Anode compartment with a collector made of amorphous-alloy

Abstract

An anode compartment for rechargeable lithium or sodium batteries, including: a solid electrolyte; a collector deposited on the solid electrolyte; and an active material made of lithium metal or sodium metal which has been grown between the solid electrolyte and the collector in order to form an electrode made of lithium metal or sodium metal with the collector, in which the collector is made of an amorphous alloy. A method for manufacturing such an anode compartment and a battery including said anode compartment is also presented.

Claims

1. A lithium or sodium rechargeable battery anode compartment comprising: a solid electrolyte; a current-collector deposited on the solid electrolyte; and an active material made of lithium metal or sodium metal that has been grown between the solid electrolyte and the current-collector, thus forming with the current-collector an electrode made of lithium metal or sodium metal, wherein the current-collector is made of an amorphous alloy, and wherein the amorphous alloy has a maximum relative coefficient of elongation of greater than 1.8%.

2. The lithium or sodium rechargeable battery anode compartment according to claim 1, wherein the amorphous alloy contains in total less than 10% by number of Si, Sn and Ag atoms.

3. The lithium or sodium rechargeable battery anode compartment according to claim 1, wherein the amorphous alloy is Cu.sub.xZr.sub.1-x, with x comprised between 0.25 and 0.75.

4. The lithium or sodium rechargeable battery anode compartment according to claim 1, wherein the current-collector is in the form of a layer with a thickness of less than 1 m.

5. The lithium or sodium rechargeable battery anode compartment according to claim 1, wherein the solid electrolyte is made of a ceramic material.

6. A method to manufacture a lithium or sodium rechargeable battery anode compartment comprising: a solid electrolyte; a current-collector made of amorphous-alloy; and an active material made of lithium metal or sodium metal between the solid electrolyte and the current-collector; the method comprising the steps of: deposition of an amorphous alloy on the solid electrolyte, thus forming the current-collector, the amorphous alloy having a maximum relative coefficient of elongation of greater than 1.8%; growing an active material made of lithium metal or sodium metal between the solid electrolyte and the current-collector; and obtaining the lithium or sodium rechargeable battery anode compartment.

7. The method according to claim 6, wherein the amorphous alloy is deposited on the solid electrolyte by cathodic sputtering or ion beam sputtering.

8. The method according to claim 6, wherein the amorphous alloy is Cu.sub.xZr.sub.1-x, with x comprised between 0.25 and 0.75.

9. The method according to claim 6, wherein the active material is grown between the solid electrolyte and the current-collector by electrochemical deposition.

10. The method according to claim 6, wherein the solid electrolyte is made of a ceramic material.

11. A battery comprising: a cathode, a liquid electrolyte and a lithium or sodium rechargeable battery anode compartment according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objectives, features and advantages will become apparent on reading the illustrative description which follows, with reference to the drawings which are given by way of example and are non-limitative, in which:

(2) FIG. 1 is a diagrammatic illustration of an anode compartment according to the invention without a coating;

(3) FIG. 2 is a diagrammatic illustration of an anode compartment according to the invention with a coating;

(4) FIG. 3 is a diagrammatic illustration of an anode compartment according to the invention without a coating and comprising a case;

(5) FIG. 4 is a diagrammatic illustration of an anode compartment according to the invention with a coating and comprising a case;

(6) FIG. 5 is a diagram schematically illustrating the different steps of the process for the manufacture of an anode compartment according to the invention, the optional steps being indicated in dotted lines;

(7) FIG. 6 is a photograph showing the state of the surface of a collector made of steel after a charging phase; and

(8) FIG. 7 is a photograph showing the appearance of an active material made of dense lithium metal.

DETAILED DESCRIPTION

(9) With reference to FIGS. 1 to 4, an anode compartment for rechargeable lithium or sodium batteries according to the invention is described hereafter.

(10) This anode compartment 1 comprises a solid electrolyte 2, a collector 3 on the solid electrolyte 2, and an active material 4 made of lithium metal or sodium metal between the solid electrolyte 2 and the collector 3. The active material 4 results from the growth of lithium metal or sodium metal between these two components and forms with the collector 3 an electrode made of lithium metal or sodium metal.

