Method for regenerating the capacity of an electrochemical lithium battery, and associated battery housing and battery

Abstract

The invention relates to a method for regenerating the capacity of an electrochemical lithium battery, including the following steps: a) evaluating the quantity of lithium ions; b) when the evaluated lithium ion quantity is less than or equal to a threshold value, applying an electric current between the cathode or the anode and the container such as to cause the delithiation of the casing, the casing is also arranged to house an element providing both electric insulation and ionic conduction between the anode and cathode electrodes of the electrochemical cell and the casing, said casing including at least one lithium ion storage zone.

Claims

1. A method for regenerating the capacity of a lithium electrochemical accumulator including at least one electrochemical cell including a cathode, an anode, and a separator impregnated with an electrolyte between the anode and the cathode, two current collectors one of which is connected to the anode and the other to the cathode, and a casing arranged to house the electrochemical cell with seal-tightness while being passed through by a portion of the current collectors forming output terminals, the method comprising: evaluating the amount of lithium ions; when the evaluated amount of lithium ions is smaller than or equal to a threshold value, applying an electrical current between the cathode or anode and the casing so as to cause delithiation of the casing, the casing being further arranged to house an element, which is both electrically insulating and ionically conductive, to insulate the casing from the anode and cathode electrodes of the electrochemical cell, while being conductive to ions, the casing having a crystal structure and further including at least one zone for storing lithium ions in the crystal structure of the casing, during the delithiation of the casing, extracting at least a part of the lithium ions stored in the crystal structure of the casing and inserting the part of the extracted lithium ions into at least one of the cathode and the anode, and thereby allowing exchangeable lithium to be recuperated.

2. The regenerating method as claimed in claim 1, wherein evaluating the amount of lithium ions is performed by measuring the electrical potential of a reference electrode.

3. The regenerating method as claimed in claim 1, wherein evaluating the amount of lithium ions is performed by measuring a capacity difference with respect to the initial capacity of the accumulator.

4. The regenerating method as claimed in claim 1, wherein evaluating the amount of lithium ions is performed by measuring electrochemical impedance.

5. The regenerating method as claimed in claim 1, wherein applying the electrical current between the cathode or anode and the casing is performed with regulation by means of an electronic device.

6. The regenerating method as claimed in claim 5, the electronic device being suitable for calculating the integral of the current as a function of time in order to determine the regenerated capacity.

7. A lithium electrochemical accumulator comprising: at least one electrochemical cell C including a cathode, an anode and a separator, impregnated with an electrolyte, between the anode and cathode; two current collectors, one of the current collectors being connected to the anode, and the other of the current collectors being connected to the cathode; a casing arranged to house the electrochemical cell with seal-tightness while being passed through by a portion of the current collectors forming output terminals, the casing having a crystal structure, the casing being further arranged to house an element, which is both electrically insulating and ionically conductive, to insulate the casing from the anode and cathode electrodes of the electrochemical cell, while being conductive to ions, at least one zone for storing lithium ions being included in the crystal structure of the casing, the at least one zone for storing lithium ions being produced in a form of a lithium-containing alloy formed through a portion of a thickness of the casing, and a lithium concentration of the at least one zone decreasing from an internal face of the casing, wherein the accumulator is configured so that, when an electrical current is applied between the cathode or anode and the casing, lithium ions are extracted from the at least one zone for storing lithium ions and are inserted into at least one of the cathode and the anode, thereby allowing exchangeable lithium to be recuperated.

8. The accumulator as claimed in claim 7, the material of the casing being a lithium-aluminum alloy of formula Li.sub.xAl with x comprised between 0 and 1.

9. The accumulator as claimed in claim 8, the lithium-aluminum alloy of formula Li.sub.xAl being obtained by a process of the electrochemical lithiation of a substrate made of aluminum.

10. The accumulator as claimed in claim 7, the casing including a diffusion barrier layer forming a barrier to diffusion of the lithium ions.

11. The accumulator as claimed in claim 10, the diffusion barrier layer being made of aluminum oxide or alumina A1.sub.2O.sub.3.

