ALKALINE METAL SECONDARY BATTERY AND USES THEREOF

Abstract

The invention relates to alkaline secondary batteries. The secondary battery contains a cathode, an anode and an electrolyte, said secondary battery being arranged between the cathode and anode and comprises an alkali metal ion conductive contact to the cathode and to the carbon layer of the anode. The anode contains or consists of a carbon layer, whereby the carbon layer, alone or in combination with an electrically conductive substrate, forms with an electrically conductive contact.

Claims

1-16. (canceled)

17. An alkali metal secondary battery comprising: a) a cathode; b) an anode comprising a carbon layer, the carbon layer alone, or in combination with an electrically conductive substrate, forming an electrically conductive contact; and c) an electrolyte arranged between the cathode and anode and having an alkali metal ion-conductive contact to the cathode and to the carbon layer of the anode; wherein the carbon layer comprises pores of a first type which are not accessible to the electrolyte and which are suitable for taking up electrochemically deposited alkali metal in metallic form during a charging process of the alkali metal secondary battery.

18. The alkali metal secondary battery according to claim 17, wherein the pores of the first type are provided with a chemical modification which favors the uptake of metallic alkali metal generated by deposition.

19. The alkali metal secondary battery according to claim 18, wherein the chemical modification is selected from the group consisting of a layer on the pore surface, nanoparticles on the pore surface, at least one chemical functional group on the pore surface, and combinations thereof.

20. The alkali metal secondary battery according to claim 17, wherein the pores of the first type have a pore size i. in the range of 0.5 to 100 nm; ii. of >2 nm; or iii. of <2 nm.

21. The alkali metal secondary battery according to claim 17, wherein the carbon layer further comprises pores of a second type and/or cavities that are accessible to the electrolyte, wherein the pores of the second type and/or the cavities have a spatial extent in all three spatial directions which is in the micrometer range.

22. The alkali metal secondary battery according to claim 17, wherein the pores of the second type and/or the cavities comprise electrolyte.

23. The alkali metal secondary battery according to claim 17, wherein the carbon layer, i) in a charged state, comprises an alkali metal, and/or ii) in an uncharged state, does not comprise any lithium or sodium.

24. The alkali metal secondary battery according to claim 17, wherein the electrolyte is a sulphidic solid electrolyte.

25. The alkali metal secondary battery according to claim 24, wherein the sulphidic solid electrolyte is selected from the system Li2S—P2S5, Li2S—GeS2, Li2S—B2S3, Li6PS5Cl, Li2S—SiS2, Li2S—P2S5-LÎX (X=Cl, Br, I), Li2S—P2S5—Li2O, Li2S—P2S5—Li2O—LiI, Li2S—SiS2—LiI, Li2S—SiS2—LiBr, Li2S—SiS2—LiCl, Li2S—SiS2—B.sub.2S3—LiI, Li2S—SiS2—P2S5—LiI, Li2S—P2S5-ZmSn, where m and n are integers and M is selected from P, Si or Ge, Li2S—SiS2—Li3PO4, Li2S—SiS2—LipMOq, where p and q are integers and M is selected from P, Si or Ge, Na2S—P2S5, Na2S—GeS2, Na2S—B2S3, NaePSsCl, Na2S—SiS2, Na2S—P2S5—NaX (X=Cl, Br, I), Na2S—P2S5—Na2O, Na2S—P2Ss-Na2O—NaI, Na2S—SiS2—NaI, Na2S—SiS2—NaBr, Na2S—SiS2—NaCl, Na2S—SiS2—B2Ss-NaI, Na2S—SiS2—P2Ss-NaI, Na2S—P2S5-ZmSn, where m and n are integers and M is selected from P, Si or Ge, Na2S—SiS2—Na3PO4, Na2S—SiS2—NapMOq, where p and q are integers and M is selected from P, Si or Ge, or a mixture thereof.