(11) The anode compartment 1 is novel in that the collector 3 is made of an amorphous alloy. In fact, as already indicated above, the inventors discovered that such a collector allowed the growth of active material in a not very dense form.

(12) Later, the inventors wished to identify the cause of this growth in a not very dense form of the active material in the collectors of the prior art. It is in this way that the inventors observed that this growth of the lithium metal in a not very dense form occurred particularly where the collector, generally made of steel, is deposited on the solid electrolyte, and under which the lithium metal grows, exhibits cracks (see FIG. 6).

(13) The inventors assume that this growth in a not very dense form is due to the fact that in these areas of cracks, the lithium metal is not subject to constraints and therefore has a tendency to form in a more uncontrolled manner.

(14) In order to explain the appearance of cracks, the inventors propose the hypothesis according to which, during the growth of the lithium metal between the collector and the solid electrolyte, a tension is created at the surface of the collector orientated collinearly to the latter and leads to its rupture.

(15) An amorphous alloy, as opposed to a crystalline alloy, has an arrangement of atoms constituting it which is irregular over an average and large distance. The collector 3 made of amorphous alloy of the invention does not crack during the charging phase of a battery comprising the anode compartment, which allows the growth of the active material in a not very dense form (stringy or porous) to be avoided. It is capable of deforming in a reversible manner (elastic deformation) in the case of significant stresses compressing the active material. In fact, the maximum relative coefficient of elongation (.sub.y) of an amorphous alloy, equal to the stress (.sub.y) divided by Young's modulus (E), is higher than that of a crystalline metal or alloy.

(16) The amorphous alloy chosen advantageously has a maximum relative coefficient of elongation (.sub.y) greater than 1.8%.

(17) The amorphous alloy is preferably composed of metals not forming an alloy with lithium metal during an electrochemical deposition of lithium metal from the collector 3 made of such an alloy. Thus, the amorphous alloy preferably contains in total less than 10% by number of silicon, tin and silver atoms.

(18) Advantageously, the amorphous alloy is Cu.sub.xZr.sub.1-x, with x comprised between 0.25 and 0.75, preferably, x is equal to approximately 0.4.

(19) The collector 3 is in the form of a fine layer, preferably with a thickness of less than 1 m. Thus, the collector 3 is flexible.

(20) The collector 3 is electrically connected to a flexible electronic conductor formed by a flexible metallic grid or film, preferably a flexible grid made of steel. This flexible metallic grid covers at least part, preferably all, of the surface of the current collector. In order to improve the electrical contact between the current collector and the electronic conductor, a silver lacquer is preferably applied to their contact area. The electronic conductor makes it possible to electrically connect the collector 3 to an element external to the anode compartment.

(21) The solid electrolyte 2 is made of a ceramic material conducting alkali metal cations, for example lithium or sodium, preferably lithium.

(22) Such lithium conducting ceramic materials are known, for example LIC-GC (for Lithium Ion Conducting Glass Ceramic from the company Ohara Inc. Japan). They are for example ceramics of formula Li.sub.1-x(M,Ga,Al).sub.x(Ge.sub.1-yTi.sub.y).sub.2-x(PO.sub.4).sub.3 where M represents one or more metals chosen from Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, and where 0<x0.8 and 0y1.0. Other materials of this type are also known in the literature, such as LATP of formula Li.sub.1-xTi.sub.2-x(PO.sub.4).sub.3 and described in the article The effects of crystallization parameters on ionic conductivity of a lithium aluminium germanium phosphate glass-ceramics by J. S. Thokchom, and B. Kumar, in J. Power Sources, vol. 195, p. 2870, 2010, or LLZ of formula Li.sub.7La.sub.3Zr.sub.2O.sub.12 and described in the article Fast Lithium Ion Conduction in Garnet-Type Li.sub.7La.sub.3Zr.sub.2O.sub.12 by R. Murugan, V. Thangadurai, and W. Weppner, in Angew. Chem. Int. Ed., 46 (2007), p. 7778.

