Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0438—Processes of manufacture in general by electrochemical processing
  • H01M4/045—Electrochemical coating; Electrochemical impregnation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
  • H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/04—Processes of manufacture in general
  • H01M4/0438—Processes of manufacture in general by electrochemical processing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the invention relates to a, preferably non-aqueous, electrochemical battery cell with a negative electrode, an electrolyte and a positive electrode, in which at least one of the electrodes has a flat, electronically conductive substrate with a surface on which an active one occurs when the cell is being charged or discharged Mass is deposited electrolytically.
• Such cells are of great importance, especially as rechargeable batteries (secondary cells).
• alkali metal cells in which the active mass is an alkali metal that is used when charging the active mass
• the electrolyte used in the context of the invention is preferably based on SO 2 .
• SO 2 based electrolyte SO 2 based electrolytes
• SO 2 based electrolytes are distinguished electrolyte loading, the SO 2 not only as an additive in low con- contain concentration, but in which the mobility of the ions of the conductive salt, which is contained in the electrolyte and causes the charge transport, is at least partially guaranteed by the SO2.
• a tetrahaloaluminate of the alkali metal for example LiAlCl 4 , is preferably used as the conductive salt.
• an alkali metal as an active composition, for example, without restricting generality.
• An alkali metal cell with an SO2-based electrolyte is referred to as an alkali metal SO 2 cell.
• the required safety is an important problem with battery cells. For many cell types, particularly strong heating can lead to safety-critical conditions. It may happen that the cell housing bursts or at least becomes leaky and harmful gaseous or solid substances or even fire escape. A rapid increase in temperature can be caused not only by improper handling, but also by internal or external short circuits when the cell is operating.
• Battery manufacturers use electronic, mechanical or chemical mechanisms to control the charging or discharging circuit in such a way that the current flow is interrupted below a critical temperature that no "thermal runaway” can occur.
• pressure-sensitive mechanical or temperature-sensitive electronic switches are integrated in the internal battery circuit.
• chemical reactions in the electrolyte or mechanical changes in the battery separator irreversibly interrupt the current transport within these components as soon as a critical temperature threshold is reached.
• Li-ion cells are only used with complex electronic monitoring because the security risks based on the current state of the art are very high.
• the invention is based on the problem of improving the function, in particular the safety, of electrochemical battery cells in a simple and inexpensive manner.
• Battery cells are essentially related to the fact that the active mass, in particular after several charging and discharging cycles, is not deposited as a smooth layer with a flat surface, but rather as thread-like structures in sections.
• the active mass in particular after several charging and discharging cycles, is not deposited as a smooth layer with a flat surface, but rather as thread-like structures in sections.
• unbranched threads with (for a certain cell) essentially the same diameter are formed when the cell is loaded, which grow together into balls and are referred to as whiskers.
• the formation of the whiskers is attributed to the fact that a thin cover layer forms on the surface of the reactive active metal as a result of a self-discharge reaction, which in the case of a Li-S ⁇ 2 ⁇ cell consists of Li 2 S 2 ⁇ 4 .
• This top layer is not completely uniform.
• the electrolytically deposited active metal preferably grows through the cover layer at the thinner points and then continues at the end of the thread.
• section-like thread-like structures in which the active mass is deposited in some cell types, are dendrites, which differ from the whiskers mainly in that they branch out like a tree.
• the separation of the active mass in the form of whiskers, dendrites or other thread-like structures, at least in sections, has, as was found in the context of the present invention, significant safety-relevant disadvantages:
• the large surface accelerates the reaction in the event of a "thermal runaway" or other uncontrolled safety-relevant reactions.
• - Self-discharge reactions which lead to the formation of a cover layer on the surface of the active mass, are also promoted by the large surface of the lithium.
• microporous layer is applied directly to the electronically conductive substrate on which the deposition process takes place, the pore size of which is dimensioned such that the Active mass deposited during the charging process grows into the pores in a controlled manner and largely fills them completely, so that the electrolyte is essentially only in contact with the active mass via the end face of the column of active mass growing through the pores.
• the narrow channels lead to an increase in electrolyte resistance. - In the channels formed by the pores of the deposition layer, a concentration gradient arises during the charging and discharging process, which leads to a voltage drop.
• the deposition layer contained materials that were not wetted by the electrolyte. This applies in particular to polymeric binders preferably used in the deposition layer, in particular polytetrafluoroethylene.
• the barrier layer serves to limit the growth of the active mass at the boundary between the deposition layer and the barrier layer. Therefore, it consists of a material that is impermeable for active mass that penetrates to the barrier layer on the one hand and for the charge transport in the electrolyte on the other hand causing ions is permeable.
