BATTERY CELL COMPRISING SPECIAL POROUS SOLID ELECTROLYTE FOAMS

Abstract

A battery cell includes at least one positive electrode, at least one negative electrode, and at least one separator. The positive electrode includes a positive electrode porous solid-state electrolyte polymer foam that includes at least one lithium salt, and a positive electrode material located in the pores of the positive electrode foam. The negative electrode includes a negative electrode porous solid-state electrolyte polymer foam that includes at least one lithium salt, and a negative electrode material located in the pores of the negative electrode foam.

Claims

1-13. (canceled)

14. A battery cell comprising: at least one positive electrode, at least one negative electrode, and at least one separator, said positive electrode comprising: a positive electrode porous solid-state electrolyte polymer foam, said positive electrode foam comprising at least one lithium salt, and a positive electrode material located in pores of said positive electrode foam, said negative electrode comprising: a negative electrode porous solid-state electrolyte polymer foam, said negative electrode foam comprising at least one lithium salt, and a negative electrode material located in pores of said negative electrode foam.

15. The cell as claimed in claim 14, wherein said positive electrode foam and said negative electrode foam are of a same chemical nature.

16. The cell as claimed in claim 14, wherein said positive electrode foam comprises poly(ethylene oxide).

17. The cell as claimed in claim 14, wherein the negative electrode foam comprises poly(ethylene oxide).

18. The cell as claimed in claim 14, wherein said lithium salt is chosen from lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate (LiPF.sub.6), and mixtures thereof.

19. The cell as claimed in claim 14, wherein the separator is a polymer film comprising poly(ethylene oxide).

20. A battery comprising: at least one of the cell claimed in claim 14.

21. A method for manufacturing the cell as claimed in claim 14, the method comprising: a) manufacturing the separator; b) producing a first mixture comprising at least one porosity-forming agent, at least one polymer, at least one lithium salt and at least one solvent; c) coating said first mixture on a first face of said separator, said coating being followed by drying at temperature to obtain a first electrode foam, the first electrode foam being the negative electrode foam or positive electrode foam, forming a single structure with the separator; d) producing a second mixture comprising at least one porosity-forming agent, at least one polymer, at least one lithium salt and at least one solvent; e) coating said second mixture on a second face of the separator, said coating being followed by drying at temperature to obtain a second electrode foam, the second electrode foam being the negative electrode foam when the positive electrode foam was produced in step c) or the positive electrode foam when the negative electrode foam was produced in step c); steps a) to e) being successive, f) impregnating the negative electrode foam with a mixture comprising the negative electrode material, said impregnation being followed by drying at temperature; g) impregnating the positive electrode foam with a mixture comprising the positive electrode material, said impregnation being followed by drying at temperature; wherein step f) takes place before step g), or after step g), or at a same time as step g); then h) drying the assembly at temperature.

22. The method as claimed in claim 21, wherein the first mixture and the second mixture are identical.

23. The method as claimed in claim 22, wherein the porosity-forming agent is chosen from glycerol, isopropanol, dibutyl phthalate, and mixtures thereof.

24. The method as claimed in claim 22, wherein the polymer of said first mixture and/or of said second mixture comprises poly(ethylene oxide).

25. The method as claimed in claim 22, wherein, during step c) and/or e), the drying at temperature is carried out at a temperature ranging from 105 to 135° C.

26. The method as claimed in claim 22, wherein, during step c) and/or e), the drying at temperature is carried out at a temperature ranging from 110 to 130° C.

27. The method as claimed in claim 22, wherein, during step c) and/or e), the drying at temperature is carried out under vacuum.

28. The method as claimed in claim 22, wherein, during steps f), g) and h), the drying at temperature is carried out at a temperature ranging from 90 to 110° C.

Description

[0107] Other advantages and features of the invention will become more clearly apparent on examination of the detailed description, given solely by way of non-limiting examples, and with reference to the appended drawings in which:

[0108] FIG. 1 is a schematic view of an embodiment of a battery cell according to the invention;

[0109] FIG. 2 is a schematic view of another embodiment of a battery cell according to the invention;

[0110] FIG. 3 is a schematic view of another embodiment of a battery cell according to the invention;

[0111] FIG. 4 is a schematic view of a structure comprising in particular porous polymer foams.

EXAMPLES

[0112] Hereinbelow, reference will be made to FIGS. 1 to 3 which illustrate several embodiments of a battery cell according to the invention. Reference will also be made to FIG. 4 which shows a structure comprising in particular a positive electrode polymer foam and a negative electrode polymer foam.

[0113] As can be seen in FIG. 1, the battery cell according to the invention 1 comprises a positive electrode 2, a negative electrode 3 and a separator 4.

[0114] The positive electrode 2 comprises a positive electrode porous solid-state electrolyte polymer foam 5, and a positive electrode material 6, said material 6 being located in the pores 7 of said positive electrode foam.

[0115] The negative electrode 3 comprises a negative electrode porous solid-state electrolyte polymer foam 8, and a negative electrode material 9, being located in the pores 10 of said negative electrode foam.

[0116] The foam 5 is connected to the current collector 11, which is a current collector made of aluminum. The foam 8 is connected to the current collector 12, which is a current collector made of copper.

[0117] In this FIG. 1, the pores 7 and 10 have a similar diameter throughout the volume of the positive electrode and throughout the volume of the negative electrode, respectively.

[0118] However, as stated above, a different pore distribution is possible.

[0119] According to another embodiment, as illustrated in FIG. 2, the distribution of the pores is such that the pores 7 and 10 located on the current collector side have a small diameter and the pores 7 and 10 located on the separator side have a larger diameter. In this FIG. 2, the pores 7 and 10 have a diameter increasing from the current collector towards the separator.