(23) Sodium conducting ceramic materials are for example materials of formula Na.sub.1-xZr.sub.2Si.sub.xP.sub.3-xO.sub.12 where 0x3. They are described in particular in U.S. Pat. No. 6,485,622 and in the article Comparison of Different Synthesis Methods for Nasicon Ceramics by N. Gasmi et al., J. from Sol-Gel Science and Technology 4(3) (1995) p. 231-237, and known in the literature under the name Nasicon.

(24) The solid electrolyte 2 is preferably in the form of a membrane. Its thickness depends on its two other dimensions. The greater the surface of the membrane the greater the thickness must be in order to resist mechanical stresses. Moreover, the electrical efficiency of a battery is partially governed by the specific resistance of the electrolyte, and this specific resistance R is expressed by the formula:
R=(r.Math.e)/A,

(25) where r denotes the resistivity of the electrolyte, e the thickness of the membrane and A its surface area. Thus, it is generally sought to use, where possible, thin solid electrolytes. The thickness of the membrane is advantageously comprised between 30 m and 500 m, preferably between 50 m and 160 m. These thicknesses are adequate for surface areas which are greater than 1 mm.sup.2, preferably comprised between 1 mm.sup.2 and 400 cm.sup.2, yet more preferably between 4 cm.sup.2 and 100 cm.sup.2.

(26) The ceramic electrolyte 2 can be coated on at least one of its surfaces from which the active material will grow, in particular when this is made of lithium metal. As examples of coatings 5 based on Li.sub.3N, Li.sub.3P, LiI, LiBr, LiF or lithium phosphorus oxynitride (LiPON) (see for example X. Yu et al., J. Electrochem. Soc. (1997) 144(2), page 524) can be mentioned for the conduction of lithium, and for example borosilicate glass with the addition of Na.sub.2O or sodium phosphorus oxynitride (NaPON) (see for example S. Chun et al., Proc. 124th Meeting Electrochem. Soc. (2008) 195) can be mentioned for the conduction of sodium.

(27) The active material 4 advantageously has a maximum thickness comprised between 50 m and 5 mm, preferably between 100 m and 500 m, at the end of the charging phase.

(28) The anode compartment 1 can comprise a sealed and rigid case 6 in which the solid electrolyte 2, the collector 3 and the active material 2 are found. The surface of the solid electrolyte 2 opposite to that turned towards the collector 3 at least partially forms an external surface of the case 6. The case 6 can have any appropriate shape allowing incorporation in a battery, for example a cylindrical or parallelepipedal shape. Thus, the case 6 and the solid electrolyte 2 delimit a sealed internal space. The case 6 can be produced of synthetic resin, preferably of a thermosetting or cold-setting resin. The chemical nature of this resin is not critical, provided that it does not adversely interact with the components contained inside the anode compartment 1 and the elements of the battery in which the anode compartment 1 is used. For example, epoxide, unsaturated polyester, phenolic and polyimide resins are suitable.

(29) In this case, and advantageously, the collector 3 covers virtually all the surface of the solid electrolyte 2 but not entirely, in particular in order to avoid it coming into contact with the walls of the sealed case 6. In fact, if the active material has a relatively large thickness at the end of the charging phase, and if the collector 3 is in contact with the internal walls of the case 6, the collector 3 risks deforming and/or breaking as it moves away from the solid electrolyte 2 when the active material 4 grows during the charging phase. The extent of the collector 3 on the solid electrolyte 2 is chosen so that the distance between the edges of the collector 3 and the walls of the case 6 is preferably at the most equal to a few hundreds of microns.

(30) Still in this case, the anode compartment 1 can then also comprise a resilient element acting on the collector 3 so that this is forced in the direction of the solid electrolyte 2 thus allowing the continuous compression of the active material 4. The resilient element can be one or more of the walls of the case 6 itself or a block 7 made of resilient material such as a foam. In the second case, the block made of resilient material occupies all of the space left free in the cassette when the active material is completely consumed, i.e. at the end of the discharging phase.

(31) The block 7 made of resilient material is for example made of poly(chloroprene) foams (also called Neoprene), preferably the neoprene foams marketed under the name Bulatex, in particular Bulatex C166, by the Hutchinson company. Another example would be the product Sylomer G, a poly(ether urethane) foam marketed by the Plastiform company.