• the barrier layer can be porous, and its pores must be so small that the active mass cannot grow into it. In practice, this means that the average pore diameter of the barrier layer is at most 30%, preferably at most 10%, of the average pore diameter of the deposition layer.
• a pore-free ion-conducting barrier layer for example made of an ion-conducting polymer, can also be used.
• ion-conducting polymer e.g
• 1 shows a battery cell with a wound electrode arrangement in a perspective view
• 2 shows a cross section through the electrode arrangement of a battery cell according to the invention in a highly schematic, not to scale cross-sectional representation
• 3 shows a highly schematic basic illustration of an electrode arrangement in cross section
• FIG. 4 shows a schematic diagram to explain the microscopic structure of a deposition layer suitable for the invention
• 5 shows a schematic diagram to explain the microscopic structure of a second embodiment of a deposition layer suitable for the invention
• FIG. 1 shows the essential construction elements of a battery cell 1 with a wound electrode arrangement.
• a cylindrical housing 2 with a cover part 3 there is an electrode arrangement 5, which is wound from a web-shaped starting material.
• the web consists of several layers, which include a positive electrode, a negative electrode and a separator running between the electrodes, which electrically and mechanically isolates the electrodes from one another, but is sufficiently porous or ion-conductive to enable the required ion exchange ,
• the cavity of the housing 2, insofar as it is not occupied by the electrode arrangement 5, is filled with an electrolyte, not shown.
• the electrodes of the electrode arrangement 5 are connected via corresponding connection lugs 6, 7 to connection contacts 8, 9, which enable electrical connection of the battery cell.
• connection contacts 8, 9 which enable electrical connection of the battery cell.
• the invention can be used both for battery cells with a flat electrode arrangement and for battery cells with the wound electrode arrangement shown.
• the negative electrode 10 shown consists of an electronically conductive substrate 11 and a deposition layer 12.
• a barrier layer 13 which is connected to the deposition layer 12 to form a layer composite 14.
• the positive electrode 15 runs on the side of the barrier layer 14 facing away from the deposition layer 12.
• the barrier layer 14 consequently forms a separator which electrically and mechanically separates the electrodes 10, 15.
• the positive electrode preferably contains an intercalation compound of a metal oxide, such as, for example, lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide or mixtures of these materials (see, for example, US Pat. No. 5,656,391).
• the substrate 11 can be designed as a film 18, which is preferably provided with holes 19.
• other structures can also be used, for example in the form of a lattice or woven fabric made of metal or another electronically conductive material.
• a structure of the substrate 11 provided with holes or pores is advantageous because it enables the two-sided deposition layers 12 to be glued through the holes ,
• the function of the layer composite consisting of the deposition layer 12 and the barrier layer 13 can best be illustrated with reference to FIG. 3, it being emphasized that this representation is highly schematic. In particular, depending on the materials used, the pores usually do not run straight through the entire layer thickness, as shown in FIG. 3.
• the active metal is deposited on the substrate 11, this process begins on the surface 21 thereof. Because the deposition layer 12 lies against the surface 21 without gaps, the active metal 22 can only penetrate into the pores 23 of the deposition layer Spread out 12. The separation of the active mass thus takes place practically completely in the pores 23 of the deposition layer 12.
• the end face 24 of the active mass 22 growing into the pores 23 is shown in broken lines in two later phases and is designated by 24a or 24b.
• the pores 23 of the deposition layer 12 should preferably be dimensioned such that they are largely completely filled by the deposited mass up to its end face 24.
• the pore size of the deposition layer should be matched to the diameter of the thread-like sections, the mean pore diameter preferably being somewhat smaller than the diameter of the thread-like sections of free-growing whiskers or dendrites.
• the porosity of the deposition layer 12 must be optimized experimentally in the individual case. As a general rule, it can be stated that their average pore diameter should be at most 200 ⁇ m, preferably at most 100 ⁇ m, particularly preferably at most 40 ⁇ m.
• the lower limit of the average pore diameter of deposit layers which can advantageously be used is 0.1 ⁇ m, preferably 0.5 ⁇ m and particularly preferably 1 ⁇ m.
• the thickness of the deposition layer 12 is dimensioned taking into account its pore content so that the maximum mass deposited in any operating state of the cell can be completely absorbed in its pore volume.
• this alone cannot prevent the active composition 22 from exiting the deposition layer 12 on the side facing away from the substrate 11, because the active composition does not spread uniformly in the deposition layer 12.
• the barrier layer 13 is provided.
• its pores 25 are so much smaller than the pores 23 of the deposition layer 12 that the active mass 22 cannot penetrate them.
• a continuous transition from its deposition layer 12 to its barrier layer 13 is also possible, depending on the production method of the layer composite 14.
• the porosity of the barrier layer should be experimentally optimized in individual cases. As a general rule, it can be stated that their average pore diameter should be at most 100 ⁇ m, preferably at most 10 ⁇ m, particularly preferably at most 1 ⁇ m. With regard to the desired barrier layer, the rule already mentioned should also be observed that the average pore diameter of the barrier layer is at most 30%, preferably at most 10%, of the average pore diameter of the deposition layer.