12. The accumulator as claimed in claim 7, the electrically insulating and ionically conductive element consisting of at least one film made of a polymer chosen from polyvinylidene fluoride (PVDF), polyvinyl acetate (PVA), polymethyl methacrylate (PMMA), polyoxyethylene (POE) and polyethylene terephthalate (PET), or of a polymer chosen from polyolefins such as polypropylene, polyethylene or cellulose.

13. The accumulator as claimed in claim 7, the electrically insulating and ionically conductive element being a protective layer deposited on an internal face of the casing.

Description

DETAILED DESCRIPTION

(1) Other advantages and features will become more clearly apparent on reading the detailed description, which is given by way of illustration and with reference to the following figures, in which:

(2) FIG. 1 is a schematic exploded perspective view showing the various elements of a lithium-ion accumulator;

(3) FIG. 2 is a front view showing a lithium-ion accumulator with its flexible package according to the prior art;

(4) FIG. 3 is a perspective see-through view of a lithium-ion accumulator with its flexible package according to the prior art;

(5) FIG. 4 is a perspective view of a cylindrical lithium-ion accumulator according to the prior art with its rigid package consisting of a casing;

(6) FIGS. 5A and 5B illustrate curves of the potential of the electrodes (cathode above and anode below) of a Li-ion accumulator as a function of their charge, at an initial capacity corresponding to 100% of the state of charge and at a lower capacity corresponding to 100-x % of the state of charge with a loss of x % of charge at the negative electrode generated by the lack of exchangeable lithium ions, respectively;

(7) FIG. 6 is a schematic view of a lithium-ion accumulator according to the invention with its rigid package consisting of a casing.

(8) For the sake of clarity, the same references have been used to designate the same elements of a Li-ion accumulator according to the prior art and according to the invention in all of FIGS. 1 to 6.

(9) It will be noted that the various elements according to the invention are shown merely for the sake of clarity and that they are not to scale.

(10) FIGS. 1 to 5B have already been commented on in detail in the preamble. They are therefore not described below.

(11) An accumulator according to the invention is shown in FIG. 6. It includes at least one electrochemical cell C consisting of a separator 4 impregnated with a constituent electrolyte between a cathode 2 and an anode 3, a current collector 40 connected to the cathode 2, a current collector 50 connected to the anode 3 and lastly, a casing 6 by way of package arranged to contain the electrochemical cell with seal-tightness while being passed through by a portion of the current collectors 40, 50, forming the output terminals.

(12) The casing 6, of longitudinal axis X, includes a cylindrical lateral jacket 7, a bottom 8 at one end, and a cover 9 at the other end. The cover 9 bears the poles or terminals 40, 50 through which the current is output. Each of the output terminals (poles), i.e. the positive terminal 40 and the negative terminal 50, passes through the cover 9 with interposition of a seal 41, 51 that electrically insulates the positive and negative terminals 40, 50, respectively, from the cover 9. In other words, the two terminals 40, 50 are electrically insulated from the casing 6.

(13) The casing 6 is made of aluminum.

(14) The casing 6 includes a zone 61 for storing lithium ions, which zone is produced in the form of a lithium-containing alloy formed through some of the thickness of the casing and the lithium concentration of which decreases from the internal face of the casing 6 and uniformly over the entirety of this area.

(15) The accumulator furthermore includes, between the anode 3 and cathode 2 of the electrochemical cell and the casing 6, an element 71, taking the form of a film, that is both electrically insulating and ionically conductive.

(16) Lastly, the casing 6 includes a protruding portion that forms a terminal 62, which allows the capacity of the accumulator to be regenerated as explained below. In contrast to prior-art accumulators comprising a third terminal connected to a third electrode, there is no need to seal the terminal 62 according to the invention since said terminal serves for external connection to the casing 6.

(17) An exemplary accumulator according to the invention has been produced with a cylindrical geometry by spooling a cell, said accumulator being of 50 mm diameter, 125 mm height and of an initial capacity of about 18 Ah.

(18) The casing 6 is produced from an aluminum sheet; its weight is 75 g.

(19) The electrode materials are graphite for the anode 3 and lithium iron phosphate (LiFePO.sub.4) for the cathode 2.