(32) A battery comprising the anode compartment described above is described hereafter.

(33) This battery comprises, in addition to the anode compartment, a positive electrode, optionally a liquid electrolyte.

(34) The positive electrode can be for example an air electrode or an electrode using sulphur.

(35) When the positive electrode is an air electrode, it is preferably made of a porous material that conducts electrons. This porous material is for example a compound of carbon black, a catalyst based on manganese or cobalt oxide, a hydrophobic binder such as HFP (hexafluoropropylene) or PTFE (polytetrafluoroethylene), and a current collector such as a collector in the form of a nickel grid. An anion-conducing polymer can be added into the electrode as described in patent WO 2010/128242 A1, in particular when the electrolyte is aqueous. This polymer has the function of preventing the carbonation of the aqueous electrolyte by the CO.sub.2 contained in the air. The hydrophobic binder has the double function of producing a mechanically integrated porous structure from a powder the electronic percolation of which is ensured by contact between the carbon grains, and being sufficiently hydrophobic in order to prevent the electrolyte from passing through the electrode when this is liquid.

(36) This battery is for example a lithium-air or sodium-air battery or also a lithium-sulphur battery, or any battery using an anode made of lithium metal or sodium metal

(37) With reference to FIG. 5 a process for the manufacture of an anode compartment as presented above is described hereafter.

(38) This process comprises the deposition of an amorphous alloy on the solid electrolyte in order to form the collector and the growth of an active material made of lithium metal or sodium metal between the solid electrolyte and the collector thus obtaining the anode compartment.

(39) The amorphous alloy can be deposited on the solid electrolyte by cathodic sputtering or by ion beam sputtering.

(40) In the case of cathodic sputtering, the material of the target used can be directly the alloy that is desired to be deposited on the solid electrolyte, the material can be crystalline or already amorphous. As a variant several targets can be used and the maximum number of which is the number of metallic elements composing the amorphous alloy that is desired to be deposited on the solid electrolyte. In the case where the number of targets is lower than the number of metallic elements composing the amorphous alloy, at least one of the targets is made of an alloy. The definition of metallic element is understood as including all the transition chemical elements as well as steel. For example, the material of the target is made of an amorphous or crystalline alloy of CuZr. By way of another example, two targets are used, one made of Cu and the other of Zr.

(41) The amorphous alloy is deposited on the solid electrolyte until a thickness of less than 2 m is reached, preferably comprised between 200 and 400 nm.

(42) The growth of the active material between the solid electrolyte and the collector can be produced as follows. The face of the solid electrolyte which is not turned towards the collector is placed in contact, at least partially, with a liquid electrolyte containing the cations of the alkali metal which will form the active material. A reduction potential is then applied between the collector and a positive electrode immersed in the liquid electrolyte containing the cations of the alkali metal. The reduction potential is maintained between the collector and the positive electrode for a sufficient duration for the active material to cross between the solid electrolyte and the collector up to a desired thickness.

(43) The liquid electrolyte can be for example LiOH in the case of an active material made of lithium metal, or NaOH in the case of an active material made of sodium metal. The concentration of LiOH or NaOH is preferably at least equal to 1 mol/L and can range up to saturation or even beyond.

(44) The positive electrode used for the growth of lithium metal or sodium metal can be an electrode made of metal or alloy that is stable in the liquid electrolyte used and at the oxidation potentials of the ions of the liquid electrolyte.

(45) The reduction potential applied is maintained preferably at a value comprised between 3.1 V and 3.6 V with respect to a reference electrode Hg/HgO/KOH 1M in the liquid electrolyte. This potential must in fact be sufficiently high in absolute value for the alkali ion to be reduced to alkali metal. Preferably, the current strength is comprised between 0.1 mAh/cm.sup.2 and 100 mAh/cm.sup.2.

(46) In the case where a coating is provided on the solid electrolyte, this is deposited on the solid electrolyte before the deposition of the amorphous alloy by cathodic sputtering for example.

(47) In the case where the anode compartment is in the form of a case, the case is poured around the assembly constituted by the solid electrolyte, optionally the coating, the active material, the collector and optionally the block made of resilient material.