DE102004014383A1 - Galvanic element - Google Patents

Abstract

In a galvanic element having at least one lithium intercalating electrode whose positive electrode has a collector consisting essentially of aluminum, the aluminum collector is coated with an adhesion promoter consisting of a polar modified polyvinylidene difluoride (PVDF) and an electrical conductivity improver. DOLLAR A The conductivity improver is Leitruß and / or graphite or an electrically conductive polymer. The collector receives a coating of thickness 1 and 10 microns by spraying or rolling, by lamination or by direct wet coating.

Description

object The invention is a galvanic element having at least one Lithium intercalating electrode whose positive electrode has an im consists essentially of existing aluminum collector, and a Process for the preparation of the element.

In Lithium-ion cells or lithium-polymer cells are used as collector material on the positive side usually used aluminum. The natural oxide layer However, the aluminum prevents optimal electrode connection. One consequence of this is poor resilience, especially with pulse profiles like GSM (every 4.6 ms pulse of 575 μs, pulse high 2A, pulse low 0,2A) and GPRS (every 4.6 ms pulse of 1150 μs; pulse high 2A, pulse low 0.2A) and a high capacity drop in the course of cyclic loading and charging. This results for the user lower useful capacity.

to Pretreatment of aluminum collectors in lithium-ion or lithium-polymer batteries are Various methods known.

The document DE 198 07 192 A1 describes a coating of the aluminum collector for a lithium-ion cell by means of zinc and zinc oxide. In our own experiments, however, this type of pretreatment of the aluminum showed poor cyclization behavior.

The documents DE 101 14 232 C2 and DE 34 12 234 A1 describe a coupling agent which is rendered electrically conductive by the addition of metallic particles. The adhesion-promoting component is a plastic. The electrically conductive component is metallic.

The most common method for the pretreatment of aluminum collectors is the coating with a so-called primer. The primer consists of an organic adhesion promoter, electrical conductive material (in particular Leitruße, Leitgraphite or mixtures thereof) and optionally a dispersion medium. These ingredients are dissolved or suspended in a carrier solvent. An example of an application in a lithium polymer battery is in the document DE 100 30 571 C1 cited. In the adhesion promoter used there free acid groups (-COOH) are present. These polyacids build up chemical bonding forces to the aluminum surface and cause adhesion. The binding of the positive electrode material to the organic adhesion promoter in the primer is effected by a direct coating or hot lamination.

By Presence of highly electrically conductive components in the primer Obviously the breakdown voltage between aluminum and positive Electrode lowered by the aluminum oxide layer and thus the contact resistance significantly reduced. This results in low impedances and a high load capacity for the Cell despite the presence of this oxide layer.

Of the size Advantage of collectors with bonding agents is the ability to to use special low-adhesion electrode formulations. Examples are strong binder-reduced formulations. Often occurs when using metallic coated or etched Aluminum collectors on the problem that no sufficient adhesion to such a positive electrode takes place. A known problem however, when using organically based adhesion promoters their electrochemical instability at high temperatures (eg. B. 80 ° C) and maximum allowable Cell voltages (about 4.2V). This results in an irreversible Process gaseous reaction products, and the cell swells up. This is especially flexible Softpack packaging made of aluminum composite film clearly visible. In addition, the impedance increases strongly during storage at 80 ° C, and the usable capacity sinks. Overall, the cell is irreversibly damaged.

Of the Invention is based on the object of providing a bonding agent, under the storage conditions described (4.2 V, 80 ° C) not decomposed.

These The object is achieved by the Characteristics of claim 1 solved. In the dependent claims are advantageous embodiments of the invention and manufacturing methods specified.

Of the Aluminum collector of the positive electrode is with a bonding agent consisting of a polar modified polyvinylidene difluoride (PVDF) and an electrical conductivity improver coated. The conductivity improver consists of carbon black and / or Graphite.

fluoro-organic Polymers such as polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF) and the polyvinylidene difluoride-hexafluoropropylene co-polymer (PVDF-HFP) are electrochemical under the conditions in galvanic elements of the type mentioned very stable. These polymers are due to their remarkable electrochemical resistance as binder for the electrode materials used in 4 V cells.

From the document Benoit Barriere, Yoshiy uki Miyaki, Marina Despotopoulou, Mike Burchill New PVDF binders for Li-ION Batteries. "10th International Meeting on Lithium Batteries IMLB-10 - Lithium 2000." Cernobbio (Como), 28 May - 2 June 2000 it can be seen that the PVDFs stable in the 4 V range can be provided with additional, polar groups.