26. The alkali metal secondary battery according to claim 17, wherein the electrolyte is a liquid electrolyte or gel electrolyte, and all components of the electrolyte, have a size which i) exceeds the size of the pores of the first type; and/or ii) exceeds the size of pores of a protective layer arranged between the electrolyte and the porous carbon particles, wherein the protective layer is conductive for alkali metal ions.

27. The alkali metal secondary battery according to claim 17, wherein the carbon layer forms a carbon network suitable for transporting alkali metal ions along the carbon network.

28. The alkali metal secondary battery according to claim 17, wherein the carbon layer i) comprises pores of the first type which together have a pore volume of ≥0.5 cm.sup.3/g carbon; and/or ii) comprises micropores, mesopores and/or macropores classified according to IUPAC.

29. The alkali metal secondary battery according to claim 17, wherein the carbon layer is suitable for taking up metallic alkali metal produced by electrochemical deposition in an amount such that the carbon layer has a specific capacity of ≥400 mAh/g, based on the mass of the carbon material.

30. The alkali metal secondary battery according to claim 17, wherein the electrolyte i) has an ionic conductivity a of at least 10.sup.−10 S.Math.cm.sup.−1; and/or ii) has a lower conductivity for electrons than the electrically conductive substrate of the anode and/or than the cathode.

31. The alkali metal secondary battery according to claim 17, wherein the electrolyte i) is designed as a foil; and/or ii) from the anode in the direction of the cathode, has a maximum extension in a range from 1 μm to 100 μm, preferably 10 μm to 50 μm.

32. The alkali metal secondary battery according to claim 17, wherein the cathode i) comprises a current collector; ii) does not comprise an alkali metal source, or comprises an alkali metal source; iii) comprises a solid electrolyte; iv) comprises an electrically conductive additive; and v) at least partially comprises fibrillar polytetrafluoroethylene.

33. The alkali metal secondary battery according to claim 17, wherein the alkali metal secondary battery is a lithium secondary battery or a sodium secondary battery.

Description

[0044] FIGS. 1A-C show schematically the processes at the interface between a carbon particle 6 of the carbon layer of the anode and the electrolyte 8 of the alkali metal secondary battery according to the invention, which is a lithium secondary battery here. In the charging process depicted in FIG. 1A, lithium ions are transported from the cathode (not shown) through the electrolyte 8 into a pore 7 of the first type of the carbon particle 6. There the lithium ions take up electrons which flow from the conductive layer of the anode (not shown) to the carbon particle 6, and are reduced to lithium metal 10, which is now located within the pores 7 of the first type. During the discharge process depicted in FIG. 1B, the metallic lithium 10 is oxidized to lithium ions by withdrawing electrons (that is, metallic lithium is dissolved) and the lithium ions can be taken up by the electrolyte and transported to the cathode. The situation depicted in FIG. 1C describes the surprising finding that even lithium metal 10, which is dissolved to lithium ions far away from the electrolyte 8, is still efficiently transported to the electrolyte 8 and from there to the cathode. An efficient transport of lithium ions along the pore 7 of the first type in the direction of the electrolyte 8 must therefore be possible.

[0045] FIGS. 2A-B schematically show the structure of an alkali metal secondary battery according to the invention. In FIG. 2A, the secondary battery is depicted in the uncharged state and in FIG. 2B, the secondary battery is depicted in the charged state. The alkali metal secondary battery depicted comprises a cathode 1 and an anode 2 comprising an electrically conductive substrate 3, the electrically conductive substrate 3 extending over a certain geometrical area 4 and a carbon layer 5 being arranged at least in some regions on this area 4, the carbon layer 5 comprising carbon particles 6 having pores 7 of the first type and forming an electrically conductive contact with the electrically conductive substrate 3 of the anode 2 and with one another. The secondary battery further comprises an electrolyte 8 arranged between the cathode 1 and anode 2 and having an alkali metal ion-conductive contact with the cathode 1 and with the carbon particles 6 of the anode 2. The carbon layer 5 has pores 9 of the second type between the carbon particles 6, which pores at least in regions comprise the electrolyte 8, the pores 7 of the first type having such a small pore size that they are unsuitable for taking up the electrolyte and are suitable for taking up metallic alkali metal 10 generated by deposition. In FIG. 10, the deposition of metallic alkali metal 10 is depicted in simplified form in only a few pores 7 of the first type.