[0120] According to yet another embodiment, as illustrated in FIG. 3, the distribution of the pores is such that the pores 7 and 10 located on the separator side have a small diameter and the pores 7 and 10 located on the current collector side have a larger diameter. In this FIG. 3, the pores 7 and 10 have a diameter increasing from the separator towards the current collector.

[0121] The battery cell according to the invention 1 can be prepared according to an example of a manufacturing method as described hereinbelow.

[0122] Separator

[0123] The separator 4 is manufactured first of all. It is preferentially a nonporous polymer film 4.

[0124] Poly(ethylene oxide) (PEO), a polymer binder, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), and at least one lithium salt (chosen from LiTFSI, LiFSI, LiPF.sub.6 and mixtures thereof) are dissolved in a solvent chosen from dimethylformamide (DMF), acetonitrile, and a mixture thereof.

[0125] The content of PVdF-HFP can range from 5% to 50% by mass, relative to the mass of the PEO.

[0126] The content of lithium salt can range from 5% to 20% by mass, relative to the PEO.

[0127] The polymer (PEO+PVdF-HFP)/solvent mass ratio is preferably set at 1:4.

[0128] Degassing of the solution is then carried out by magnetic stirring under vacuum.

[0129] The coating of the film is then carried out with a doctor blade or nozzle system. Next, drying at temperature is carried out at a temperature that can range from 60 to 130° C., optionally under vacuum, to evaporate the solvent.

[0130] The thickness of the film is then reduced by calendering.

[0131] Thus, a preferentially nonporous film 4 is obtained. It is used as separator between the two electrodes 2 and 3, with its role of insulating electrically and conducting ions.

[0132] Negative Electrode or Positive Electrode Foam

[0133] A foam 5 or a foam 8 is then produced on the separator 4 manufactured in the previous step.

[0134] A porosity-forming agent, as indicated above, may be used. This is a liquid referred to as non-solvent which, once removed, leaves a network of porosity in the sample. A “star polymer” PEO is used. This polymer is from the same family of materials as the PEO of the separator film 4.

[0135] Thus, compatibility between the layers is promoted and hence ion transport is promoted.

[0136] A mass content of 40% by mass of PEO “star polymer” may be used. This content can make it possible to achieve a porosity of close to 80%. Then, PVdF-HFP is used. Its use promotes mechanical strength.

[0137] The PVdF-HFP powder, the PEO and at least one lithium salt (chosen from LiTFSI, LiFSI, LiPF.sub.6, and mixtures thereof) are dissolved in a mixture of DMF (solvent) and glycerol (non-solvent). Mixing is effected by magnetic stirring at 80° C. for 10 hours. A step of degassing by magnetic stirring under vacuum is then carried out.

[0138] Then, a conventional coating step carried out with a doctor blade or nozzle system is carried out on a first surface of the separator 4 obtained in the previous step.

[0139] The presence of DMF at the interface between the film and the solution makes it possible to redissolve the PVdF-HFP at the surface of the film 4.

[0140] Drying at temperature at 120° C. for 12 hours is then carried out, allowing the evaporation of the solvent and the non-solvent.

[0141] The structure is then fixed, and the first negative electrode or positive electrode electrolyte foam is formed. It may therefore be foam 5 or foam 8.

[0142] In addition, the interface between the foam 5 (or 8) and the separator 4 is merged, and there is then no longer any physical interface between the foam 5 (or 8) and the separator 4. The observation can be carried out by scanning electron microscopy on a section of the sample, by measuring conductivity/resistivity. In the present case, an absence of demarcation between the two layers is observed.

[0143] At this stage, a single structure formed by the separator and a first negative electrode or positive electrode foam (foam 5 or foam 8) is obtained.

[0144] Negative Electrode or Positive Electrode Foam

[0145] A negative electrode or positive electrode polymer foam is then produced (foam 5 or foam 8) on the single structure obtained on conclusion of the previous step.

[0146] Thus, if foam 5 was produced in the previous step, then foam 8 is produced. If foam 8 was produced in the previous step, then foam 5 is produced.

[0147] In this step, the entire procedure used in the previous step is repeated, but the step of coating the second mixture comprising at least one porosity-forming agent, at least one polymer, at least one lithium salt and at least one solvent, is carried out on the second face of the separator 4.

[0148] Thus, the assembly formed by the foam 5, the foam 8 and the separator 4 forms a one-piece structure.

[0149] At this stage, the pores 7 and 10 of the foams 5 and 8 are empty, as illustrated in FIG. 4 which then represents a structure 1a.

[0150] The filling of the pores 7 and 10 is carried out by impregnating a mixture comprising a positive electrode material, material 6, with regard to foam 5, and by impregnating a mixture comprising a negative electrode material, material 9, with regard to foam 8.

[0151] Said mixtures comprising materials 6 and 9 can be in the form of an ink.

[0152] For example, foams 5 and 8 can be immersed in a bath of said inks. The ink infiltrates the pores 7 and 10 of foams 5 and 8.

[0153] Impregnation may also be carried out by coating with a doctor blade or nozzle system.

[0154] This impregnation is followed by drying at temperature, at a temperature ranging from 90 to 110° C., optionally under vacuum, which makes it possible to dry the mixture and fix it within the foam.

[0155] Then, in a conventional manner, the current collector for the negative electrode and the current collector for the positive electrode are installed. Thus, in the present embodiment, the aluminum current collector 11 is connected to the foam 5. The copper current collector 12 is connected to the foam 8.

[0156] The anode and cathode current collectors may have a coating of carbon or of carbon mixed with PEO/poly(vinylidene fluoride-co-hexafluoropropylene) to improve the interface with the active material and the polymer foam.

[0157] Thus, a battery cell according to the invention is obtained.