• FIGS. 4 to 6 give a more realistic picture of the inner structure of a deposition layer 12 compared to FIG. 3. Its porosity is preferably determined by a particulate, fibrous or tubular solid material which is referred to as the pore structure material of the deposition layer 12.
• the pore structure material consists of irregularly shaped particles 30 which are connected to one another by a suitable binder 31.
• Salts especially alkali halides such as LiF, NaCl or LiCl.
• alkali halides such as LiF, NaCl or LiCl.
• the arrangement of such a salt in the area of an electrode of a battery cell has significant safety-related advantages which can be attributed to the physicochemical and chemical properties of the salt. Further details can be found in the international patent application PCT / DE 00/00177.
• An oxide ceramic material such as Al 2 O 3 , MgO, Zr0 2 or MgAl 2 0 4 .
• Particularly suitable binders are polymers which do not contain any hydrogen atoms, especially perhalogenated, preferably perfluorinated, hydrocarbons, in particular polytetrafluoroethylene.
• the nanodisperse material 32 is preferably mixed with the binder 31.
• the binder 31 with the nanodisperse material 32 distributed therein is concentrated in the interstices 33 between the particles 30.
• the nanodisperse material can also be advantageously introduced into the deposition layer independently of the binder (even in the case of a binder-free deposition layer). Regardless of the type of introduction, the use of the nanodisperse material in the deposition layer has several major advantages.
• the uniform distribution of the electrolyte within the pores of the deposition layer is improved.
• an additional safety effect is achieved, which, according to the present knowledge of the inventors, is due to the fact that in the event of an uncontrolled heating of the cell, the lithium reacts with the SiO 2 contained in the deposition layer to form lithium oxide and silicon, and this reaction is significantly less exothermic than that Reactions that lead to the "thermal runaway".
• FIG. 5 shows the structure of a deposition layer in which a fibrous pore structure material is used instead of the particulate pore structure material.
• the fibers 34 have a circular cross section and run essentially parallel in the illustrated case. Such a fiber orientation corresponds to a nonwoven fabric. However, other textile fiber composite structures (fabrics, knitted fabrics) can also be used.
• the fibers of the pore structural material are also connected here by a polymeric binder 31, preferably with the addition of a nanodisperse material.
• FIG. 6 shows a further structure of a deposition layer in which a tubular pore structure material is used.
• These are very short pipe sections 35 which run perpendicular to the main surface of the deposition layer and are connected to one another at their circumferential surfaces 36. In the case shown, the connection of the pipe sections 35 is free of binding agents.
• Such layer materials are made, for example, of aluminum oxide and sold (for example by Whatman PLC, Great Britain).
• Binder-free production of the deposition layer 12 is also possible with other pore structure materials - in particular by sintering together the particles, fibers or pipe pieces.
• the proportion of the binder must not be too high. It was found in the context of the invention that sufficient strength is achieved with a relatively small proportion of binder of less than 30%, preferably less than 20%.
• the structure of the barrier layer 13 can have essentially the same features as the structure of the deposition layer 12 explained above with reference to FIGS. 4 to 6, although the dimensions of the particles 30, fibers 34 or pipe pieces 35 are considerably smaller. Their diameter is preferably less than 200 ⁇ m, values of at most 10 ⁇ m, in particular values of at most 1 ⁇ m, being particularly preferred.
• a binder-free nonwoven made of microglass fibers has proven itself as a pore structure material for the barrier layer.
• a sandwich structure of the type shown in FIG. 2 can be produced, for example, by first producing a film of the deposition layer material 12 as described above and cutting it slightly larger than the surface dimensions of the substrate 11.
• a sandwich deposition layer-substrate deposition layer (as shown in FIG. 2) is then formed and the protruding edges of the deposition layer are glued with a suitable inorganic adhesive, for example based on aluminate.
• the barrier layer can be put on.
• the binder-free glass fiber fleece is immersed in a dispersion of PTFE and Aerosil (in equal proportions) in water and (after excess liquid has dripped off) placed on the separating layer.
• the wrapable sandwich which now consists of five layers, is pressed (for example by means of a calender).
• the final connection can be achieved by applying pressure and / or temperature. If - which is preferred - the layers are baked together in an oven process, the maximum temperature during the oven process should be somewhat above the softening temperature range of the binder. In the case of PTFE as a binder, a temperature of approximately 380 ° C has proven itself.
• the described structure of the cell and the electrode arrangement contained therein can of course be varied in many ways.
• a special separator layer which is not part of the layer composite 14, between the barrier layer 13 and the positive electrode 15.
• Embodiments are also possible in which the one consisting of the deposition layer 12 and the barrier layer 13
• Layer composite 14 is arranged only on one side of the substrate 11.

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=7649986

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (2)

Family Cites Families (1)

• 2001
  • 2001-07-07 AU AU2001276321A patent/AU2001276321A1/en not_active Abandoned
  • 2001-07-07 WO PCT/DE2001/002587 patent/WO2002009213A1/de active Application Filing
  • 2001-07-07 DE DE10192980T patent/DE10192980B4/de not_active Expired - Fee Related

Patent Citations (2)

Also Published As

Similar Documents

Legal Events