[0046] FIG. 3 shows the result of an experiment carried out with an alkali metal secondary battery (lithium secondary battery) according to the invention. The voltage profile for the lithiation is depicted in dashed lines and the voltage profile for the delithiation is depicted as a solid line. The lithium secondary battery was a half-cell having an anode described in claim 1, a lithium metal foil as the cathode and a sulfidic solid electrolyte. The lithiation or delithiation took place at a constant current of 0.05 mA/cm.sup.2. The specific capacity of the delithiation was determined to be 423 mAh/g.

[0047] FIG. 4 shows the resulting potential profiles of the third and fourth cycle of lithiation and delithiation for the TiC-CDC cell from the example. A reversible lithiation capacity of 521.0 mAh/gTiC-CDC could be observed in the third cycle of the half-cell.

Example—Capacity of an Alkali Metal Secondary Battery According to the Invention

[0048] All material treatments were carried out under inert gas.

[0049] First, the carbon material TiC-CDC was dried for 12 h at 200° C. under inert gas conditions. This carbon material has pores of the first type having a pore size of <2 nm, the pore size being determinable with nitrogen physisorption.

[0050] To produce a powdery composite electrode (anode), the dried TiC-CDC was then manually mixed i) with carbon nanofibers (VG-CNF) grown from the gas phase, ii) with a conductive carbon additive and iii) with a solid electrolyte (Li6PS5Cl=SE) in an agate mortar for 30 minutes in a mass ratio of 60:5:35.

[0051] A half-cell was then produced in a stainless steel outer casing having a Teflon liner using a die having a diameter of 13 mm. For this purpose, a Li foil having a diameter of 13 mm and a thickness of 50 μm (counter electrode) was arranged in the die and 150 g of solid electrolyte powder (Li6PS5Cl powder=SE powder) was evenly distributed thereon using a micro spatula. This composition was compressed and compacted into a pellet.

[0052] Then the TiC-CDC composite powder (7.44 mg) (test electrode) was distributed homogeneously over the compacted solid electrolyte surface in the die and compacted again using a hydraulic press with 4 tons for 30 s. The resulting active material stressing of the cell was 3.36 mg/cm′.

[0053] The electrochemical behavior of the cell was measured with a battery tester VMP3 (BioLogic, France). Here, at a constant temperature of 25° C., the reversible capacity of the anode (having the carbon layer according to the invention) was tested against the counter electrode (lithium metal foil) at potentials above 0 V and at potentials of 0 V (vs. Li/Li+).

[0054] Various cycles were carried out, with the lithiation of the carbon-active material of the carbon layer to 0 V with a subsequent step with constant voltage at 0 V until the current exceeds −0.01 mA, and the delithiation of the carbon-active material of the carbon layer to 2 V. The applied current was 0.065 mA.

[0055] The resulting potential profiles of the third and fourth cycle of lithiation and delithiation for the TiC-CDC cell are depicted in FIG. 4. A reversible lithiation capacity of 521.0 mAh/gTiC-CDC could be observed in the third cycle of the half-cell.

LIST OF REFERENCE SYMBOLS

[0056] 1: cathode; [0057] 2: anode; [0058] 3: electrically conductive substrate of the anode; [0059] 4: extension over a certain geometric area; [0060] 5: carbon layer; [0061] 6: carbon particles; [0062] 7: pores of the first type of the carbon layer; [0063] 8: electrolyte; [0064] 9: pores of the second type of the carbon layer; [0065] 10: metallic alkali metal produced by deposition (for example, lithium) in pores of the first type.