(20) Since the initial capacity is known, it is possible to calculate the amount of exchangeable lithium ions contained in the accumulator by the following calculation:
C*3600*M.sub.Li/F.

(21) with the following respective values:

(22) M.sub.Li=6.9 g/mol (molar mass of lithium),

(23) F=96500 C/mol (Faraday's constant),

(24) and C=18 Ah.

(25) The accumulator contains an amount of exchangeable lithium ions equal to 4.63 g.

(26) It is also possible to calculate the amount of lithium ions that can be stored in the casing 6 of this accumulator in the case of complete lithiation of the aluminum casing, or of a Li—Al alloy, by the following calculation:
M*M.sub.Li/M.sub.Al.

(27) With a mass M of the casing 6 equal to 75 g and a molar mass of aluminum M.sub.Al equal to 27 g/mol, an amount of storable lithium equal to 19.17 g is obtained, i.e. a value more than 4 times higher than the amount of exchangeable lithium ions initially used by the accumulator.

(28) The casing 6 is therefore entirely sufficient as a lithium storage zone. Specifically, the inventors consider that it is reasonable, to regenerate the capacity of a Li-ion accumulator, to store about half the amount of exchangeable lithium. Injecting more than this amount of lithium into the accumulator may lead to other degradation effects becoming preponderant, and it then proves to be impossible to regenerate the accumulator according to the invention. In addition, complete lithiation of the casing 6 would produce a material the mechanical properties of which would be unsatisfactory for the targeted applications of the accumulator.

(29) Thus, in the case of a storage zone loaded with half the amount of exchangeable lithium, i.e. 2.32 g, the alloy obtained is of formula Li.sub.0.12Al (for uniform lithiation of the bulk of the casing 6).

(30) In practice, the use of such an accumulator, the casing 6 of which is insulated from the two electrodes 2, 3 and lithiated during its manufacture, allows Li.sup.+ ions to be injected to increase the amount of exchangeable lithium. This operation is carried out by passing a current between the regenerating terminal 62 of the casing 6 and one of the two electrodes 2 or 3.

(31) The initial capacity of the accumulator is thus regenerated.

(32) In one example according to the invention, it is possible to regenerate the capacity of the Li-ion accumulator by inserting Li.sup.+ ions into the cathode 2. Li.sup.+ ions may also be inserted into the anode 3.

(33) After the amount of capacity to be regenerated has been calculated, the casing 6 and the cathode 2 are electrically connected to an electronic device (not shown) suitable for regulating current. Specifically, since the redox potential of the positive electrode is higher than that of lithiated aluminum, and as the architecture allows ions to be exchanged between these two components, a negative current may be established leading to the desired effect of injection of exchangeable lithium.

(34) The electronic device allows a current between the casing 6 and the cathode 2 to be regulated.

(35) Advantageously, this device may also integrate the current as a function of time, in order to calculate the regeneration capacity. Preferably, the current must be very low, in order to allow uniform insertion of lithium ions into the active material, and also in order not to destructure the metal of the casing 6.

(36) This device may be integrated into a BMS, or controlled by an exterior operator who wants to regenerate the accumulator.

(37) The limited current is calculated relative to the capacity of lithium ions integrated into the casing. In the case of the preceding example, in which 2.32 g of lithium is inserted into the casing, i.e. a capacity of 9 Ah, a current regime of C/100 or less is used (9 Ah/100h i.e. 90 mA).

(38) Once the amount of lithium to be inserted has been inserted, a cycle of charging/discharging the accumulator may be carried out in order to verify that the regeneration has been effective.

(39) The casing 6 containing lithium ions stored in its internal face 61 may be obtained, before design of the accumulator, by lithiation processes. For example, it is envisionable to perform an electrochemical lithiation. It may also be envisioned to produce a lithium-containing aluminum alloy metallurgically.

(40) The invention is not limited to the examples just described and features of the illustrated examples may be combined together in non-illustrated variants.

(41) Although described with reference to a Li-ion accumulator, the invention may equally well be applied to any electrochemical generator operating on the principle of insertion-deinsertion of Li.sup.+ lithium ions.