According to the invention used such polar modified PVDF polymers as a primer component, since they have electrochemical stability combine with good adhesive properties. The polar group is here too a free acid group (-COOH).

Of the inventive primer may consist of a mixture of a polar modified fluorinated PVDF, a carrier solvent, for example, N-methyl-2-pyrrolidone (NMP), and from proportions of electrical conductive filler (Russian or graphites or mixtures thereof).

These Mix can be good in thin layers in the μm range on aluminum. Cells according to the invention with these coated aluminum collectors show due to their excellent mechanical adhesion and the good electrical connection very low internal resistances (impedances).

The Coating thickness is between 1 and 10 microns, preferably between 1 to 3 μm. The Preparation of the coating can be done by spraying or rolling, or the connection between the bonding agent and the positive Electrode takes place during a lamination. It is also a direct wet coating possible. The carrier solvent becomes then removed by drying.

The Aluminum collector foil can, for example, an expanded metal or a perforated foil.

Example: production the primer suspension and coating of the aluminum collector:

In 100 ml of NMP is added to 1.5 g of polar modified fluorinated PVDF 40 ° C dissolved (magnetic stirrer). It A yellow-brown solution is formed, stirred for an hour becomes. Thereafter, the guide materials are added with a disolver stirrer, namely 1.0 g of soot and 2.0 g of graphite, and 20 min. stirred.

These Primer suspension is applied to the aluminum expanded metal using an airbrush gun sprayed. The coated aluminum collector will be at room temperature for a few hours dried. The layer thickness of the primer layer is per side approx. 2 μm. The inventively produced Aluminum collectors are optionally against a positive electrode laminated or directly with positive electrode coating compound coated.

To the collector pretreatment invention the preparation of the electrode coating compositions and the Electrode film production. Subsequently becomes the cathode (positive electrode) and the anode (negative electrode) on the pretreated aluminum or Copper collector laminated, electrodes are punched out and with Separators combined into one element. Finally, the packaging is done in aluminum composite foil and the formation.

So Polymer cells obtained were incubated at room temperature (in a plant 1) and at 60 ° C (in a Appendix 2) cyclized and also in the fully charged state stored in a temperature cabinet (4.2 V / 80 ° C / 62 h). There were lithium polymer cells with this inventive aluminum collector and cells with a collector with commercial primer application (EB-012 Fa. Acheson; This primer layer consists of a mixture of carbon black and graphite and an acrylic acid-containing organic binder) built.

At room temperature cyclizations, the cycle stability is comparable to that of commercially available primers. 1 shows the discharge capacity as a function of the number of cycles N at cyclization at room temperature and 1 C (one-hour current) load. Curve A applies to commercially available primers, curve B for primers according to the invention.

2 shows the same cyclization at 60 ° C. Particularly noteworthy is the outstanding in comparison to polymer cells with commercial primers cycle stability at elevated temperature.

at appropriate storage tests at 80 ° C, 4.2 V, show cells with the primer of the invention that the gassing across from corresponding cells with commercial primer time strong delayed and that is 1 kHz AC AC resistance in these extreme storage conditions only slightly increases.

Claims (8)

Galvanic element having at least one lithium intercalating electrode whose positive electrode has a collector consisting essentially of aluminum, characterized in that the aluminum collector is coated with an adhesion promoter consisting of a polar modified polyvinylidene difluoride (PVDF) and an electrical conductivity improver. Galvanic element according to Claim 1, characterized that the conductivity from Leitruß and / or Graphite exists. Galvanic element according to Claim 1, characterized that the conductivity an electrically conductive Polymer is. Galvanic element according to one of claims 1 to 3, characterized in that the collector is an aluminum mesh or a perforated aluminum foil. Galvanic element according to one of claims 1 to 4, characterized in that the coating thickness between 1 and 10 μm, preferably between 1 to 3 μm, lies. Process for producing a galvanic element according to one of the claims 1 to 5, characterized in that the coating by spraying or Rolling is done. Method according to Claim 6, characterized that the Connection between the primer and the positive electrode occurs during a lamination. Method according to one of claims 5 or 5, characterized that the Connection between the bonding agent and the positive electrode by a direct wet coating he follows.