which can be applied to the essential elements mentioned above, in agreement with the scope of the following claims.

Claims (32)

1. An electrochemical generator comprising a cathode and anode of which less one of them is a composite electrode comprising an active material, a collector current, and at least a first and a second solid electrolyte in the composite, the first or the second electrolyte comprising at least one conduction additive electronics under dispersed form; the first electrolyte being a solid conductor of nature mineral; the second electrolyte being solid and organic in nature; in which a thin layer of first electrolyte wets and covers at least a portion of the surface of the particles of active material so as to protect the surface covered with the particles of reactions of passivation or degradation and maintain the quality of ion exchange and electronics between the active material of the electrode and the other constituents of the composite, the first electrolyte being impervious to the components of the second electrolyte. 2. A generator according to claim 1 wherein the first electrolyte is a conductive lithium ions. 3. A generator according to claim 1 of the lithium generator type. 4. A generator according to claim 1 wherein the first electrolyte is vitreous or partially vitreous and conductive alkaline ions lithium or potassium. 5. A generator according to claim 4 wherein the first electrolyte is partially vitreous and includes metal phosphates or polyphosphates alkaline or alkali metal borates or polyborates, or mixtures thereof. 6. A generator according to claim 5 wherein the first electrolyte comprises predominantly lithium polyphosphate of formula (LiPO3) n where n> 3, and has a minimum ionic conductivity of 10-10 S / cm at operating temperature. 7. A generator according to claim 6 wherein (LiPO3) n is soluble in water. 8. A generator according to claim 1 wherein the first electrolyte contains an electronic conduction additive in dispersed form and is a mixed driver ionic and electronic. 9. A generator according to claim 1 wherein the second electrolyte comprises:
a solvating polymer which is dry or gelled by a polar aprotic solvent conductive by the addition of a soluble lithium salt or a polyelectrolyte;
or a gel comprising a low solvating polymer, an aprotic liquid solvent polar and a dissolved lithium salt 10. A generator according to claim 9 wherein the solvating polymer comprises a polymer electrolyte containing a conduction additive scattered electronics and is a mixed ionic and electronic conductor. 11. A generator according to claim 1 wherein the active material is in use as cathode. 12. A generator according to claim 11 wherein the active material includes a vanadium oxide, or a mixture of vanadium oxides. 13. A generator according to claim 1 wherein the active material is in use as anode and includes oxides, nitrides, carbon, graphites or their mixtures operating at a potential lower than 1.6 volts compared to a electrode metallic lithium. 14. A generator according to claim 1 wherein the collector of current of the composite electrode is coated with a conductive coating based on carbon and a binder inert adherent. 15. A generator according to claim 1 wherein the generator comprises a separator, the separator being at least one polymer electrolyte. 16. A generator according to claim 1 wherein the anode comprises lithium, a lithium alloy, a carbon insertion compound or graphite. 17. A composite electrode comprising an active material, a collector of current, a first inorganic solid electrolyte and a second organic electrolyte, the first or the second electrolyte comprising one or more conduction additives electronic form dispersed; the second electrolyte being in contact with the collector; in which the first electrolyte wets and covers at least a portion of the surface of the particles of the material active in order to protect the surface from passivation reactions or degradation and maintain the quality of the ionic and electronic exchanges between the material active and others constituents of the composite, the first electrolyte being impermeable to components of second electrolyte. 18. An electrode according to claim 17 wherein the second electrolyte comprises a dry or gelled polymer electrolyte. 19. An electrode according to 17 in which the first electrolyte is glassy or partially vitreous and conductive alkaline ions lithium or potassium. 20. An electrode according to claim 19 wherein the first electrolyte is partially vitreous and includes metal phosphates or polyphosphates alkaline or alkali metal borates or mixtures thereof. 21. An electrode according to claim 20 wherein the first electrolyte comprises predominantly lithium polyphosphate of formula (LiPO 3) n where n > 3, and has a minimum ionic conductivity of 10-10 S / cm at room temperature operation. 22. An electrode according to claim 21 wherein (LiPO3) n is soluble in the water. 23. An electrode according to claim 20 wherein the active material comprises a vanadium oxide, or a mixture of vanadium oxides. 24. A method of manufacturing an electrode according to claim 17 comprising:
a) mixing particles of electrode active material in a solution aqueous of the first mineral electrolyte;

b) drying the solution of step a) to obtain a powder of particle of material 15 active partially or completely covered with the first mineral electrolyte;

c) mixing the powder obtained in b) with a second organic electrolyte;
and d) coating a current collector with the mixture obtained in c). 25. A process according to claim 24 wherein the aqueous solution comprises a lower alcohol. The method of claim 24 wherein the second electrolyte is deformable. 27. The method of claim 24 wherein the second electrolyte includes a dry or gelled polymer electrolyte. 28. The method of claim 24 wherein the first electrolyte is glassy or partially vitreous and conductive alkaline ions lithium or potassium. 29. The method of claim 28 wherein the first electrolyte is partially vitreous and includes metal phosphates or polyphosphates alkaline or alkali metal borates or polyborates or mixtures thereof. 30. The method of claim 24 wherein the first electrolyte comprises predominantly lithium polyphosphate of formula (LiPO3) n where n> 3, and has a minimum ionic conductivity of 10-10 S / cm at operating temperature. 31. The method of claim 30 wherein (LiPO3) n is soluble in the water. The method of claim 24 wherein the active material comprises a vanadium oxide, or a mixture of vanadium oxides.